Title of Invention	TRANSMIT METHODS WITH DELAY DIVERSITY AND SPACE-FREQUENCY DIVERSITY
Abstract	In this invention, several open-loop solutions that encompass the small delay CDD codeword cycling, codeword cycling between different re-transmissions of both small and large delay CDD are proposed. In addition, an open-loop codeword cycling method for SFBC+FSTD scheme, as well as its extension to SFBC+FSTD based HARQ, are proposed. In one method, a plurality of information bits are encoded, scrambled and modulated to generate a plurality of modulation symbols. The plurality of modulation symbols are mapped onto the subcarriers in at least one transmission layer of a transmission resource. The modulation symbols are then precoded by using a matrix for cyclic delay diversity and a set of codewords from a certain codebook to generate a plurality of precoded symbols. The codewords are cycled for every a certain number of subcarriers. Finally, the precoded symbols are transmitted via a plurality of transmission antennas.

Title of Invention

TRANSMIT METHODS WITH DELAY DIVERSITY AND SPACE-FREQUENCY DIVERSITY

Abstract

In this invention, several open-loop solutions that encompass the small delay CDD codeword cycling, codeword cycling between different re-transmissions of both small and large delay CDD are proposed. In addition, an open-loop codeword cycling method for SFBC+FSTD scheme, as well as its extension to SFBC+FSTD based HARQ, are proposed. In one method, a plurality of information bits are encoded, scrambled and modulated to generate a plurality of modulation symbols. The plurality of modulation symbols are mapped onto the subcarriers in at least one transmission layer of a transmission resource. The modulation symbols are then precoded by using a matrix for cyclic delay diversity and a set of codewords from a certain codebook to generate a plurality of precoded symbols. The codewords are cycled for every a certain number of subcarriers. Finally, the precoded symbols are transmitted via a plurality of transmission antennas.

Full Text	TRANSMIT METHODS WITH DELAY DIVERSITY AND SPACE-FREQUENCY DIVERSITY BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to methods to transmit signal by using delay diversity and space frequency diversity. Description of the Related Art This application incorporates by reference the following publications, copies of same material are annexed to this specification, and which are made a part of this application: [1]. 3GPP RAN1 contribution R1-072461, "High Delay CDD in Rank Adapted Spatial Multiplexing Mode for LTE DL", May 2007, Kobe, Japan; [2]. 3GPP RAN1 contribution R1-072019, "CDD precoding for 4 Tx antennas", May 2007, Kobe, Japan; [3]. 3GPP TS 36.211, "Physical Channels and Modulation", v 1.1.0; [4]. 3GPP RAN1 contribution Rl-073096, "Text Proposal for 36.211 regarding CDD Design", June 2007, Orlando, USA; and [5]. 3GPP TS 36.211, "Physical Channels and Modulation", v 8.2.0. A typical cellular radio system includes a number of fixed base stations and a number of mobile stations. Each base station covers a geographical area, which is defined as a cell. Typically, a non-line-of-sight (NLOS) radio propagation path exists between a base station and a mobile station due to natural and man-made objects disposed between the base station and the mobile station. As a consequence, radio waves propagate while experiencing reflections, diffractions and scattering. The radio wave which arrives at the antenna of the mobile station in a downlink direction, or at the antenna of the base station in an uplink direction, experiences constructive and destructive additions because of different phases of individual waves generated due to the reflections, diffractions, scattering and out-of-phase recombination. This is due to the fact that, at high carrier frequencies typically used in a contemporary cellular wireless communication, small changes in differential propagation delays introduces large changes in the phases of the individual waves. If the mobile station is moving or there are changes in the scattering environment, then the spatial variations in the amplitude and phase of the composite received signal will manifest themselves as the time variations known as Rayleigh fading or fast fading attributable to multipath reception. The time-varying nature of the wireless channel require very high signal-to-noise ratio (SNR) in order to provide desired bit error or packet error reliability. The scheme of diversity is widely used to combat the effect of fast fading by providing a receiver with multiple faded replicas of the same information-bearing signal. The schemes of diversity in general fall into the following categories: space, angle, polarization, field, frequency, time and multipath diversity. Space diversity can be achieved by using multiple transmit or receive antennas. The spatial separation between the multiple antennas is chosen so that the diversity branches, i.e., the signals transmitted from the multiple antennas, experience fading with little or no correlation. Transmit diversity, which is one type of space diversity, uses multiple transmission antennas to provide the receiver with multiple uncorrelated replicas of the same signal. Transmission diversity schemes can further be divided into open loop transmit diversity and closed-loop transmission diversity schemes. In the open loop transmit diversity approach no feedback is required from the receiver. In one type of closed loop transmit diversity, a receiver knows an arrangement of transmission antennas, computes a phase and amplitude adjustment that should be applied at the transmitter antennas in order to maximize a power of the signal received at the receiver. In another arrangement of closed