Title of Invention	METHOD AND APPARATUS FOR A SYNCHRONIZATION CHANNEL IN AN OFDMA SYSTEM
Abstract	A method and apparatus is provided for transmitting an orthogonal frequency domain multiple access (OFDMA) signal including a synchronization channel signal transmitted within a localized portion of a bandwidth of the OFDMA signal (818), the synchronization channel signal having predetermined time domain symmetry within the localized portion of the bandwidth (816). The synchronization channel signal enables an initial acquisition and cell search method with low computational load which provides OFDMA symbol timing detection and frequency error detection by differential processing of sequence elements of the synchronization channel signal (1112) and frame boundary detection and cell specific information detection (1114) in an OFDMA system supporting multiple system bandwidths, both synchronized and un-synchronized systems, a large cell index and an OFDMA symbol structure with both short and long cyclic prefix length.

Title of Invention

METHOD AND APPARATUS FOR A SYNCHRONIZATION CHANNEL IN AN OFDMA SYSTEM

Abstract

A method and apparatus is provided for transmitting an orthogonal frequency domain multiple access (OFDMA) signal including a synchronization channel signal transmitted within a localized portion of a bandwidth of the OFDMA signal (818), the synchronization channel signal having predetermined time domain symmetry within the localized portion of the bandwidth (816). The synchronization channel signal enables an initial acquisition and cell search method with low computational load which provides OFDMA symbol timing detection and frequency error detection by differential processing of sequence elements of the synchronization channel signal (1112) and frame boundary detection and cell specific information detection (1114) in an OFDMA system supporting multiple system bandwidths, both synchronized and un-synchronized systems, a large cell index and an OFDMA symbol structure with both short and long cyclic prefix length.

Full Text	METHOD AND APPARATUS FOR A SYNCHRONIZATION CHANNEL IN AN OFDMA SYSTEM FIELD OF THE INVENTION The present invention generally relates to wireless communication systems, and more particularly relates to a method and apparatus for a synchronization channel in an orthogonal frequency division multiple access (OFDMA) system. BACKGROUND OF THE INVENTION In a wireless communication system which includes a number of base stations or cells, an initial task for a wireless communication device is to recognize and acquire the signals transmitted from the cells. Another primary task is to search the cells to determine which cell is the best for establishing communication with. As more and more complex signaling systems are developed, these important tasks become more difficult and more tirne-consuming. Recently, orthogonal frequency division multiple access (OFDMA) signaling systems have been proposed. The OFDMA systems are scalable bandwidth systems designed to work in different bandwidths. In addition, the OFDMA systems utilize a multi- carrier modulation approach having, perhaps, hundreds of subcarriers within a narrow (e.g., 5 MHz) frequency range. While the scalability of OFDMA systems facilitates the introduction and expansion of such systems, the complexity of OFDMA systems must nevertheless allow for signal acquisition by OFDMA wireless communication devices in a timely manner for quick activation and seamless transition from cell to cell. A synchronization channel is provided for initial signal acquisition and cell search. However, as the number of cell sites increases and the complexity of the OFDMA systems increase, the synchronization channel signal must include more and more information. Parsing the signal into sequence elements for quick and reliable reception alleviates some of the problem, but the sequence elements must themselves each carry sequence index information. Thus, what is needed is a method and apparatus for generating and processing an improved synchronization channel including a plurality of sequence elements in an ODFMA system. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. BRTEF DESCRIPTION OF THE DRAWINGS The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and FIG. 1 is a diagram of a wireless communication system in accordance with an embodiment of the present invention; FIG. 2 is a diagram of a frame structure of an orthogonal frequency domain multiple access (OFDMA) signal in accordance with an embodiment of the present invention; FIG. 3 is a diagram of a frame structure of an OFDMA signal in accordance with an alternate embodiment of the present invention; FIG. 4 is a diagram of the signal channel bandwidth occupation in accordance with an embodiment of the present invention; FIG. 5 is a diagram of the resource block mapping of the synchronization channel in accordance with an embodiment of the present invention; FIG. 6A is a diagram of the synchronization channel sequence assignment in accordance with an embodiment of the present invention; FIG. 6B is a diagram of the synchronization channel sequence assignment in accordance with an alternate embodiment of the present invention; FIG. 6C is a diagram of the synchronization channel sequence assignment in accordance with yet another alternate embodiment of the present invention; FIG. 7 is a diagram of the sub-carrier mapping of the synchronization channel signal in accordance with the embodiment of the present invention; FIG. 8 is a block diagram of a base station of the communication system of FIG. 1 in accordance with the embodiment of the present invention; FIG. 9 is a flowchart of the base station synchronization channel signaling of the base station of FIG. 8 in accordance with the embodiment of the present invention; FIG. 10 is a block diagram of a wireless communication device of the communication system of FIG. 1 in accordance with the embodiment of the present invention; and FIG. 11 is a flowchart of the initial activation and cell search of the wireless communication device of FIG. 10 in accordance with the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION In accordance with an embodiment of the present invention, a method in a wireless communication system includes the step of transmitting an orthogonal frequency domain multiple access (OFDMA) signal including a synchronization channel signal transmitted within a localized portion of a bandwidth of the OFDMA signal, the synchronization channel signal having predetermined time domain symmetry within the localized portion of bandwidth and including information for providing at least partial cell identification information. In addition, a method in a wireless communication system in accordance with an embodiment of the present invention includes the step of transmitting an OFDMA signal including a synchronization channel signal, the synchronization channel signal including a plurality of synchronization channel signal sequence elements and the OFDMA signal including a plurality of subcarriers and a plurality of OFDMA symbol periods, wherein the plurality of synchronization channel signal sequence elements are distributed among either or both of the plurality of subcarriers and a plurality of time intervals such as the plurality of OFDMA symbols periods. Also, in accordance with an embodiment of the present invention, a method for receiving OFDMA signals includes the steps of isolating a portion of a bandwidth of the OFDMA signals which includes a synchronization channel signal, detecting a position of the synchronization channel within the portion of the bandwidth of the OFDMA signals, and decoding the synchronization channel signal to derive at least partial cell identification information therefrom. Referring to FIG. 1, an orthogonal frequency division multiple access (OFDMA) wireless communication system 100 in accordance with an embodiment of the present invention includes a plurality of base stations 110 and a wireless communication device 120. The plurality of base {stations 110 communicate with the wireless communication device 120 via OFDMA radio frequency (RF) signals on a plurality of subcarriers for wireless communications. Associated with each of the plurality of base stations 110 is a coverage area 125 wherein the wireless communication device 120 can receive OFDMA signals from and transmit signals to one or more of the plurality of base stations 110. The wireless communication device 120 will typically receive signaling and other messaging from a base station having the strongest signal strength, or otherwise some preferable signal characteristics such that the particular base station 110 is the "best server" to the particular wireless communication device 120. The plurality of base stations 110 are coupled to a network system controller 130 for centralized control of the OFDMA wireless communication system. An OFDMA wireless communication system is a multi-carrier modulation scheme which has been proposed as a next generation solution for present wide- area code division multiple access (WCDMA) wireless communication systems. OFDMA is a more general case of an orthogonal frequency domain multiplexing (OFDM) system wherein data for different users can be transmitted simultaneously on different subcarriers. OFDMA wireless communication systems have a large number of subcarriers, wherein a subcarrier only occupies a small fraction of the OFDMA channel bandwidth (e.g., fifteen kilohertz (kHz) per subcarrier in a five megahertz (MHz) OFDMA channel bandwidth). Thus, for example, in a five MHz range, there could be approximately three hundred subcarriers. OFDMA system design provides a highly scaleable, multiple system bandwidth solution because, as OFDMA systems are designed to work in different bandwidths, more subcarriers can be added as needed. In addition, the OFDMA system design being contemplated for next-generation evolution of the WCDMA system supports both a synchronized system and an unsynchronized system and allows for a large number base station identifiers (cell index) and OFDMA symbol structures with both short and long cyclic prefix lengths. An OFDMA system in accordance with the embodiment of the present invention defines a synchronization channel which significantly reduces the time required for a wireless communication device 120 to synchronize to the OFDMA system by acquiring the OFDMA system timing simultaneous with identifying the strongest base station 110, or "best server" as described above, for establishing communication therewith (i.e., the initial acquisition and cell search time). The OFDMA initial acquisition and cell search process should detect an OFDMA symbol timing, a frame boundary and a frequency error as well as detect cell specific information such as an identification of the base station 110 and, if necessary, other cell specific information such as the system bandwidth, the number of transmission antennas on the base station 110 or a cyclic prefix length. The synchronization signal in accordance with the embodiment of the present invention includes at least partial cell (i.e., base station) identification information. The cell identification information of the synchronization channel could be partial cell identification information identifying a group of individual base stations 110 (e.g., cell group identification information) or could be full cell identification information identifying a unique base station 110, and may further provide sector identification information in embodiments in which base stations 110 are partitioned by antenna coverage patterns and resource allocation into multiple sectors. Referring to FIG. 2, an exemplary OFDMA frame structure depicts a single OFDMA frame 200 of ten milliseconds transmission time comprising one hundred and forty OFDMA symbols. The frame 200 includes twenty sub-frames 210, 220, where the first sub-frame 210 is the synchronization channel occupying a seven OFDMA symbol sub-frame 210 where the seven OFDMA symbols 230 form a short cyclic prefix (CP) sub-frame. The remaining nineteen sub-frames 240 can either be a long CP sub-frame having six OFDMA symbols 240 or a short CP sub- frame having seven OFDMA symbols 230. While the example in FIG. 2 depicts the synchronization channel in a first sub-frame 210 having a short cyclic prefix, location of the synchronization channel and the cyclic prefix thereof can be defined in any manner or location to accommodate the OFDMA system design. By locating the synchronization channel in the first sub-frame 230 (as shown) or the last sub-frame in accordance with another embodiment of the present invention, the frame boundary is defined by the synchronization channel. Referring to FIG. 3, an OFDMA frame structure in accordance with an alternate embodiment of the present invention is depicted. In accordance with this alternate embodiment, the synchronization channel 310 is assigned to the end of more than one of the twenty sub-frames 320 in order to detect the synchronization channel 310 regardless of the CP length. The synchronization channel 310 is transmitted every N sub-frame 320 in order to reduce the initial acquisition and cell search time and memory size of initial acquisition in unsynchronized OFMDA systems, where N is an aliquot of twenty. It will be recognized by those skilled in the art that the system parameters of the sub-frames, the length and number of symbols of the OFDMA system frame and other frame structure parameters may be modified in accordance with a plurality of system designs, and the frame structure of an OFDMA system in accordance with the present invention is not restricted to the embodiments of FIG. 2 or FIG. 3. The synchronization channel, in accordance with an embodiment of the present invention, is transmitted within a localized portion of the bandwidth of the OFDMA signal, e.g., the center 1.25 MHz bandwidth of the OFDMA signal, regardless of the system bandwidth, thereby reducing the initial acquisition and cell search time while preserving the scalability of the OFDMA wireless communication system. Referring to FIG. 4, predetermined resource blocks 410 are predefined frequency bands. While it is recognized that any frequency band can be defined for the resource blocks, in accordance with one embodiment of the present invention, the resource block (RB) size is 0.375 MHz and the synchronization channel 420 is generally defined to be 1.5 MHz, thus occupying four resource blocks 410. Subcarrier symbols in system bandwidth except for the center resource blocks 410 occupied by the synchronization channel 420 are utilized for other channels. In another embodiment, the bandwidth of the synchronization channel is related to the OFDMA signal bandwidth. Some examples of this are OFDMA system bandwidths 430, 440, 450,460, 480. In a twenty megahertz OFDMA system 430 (having forty-eight resource blocks 410) and a ten megahertz OFDMA system 440 (having twenty-four resource blocks 410), the synchronization channel 420 uses the central twelve resource blocks 410. In a five megahertz OFDMA system 450 (having twelve- resource blocks 410), the synchronization channel 420 uses all twelve resource blocks 410. In a 2.5 MHz OFDMA system 460 (having six resource blocks 410), the synchronization channel 420 uses only the central four resource blocks 410. Utilizing the symmetry of the synchronization channel 420, the spectrum 470 of the synchronization channel 420 covers the central portion of the four resource locks 410 of the synchronization channel 420. Unused subcarriers on either side of the synchronization channel spectrum 470 can be used for guard bands or data (e.g., low rate channels such as acknowledgements of received uplink traffic, or other data streams/channels). In another embodiment where the bandwidth of the synchronization channel is related to the OFDMA signal bandwidth, the synchronization channel signal may be repeated in the frequency dimension to further improve performance. For example, the synchronization channel signal information may be contained in the central four resource blocks. Then, each additional set of four resource blocks that are within the synchronization channel bandwidth may contain another transmission or repetition of the synchronization channel signal contained in the central four resource blocks. In addition to the partial or full cell identification information or the repetition or transmission of the synchronization channel signal, for five megahertz or larger bandwidth OFDMA systems, the synchronization channel 420 can use frequency bands other than the center four resource blocks to enhance cell search performance. For example, all or a portion of additional cell specific information such as frequency reference information, transmission antenna information, pilot stream information or cyclic prefix (CP) length information could be included in the synchronization channel 420 information. In addition, the OFDMA system could be designed to redundantly transmit the synchronization channel on two or more of a plurality of subcarriers the portion of bandwidth occupied by the synchronization channel 420. For the case where the OFDMA system bandwidth is 1.25 MHz 480, only three resource blocks 410 can be accommodated and the synchronization channel 420 uses all three resource blocks 410. While a number of variations of OFDMA system bandwidth have been shown, other structures are possible wherein the synchronization channel is transmitted in a localized portion of the OFDMA system bandwidth. FIG. 5 depicts a five megahertz OFDMA communication system signal bandwidth where the localized synchronization channel bandwidth 510 is located in the center 1.25 MHz of the five megahertz bandwidth and within, but smaller than a bandwidth spanned by a multiple number of resource blocks 520. Tn this instance, the synchronization channel bandwidth 510 does not cover a multiple of the resource block size 520. In accordance with the embodiment of the present invention, a data signal 530 is transmitted simultaneously with the synchronization channel in a portion of the bandwidth spanned by an integer number of resource blocks 520 that is not utilized by the synchronization channel 510. For improved detection of the data signal 530, it may be separated from the synchronization channel by bandwidths where no information is transmitted called guard bands 540. The synchronization channel signal is a sequence divided into synchronization channel signal sequence elements. An example of a preferred sequence type in accordance with the present invention is a generalized chirp like (GCL) sequence. For example, a length-NG GCL sequence of "index" u which is defined as where b is a complex scalar of unit amplitude and and NG is a prime number (i.e., NG=NGX1) is particularly suitable for a sequence divided into synchronization channel signal sequence elements in accordance with the present invention. Where NG is a prime number., the cross-correlation between any two sequences of distinct "class" is optimal and there will NG-1 unique sequences in the set that can be used as unique group identifiers or unique cell identification information. The GCL sequence can be represented more simply and compactly by choosing 6=1 and q = 0. Additional examples of sequence types that can be used for the synchronization channel sequence elements in accordance with the present invention may include a Pseudo-random Noise (PN) sequence or a maximal length binary sequence. When a structured sequence with limited choices of sequence length, (such as GCL or maximal-length binary) is used, the number of elements in the original sequence may not match size of the synchronization channel. In this case, the sequence may be modified to fit within the resources available for the synchronization channel signal sequence (e.g., by truncation or cyclic extension thereof). In accordance with another aspect of the embodiment of the present invention, the synchronization signal includes a plurality of synchronization channel signal sequence elements that are distributed over the OFDMA signal subcarriers and/or the OFDMA symbol periods as determined by the OFDMA system design or by signal propagation conditions that the system is expected to operate in. FIG. 6, comprising FIGs. 6A, 6B and 6C, depicts frame structures for synchronization channel sequence element assignment in accordance with the present invention wherein the synchronization channel sequence elements are distributed over frequency (the subcarriers) first and then over time. The present invention, however, is not limited to this synchronization channel sequence element assignment scheme and may alternatively distribute the synchronization channel sequence elements over time first and then frequency if, for example, the system design allows changes in time faster than in frequency. Referring to FIG. 6A, the synchronization channel signal is transmitted over a sub-frame 610 with a frame structure of seven OFDMA symbols, wherein the synchronization channel sequence elements are transmitted on a plurality of subcarriers in adjacent or proximal OFDMA symbol periods. While not shown, in some embodiment's pilot symbols or other symbols such as control symbols may occupy part or all of one or more of the OFDMA symbol periods in sub-frame 610, such that the time spacing between some of the aforementioned proximal OFDMA symbol periods may be more than one OFDMA symbol period. In accordance with the present invention, a first OFDMA symbol period 620 includes a common GCL sequence of modulation symbols or zeros forming thirty-eight sequence elements mapped onto thirty-eight subcarriers, the GCL sequence in the first OFDMA symbol period 620 being common for all of the base stations 110 in the OFDMA wireless communication system 100. By using every other sub-carrier (e.g., even numbered subcarriers) for this common GCL sequence 620, the waveform can have a predetermined time domain symmetry. This common GCL sequence 620 may be present in. all synchronization channel transmissions and may be located in the first OFDMA symbol period of the sub- frame 610, thereby utilized as a frame boundary indicator. Referring to FTG. 7, an example of the sub-carrier mapping of the synchronization channel signal in the first OFDMA symbol period 620 is shown where modulated symbols are mapped to every other subcarrier (the thirty-eight occupied subcarriers 702) with the intervening subcarriers 704 having zeros or nuE sets mapped thereto. The modulation symbols are mapped to even numbered subcarriers in order to create or define the symmetry of the waveform in the time domain (i.e., the predetermined time domain symmetry of the synchronization channel signal waveform). This symmetry characteristic can be utilized for coarse OFDMA symbol timing detection and frequency error detection. Referring back to FIG. 6A, the subsequent six OFDMA symbol periods 630 include the GCL sequence unique to a group of cells or base stations, or unique to the cell or base station 110 (depending on the embodiment) as a plurality of synchronization channel sequence elements mapped onto a plurality of subcarriers, each OFDMA symbol period having all seventy-five subcarriers used for the GCL synchronization channel sequence elements and filling the six OFDMA symbol periods 630 in a "zig-zag" fashion. For example, FIG. 6A depicts the synchronization channel signal GCL sequence including 449 synchronization channel sequence elements. The second OFDMA symbol period 630 is filled with synchronization channel signal sequence elements (phases) 0 to 74 ordered from top to bottom. The third OFDMA symbol period 630 is filled with synchronization channel signal sequence elements 75 to 149 ordered from bottom to top, but in an alternate embodiment could also be ordered from top to bottom. In a like manner, the remaining OFDMA symbol periods 630 are filled with the remaining synchronization channel signal sequence elements, with the sixth OFDMA symbol being filled with synchronization channel signal sequence elements (phases) 375 to 449 ordered from bottom to top. Instead of filling the OFDMA symbol periods of the synchronization channel in a "zig-zag" fashion, the OFDMA symbol periods 630 could all be filled from top to bottom or vice versa in accordance with the OFDMA system design, the sequence type and/or the processing necessary to combine the synchronization channel sequence elements. In addition, instead of filling the synchronization channel in a frequency-first fashion, the OFDMA symbol periods 630 could be filled in a time-first fashion (e.g., from left to right on each subcarrier, right to left on each subcarrier, or left to right on some subcarriers and right to left on other subcarriers). Or, instead of the above described filling methods, any arbitrary two-dimensional filling pattern could be used. Referring to FIG. 6B, a synchronization channel signal unique to a cell or base station 110 or a group of cells (e.g., a GCL sequence common to multiple cells) is also transmitted over a sub-frame 610 with a frame structure of seven OFDMA symbols, wherein the synchronization channel sequence elements are transmitted on a plurality of subcarriers in adjacent or proximal OFDMA symbol periods. In accordance with this embodiment of the present invention, the first OFDMA symbol period 620 includes zeros mapped onto 37 subcarriers and elements of a cell-specific or group-specific GCL sequence forming thirty-eight sequence elements mapped onto thirty-eight subcarriers, for one or a group of the base stations 110 in the OFDMA wireless communication system 100. The subsequent six OFDMA symbol periods 630 include additional elements of the cell-specific GCL sequence mapped onto a plurality of subcarriers, each OFDMA symbol period having all seventy-five subcarriers (phases), filling the six OFDMA symbol periods 630 in the "zig-zag" fashion. FIG. 6B depicts the synchronization channel signal GCL sequence including 487 synchronization channel sequence elements. The second OFDMA symbol period 630 is filled with synchronization channel signal sequence elements (phases) 38 to 112 ordered from bottom to top. The third OFDMA symbol period 630 is filled with synchronization channel signal sequence elements 113 to 187 ordered from top to bottom. In a like manner, the remaining OFDMA symbol periods 630 are filled with the remaining synchronization channel signal sequence elements, with the sixth OFDMA symbol being filled with synchronization channel signal sequence elements (phases) 413 to 487 ordered from top to bottom. Referring to FIG. 6C, another alternate structure of a synchronization channel sequence assignment is shown. In accordance with the present invention, the synchronization channel sequence elements may be distributed over the OFDMA symbol periods (as shown in FTG. 6A) or may be distributed over more than one of the plurality of subcarriers of the OFDMA signal, or a combination of both distributions. In the alternate embodiment of FIG. 6C, there are ten synchronization channel symbol periods in the frame structure 640. In order to accommodate a longer common GCJL sequence (e.g., longer than thirty-eight sequence elements), a first portion 650 of the synchronization channel includes two OFDMA symbol periods 660, 670. The first OFDMA symbol period 660 may be used as a frame boundary indicator. In accordance with the alternate embodiment of the present invention, the synchronization channel sequence elements are mapped to every second sub-frame such that the first synchronization channels 650, which includes seventy-five subcarriers, is mapped to the first OFDMA symbol period 660 and the second OFDMA symbol period 670. Each of the OFDMA symbol periods 660, 670 with the common GCL sequence includes thirty-eight sub-carriers, where the use of even numbered sub-carriers maintains the predetermined time domain symmetry of the synchronization channel as shown in FIG. 7 and discussed above. Channel conditions could change during a gap between the sub-frames. To accommodate the differential processing of the synchronization channel sequence elements, the subsequent OFDMA symbol period 670 may repeat, as shown in FIG. 6C, the last sequence element (e.g., phase 37) of the previous OFDMA symbol period 620. Following the first synchronization channels 660, the second synchronization channels 680 include eight OFDMA symbol periods having 592 synchronization channel sequence elements mapped to seventy-five subcarriers for each OFDMA symbol period. The eight OFDMA symbol periods 680 for the second synchronization channels use every second sub-frame and are filled in a "zig-zag" fashion (as shown) or any arbitrary two-dimensional filling pattern as discussed above, repeating the last sequence element of an OFDMA symbol period as the first sequence clement of the next OFDMA symbol period. Accordingly, the third OFDMA symbol period is filled with synchronization channel signal sequence elements (phases) 0 to 74 ordered from top to bottom. The fourth OFDMA symbol period is filled with synchronization channel signal sequence elements 74 to 148 ordered from bottom to top. Within each synchronization channel sequence element, GCL sequence elements may preferably be employed such that differential processing of the GCL sequence elements will provide determination of the sequence index. GCL sequence elements have 0 dB peak-to-average power ratio (PAPR) and optimal cross correlation properties. If a GCL sequence is applied in the frequency domain on all subcarriers, the properties still hold for the corresponding time-domain waveform since the Fourier transform of a GCL sequence is also a GCL sequence. In addition, if a GCL sequence is passed through a differential demodulator, the resulting output sequence is a complex exponential with a frequency that corresponds to the original sequence index. Thus, using GCL sequence elements, each synchronization channel signal sequence element will have sequence index properties for inherently