loop transmit diversity referred to as selection transmit diversity (STD), the receiver provides feedback information to the transmitter regarding which antenna(s) to be used for transmission. Cyclic Delay Diversity (CDD) is a diversity scheme used in OFDM-based telecommunication systems, transforming spatial diversity into frequency diversity avoiding inter symbol interference. The 3rd Generation Partnership Project (3GPP) contribution R1-072633. TS 36.211 version 1.1.0, proposed a CDD precoder structure that requires a Precoder Matrix Indication (PMI) feedback. Also, in the CDD described in TS 36.211 version 1.1.0, the open loop (i.e., large delay) and closed loop (i.e., small delay CDD) structures are different. It would be better to have one structure for both open loop and closed loop, by using different values of the precoder. The two structures are identical for the full rank cases and where the precoder matrix is an identity matrix. The closed loop structure has no solution for the case where no PMI is available for the less than full rank case. SUMMARY OF THE INVENTION It is therefore an aspect of the present invention to provide improved methods and apparatus for transmitting signals. It is another aspect of the present invention to provide an improved open loop precoder that can be applied to both large delay CDD and small delay CDD diversity schemes during transmission. According to one aspect of the present invention, a plurality of information bits are encoded, scrambled and modulated to generate a plurality of modulation symbols. The plurality of modulation symbols are mapped onto the subcarriers in at least one transmission layer of a transmission resource. The modulation symbols are then precoded by using a matrix for cyclic delay diversity and a set of codewords from a certain codebook to generate a plurality of precoded symbols. The codewords are cycled for every a certain number of subcarriers. Finally, the precoded symbols are transmitted via a plurality of transmission antennas. For large delay CDD, the precoded symbols corresponding to the i-th subcarrier is: where D(i) is a diagonal matrix for supporting small delay cyclic delay diversity. For both small delay CDD and large delay CDD, the precoded symbols corresponding to the i-th subcarrier is: where D(i) is a first diagonal matrix for supporting small delay cyclic delay diversity, and C(i) is a second diagonal matrix for supporting large delay cyclic delay diversity. The value q may be equal to 1, or may be equal to the transmission rank, or may be equal to 12m, where m is a positive integer. The set of code words may include all of the codewords in the certain codebook. Alternatively, the set of code words may include a subset of codewords in the certain codebook. According to another aspect of the present invention, a plurality of information bits are encoded, scrambled and modulated to generate a plurality of modulation symbols. The plurality of modulation symbols are mapped onto the subcarriers in at least one transmission layer of a transmission resource. The mapped symbols are repeatedly precoded and transmitted via a plurality of antennas by using a matrix for cyclic delay diversity and applying different codewords for different retransmissions. According to yet another aspect of the present invention, four symbols to be transmitted are encoded by using a rank-2 space frequency block code to generate a rank-2 space frequency block of symbols. Then, the block of symbols are precoded by using a matrix for cyclic delay diversity and a set of codewords from a certain codebook to generate a plurality of precoded symbols. The codewords cycled for every a certain number of subcarriers. Finally, the precoded symbols are transmitted via a plurality of antennas. According to still yet another aspect of the present invention, four symbols to be transmitted are encoded by using a rank-2 space frequency block code to generate a rank-2 space frequency block of symbols. The block of symbols are repeatedly precoded and transmitted via a plurality of antennas by using a matrix for cyclic delay diversity and applying different codewords for different retransmissions. According to a further aspect of the present invention, four symbols to be transmitted are encoded to generate two transmission matrices. The two transmission matrices T} and T2 are: where Tij represents the symbol to be transmitted on the ith antenna and the jth subcarrier. The four symbols are repeatedly transmitted via four antennas by alternatively applying the two transmission matrices T1 and T2 in a frequency domain. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein: FIG. 1 schematically illustrates an Orthogonal Frequency Division Multiplexing (OFDM) transceiver chain suitable for the practice of the principles of the present invention; FIGS. 2A and 2B schematically illustrate two schemes of subcarrier allocation of frequency-selective multi-user scheduling and frequency diversity in an OFDM system; FIG. 3 schematically illustrates a transmission and reception scheme in a multiple input and multiple output (MIMO) system; FIG. 4 schematically illustrates a precoding scheme is a MIMO system; FIG. 5 schematically illustrates a scheme for processing precoded signals at a receiver; FIGS. 6A and 6B illustrate two schemes of applying phase shift to subcarriers; FIG. 7 schematically illustrates a cyclic delay diversity precoding scheme; FIG. 8 schematically illustrates using different codewords in different retransmissions in a Hybrid automatic repeat and request (HARQ) scheme as one embodiment according to the principles of the present invention; FIG. 9 schematically illustrates a scheme for precoding a rank-2 space frequency block code as another