determining the sequence index thereof. As mentioned earlier, other types of sequences could also be used, but it is preferred that the sequence have properties that enable sequence index detection based on the differential demodulation of the sequence. One example of a sequence other than GCL that has such properties is a maximal-length binary sequence, since a differential demodulation of a maximal-length binary sequence produces a cyclically shifted version of the same sequence with a predetermined shift value. Thus, with a maximal-length binary sequence, each cell ID can be associated with a particular cyclic shift value of the sequence, and the cell ID can be recovered based on differential processing. Referring to FIG. 8, a block diagram of the OFDMA base station 110 includes a base station controller 810 coupled to the network controller 130 and controlling the operation of the base station 110. The controller is coupled to receiver circuitry 812 and transmitter circuitry 814, and may further include a receiver/transmitter switch 816 for controlling the transmission and reception of the OFDMA signals over the antenna 818 if communications over the antenna 818 arc duplexed. OFDMA signals received by the receiver circuitry 812 arc demodulated thereby and. provided to the controller 810 for decoding thereof. In addition, the controller 810 provides signals to the transmitter circuitry 814 for modulation thereby and transmission therefrom. While a single antenna 818 is shown, it is to be understood that base stations 110 may be, and are typically, configured into sectors and may employ multiple antennas for receive diversity, and/or transmission beamforming applications, space time coding, multiple input multiple output (MIMO), or other system design transmission signaling schemes. Therefore, many transmit and receive antenna configuration are possible in various embodiments and FIG. 8 is not intended to be a complete schematic representation of such antenna configurations but rather to exemplify components helpful toward understanding the embodiments disclosed herein. With multiple antennas, it is useful to convey the number of antennas to the wireless communication devices 120 to know how many pilot streams to search for during initial acquisition and cell search. Thus, in accordance with an embodiment of the present invention, the additional cell specific information that may be transmitted as part of the synchronization channel signal may include the number of antennas of the base station 110 or pilot stream information. The controller 810 is coupled to a storage device 820 which stores information for the operation of the base station 110 such as cell identification information and other cell specific information such as frequency reference information, transmission antenna information (such as the number of antennas), pilot stream information and cyclic prefix length information. Tn accordance with the present invention, the controller 810 includes a synchronization channel generator 822 for generating a synchronization channel signal having time domain symmetry within a portion of the OFDMA signal bandwidth and comprising at least partial cell identification information, the synchronization channel generator 822 providing the synchronization channel signal to the transmitter circuitry 816 for transmission therefrom. Sometimes the synchronization channel generator 822 generates a synchronization channel signal including at least a portion of additional cell specific information. A data signal generator 824 generates an OFDMA data signal for providing to the transmitter circuitry 816 for transmission therefrom and, in accordance with one aspect of the present invention wherein the bandwidth is divided into a set of resource blocks, the data signal is transmitted simultaneously with the synchronization channel signal on a portion of a bandwidth spanned by an integer number of predetermined resource blocks when the synchronization channel signal spans a bandwidth smaller than a bandwidth spanned by the integer number of predetermined resource blocks. Data could be voice or MBMS transmissions that are generated by a calling wireless communication device 120 or by a content provider and may be multiplexed onto the subcarriers and interleaved at the base station 110 or multiplexing may be performed by the network controller 130. The synchronization channel generator 822 defines the time domain symmetry of the synchronization channel signal in one embodiment by mapping modulation signals and zeros onto a plurality of subcarriers thereof. Referring to FIG. 9, operation of the synchronization channel generator 822 in accordance with the embodiment of the present invention begins by retrieving information 910 from the storage device 820. At a minimum, this information includes cell identification information uniquely identifying the base station 110 or at least partial cell identification information, such as group cell identification information. Additional cell specific information, as discussed above, could also be retrieved 910. Next, the synchronization channel signal is generated 912 by encoding the cell identification information. The synchronization channel signal is parsed into a plurality of synchronization channel sequence elements 914. The predetermined time domain symmetry of the synchronization channel signal is then defined 916. In accordance with the present invention, step 916 would include providing an even number of subcarriers in a resource block and may include mapping the generated synchronization channel signal as modulation symbols and zeros onto a plurality of subcarriers where the modulation symbols are mapped to every nth subcarrier of at least a portion of the subcarriers utilized for the synchronization channel signal, where n is an integer greater than or equal to two. After the time domain symmetry is defined 916, the synchronization channel signal is provided 918 to the transmitter circuitry 816 for transmission from the base station 110. The synchronization channel signal is periodically transmitted from the base station 110 to enable initial acquisition and cell search. Thus, the synchronization channel signal may, in addition to the foregoing be provided to the transmitter circuitry 816 redundantly either in time or across subcarriers for improved initial acquisition and cell search. The redundancy and the content of the synchronization channel signal can be revised and/or redefined based upon the bandwidth of the OFDMA signal (i.e., in response to the scaling of the OFDMA signal bandwidth). Referring to FIG. 10, a wireless communication device 120 in accordance with the embodiment of the present invention is shown. The wireless communication device 120 includes an antenna 1002 for receiving and transmitting radio frequency (RF) signals. A receive/transmit switch 1004 selectively couples the antenna 1002 to receiver circuitry 1006 and transmitter circuitry 1008 in a manner familiar to those skilled in the art. The receiver circuitry 1006 demodulates and decodes the RF signals to derive information therefrom and is coupled to a controller 1010 for providing the decoded information thereto for utilization thereby in accordance with the function(s) of the wireless communication device 120. The controller 1010 also provides information to the transmitter circuitry 1008 for encoding and modulating information into RF signals for transmission from the antenna 1002. While a single antenna 1002 is depicted, those skilled in the art will recognize that diversity antennas could be used with diversity receivers for improved signal reception. The controller 1010 is coupled to user interface circuitry 1012 including, for example, a display for presenting video output to a user, a speaker for providing audio output to the user, a microphone for receiving voice input, and user controls, such as a keypad, for receiving user input thereby. The controller 1010 is further coupled to a nonvolatile memory device 1014 for storing information therein and for retrieving and utilizing information therefrom. In accordance with the embodiment of the present invention, the receiver circuitry 1006 includes a synchronization channel signal filter device 1016 for isolating a portion of the OFDMA signal bandwidth which includes the synchronization channel signal. The synchronization channel signal filter device 1016 could be a bandpass filter or any other device or process for filtering the OFDMA signal to isolate a localized portion of the OFDMA signal bandwidth. For example, a fast Fourier transform (FFT) could be utilized to isolate the localized portion of the OFDMA signal bandwidth during processing instead of a hardware filter. Once isolated, the signal is provided to the controller for initial acquisition and cell search processing. Referring to FTG. 11, the initial signal acquisition and cell search process begins by examining the signal filtered by the filter 1016 to determine if there is any signal 1110. When a signal is detected 1110, the initial acquisition and cell search method is performed in accordance with the present invention. First, the predetermined time domain symmetry of the synchronization channel signal is utilized to perform coarse OFDMA symbol timing detection and fractional frequency offset detection 1112. This step 1112 could be performed by differential correlation of the received synchronization channel signal being calculated in the time domain or by correlation calculation with known synchronization channel signal sequence elements in the time domain. Generalized chirp like (GCL) sequences are preferably suited to differential processing in accordance with the embodiment of the present invention. However, as mentioned previously, the present invention can use other sequence types. The time domain waveforms of the GCL-modulated OFDM signals have low PAPR, In addition, because of the use of different indices of the GCL sequences, any pair of the sequence elements will have low cross correlation at all time lags, which improves the code detection and CIR estimation. Also, GCL sequences have constant amplitude, and the NG-point DFT of GCL sequences also have constant amplitude. GCL sequences of any length additionally have an "ideal" cyclic autocorrelation (i.e., the correlation with the circularly shifted version of itself is a delta function). And, the absolute value of the cyclic cross-correlation function between any two GCL sequences is constant and equal to u1, and u2 are all relatively prime to NG (a condition that can be easily guaranteed if NG is a prime number). The cross-correlation at all lags actually achieves the minimum cross-correlation value for any two sequence elements that have the ideal autocorrelation property (meaning that the theoretical minimum of the maximum value of the cross-correlation over all lags is achieved). The minimum is achieved when the cross correlations at all lags is equal to The cross correlation property allows the impact of an interfering signal be evenly spread in the time domain after correlating the received signal with the desired sequence in the time domain. Hence, the cell-search symbol can also be used to perform or assist coherent channel estimation at the wireless device even before the broadcast pilot symbols are processed. Compared with BPSK or even QPSK preambles, the complex-valued GCL sequences can be systematically constructed with guaranteed good PAPR and good correlation. Differential processing of the GCL sequence elements enables the one step fast cell search for GCL sequence elements, step 1112. To facilitate differential processing in accordance with the embodiment of the present invention, the sequence elements have preferably been generated in accordance with a sequence design methodology for a sequence length Np where a prime number NG is the smallest prime number larger than Np. The integer "u" is the sequence index. The sequence elements were generated according to NG-1 sequence elements are generated having an optimal cyclic cross correlation between any pair of them. The sequence elements have been truncated to Np and distributed over Np subcarriers. Due to the oversampling introduced in OFDMA signaling with null subcarriers, and also the use of localized bandwidth for the synchronization signal, the PAPR will be degraded to different degrees for different "u" from the theoretical OdB value (at Nyquist sampling rate). If desired, indices that have the best PAPR among NG-1 candidates can be chosen. The cell search sequences used by different cells are obtained from different indices "u" of these GCL sequence elements. The index "u" will also act as a cell ID. The cell search 1112 determines directly the sequence indices "u" (and hence the strongest or candidate cell ID's or group ID's) from the received signal. First, the coarse OFDMA cell-search symbol timing is determined (e.g., using the time domain symmetry of the cell-search symbol). Then, the fractional part of the frequency offset is estimated and removed (e.g., based on the phase of the half- symbol differential correlation, peak). After these steps, a block of N received time- domain samples representing the received cell-search symbol is transformed to the frequency domain using the usual FFT process. Assuming that an integer frequency offset may still be present, the occupied subcarriers (even vs. odd) can be determined next by various techniques such as a maximum energy detector (e.g., total energy in the even subcarriers of the cell-search symbol vs. energy in the odd subcarriers). The frequency domain data on the occupied subcarriers as Y(m) for m = 1 to Np (i.e., ignoring the unused subcarriers) is denoted where Su(m) is the GCL sequence mapped onto those subcarriers. Next, a vector of "differential-based" values is computed based on the pairs of occupied subcarriers. These values, which are obtained by differentially demodulating the occupied subcarriers of the received symbol, are conveniently collected into vector format (e.g., a differential-based vector) for efficient FFT- based processing. The differential-based vector is computed as where "O " denotes conjugation. Other ways to obtain the "differential-based" vector may include, but are not limited to: or where "abs( )" denotes the absolute value. Assuming that there is only one base station, and that it is transmitting a cell-search symbol with a GCL sequence index of u, and that the channel does not change significantly between two adjacent occupied subcarriers, which is approximately satisfied as long as the spacing of occupied subcarriers is not too large, ignoring the channel amplitude and frequency offset, Y(m)* Y*(m+1) is approximately equal to Thus, the sequence index information u is carried in the differential-based vector. In the multi-cell case, by processing the differential-based vector and identifying a set of prominent frequency components of the vector, we can identify the strongest cell index and one or more indices of potential handoff candidates as well. To obtain the frequency domain components, a commonly used tool is to take an FFT or IFFT (say T-point, T>=NP-1) on {Z(m)} (step 1114) to get The peak position (say nmax) of {z(n)} gives information about the strongest cell's index u, i.e., the mapping between the identified prominent frequency component at nmax to a corresponding transmitted sequence index is determined as The peak values are also rough estimates of the channel power at the occupied subcarriers. Thus, IFFT of the synchronization channel signal in the frequency domain is used to detect the frame boundary and decode the cell identification information 1114. Thus, utilizing the sequence index properties of the synchronization channel sequence elements, multiplying one sequence element by the complex conjugate of a next sequence element will derive the sequence index u 1114. Accordingly, in a single step, the controller 1010 can perform GCL sequence index detect to extract the cell specific information (e.g., u) from the synchronization channel signal. When the synchronization channel signal is determined to be, in some embodiments, the strongest synchronization channel signal 1116, wireless OFDMA communication is established with the base station 1118. Note that for the purpose of explanation, the above equations were described for the case of the GCL sequence elements being mapped to different subcarriers of one OFDMA symbol period. However, the proposed detection method can also be applied when the sequence is mapped in other ways, such as "zig-zag". In general, the differential demodulation step can be performed over adjacent sequence elements even if the adjacent sequence elements are mapped to different OFMDA symbol periods and/or different subcarriers. In addition, the differential processing from multiple received instances of the synchronization channel can be combined to further improve the detection robustness. Multiple received instances of the synchronization channel may be available due to either receive diversity with multiple antennas, or from subsequently received synchronization signals that are transmitted periodically by the base station, for example. As described for some embodiments of the invention, the time domain symmetry of the synchronization signal can be provided by mapping modulation symbols or sequence elements to even-numbered subcarriers in the localized synchronization channel bandwidth and zeros to other subcarriers in the localized synchronization channel bandwidth. Other embodiments of the invention may utilize other methods for providing time domain symmetry. One example includes mapping modulation symbols or sequence elements to every Nth subcarrier in the localized synchronization channel bandwidth and zeros to the other subcarriers in the localized synchronization channel bandwidth, where N is a positive integer, and where the subcarrier in the localized synchronization channel bandwidth containing the first of the every Nth subcarrier can be arbitrarily chosen. An additional example is to use modulation symbols or sequence elements that are purely real (i.e., their imaginary part is zero) in the localized synchronization channel bandwidth, since the Fourier transform of a real signal is symmetric in magnitude around, its central portion. Methods of sequence design and/or mapping and/or signal repetition other than the provided examples can also be used to provide predetermined time domain symmetry. Thus, it can be seen that the present invention provides an initial acquisition and cell search method utilizing synchronization channel signal sequence elements with low computational load and a small number of receiver processing steps which nevertheless provides the four main function of initial acquisition and cell search (i.e., OFDMA symbol timing detection, frequency error detection, frame boundary detection and cell specific information detection) in an OFDMA system supporting multiple system bandwidths, both synchronized and un-synchronized systems, a large cell index and an OFDMA symbol structure with both short and long cyclic prefix length. While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments arc only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their equivalents. CLAIMS 1. A method in a wireless communication system, the method comprising the step of transmitting an orthogonal frequency domain multiple access (OFDMA) signal including a synchronization channel signal, the synchronization channel signal comprising a plurality of synchronization channel signal sequence elements and the OFDMA signal comprising a plurality of subcarriers, wherein each of the plurality of synchronization channel signal sequence elements have sequence index properties associated therewith for inherently determining a sequence index in response to the sequence index properties. 2. The method of Claim 1 wherein the sequence index properties correspond to differential processing, and wherein the sequence index of the plurality of synchronization channel signal sequence elements are determined by differential processing thereof. 3. The method of Claim 1 wherein the step of transmitting an OFDMA signal comprises the step of transmitting an OFDMA signal including the synchronization channel signal transmitted within a localized portion of a bandwidth of the OFDMA signal, the synchronization channel signal having predetermined time domain symmetry within the localized portion of the bandwidth and comprising first information for providing at least partial cell identification information. 4. The method of Claim 1 wherein the synchronization channel signal sequence elements form a general chirp like (GCL) sequence. 5. The method of Claim 1 wherein the synchronization channel signal sequence elements form a Pseudo-random Noise (PN) sequence. 6. The method of Claim 1 wherein the synchronization channel signal sequence elements form a maximal length binary sequence. 7. An orthogonal frequency domain multiple access (OFDMA) base station comprising: a synchronization channel generator generating a synchronization channel signal comprising a plurality of synchronization channel signal sequence elements, each of the plurality of synchronization channel signal sequence elements have sequence index properties associated therewith for inherently determining the sequence index in response to the sequence index properties; and transmitter circuitry transmitting an OFDMA signal comprising a plurality of subcarriers, wherein the transmitter circuitry is coupled to the synchronization channel generator and transmits the OFDMA signal comprising the plurality of synchronization channel signal sequence elements distributed over a portion of the plurality of subcarriers. 8. The OFDMA base station of Claim 7 further comprising a storage device storing cell identification information, wherein the synchronization channel generator is coupled to the storage means and generates the synchronization channel signal having predetermined time domain symmetry within a localized portion of a bandwidth of an OFDMA signal and comprising the cell identification information, and wherein the transmitter circuitry transmits the synchronization channel signal within the localized portion of the bandwidth of the OFDMA signal. 9. A wireless communication receiver for receiving orthogonal frequency domain multiple access (OFDMA) signals comprising: receiver circuitry receiving and demodulating OFDMA signals, the receiver circuitry comprising a filter filtering the OFDMA signals to isolate a bandwidth of the OFDMA signals which includes a synchronization channel signal, the synchronization channel signal comprising a plurality of synchronization channel signal sequence elements, each of the plurality of synchronization channel signal sequence elements have sequence index properties associated therewith for inherently determining the sequence index in response to the sequence index properties; and a controller coupled to the receiver circuitry and decoding the synchronization channel signal in response to detecting the plurality of synchronization channel signal sequence elements distributed over a portion of the OFDMA signals, the controller decoding the synchronization channel signal in response to detecting the plurality of synchronization channel signal sequence elements and decoding the plurality of synchronization channel signal sequence elements in response to the sequence index properties associated therewith. 10. The wireless communication receiver of Claim 9 wherein the controller decodes the plurality of synchronization channel signal sequence elements by differential processing thereof. 11. The wireless communication receiver of Claim 10 wherein the controller decodes the plurality of synchronization channel signal sequence elements by general chirp like (GCL) sequence differential processing thereof. 12. The wireless communication receiver of Claim 9 wherein the filter filters the OFDMA signals to isolate a portion of the bandwidth of the OFDMA signals which includes a synchronization channel signal, and wherein the controller detects a position of the synchronization channel within the portion of the bandwidth of the OFDMA signals in response to predetermined time domain symmetry of the synchronization channel, the controller decoding the synchronization channel signal to derive at least partial cell identification information therefrom. 13. A method for receiving orthogonal frequency domain multiple access (OFDMA) signals comprising the steps of: isolating a portion of a bandwidth of the OFDMA signals which includes a synchronization channel signal, the synchronization channel signal comprising a plurality of synchronization channel signal sequence elements, each of the plurality of synchronization channel signal sequence elements have sequence index properties associated therewith for inherently determining the sequence index in response to the sequence index properties; detecting the plurality of synchronization channel signal sequences distributed over at least part of the portion of the bandwidth of the OFDMA signals; and decoding the plurality of synchronization channel signal sequence elements in response to the sequence index properties associated therewith. 14. The method of Claim 13 wherein the step of decoding the plurality of synchronization channel signal sequence elements comprises the step of differential processing the plurality of synchronization channel signal sequence elements to derive at least partial cell identification information therefrom. 15. The method of Claim 14 wherein the step of differential processing the plurality of synchronization channel signal sequence elements comprises the step of general chirp like (GCL) sequence differential processing the plurality of synchronization channel signal sequence elements to derive at least partial cell identification information therefrom. 16. The method of Claim 14 wherein the step of differential processing the plurality of synchronization channel signal sequence elements comprises the step of Pseudo-random Noise (PN) sequence differential processing the plurality of synchronization channel signal sequence elements to derive at least partial cell identification information therefrom. 17. The method of Claim 14 wherein the step of differential processing the plurality of synchronization channel signal sequence elements comprises the step of maximal length binary sequence differential processing the plurality of synchronization channel signal sequence elements to derive at least partial cell identification information therefrom. 18. The method of Claim 13 wherein the step of detecting comprises the step of detecting a position of the synchronization channel as a synchronization channel signal within the portion of the bandwidth of the OFDMA signals, and wherein the step of decoding comprises the step of decoding the synchronization channel signal to derive at least partial cell identification information therefrom. A method and apparatus is provided for transmitting an orthogonal frequency domain multiple access (OFDMA) signal including a synchronization channel signal transmitted within a localized portion of a bandwidth of the OFDMA signal (818), the synchronization channel signal having predetermined time domain symmetry within the localized portion of the bandwidth (816). The synchronization channel signal enables an initial acquisition and cell search method with low computational load which provides OFDMA symbol timing detection and frequency error detection by differential processing of sequence elements of the synchronization channel signal (1112) and frame boundary detection and cell specific information detection (1114) in an OFDMA system supporting multiple system bandwidths, both synchronized and un-synchronized systems, a large cell index and an OFDMA symbol structure with both short and long cyclic prefix length.