embodiment according to the principles of the present invention; FIG. 10 schematically illustrates a scheme for precoding a rank-2 space frequency block code by applying different codewords in different retransmissions in a HARQ scheme as another embodiment according to the principles of the present invention; and FIG. 11 schematically illustrates mapping of symbols to antennas for a Space Frequency Block Code (SFBC) combined with frequency Switched Transmit Diversity (FSTD) scheme as still another embodiment according to the principles of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS FIG. 1 illustrates an Orthogonal Frequency Division Multiplexing (OFDM) transceiver chain. In a communication system using OFDM technology, at transmitter chain 110, control signals or data 111 is modulated by modulator 112 into a series of modulation symbols, that are subsequently serial-to-parallel converted by Serial/Parallel (S/P) converter 113. Inverse Fast Fourier Transform (IFFT) unit 114 is used to transfer the signals from frequency domain to time domain into a plurality of OFDM symbols. Cyclic prefix (CP) or zero prefix (ZP) is added to each OFDM symbol by CP insertion unit 116 to avoid or mitigate the impact due to multipath fading. Consequently, the signal is transmitted by transmitter (Tx) front end processing unit 117, such as an antenna (not shown), or alternatively, by fixed wire or cable. At receiver chain 120, assuming perfect time and frequency synchronization are achieved, the signal received by receiver (Rx) front end processing unit 121 is processed by CP removal unit 122. Fast Fourier Transform (FFT) unit 124 transfers the received signal from time domain to frequency domain for further processing. The total bandwidth in an OFDM system is divided into narrowband frequency units called subcarriers. The number of subcarriers is equal to the FFT/IFFT size N used in the OFDM system. In general, the number of subcarriers used for data is less than N because some subcarriers at the edge of the frequency spectrum are reserved as guard subcarriers. In general, no information is transmitted on guard subcarriers. In a communication link, a multi-path channel results in a frequency-selective fading. Moreover, in a mobile wireless environment, the channel also results in a time-varying fading. Therefore, in a wireless mobile system employing OFDM based access, the overall system performance and efficiency can be improved by using, in addition to time-domain scheduling, frequency-selective multi-user scheduling. In a time-varying frequency-selective mobile wireless channel, it is also possible to improve the reliability of the channel by spreading and/or coding the information over the subcarriers. In case of frequency-selective multi-user scheduling, a contiguous set of subcarriers potentially experiencing an upfade is allocated for transmission to a user. The total bandwidth is divided into subbands grouping multiple contiguous subcarriers as shown in FIG. 2A where subcarriers f1, f2, f3 and f4 are grouped into a subband for transmission to a user in frequency-selective multi-user scheduling mode. In case of frequency-diversity transmission, however, the allocated subcarriers are preferably uniformly distributed over the whole spectrum. As shown in FIG. 2B, subcarriers f1, f5, f9 and f13 are grouped into a subband for transmission. The frequency-selective multi-user scheduling is generally beneficial for low mobility users for which the channel quality can be tracked. But the channel quality generally can not be tracked for high mobility users (particularly in a frequency-division-duplex system where the fading between the downlink and uplink is independent) due to channel quality feedback delays and hence the frequency diversity transmission mode is preferred. Multiple Input Multiple Output (MIMO) schemes use multiple transmit antennas and multiple receive antennas to improve the capacity and reliability of a wireless communication channel. A MIMO system promises linear increase in capacity with K where K is the minimum of number of transmit (M) and receive antennas (N), i.e. K = min (M,N). A simplified example of a 4 x 4 MIMO system is shown in FIG. 3. In this example, four different data streams are transmitted separately from the four transmit antennas. The transmitted signals are received at the four receive antennas. Some form of spatial signal processing is performed on the received signals in order to recover the four data streams. An example of spatial signal processing is vertical Bell Laboratories Layered Space-Time (V-BLAST) which uses the successive interference cancellation principle to recover the transmitted data streams. Other variants of MIMO schemes include schemes that perform some kind of space-time coding across the transmit antennas (e.g., diagonal Bell Laboratories Layered Space-Time (D-BLAST)) and also beamforming schemes such as Spatial Division multiple Access (SDMA). The MIMO channel estimation consists of estimating the channel gain and phase information for links from each of the transmit antennas to each of the receive antennas. Therefore, the channel for M x N MIMO system consists of an N x M matrix: where aij represents the channel gain from transmit antenna j to receive antenna i. In order to enable the estimations of the elements of the MIMO channel matrix, separate pilots are transmitted from each of the transmit antennas. An optional precoding protocol that employs a unitary pre-coding before mapping the data streams to physical antennas is shown in FIGS. 5A and 5B. The optional precoding creates a set of virtual antennas (VA) 171 before the pre-coding. In this case, each of the codewords is potentially transmitted through all the physical transmission antennas 172. Two examples of unitary precoding matrices, P1 and P2 for the case of two transmission antennas 172 may be: Assuming modulation symbols S1 and S2 are transmitted at a given time through stream 1 and stream 2 respectively. Then the modulation symbol T1 after precoding with matrix P1 in the example as shown in FIG. 5A and the modulation symbol T2 after precoding with matrix P2 in the example as shown in FIG. 5B can be respectively written as: transmitted via antenna 1 and antenna 2, respectively, when precoding is done using precoding matrix P1 as shown in FIG. 4A. Similarly, the symbols T vill be transmitted via antenna 1 and antenna 2, respectively, when precoding is done using precoding matrix P2 as shown in FIG. 4B. It should be noted that precoding is done on an OFDM subcarrier level before the IFFT operation as illustrated in FIGS. 4A and 4B. In a pre-coded MIMO system, inverse operations are performed at the receiver to recover the transmitted symbols. The received symbols are multiplied with the inverse precoding matrices. The inverse precoding matrices are given as: It should be noted that the inverse of a unitary precoding matrix can simply be obtained by taking the complex conjugate transpose of the pre-coding matrix. The transmitted symbols are decoded by multiplying the received symbol vector with the inverse pre-coding matrices. Therefore, the transmitted symbols are given as: A downlink physical channel corresponds to a set of resource elements carrying information originating from higher layers. First, a plurality of information bits are coded with a plurality of code words to generate a plurality of We described a precoding approach that applies to both transmit diversity and MIMO spatial multiplexing. A composite precoder is constructed based on a unitary precoder such as Fourier matrix precoder multiplied with another unitary precoder representing a transmit diversity scheme such as cyclic delay- diversity. It should be noted that the principles of the current invention also applies to the cases of non-unitary precoding or unitary precoders other than Fourier matrix precoder. Multiple Fourier matrices can be defined by introducing a shift parameter (g/G) in the Fourier matrix. The entry of the multiple Fourier matrices is given by: A set of four 2x2 Fourier matrices can be defined by taking G=4, and g=0. 1, 2 and 3, and are written as: A cyclic delay diversity scheme can be implemented in the frequency domain with a phase shift of e"Plk applied to subcarrier k transmitted from the i-th transmission antenna. The angle p, is given as: where D, is the cyclic delay in samples applied from the i-th antenna. It should be noted that other functions can be used to derive the frequency domain phase shift. The phase shift may be kept constant for a group of subcarriers. As shown in FIG. 6A, phase shift is constant over subband (SB) 1,Q2 is constant SB2, and so on. It is also possible to allow the phase shift to vary from one group of subcarriers to the next. As shown in FIG. 6B, the phase shift varies from 2x/N to 2n over a frequency range from subcarrier 1 to subcarrier 512. The cyclic delay diversity can be seen as precoding with the following precoding matrix for the case of four transmission antennas: FIG. 7 schematically illustrates a transmitter provided with the CDD precoding scheme using the above precoding matrix. It can be noted that the same symbol with antenna and frequency (subcarrier) dependent phase shifts are transmitted from multiple antenna. No phase shift is applied for the symbol transmitted from the first antenna. In 3GPP RANI contribution Rl-073096, "Text Proposal for 36.211 regarding CDD Design", published in June 2007, Orlando, USA, a joint proposal is depicted that includes both small and large delay CDD. For zero-delay and small-delay CDD, precoding for spatial multiplexing shall be performed according to the following equation: where the precoding matrix w(i) is of size P x v, P is the number of antenna ports, v is the number of layers, the matrix D(i) is a diagonal matrix Note that these values apply only when transmit diversity is not configured for transmission rank 1. For spatial multiplexing, the values of w(i) shall be selected among the precoder elements in the codebook configured in the Node B and the UE. Node B can further confine the precoder selection in the UE to a subset of the elements in the codebook using codebook subset restriction. According to TS 36.211. version 1.1.0, the configured codebook shall be equal to Table 2. Note that the number of layers v is equal to the transmission rank p in case of spatial multiplexing. According to TS 36.211, version 8.2.0, For transmission on two antenna ports, p e {0,l}, the precoding matrix W(i) for zero, small, and large-delay CDD shall be selected from Table 3 or a subset thereof. For transmission on four antenna ports, p e {0,1,2,3}, the precoding matrix w for zero, small, and large-delay CDD shall be selected from Table 4 or a subset thereof. The quantity w>s] denotes the matrix defined by the columns given by the set {.?