Full Text

METHOD AND APPARATUS FOR A SYNCHRONIZATION CHANNEL
IN AN OFDMA SYSTEM
FIELD OF THE INVENTION
The present invention generally relates to wireless communication systems,
and more particularly relates to a method and apparatus for a synchronization
channel in an orthogonal frequency division multiple access (OFDMA) system.
BACKGROUND OF THE INVENTION
In a wireless communication system which includes a number of base
stations or cells, an initial task for a wireless communication device is to recognize
and acquire the signals transmitted from the cells. Another primary task is to
search the cells to determine which cell is the best for establishing communication
with. As more and more complex signaling systems are developed, these
important tasks become more difficult and more tirne-consuming. Recently,
orthogonal frequency division multiple access (OFDMA) signaling systems have
been proposed. The OFDMA systems are scalable bandwidth systems designed to
work in different bandwidths. In addition, the OFDMA systems utilize a multi-
carrier modulation approach having, perhaps, hundreds of subcarriers within a
narrow (e.g., 5 MHz) frequency range. While the scalability of OFDMA systems
facilitates the introduction and expansion of such systems, the complexity of
OFDMA systems must nevertheless allow for signal acquisition by OFDMA
wireless communication devices in a timely manner for quick activation and
seamless transition from cell to cell. A synchronization channel is provided for
initial signal acquisition and cell search. However, as the number of cell sites
increases and the complexity of the OFDMA systems increase, the synchronization
channel signal must include more and more information. Parsing the signal into
sequence elements for quick and reliable reception alleviates some of the problem,
but the sequence elements must themselves each carry sequence index information.
Thus, what is needed is a method and apparatus for generating and
processing an improved synchronization channel including a plurality of sequence
elements in an ODFMA system. Furthermore, other desirable features and