} from the expression wn = i-2unu"/u"u„ where / is the 4x4 identity matrix and the vector u„ is given by Table 4. For large-delay CDD, the precoding for spatial multiplexing shall be performed according to the following equation: where the precoding matrix W{i) is of size Pxu, P is the number of antenna ports, v is the number of layers, the quantity £)(/) is a diagonal matrix for support of large cyclic delay diversity, and U is a fixed matrix. The For spatial multiplexing, the values of w(i) shall be selected among the precoder elements in the codebook configured in the Node B and the UE. Node B can further confine the precoder selection in the UE to a subset of the elements in the codebook using codebook subset restriction. The configured codebook shall be equal to Table 3 and Table 4. Note that the number of layers v is equal to the transmission rank p in case of spatial multiplexing. Furthermore, a codeword cycling method is proposed for the large delay equation, y(i)= D(i)-W(i)-U . x(i), so that W(i) is cyclically selected as one of the codeword in either the codebook in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset of the codebooks. It is proposed that the codeword changes either every subcarrier, or every v subcarriers, where v is the transmission rank. In a first embodiment according to the principles of the present invention, we propose to perform codeword cycling in the large delay CDD method y(i) = W(i)-D(i)-U-x(i) for every resource block (RB) or every integer number of RBs. For LTE system one RB consists of twelve subcarriers. Therefore, the codeword W(i) is selected according to W(i) = Ck, where k is given by non-negative integer and 12 is the number of subcarriers in a RB. Furthermore. Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding codebooks defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset thereof, and N is the codebook size or the size of the subset. Also note that mod(x) is a modulo operation and [x] is a ceiling operation. In a second embodiment according to the principles of the present invention, we propose to perform codeword cycling in the small delay CDD method y(i)= D(i)-W(i)-x(i) for every q subcarriers. Therefore, the codeword W(i) is selected according to W(i) = Ck, where k is given by non-negative integer. Examples of q value include q = 1, or q - u where v is the transmission rank, or q = 12m (cycle every m RBs) where m > 0 is a non-negative number and 12 is the number of subcarriers in a RB. Furthermore. Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding codebooks defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset thereof, and N is the codebook size or the size of the subset. Also note that mod(x) is a modulo operation and [x] is a ceiling operation. In a third embodiment according to the principles of the present invention, we propose to perform codeword cycling in a uniform small and large delay CDD method as given by: Table 6. Therefore, the codeword W(i) is selected according to w(i) = Ck, where k is given by: non-negative integer. Examples of q value include q = 1, or q = v where v is the transmission rank, or q = 12m (cycle every m RBs) where m>0 is a non-negative number and 12 is the number of subcarriers in a RB. Furthermore. Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding codebooks defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset thereof, and N is the codebook size or the size ot the subset. Also note that mod(x) is a modulo operation and [x] is a ceiling operation. for uniform small and large delay CDD. Furthermore, we propose to select these codewords in such a way that Wl{i)=Ck for t = \,...,T, where Q denotes the k, -th codeword in the codebook of the precoding codebook defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset thereof, and such that the choice of Ck is independent for each retransmission. i.e, for the t-th transmission, Q can be any of the N codewords, regardless of which codeword is used in the previous transmissions. FIG.8 illustrates how the different codewords are used in different re-transmissions. In a fifth embodiment according to the principles of the present invention, we propose to add a pre-coding process, denoted by matrix w(i) where / is the subcarrier index, at the output of the rank-2 space frequency block code (SFBC) block given by: and this precoded rank-2 method is illustrated in FIG. 9. And the overall transmit signal is given by: where we used the notation A(i) to emphasize the fact that the rank-2 SFBC transmission matrix is a function of the subcarrier index. That is, In addition, note that Sj to S4 are generated from the same codeword. One way to choose the codeword is to choose the w(i) according to the precoding matrix index (PMI) in the feedback, and W{i) belongs the codebook defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset thereof. Another way to choose the codeword is to choose W(i) as an arbitrary unitary matrix that varies every q subcarriers, where q > 0 is an arbitrary non-negative integer. Therefore, the codeword W{i) is selected according to w{i)=Ck, where k is given by: include q = \, or q = o where v is the transmission rank, or q = \2m (cycle every m RBs) where m>0 is a non-negative number and 12 is the number of subcarriers in a RB. Furthermore, Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding codebook defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset thereof, and A' is the codebook size or the size of the subset. Also note that mod(x) is a modulo operation and \x~\ is a ceiling operation. In a sixth embodiment according to the principles of the present invention, we propose to apply different codewords for different retransmission in a Hybrid automatic repeat-request (HARQ) system that uses the rank-2 SFBC transmission. Let there be T re-transmissions in the HARQ system, and let W\{j\W2{i),---,Wr{i) be the codeword used for these T retransmissions, the transmit signal for each retransmission is then given by: Furthermore, we propose to select these codewords in such a way that W, (/) =Cki for / = 1,..., T , where Ck denotes the k, -th codeword in the codebook of the precoding codebook defined in Table 3 for two antenna ports. and in Table 4 for four antenna ports, or a subset thereof, and such that the choice of Cki is independent for each retransmission, i.e, for the t-th transmission, Ccan be any of the N codewords, regardless of