characteristics of the present invention will become apparent from the subsequent
detailed description of the invention and the appended claims, taken in conjunction
with the accompanying drawings and this background of the invention.
BRTEF DESCRIPTION OF THE DRAWINGS
The present invention will hereinafter be described in conjunction with the
following drawing figures, wherein like numerals denote like elements, and
FIG. 1 is a diagram of a wireless communication system in accordance with an
embodiment of the present invention;
FIG. 2 is a diagram of a frame structure of an orthogonal frequency domain
multiple access (OFDMA) signal in accordance with an embodiment of the present
invention;
FIG. 3 is a diagram of a frame structure of an OFDMA signal in accordance with
an alternate embodiment of the present invention;
FIG. 4 is a diagram of the signal channel bandwidth occupation in accordance with
an embodiment of the present invention;
FIG. 5 is a diagram of the resource block mapping of the synchronization channel
in accordance with an embodiment of the present invention;
FIG. 6A is a diagram of the synchronization channel sequence assignment in
accordance with an embodiment of the present invention;
FIG. 6B is a diagram of the synchronization channel sequence assignment in
accordance with an alternate embodiment of the present invention;
FIG. 6C is a diagram of the synchronization channel sequence assignment in
accordance with yet another alternate embodiment of the present invention;
FIG. 7 is a diagram of the sub-carrier mapping of the synchronization channel
signal in accordance with the embodiment of the present invention;
FIG. 8 is a block diagram of a base station of the communication system of FIG. 1
in accordance with the embodiment of the present invention;
FIG. 9 is a flowchart of the base station synchronization channel signaling of the
base station of FIG. 8 in accordance with the embodiment of the present invention;

FIG. 10 is a block diagram of a wireless communication device of the
communication system of FIG. 1 in accordance with the embodiment of the present
invention; and
FIG. 11 is a flowchart of the initial activation and cell search of the wireless
communication device of FIG. 10 in accordance with the embodiment of the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with an embodiment of the present invention, a method in a
wireless communication system includes the step of transmitting an orthogonal
frequency domain multiple access (OFDMA) signal including a synchronization
channel signal transmitted within a localized portion of a bandwidth of the
OFDMA signal, the synchronization channel signal having predetermined time
domain symmetry within the localized portion of bandwidth and including
information for providing at least partial cell identification information. In
addition, a method in a wireless communication system in accordance with an
embodiment of the present invention includes the step of transmitting an OFDMA
signal including a synchronization channel signal, the synchronization channel
signal including a plurality of synchronization channel signal sequence elements
and the OFDMA signal including a plurality of subcarriers and a plurality of
OFDMA symbol periods, wherein the plurality of synchronization channel signal
sequence elements are distributed among either or both of the plurality of
subcarriers and a plurality of time intervals such as the plurality of OFDMA
symbols periods.
Also, in accordance with an embodiment of the present invention, a method
for receiving OFDMA signals includes the steps of isolating a portion of a
bandwidth of the OFDMA signals which includes a synchronization channel
signal, detecting a position of the synchronization channel within the portion of the
bandwidth of the OFDMA signals, and decoding the synchronization channel
signal to derive at least partial cell identification information therefrom.
Referring to FIG. 1, an orthogonal frequency division multiple access
(OFDMA) wireless communication system 100 in accordance with an embodiment

of the present invention includes a plurality of base stations 110 and a wireless
communication device 120. The plurality of base {stations 110 communicate with
the wireless communication device 120 via OFDMA radio frequency (RF) signals
on a plurality of subcarriers for wireless communications. Associated with each of
the plurality of base stations 110 is a coverage area 125 wherein the wireless
communication device 120 can receive OFDMA signals from and transmit signals
to one or more of the plurality of base stations 110. The wireless communication
device 120 will typically receive signaling and other messaging from a base station
having the strongest signal strength, or otherwise some preferable signal
characteristics such that the particular base station 110 is the "best server" to the
particular wireless communication device 120. The plurality of base stations 110
are coupled to a network system controller 130 for centralized control of the
OFDMA wireless communication system.
An OFDMA wireless communication system is a multi-carrier modulation
scheme which has been proposed as a next generation solution for present wide-
area code division multiple access (WCDMA) wireless communication systems.
OFDMA is a more general case of an orthogonal frequency domain multiplexing
(OFDM) system wherein data for different users can be transmitted simultaneously
on different subcarriers. OFDMA wireless communication systems have a large
number of subcarriers, wherein a subcarrier only occupies a small fraction of the
OFDMA channel bandwidth (e.g., fifteen kilohertz (kHz) per subcarrier in a five
megahertz (MHz) OFDMA channel bandwidth). Thus, for example, in a five MHz
range, there could be approximately three hundred subcarriers. OFDMA system
design provides a highly scaleable, multiple system bandwidth solution because, as
OFDMA systems are designed to work in different bandwidths, more subcarriers
can be added as needed. In addition, the OFDMA system design being
contemplated for next-generation evolution of the WCDMA system supports both
a synchronized system and an unsynchronized system and allows for a large
number base station identifiers (cell index) and OFDMA symbol structures with
both short and long cyclic prefix lengths.
An OFDMA system in accordance with the embodiment of the present
invention defines a synchronization channel which significantly reduces the time

required for a wireless communication device 120 to synchronize to the OFDMA
system by acquiring the OFDMA system timing simultaneous with identifying the
strongest base station 110, or "best server" as described above, for establishing
communication therewith (i.e., the initial acquisition and cell search time). The
OFDMA initial acquisition and cell search process should detect an OFDMA
symbol timing, a frame boundary and a frequency error as well as detect cell
specific information such as an identification of the base station 110 and, if
necessary, other cell specific information such as the system bandwidth, the
number of transmission antennas on the base station 110 or a cyclic prefix length.
The synchronization signal in accordance with the embodiment of the present
invention includes at least partial cell (i.e., base station) identification information.
The cell identification information of the synchronization channel could be partial
cell identification information identifying a group of individual base stations 110
(e.g., cell group identification information) or could be full cell identification
information identifying a unique base station 110, and may further provide sector
identification information in embodiments in which base stations 110 are
partitioned by antenna coverage patterns and resource allocation into multiple
sectors.
Referring to FIG. 2, an exemplary OFDMA frame structure depicts a single
OFDMA frame 200 of ten milliseconds transmission time comprising one hundred
and forty OFDMA symbols. The frame 200 includes twenty sub-frames 210, 220,
where the first sub-frame 210 is the synchronization channel occupying a seven
OFDMA symbol sub-frame 210 where the seven OFDMA symbols 230 form a
short cyclic prefix (CP) sub-frame. The remaining nineteen sub-frames 240 can
either be a long CP sub-frame having six OFDMA symbols 240 or a short CP sub-
frame having seven OFDMA symbols 230. While the example in FIG. 2 depicts
the synchronization channel in a first sub-frame 210 having a short cyclic prefix,
location of the synchronization channel and the cyclic prefix thereof can be defined
in any manner or location to accommodate the OFDMA system design. By
locating the synchronization channel in the first sub-frame 230 (as shown) or the
last sub-frame in accordance with another embodiment of the present invention,
the frame boundary is defined by the synchronization channel.

Referring to FIG. 3, an OFDMA frame structure in accordance with an
alternate embodiment of the present invention is depicted. In accordance with this
alternate embodiment, the synchronization channel 310 is assigned to the end of
more than one of the twenty sub-frames 320 in order to detect the synchronization
channel 310 regardless of the CP length. The synchronization channel 310 is
transmitted every N sub-frame 320 in order to reduce the initial acquisition and cell
search time and memory size of initial acquisition in unsynchronized OFMDA
systems, where N is an aliquot of twenty. It will be recognized by those skilled in
the art that the system parameters of the sub-frames, the length and number of
symbols of the OFDMA system frame and other frame structure parameters may
be modified in accordance with a plurality of system designs, and the frame
structure of an OFDMA system in accordance with the present invention is not
restricted to the embodiments of FIG. 2 or FIG. 3.
The synchronization channel, in accordance with an embodiment of the
present invention, is transmitted within a localized portion of the bandwidth of the
OFDMA signal, e.g., the center 1.25 MHz bandwidth of the OFDMA signal,
regardless of the system bandwidth, thereby reducing the initial acquisition and
cell search time while preserving the scalability of the OFDMA wireless
communication system. Referring to FIG. 4, predetermined resource blocks 410
are predefined frequency bands. While it is recognized that any frequency band
can be defined for the resource blocks, in accordance with one embodiment of the
present invention, the resource block (RB) size is 0.375 MHz and the
synchronization channel 420 is generally defined to be 1.5 MHz, thus occupying
four resource blocks 410. Subcarrier symbols in system bandwidth except for the
center resource blocks 410 occupied by the synchronization channel 420 are
utilized for other channels. In another embodiment, the bandwidth of the
synchronization channel is related to the OFDMA signal bandwidth. Some
examples of this are OFDMA system bandwidths 430, 440, 450,460, 480.
In a twenty megahertz OFDMA system 430 (having forty-eight resource
blocks 410) and a ten megahertz OFDMA system 440 (having twenty-four
resource blocks 410), the synchronization channel 420 uses the central twelve
resource blocks 410. In a five megahertz OFDMA system 450 (having twelve-

resource blocks 410), the synchronization channel 420 uses all twelve resource
blocks 410. In a 2.5 MHz OFDMA system 460 (having six resource blocks 410),
the synchronization channel 420 uses only the central four resource blocks 410.
Utilizing the symmetry of the synchronization channel 420, the spectrum 470 of
the synchronization channel 420 covers the central portion of the four resource
locks 410 of the synchronization channel 420. Unused subcarriers on either side of
the synchronization channel spectrum 470 can be used for guard bands or data
(e.g., low rate channels such as acknowledgements of received uplink traffic, or
other data streams/channels).
In another embodiment where the bandwidth of the synchronization
channel is related to the OFDMA signal bandwidth, the synchronization channel
signal may be repeated in the frequency dimension to further improve
performance. For example, the synchronization channel signal information may be
contained in the central four resource blocks. Then, each additional set of four
resource blocks that are within the synchronization channel bandwidth may contain
another transmission or repetition of the synchronization channel signal contained
in the central four resource blocks.
In addition to the partial or full cell identification information or the
repetition or transmission of the synchronization channel signal, for five megahertz
or larger bandwidth OFDMA systems, the synchronization channel 420 can use
frequency bands other than the center four resource blocks to enhance cell search
performance. For example, all or a portion of additional cell specific information
such as frequency reference information, transmission antenna information, pilot
stream information or cyclic prefix (CP) length information could be included in
the synchronization channel 420 information. In addition, the OFDMA system
could be designed to redundantly transmit the synchronization channel on two or
more of a plurality of subcarriers the portion of bandwidth occupied by the
synchronization channel 420.
For the case where the OFDMA system bandwidth is 1.25 MHz 480, only
three resource blocks 410 can be accommodated and the synchronization channel
420 uses all three resource blocks 410. While a number of variations of OFDMA
system bandwidth have been shown, other structures are possible wherein the