which codeword is used in the previous transmissions. FIG. 10 illustrates how the different codewords are used in different re-transmissions. In a seventh embodiment according to the principles of the present invention, we propose a scheme where mapping of symbols to antennas is changed on repeated symbols as shown in FIG. 11. In this example we assumed that four symbols 5,, S2, S3 and S4 are transmitted with one repetition over eight subcarriers, or two groups of subcarriers in two subframes, with four subcarriers in each group. In the first four subcarriers, symbols S, and S2 are transmitted on antennas ports ANTO and ANT1, while symbols S^ and S4 are transmitted on antennas ports ANT2 and ANT3. On repetition in the last four subcarriers, the symbols 5, and S2 are transmitted on antennas ports ANT2 and ANT3 while symbols 53 and S4 are transmitted on antennas ports ANTO and ANT1. This proposed mapping results in greater diversity gain compared to the transmission where mapping does not change on repetition. This diversity gains stems from the fact that after one repetition all the four symbols are transmitted from all the four transmit antennas. In the proposed mapping scheme, the transmission matrix 7j shown below is used for initial transmission: where T-,j represents symbol transmitted on the ith antenna and the jth subcarrier ox jth time slot (i=J,2,3,4, j=J,2,3,4) for the case of 4-Tx antennas. When the same symbols are repeated, a different mapping matrix T2 shown below is used for transmission: Note that the principles of the present invention may be applied to decoding information received from a transmitter. In this case, since the selection of precoding matrices is a function of time (subframe number) and frequency (subcarrier number), the receiver can simply observe the subframe number and subcarrier number, and use the same function to figure out the precoder matrix. The dependence of the precoding matrix selection on frequency is explicit from Equations (13) and (14). The dependence of the precoding matrix selection on time is explicit in the HARQ transmission scheme. While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims. WE CLAIM 1. A method for transmission in a communication system, the method comprising: encoding a plurality of information bits to generate a plurality of coded bits; scrambling the plurality coded bits to generate a plurality of scrambled bits; modulating the plurality of scrambled bits to generate a plurality of modulation symbols; mapping the plurality of modulation symbols onto the subcarriers in at least one transmission layer of a transmission resource; precoding the modulation symbols by using a precoding matrix of which codewords of a codebook are changed every subcarriers. 2. An apparatus for transmission in a communication system, the method comprising: means for encoding a plurality of information bits to generate a plurality of coded bits; means for scrambling the plurality coded bits to generate a plurality of scrambled bits; means for modulating the plurality of scrambled bits to generate a plurality of modulation symbols; means for mapping the plurality of modulation symbols onto the subcarriers in at least one transmission layer of a transmission resource; means for precoding the modulation symbols by using a precoding matrix of which codewords of a codebook precoding matrix are changed every subcarriers. 3. The method of claim 1 apparatus of claim 2, wherein a index of the codeword is determined by performing a modulo operation, subband index mod a size of the codebook. 4. The method of claim 1 or apparatus of claim 2, wherein the codewords are used for precoding the modulation symbols corresponding to an i-th subcarrier being established by: where Ck is the k-th codeword in the set of codewords, with the index k being established by: where q is a certain positive integer, and N is the size of the codewords; and transmitting the precoded symbols via a plurality of transmission antennas. 5. The method of claim 1 or apparatus of claim 2, comprised of the precoded symbols corresponding to the i-th subcarrier being established by: with: x(i) being a block of modulation symbols corresponding to the i-th subcarrier and where v is the number of transmission layers; U being a certain fixed matrix and the elements of U being established by for m = 0, l,...,v-1, and n = 0,1,...,v-1; and D(i) being a diagonal matrix for supporting large delay cyclic delay diversity. 6. The method of claim 1 or apparatus of claim 2, comprised of the precoded symbols corresponding to the i-th subcarrier being established by: with: x(i) being a block of modulation symbols corresponding to the i-th subcarrier and where v is the number of transmission layers; and D(i) being a diagonal matrix for supporting small delay cyclic delay diversity. In this invention, several open-loop solutions that encompass the small delay CDD codeword cycling, codeword cycling between different re-transmissions of both small and large delay CDD are proposed. In addition, an open-loop codeword cycling method for SFBC+FSTD scheme, as well as its extension to SFBC+FSTD based HARQ, are proposed. In one method, a plurality of information bits are encoded, scrambled and modulated to generate a plurality of modulation symbols. The plurality of modulation symbols are mapped onto the subcarriers in at least one transmission layer of a transmission resource. The modulation symbols are then precoded by using a matrix for cyclic delay diversity and a set of codewords from a certain codebook to generate a plurality of precoded symbols. The codewords are cycled for every a certain number of subcarriers. Finally, the precoded symbols are transmitted via a plurality of transmission antennas.