synchronization channel is transmitted in a localized portion of the OFDMA
system bandwidth.
FIG. 5 depicts a five megahertz OFDMA communication system signal
bandwidth where the localized synchronization channel bandwidth 510 is located
in the center 1.25 MHz of the five megahertz bandwidth and within, but smaller
than a bandwidth spanned by a multiple number of resource blocks 520. Tn this
instance, the synchronization channel bandwidth 510 does not cover a multiple of
the resource block size 520. In accordance with the embodiment of the present
invention, a data signal 530 is transmitted simultaneously with the synchronization
channel in a portion of the bandwidth spanned by an integer number of resource
blocks 520 that is not utilized by the synchronization channel 510. For improved
detection of the data signal 530, it may be separated from the synchronization
channel by bandwidths where no information is transmitted called guard bands
540.
The synchronization channel signal is a sequence divided into
synchronization channel signal sequence elements. An example of a preferred
sequence type in accordance with the present invention is a generalized chirp like
(GCL) sequence. For example, a length-NG GCL sequence of "index" u which is
defined as

where b is a complex scalar of unit amplitude and

and NG is a prime number (i.e., NG=NGX1) is particularly suitable for a sequence
divided into synchronization channel signal sequence elements in accordance with
the present invention. Where NG is a prime number., the cross-correlation between
any two sequences of distinct "class" is optimal and there will NG-1 unique
sequences in the set that can be used as unique group identifiers or unique cell
identification information. The GCL sequence can be represented more simply
and compactly by choosing 6=1 and q = 0.
Additional examples of sequence types that can be used for the
synchronization channel sequence elements in accordance with the present

invention may include a Pseudo-random Noise (PN) sequence or a maximal length
binary sequence. When a structured sequence with limited choices of sequence
length, (such as GCL or maximal-length binary) is used, the number of elements in
the original sequence may not match size of the synchronization channel. In this
case, the sequence may be modified to fit within the resources available for the
synchronization channel signal sequence (e.g., by truncation or cyclic extension
thereof). In accordance with another aspect of the embodiment of the present
invention, the synchronization signal includes a plurality of synchronization
channel signal sequence elements that are distributed over the OFDMA signal
subcarriers and/or the OFDMA symbol periods as determined by the OFDMA
system design or by signal propagation conditions that the system is expected to
operate in.
FIG. 6, comprising FIGs. 6A, 6B and 6C, depicts frame structures for
synchronization channel sequence element assignment in accordance with the
present invention wherein the synchronization channel sequence elements are
distributed over frequency (the subcarriers) first and then over time. The present
invention, however, is not limited to this synchronization channel sequence
element assignment scheme and may alternatively distribute the synchronization
channel sequence elements over time first and then frequency if, for example, the
system design allows changes in time faster than in frequency. Referring to FIG.
6A, the synchronization channel signal is transmitted over a sub-frame 610 with a
frame structure of seven OFDMA symbols, wherein the synchronization channel
sequence elements are transmitted on a plurality of subcarriers in adjacent or
proximal OFDMA symbol periods. While not shown, in some embodiment's pilot
symbols or other symbols such as control symbols may occupy part or all of one or
more of the OFDMA symbol periods in sub-frame 610, such that the time spacing
between some of the aforementioned proximal OFDMA symbol periods may be
more than one OFDMA symbol period.
In accordance with the present invention, a first OFDMA symbol period
620 includes a common GCL sequence of modulation symbols or zeros forming
thirty-eight sequence elements mapped onto thirty-eight subcarriers, the GCL
sequence in the first OFDMA symbol period 620 being common for all of the base

stations 110 in the OFDMA wireless communication system 100. By using every
other sub-carrier (e.g., even numbered subcarriers) for this common GCL sequence
620, the waveform can have a predetermined time domain symmetry. This
common GCL sequence 620 may be present in. all synchronization channel
transmissions and may be located in the first OFDMA symbol period of the sub-
frame 610, thereby utilized as a frame boundary indicator. Referring to FTG. 7, an
example of the sub-carrier mapping of the synchronization channel signal in the
first OFDMA symbol period 620 is shown where modulated symbols are mapped
to every other subcarrier (the thirty-eight occupied subcarriers 702) with the
intervening subcarriers 704 having zeros or nuE sets mapped thereto. The
modulation symbols are mapped to even numbered subcarriers in order to create or
define the symmetry of the waveform in the time domain (i.e., the predetermined
time domain symmetry of the synchronization channel signal waveform). This
symmetry characteristic can be utilized for coarse OFDMA symbol timing
detection and frequency error detection.
Referring back to FIG. 6A, the subsequent six OFDMA symbol periods
630 include the GCL sequence unique to a group of cells or base stations, or
unique to the cell or base station 110 (depending on the embodiment) as a plurality
of synchronization channel sequence elements mapped onto a plurality of
subcarriers, each OFDMA symbol period having all seventy-five subcarriers used
for the GCL synchronization channel sequence elements and filling the six
OFDMA symbol periods 630 in a "zig-zag" fashion. For example, FIG. 6A
depicts the synchronization channel signal GCL sequence including 449
synchronization channel sequence elements. The second OFDMA symbol period
630 is filled with synchronization channel signal sequence elements (phases) 0 to
74 ordered from top to bottom. The third OFDMA symbol period 630 is filled
with synchronization channel signal sequence elements 75 to 149 ordered from
bottom to top, but in an alternate embodiment could also be ordered from top to
bottom. In a like manner, the remaining OFDMA symbol periods 630 are filled
with the remaining synchronization channel signal sequence elements, with the
sixth OFDMA symbol being filled with synchronization channel signal sequence
elements (phases) 375 to 449 ordered from bottom to top. Instead of filling the

OFDMA symbol periods of the synchronization channel in a "zig-zag" fashion, the
OFDMA symbol periods 630 could all be filled from top to bottom or vice versa in
accordance with the OFDMA system design, the sequence type and/or the
processing necessary to combine the synchronization channel sequence elements.
In addition, instead of filling the synchronization channel in a frequency-first
fashion, the OFDMA symbol periods 630 could be filled in a time-first fashion
(e.g., from left to right on each subcarrier, right to left on each subcarrier, or left to
right on some subcarriers and right to left on other subcarriers). Or, instead of the
above described filling methods, any arbitrary two-dimensional filling pattern
could be used.
Referring to FIG. 6B, a synchronization channel signal unique to a cell or
base station 110 or a group of cells (e.g., a GCL sequence common to multiple
cells) is also transmitted over a sub-frame 610 with a frame structure of seven
OFDMA symbols, wherein the synchronization channel sequence elements are
transmitted on a plurality of subcarriers in adjacent or proximal OFDMA symbol
periods. In accordance with this embodiment of the present invention, the first
OFDMA symbol period 620 includes zeros mapped onto 37 subcarriers and
elements of a cell-specific or group-specific GCL sequence forming thirty-eight
sequence elements mapped onto thirty-eight subcarriers, for one or a group of the
base stations 110 in the OFDMA wireless communication system 100. The
subsequent six OFDMA symbol periods 630 include additional elements of the
cell-specific GCL sequence mapped onto a plurality of subcarriers, each OFDMA
symbol period having all seventy-five subcarriers (phases), filling the six OFDMA
symbol periods 630 in the "zig-zag" fashion. FIG. 6B depicts the synchronization
channel signal GCL sequence including 487 synchronization channel sequence
elements. The second OFDMA symbol period 630 is filled with synchronization
channel signal sequence elements (phases) 38 to 112 ordered from bottom to top.
The third OFDMA symbol period 630 is filled with synchronization channel signal
sequence elements 113 to 187 ordered from top to bottom. In a like manner, the
remaining OFDMA symbol periods 630 are filled with the remaining
synchronization channel signal sequence elements, with the sixth OFDMA symbol

being filled with synchronization channel signal sequence elements (phases) 413 to
487 ordered from top to bottom.
Referring to FIG. 6C, another alternate structure of a synchronization
channel sequence assignment is shown. In accordance with the present invention,
the synchronization channel sequence elements may be distributed over the
OFDMA symbol periods (as shown in FTG. 6A) or may be distributed over more
than one of the plurality of subcarriers of the OFDMA signal, or a combination of
both distributions. In the alternate embodiment of FIG. 6C, there are ten
synchronization channel symbol periods in the frame structure 640. In order to
accommodate a longer common GCJL sequence (e.g., longer than thirty-eight
sequence elements), a first portion 650 of the synchronization channel includes two
OFDMA symbol periods 660, 670. The first OFDMA symbol period 660 may be
used as a frame boundary indicator. In accordance with the alternate embodiment
of the present invention, the synchronization channel sequence elements are
mapped to every second sub-frame such that the first synchronization channels
650, which includes seventy-five subcarriers, is mapped to the first OFDMA
symbol period 660 and the second OFDMA symbol period 670. Each of the
OFDMA symbol periods 660, 670 with the common GCL sequence includes
thirty-eight sub-carriers, where the use of even numbered sub-carriers maintains
the predetermined time domain symmetry of the synchronization channel as shown
in FIG. 7 and discussed above.
Channel conditions could change during a gap between the sub-frames. To
accommodate the differential processing of the synchronization channel sequence
elements, the subsequent OFDMA symbol period 670 may repeat, as shown in
FIG. 6C, the last sequence element (e.g., phase 37) of the previous OFDMA
symbol period 620. Following the first synchronization channels 660, the second
synchronization channels 680 include eight OFDMA symbol periods having 592
synchronization channel sequence elements mapped to seventy-five subcarriers for
each OFDMA symbol period. The eight OFDMA symbol periods 680 for the
second synchronization channels use every second sub-frame and are filled in a
"zig-zag" fashion (as shown) or any arbitrary two-dimensional filling pattern as
discussed above, repeating the last sequence element of an OFDMA symbol period

as the first sequence clement of the next OFDMA symbol period. Accordingly, the
third OFDMA symbol period is filled with synchronization channel signal
sequence elements (phases) 0 to 74 ordered from top to bottom. The fourth
OFDMA symbol period is filled with synchronization channel signal sequence
elements 74 to 148 ordered from bottom to top.
Within each synchronization channel sequence element, GCL sequence
elements may preferably be employed such that differential processing of the GCL
sequence elements will provide determination of the sequence index. GCL
sequence elements have 0 dB peak-to-average power ratio (PAPR) and optimal
cross correlation properties. If a GCL sequence is applied in the frequency domain
on all subcarriers, the properties still hold for the corresponding time-domain
waveform since the Fourier transform of a GCL sequence is also a GCL sequence.
In addition, if a GCL sequence is passed through a differential demodulator, the
resulting output sequence is a complex exponential with a frequency that
corresponds to the original sequence index. Thus, using GCL sequence elements,
each synchronization channel signal sequence element will have sequence index
properties for inherently determining the sequence index thereof. As mentioned
earlier, other types of sequences could also be used, but it is preferred that the
sequence have properties that enable sequence index detection based on the
differential demodulation of the sequence. One example of a sequence other than
GCL that has such properties is a maximal-length binary sequence, since a
differential demodulation of a maximal-length binary sequence produces a
cyclically shifted version of the same sequence with a predetermined shift value.
Thus, with a maximal-length binary sequence, each cell ID can be associated with
a particular cyclic shift value of the sequence, and the cell ID can be recovered
based on differential processing.
Referring to FIG. 8, a block diagram of the OFDMA base station 110
includes a base station controller 810 coupled to the network controller 130 and
controlling the operation of the base station 110. The controller is coupled to
receiver circuitry 812 and transmitter circuitry 814, and may further include a
receiver/transmitter switch 816 for controlling the transmission and reception of
the OFDMA signals over the antenna 818 if communications over the antenna 818