Full Text

TRANSMIT METHODS WITH DELAY DIVERSITY AND
SPACE-FREQUENCY DIVERSITY
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to methods to transmit signal by using delay
diversity and space frequency diversity.
Description of the Related Art
This application incorporates by reference the following publications,
copies of same material are annexed to this specification, and which are made a
part of this application:
[1]. 3GPP RAN1 contribution R1-072461, "High Delay CDD in Rank
Adapted Spatial Multiplexing Mode for LTE DL", May 2007, Kobe, Japan;
[2]. 3GPP RAN1 contribution R1-072019, "CDD precoding for 4 Tx
antennas", May 2007, Kobe, Japan;
[3]. 3GPP TS 36.211, "Physical Channels and Modulation", v 1.1.0;
[4]. 3GPP RAN1 contribution Rl-073096, "Text Proposal for 36.211
regarding CDD Design", June 2007, Orlando, USA; and
[5]. 3GPP TS 36.211, "Physical Channels and Modulation", v 8.2.0.
A typical cellular radio system includes a number of fixed base stations
and a number of mobile stations. Each base station covers a geographical area,
which is defined as a cell.
Typically, a non-line-of-sight (NLOS) radio propagation path exists
between a base station and a mobile station due to natural and man-made objects
disposed between the base station and the mobile station. As a consequence,
radio waves propagate while experiencing reflections, diffractions and scattering.
The radio wave which arrives at the antenna of the mobile station in a downlink
direction, or at the antenna of the base station in an uplink direction, experiences
constructive and destructive additions because of different phases of individual
waves generated due to the reflections, diffractions, scattering and out-of-phase
recombination. This is due to the fact that, at high carrier frequencies typically
used in a contemporary cellular wireless communication, small changes in
differential propagation delays introduces large changes in the phases of the
individual waves. If the mobile station is moving or there are changes in the
scattering environment, then the spatial variations in the amplitude and phase of
the composite received signal will manifest themselves as the time variations
known as Rayleigh fading or fast fading attributable to multipath reception. The
time-varying nature of the wireless channel require very high signal-to-noise ratio
(SNR) in order to provide desired bit error or packet error reliability.
The scheme of diversity is widely used to combat the effect of fast fading
by providing a receiver with multiple faded replicas of the same
information-bearing signal.
The schemes of diversity in general fall into the following categories:
space, angle, polarization, field, frequency, time and multipath diversity. Space
diversity can be achieved by using multiple transmit or receive antennas. The
spatial separation between the multiple antennas is chosen so that the diversity
branches, i.e., the signals transmitted from the multiple antennas, experience
fading with little or no correlation. Transmit diversity, which is one type of
space diversity, uses multiple transmission antennas to provide the receiver with
multiple uncorrelated replicas of the same signal. Transmission diversity
schemes can further be divided into open loop transmit diversity and closed-loop
transmission diversity schemes. In the open loop transmit diversity approach no
feedback is required from the receiver. In one type of closed loop transmit
diversity, a receiver knows an arrangement of transmission antennas, computes a
phase and amplitude adjustment that should be applied at the transmitter antennas
in order to maximize a power of the signal received at the receiver. In another
arrangement of closed loop transmit diversity referred to as selection transmit
diversity (STD), the receiver provides feedback information to the transmitter
regarding which antenna(s) to be used for transmission.