arc duplexed. OFDMA signals received by the receiver circuitry 812 arc
demodulated thereby and. provided to the controller 810 for decoding thereof. In
addition, the controller 810 provides signals to the transmitter circuitry 814 for
modulation thereby and transmission therefrom. While a single antenna 818 is
shown, it is to be understood that base stations 110 may be, and are typically,
configured into sectors and may employ multiple antennas for receive diversity,
and/or transmission beamforming applications, space time coding, multiple input
multiple output (MIMO), or other system design transmission signaling schemes.
Therefore, many transmit and receive antenna configuration are possible in various
embodiments and FIG. 8 is not intended to be a complete schematic representation
of such antenna configurations but rather to exemplify components helpful toward
understanding the embodiments disclosed herein. With multiple antennas, it is
useful to convey the number of antennas to the wireless communication devices
120 to know how many pilot streams to search for during initial acquisition and
cell search. Thus, in accordance with an embodiment of the present invention, the
additional cell specific information that may be transmitted as part of the
synchronization channel signal may include the number of antennas of the base
station 110 or pilot stream information. The controller 810 is coupled to a storage
device 820 which stores information for the operation of the base station 110 such
as cell identification information and other cell specific information such as
frequency reference information, transmission antenna information (such as the
number of antennas), pilot stream information and cyclic prefix length information.
Tn accordance with the present invention, the controller 810 includes a
synchronization channel generator 822 for generating a synchronization channel
signal having time domain symmetry within a portion of the OFDMA signal
bandwidth and comprising at least partial cell identification information, the
synchronization channel generator 822 providing the synchronization channel
signal to the transmitter circuitry 816 for transmission therefrom. Sometimes the
synchronization channel generator 822 generates a synchronization channel signal
including at least a portion of additional cell specific information. A data signal
generator 824 generates an OFDMA data signal for providing to the transmitter
circuitry 816 for transmission therefrom and, in accordance with one aspect of the

present invention wherein the bandwidth is divided into a set of resource blocks,
the data signal is transmitted simultaneously with the synchronization channel
signal on a portion of a bandwidth spanned by an integer number of predetermined
resource blocks when the synchronization channel signal spans a bandwidth
smaller than a bandwidth spanned by the integer number of predetermined resource
blocks. Data could be voice or MBMS transmissions that are generated by a
calling wireless communication device 120 or by a content provider and may be
multiplexed onto the subcarriers and interleaved at the base station 110 or
multiplexing may be performed by the network controller 130. The
synchronization channel generator 822 defines the time domain symmetry of the
synchronization channel signal in one embodiment by mapping modulation signals
and zeros onto a plurality of subcarriers thereof.
Referring to FIG. 9, operation of the synchronization channel generator 822
in accordance with the embodiment of the present invention begins by retrieving
information 910 from the storage device 820. At a minimum, this information
includes cell identification information uniquely identifying the base station 110 or
at least partial cell identification information, such as group cell identification
information. Additional cell specific information, as discussed above, could also
be retrieved 910.
Next, the synchronization channel signal is generated 912 by encoding the
cell identification information. The synchronization channel signal is parsed into a
plurality of synchronization channel sequence elements 914. The predetermined
time domain symmetry of the synchronization channel signal is then defined 916.
In accordance with the present invention, step 916 would include providing an
even number of subcarriers in a resource block and may include mapping the
generated synchronization channel signal as modulation symbols and zeros onto a
plurality of subcarriers where the modulation symbols are mapped to every nth
subcarrier of at least a portion of the subcarriers utilized for the synchronization
channel signal, where n is an integer greater than or equal to two.
After the time domain symmetry is defined 916, the synchronization
channel signal is provided 918 to the transmitter circuitry 816 for transmission
from the base station 110. The synchronization channel signal is periodically

transmitted from the base station 110 to enable initial acquisition and cell search.
Thus, the synchronization channel signal may, in addition to the foregoing be
provided to the transmitter circuitry 816 redundantly either in time or across
subcarriers for improved initial acquisition and cell search. The redundancy and
the content of the synchronization channel signal can be revised and/or redefined
based upon the bandwidth of the OFDMA signal (i.e., in response to the scaling of
the OFDMA signal bandwidth).
Referring to FIG. 10, a wireless communication device 120 in accordance
with the embodiment of the present invention is shown. The wireless
communication device 120 includes an antenna 1002 for receiving and transmitting
radio frequency (RF) signals. A receive/transmit switch 1004 selectively couples
the antenna 1002 to receiver circuitry 1006 and transmitter circuitry 1008 in a
manner familiar to those skilled in the art. The receiver circuitry 1006
demodulates and decodes the RF signals to derive information therefrom and is
coupled to a controller 1010 for providing the decoded information thereto for
utilization thereby in accordance with the function(s) of the wireless
communication device 120. The controller 1010 also provides information to the
transmitter circuitry 1008 for encoding and modulating information into RF signals
for transmission from the antenna 1002. While a single antenna 1002 is depicted,
those skilled in the art will recognize that diversity antennas could be used with
diversity receivers for improved signal reception.
The controller 1010 is coupled to user interface circuitry 1012 including,
for example, a display for presenting video output to a user, a speaker for
providing audio output to the user, a microphone for receiving voice input, and
user controls, such as a keypad, for receiving user input thereby. The controller
1010 is further coupled to a nonvolatile memory device 1014 for storing
information therein and for retrieving and utilizing information therefrom.
In accordance with the embodiment of the present invention, the receiver
circuitry 1006 includes a synchronization channel signal filter device 1016 for
isolating a portion of the OFDMA signal bandwidth which includes the
synchronization channel signal. The synchronization channel signal filter device
1016 could be a bandpass filter or any other device or process for filtering the

OFDMA signal to isolate a localized portion of the OFDMA signal bandwidth.
For example, a fast Fourier transform (FFT) could be utilized to isolate the
localized portion of the OFDMA signal bandwidth during processing instead of a
hardware filter. Once isolated, the signal is provided to the controller for initial
acquisition and cell search processing.
Referring to FTG. 11, the initial signal acquisition and cell search process
begins by examining the signal filtered by the filter 1016 to determine if there is
any signal 1110. When a signal is detected 1110, the initial acquisition and cell
search method is performed in accordance with the present invention. First, the
predetermined time domain symmetry of the synchronization channel signal is
utilized to perform coarse OFDMA symbol timing detection and fractional
frequency offset detection 1112. This step 1112 could be performed by differential
correlation of the received synchronization channel signal being calculated in the
time domain or by correlation calculation with known synchronization channel
signal sequence elements in the time domain.
Generalized chirp like (GCL) sequences are preferably suited to differential
processing in accordance with the embodiment of the present invention. However,
as mentioned previously, the present invention can use other sequence types. The
time domain waveforms of the GCL-modulated OFDM signals have low PAPR,
In addition, because of the use of different indices of the GCL sequences, any pair
of the sequence elements will have low cross correlation at all time lags, which
improves the code detection and CIR estimation. Also, GCL sequences have
constant amplitude, and the NG-point DFT of GCL sequences also have constant
amplitude. GCL sequences of any length additionally have an "ideal" cyclic
autocorrelation (i.e., the correlation with the circularly shifted version of itself is a
delta function). And, the absolute value of the cyclic cross-correlation function
between any two GCL sequences is constant and equal to
u1, and u2 are all relatively prime to NG (a condition that can be easily guaranteed if
NG is a prime number).
The cross-correlation at all lags actually achieves the minimum
cross-correlation value for any two sequence elements that have the ideal
autocorrelation property (meaning that the theoretical minimum of the maximum

value of the cross-correlation over all lags is achieved). The minimum is achieved
when the cross correlations at all lags is equal to The cross correlation
property allows the impact of an interfering signal be evenly spread in the time
domain after correlating the received signal with the desired sequence in the time
domain. Hence, the cell-search symbol can also be used to perform or assist
coherent channel estimation at the wireless device even before the broadcast pilot
symbols are processed. Compared with BPSK or even QPSK preambles, the
complex-valued GCL sequences can be systematically constructed with guaranteed
good PAPR and good correlation.
Differential processing of the GCL sequence elements enables the one step
fast cell search for GCL sequence elements, step 1112. To facilitate differential
processing in accordance with the embodiment of the present invention, the
sequence elements have preferably been generated in accordance with a sequence
design methodology for a sequence length Np where a prime number NG is the
smallest prime number larger than Np. The integer "u" is the sequence index. The
sequence elements were generated according to

NG-1 sequence elements are generated having an optimal cyclic cross
correlation between any pair of them. The sequence elements have been truncated
to Np and distributed over Np subcarriers. Due to the oversampling introduced in
OFDMA signaling with null subcarriers, and also the use of localized bandwidth
for the synchronization signal, the PAPR will be degraded to different degrees for
different "u" from the theoretical OdB value (at Nyquist sampling rate). If desired,
indices that have the best PAPR among NG-1 candidates can be chosen. The cell
search sequences used by different cells are obtained from different indices "u" of
these GCL sequence elements. The index "u" will also act as a cell ID.
The cell search 1112 determines directly the sequence indices "u" (and
hence the strongest or candidate cell ID's or group ID's) from the received signal.
First, the coarse OFDMA cell-search symbol timing is determined (e.g., using the
time domain symmetry of the cell-search symbol). Then, the fractional part of the
frequency offset is estimated and removed (e.g., based on the phase of the half-

symbol differential correlation, peak). After these steps, a block of N received time-
domain samples representing the received cell-search symbol is transformed to the
frequency domain using the usual FFT process.
Assuming that an integer frequency offset may still be present, the
occupied subcarriers (even vs. odd) can be determined next by various techniques
such as a maximum energy detector (e.g., total energy in the even subcarriers of
the cell-search symbol vs. energy in the odd subcarriers). The frequency domain
data on the occupied subcarriers as Y(m) for m = 1 to Np (i.e., ignoring the unused
subcarriers) is denoted where Su(m) is the GCL sequence mapped onto those
subcarriers.
Next, a vector of "differential-based" values is computed based on the pairs
of occupied subcarriers. These values, which are obtained by differentially
demodulating the occupied subcarriers of the received symbol, are conveniently
collected into vector format (e.g., a differential-based vector) for efficient FFT-
based processing. The differential-based vector is computed as

where "O " denotes conjugation. Other ways to obtain the "differential-based"
vector may include, but are not limited to:

or

where "abs( )" denotes the absolute value.
Assuming that there is only one base station, and that it is transmitting a
cell-search symbol with a GCL sequence index of u, and that the channel does not
change significantly between two adjacent occupied subcarriers, which is
approximately satisfied as long as the spacing of occupied subcarriers is not too
large, ignoring the channel amplitude and frequency offset, Y(m)* Y*(m+1) is
approximately equal to

Thus, the sequence index information u is carried in the differential-based
vector. In the multi-cell case, by processing the differential-based vector and
identifying a set of prominent frequency components of the vector, we can identify
the strongest cell index and one or more indices of potential handoff candidates as
well. To obtain the frequency domain components, a commonly used tool is to
take an FFT or IFFT (say T-point, T>=NP-1) on {Z(m)} (step 1114) to get

The peak position (say nmax) of {z(n)} gives information about the strongest
cell's index u, i.e., the mapping between the identified prominent frequency
component at nmax to a corresponding transmitted sequence index is determined as

The peak values are also rough estimates of the channel power at the
occupied subcarriers. Thus, IFFT of the synchronization channel signal in the
frequency domain is used to detect the frame boundary and decode the cell
identification information 1114. Thus, utilizing the sequence index properties of
the synchronization channel sequence elements, multiplying one sequence element
by the complex conjugate of a next sequence element will derive the sequence
index u 1114. Accordingly, in a single step, the controller 1010 can perform GCL
sequence index detect to extract the cell specific information (e.g., u) from the
synchronization channel signal. When the synchronization channel signal is
determined to be, in some embodiments, the strongest synchronization channel
signal 1116, wireless OFDMA communication is established with the base station
1118.
Note that for the purpose of explanation, the above equations were
described for the case of the GCL sequence elements being mapped to different
subcarriers of one OFDMA symbol period. However, the proposed detection
method can also be applied when the sequence is mapped in other ways, such as
"zig-zag". In general, the differential demodulation step can be performed over
adjacent sequence elements even if the adjacent sequence elements are mapped to
different OFMDA symbol periods and/or different subcarriers. In addition, the
differential processing from multiple received instances of the synchronization
channel can be combined to further improve the detection robustness. Multiple

received instances of the synchronization channel may be available due to either
receive diversity with multiple antennas, or from subsequently received
synchronization signals that are transmitted periodically by the base station, for
example.
As described for some embodiments of the invention, the time domain
symmetry of the synchronization signal can be provided by mapping modulation
symbols or sequence elements to even-numbered subcarriers in the localized
synchronization channel bandwidth and zeros to other subcarriers in the localized
synchronization channel bandwidth. Other embodiments of the invention may
utilize other methods for providing time domain symmetry. One example includes
mapping modulation symbols or sequence elements to every Nth subcarrier in the
localized synchronization channel bandwidth and zeros to the other subcarriers in
the localized synchronization channel bandwidth, where N is a positive integer,
and where the subcarrier in the localized synchronization channel bandwidth
containing the first of the every Nth subcarrier can be arbitrarily chosen. An
additional example is to use modulation symbols or sequence elements that are
purely real (i.e., their imaginary part is zero) in the localized synchronization
channel bandwidth, since the Fourier transform of a real signal is symmetric in
magnitude around, its central portion. Methods of sequence design and/or mapping
and/or signal repetition other than the provided examples can also be used to
provide predetermined time domain symmetry.
Thus, it can be seen that the present invention provides an initial acquisition
and cell search method utilizing synchronization channel signal sequence elements
with low computational load and a small number of receiver processing steps
which nevertheless provides the four main function of initial acquisition and cell
search (i.e., OFDMA symbol timing detection, frequency error detection, frame
boundary detection and cell specific information detection) in an OFDMA system
supporting multiple system bandwidths, both synchronized and un-synchronized
systems, a large cell index and an OFDMA symbol structure with both short and
long cyclic prefix length. While at least one exemplary embodiment has been
presented in the foregoing detailed description of the invention, it should be
appreciated that a vast number of variations exist. It should also be appreciated

that the exemplary embodiment or exemplary embodiments arc only examples, and
are not intended to limit the scope, applicability, or configuration of the invention
in any way. Rather, the foregoing detailed description will provide those skilled in
the art with a convenient road map for implementing an exemplary embodiment of
the invention, it being understood that various changes may be made in the
function and arrangement of elements described in an exemplary embodiment
without departing from the scope of the invention as set forth in the appended
claims and their equivalents.

CLAIMS
1. A method in a wireless communication system, the method comprising the step of
transmitting an orthogonal frequency domain multiple access (OFDMA) signal including a
synchronization channel signal, the synchronization channel signal comprising a plurality of
synchronization channel signal sequence elements and the OFDMA signal comprising a
plurality of subcarriers, wherein each of the plurality of synchronization channel signal
sequence elements have sequence index properties associated therewith for inherently
determining a sequence index in response to the sequence index properties.
2. The method of Claim 1 wherein the sequence index properties correspond to
differential processing, and wherein the sequence index of the plurality of synchronization
channel signal sequence elements are determined by differential processing thereof.
3. The method of Claim 1 wherein the step of transmitting an OFDMA signal
comprises the step of transmitting an OFDMA signal including the synchronization channel
signal transmitted within a localized portion of a bandwidth of the OFDMA signal, the
synchronization channel signal having predetermined time domain symmetry within the
localized portion of the bandwidth and comprising first information for providing at least
partial cell identification information.
4. The method of Claim 1 wherein the synchronization channel signal sequence
elements form a general chirp like (GCL) sequence.
5. The method of Claim 1 wherein the synchronization channel signal sequence
elements form a Pseudo-random Noise (PN) sequence.
6. The method of Claim 1 wherein the synchronization channel signal sequence
elements form a maximal length binary sequence.

7. An orthogonal frequency domain multiple access (OFDMA) base station
comprising:
a synchronization channel generator generating a synchronization channel signal
comprising a plurality of synchronization channel signal sequence elements, each of the
plurality of synchronization channel signal sequence elements have sequence index
properties associated therewith for inherently determining the sequence index in response to
the sequence index properties; and
transmitter circuitry transmitting an OFDMA signal comprising a plurality of
subcarriers, wherein the transmitter circuitry is coupled to the synchronization channel
generator and transmits the OFDMA signal comprising the plurality of synchronization
channel signal sequence elements distributed over a portion of the plurality of subcarriers.
8. The OFDMA base station of Claim 7 further comprising a storage device storing cell
identification information, wherein the synchronization channel generator is coupled to the
storage means and generates the synchronization channel signal having predetermined time
domain symmetry within a localized portion of a bandwidth of an OFDMA signal and
comprising the cell identification information, and wherein the transmitter circuitry
transmits the synchronization channel signal within the localized portion of the bandwidth
of the OFDMA signal.
9. A wireless communication receiver for receiving orthogonal frequency domain
multiple access (OFDMA) signals comprising:
receiver circuitry receiving and demodulating OFDMA signals, the receiver circuitry
comprising a filter filtering the OFDMA signals to isolate a bandwidth of the OFDMA
signals which includes a synchronization channel signal, the synchronization channel signal
comprising a plurality of synchronization channel signal sequence elements, each of the
plurality of synchronization channel signal sequence elements have sequence index
properties associated therewith for inherently determining the sequence index in response to
the sequence index properties; and
a controller coupled to the receiver circuitry and decoding the synchronization
channel signal in response to detecting the plurality of synchronization channel signal
sequence elements distributed over a portion of the OFDMA signals, the controller decoding
the synchronization channel signal in response to detecting the plurality of synchronization

channel signal sequence elements and decoding the plurality of synchronization channel
signal sequence elements in response to the sequence index properties associated therewith.
10. The wireless communication receiver of Claim 9 wherein the controller decodes the
plurality of synchronization channel signal sequence elements by differential processing
thereof.
11. The wireless communication receiver of Claim 10 wherein the controller decodes the
plurality of synchronization channel signal sequence elements by general chirp like (GCL)
sequence differential processing thereof.
12. The wireless communication receiver of Claim 9 wherein the filter filters the
OFDMA signals to isolate a portion of the bandwidth of the OFDMA signals which includes
a synchronization channel signal, and wherein the controller detects a position of the
synchronization channel within the portion of the bandwidth of the OFDMA signals in
response to predetermined time domain symmetry of the synchronization channel, the
controller decoding the synchronization channel signal to derive at least partial cell
identification information therefrom.
13. A method for receiving orthogonal frequency domain multiple access (OFDMA)
signals comprising the steps of:
isolating a portion of a bandwidth of the OFDMA signals which includes a
synchronization channel signal, the synchronization channel signal comprising a plurality of
synchronization channel signal sequence elements, each of the plurality of synchronization
channel signal sequence elements have sequence index properties associated therewith for
inherently determining the sequence index in response to the sequence index properties;
detecting the plurality of synchronization channel signal sequences distributed over at least
part of the portion of the bandwidth of the OFDMA signals; and
decoding the plurality of synchronization channel signal sequence elements in
response to the sequence index properties associated therewith.

14. The method of Claim 13 wherein the step of decoding the plurality of
synchronization channel signal sequence elements comprises the step of differential
processing the plurality of synchronization channel signal sequence elements to derive at
least partial cell identification information therefrom.
15. The method of Claim 14 wherein the step of differential processing the plurality of
synchronization channel signal sequence elements comprises the step of general chirp like
(GCL) sequence differential processing the plurality of synchronization channel signal
sequence elements to derive at least partial cell identification information therefrom.
16. The method of Claim 14 wherein the step of differential processing the plurality of
synchronization channel signal sequence elements comprises the step of Pseudo-random
Noise (PN) sequence differential processing the plurality of synchronization channel signal
sequence elements to derive at least partial cell identification information therefrom.
17. The method of Claim 14 wherein the step of differential processing the plurality of
synchronization channel signal sequence elements comprises the step of maximal length
binary sequence differential processing the plurality of synchronization channel signal
sequence elements to derive at least partial cell identification information therefrom.
18. The method of Claim 13 wherein the step of detecting comprises the step of
detecting a position of the synchronization channel as a synchronization channel signal
within the portion of the bandwidth of the OFDMA signals, and wherein the step of
decoding comprises the step of decoding the synchronization channel signal to derive at
least partial cell identification information therefrom.

A method and apparatus is provided for
transmitting an orthogonal frequency domain multiple
access (OFDMA) signal including a synchronization
channel signal transmitted within a localized portion
of a bandwidth of the OFDMA signal (818), the
synchronization channel signal having predetermined
time domain symmetry within the localized portion
of the bandwidth (816). The synchronization channel
signal enables an initial acquisition and cell search
method with low computational load which provides
OFDMA symbol timing detection and frequency error
detection by differential processing of sequence elements
of the synchronization channel signal (1112) and
frame boundary detection and cell specific information
detection (1114) in an OFDMA system supporting
multiple system bandwidths, both synchronized and
un-synchronized systems, a large cell index and an
OFDMA symbol structure with both short and long
cyclic prefix length.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=b8f1p2FE2kKONZPPWxbvtw==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

268345

Indian Patent Application Number

3057/KOLNP/2008

PG Journal Number

35/2015

Publication Date

28-Aug-2015

Grant Date

26-Aug-2015

Date of Filing

28-Jul-2008

Name of Patentee

MOTOROLA MOBILITY, INC.

Applicant Address

600 NOR Til US HIGHWAY 45, LIBERTYVILLE, IL 60048, UNITED STATES OF AMERICA

Inventors:

#	Inventor's Name	Inventor's Address
1	BAUM, KEVIN, L.	3450 RICHNEE LANE, ROLLING MEADOWS, ILLINOIS 60008
2	AKITA, HIDENORI	4-13-33 AKITSU-CHO, HIGASHIMURAYAMA-SHI, TOKYO 198-0001
3	FUKUTA, MASAYA	KAKINOKIZAKA 2-26-11, MEGURO-KU, TOKYO 152-0022
4	NANGIA, VIJAY	185 ABERDEEN DRIVE, ALGONQUIN, ILLINOIS 60102
5	LOVE, ROBERT, T.	817 S. HOUGH STREET, BARRINGTON, ILLINOIS 60010
6	STEWART, KENNETH, A.	251 PARKER DRIVE, GRAYSLAKE, ILLINOIS 60030
7	CLASSON, BRIAN, K.	756 W. BLOOMFIELD COURT, PALATINE, ILLINOIS 60067
8	HAYASHI, HIROSHI	FUJIMACHI 1-8-1-306, NISHITOKYO-SHI, TOKYO 202-0014

PCT International Classification Number

H04J 11/00

PCT International Application Number

PCT/US2007/061180

PCT International Filing date

2007-01-27

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/351304	2006-02-08	U.S.A.