Cyclic Delay Diversity (CDD) is a diversity scheme used in OFDM-based
telecommunication systems, transforming spatial diversity into frequency
diversity avoiding inter symbol interference.
The 3rd Generation Partnership Project (3GPP) contribution R1-072633.
TS 36.211 version 1.1.0, proposed a CDD precoder structure that requires a
Precoder Matrix Indication (PMI) feedback. Also, in the CDD described in TS
36.211 version 1.1.0, the open loop (i.e., large delay) and closed loop (i.e., small
delay CDD) structures are different. It would be better to have one structure for
both open loop and closed loop, by using different values of the precoder. The
two structures are identical for the full rank cases and where the precoder matrix
is an identity matrix. The closed loop structure has no solution for the case
where no PMI is available for the less than full rank case.
SUMMARY OF THE INVENTION
It is therefore an aspect of the present invention to provide improved
methods and apparatus for transmitting signals.
It is another aspect of the present invention to provide an improved open
loop precoder that can be applied to both large delay CDD and small delay CDD
diversity schemes during transmission.
According to one aspect of the present invention, a plurality of
information bits are encoded, scrambled and modulated to generate a plurality of
modulation symbols. The plurality of modulation symbols are mapped onto the
subcarriers in at least one transmission layer of a transmission resource. The
modulation symbols are then precoded by using a matrix for cyclic delay
diversity and a set of codewords from a certain codebook to generate a plurality
of precoded symbols. The codewords are cycled for every a certain number of
subcarriers. Finally, the precoded symbols are transmitted via a plurality of
transmission antennas.
For large delay CDD, the precoded symbols corresponding to the i-th
subcarrier is:

where D(i) is a diagonal matrix for supporting small delay cyclic delay
diversity.
For both small delay CDD and large delay CDD, the precoded symbols
corresponding to the i-th subcarrier is:

where D(i) is a first diagonal matrix for supporting small delay cyclic
delay diversity, and C(i) is a second diagonal matrix for supporting large delay
cyclic delay diversity.
The value q may be equal to 1, or may be equal to the transmission rank,
or may be equal to 12m, where m is a positive integer.
The set of code words may include all of the codewords in the certain
codebook. Alternatively, the set of code words may include a subset of
codewords in the certain codebook.
According to another aspect of the present invention, a plurality of
information bits are encoded, scrambled and modulated to generate a plurality of
modulation symbols. The plurality of modulation symbols are mapped onto the
subcarriers in at least one transmission layer of a transmission resource. The
mapped symbols are repeatedly precoded and transmitted via a plurality of
antennas by using a matrix for cyclic delay diversity and applying different
codewords for different retransmissions.
According to yet another aspect of the present invention, four symbols to
be transmitted are encoded by using a rank-2 space frequency block code to
generate a rank-2 space frequency block of symbols. Then, the block of
symbols are precoded by using a matrix for cyclic delay diversity and a set of
codewords from a certain codebook to generate a plurality of precoded symbols.
The codewords cycled for every a certain number of subcarriers. Finally, the
precoded symbols are transmitted via a plurality of antennas.
According to still yet another aspect of the present invention, four
symbols to be transmitted are encoded by using a rank-2 space frequency block
code to generate a rank-2 space frequency block of symbols. The block of
symbols are repeatedly precoded and transmitted via a plurality of antennas by
using a matrix for cyclic delay diversity and applying different codewords for
different retransmissions.
According to a further aspect of the present invention, four symbols to be
transmitted are encoded to generate two transmission matrices. The two
transmission matrices T} and T2 are:

where Tij represents the symbol to be transmitted on the ith antenna and
the jth subcarrier. The four symbols are repeatedly transmitted via four antennas
by alternatively applying the two transmission matrices T1 and T2 in a
frequency domain.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant
advantages thereof, will be readily apparent as the same becomes better
understood by reference to the following detailed description when considered in
conjunction with the accompanying drawings in which like reference symbols
indicate the same or similar components, wherein:
FIG. 1 schematically illustrates an Orthogonal Frequency Division
Multiplexing (OFDM) transceiver chain suitable for the practice of the principles
of the present invention;
FIGS. 2A and 2B schematically illustrate two schemes of subcarrier
allocation of frequency-selective multi-user scheduling and frequency diversity in
an OFDM system;
FIG. 3 schematically illustrates a transmission and reception scheme in a
multiple input and multiple output (MIMO) system;
FIG. 4 schematically illustrates a precoding scheme is a MIMO system;
FIG. 5 schematically illustrates a scheme for processing precoded signals
at a receiver;
FIGS. 6A and 6B illustrate two schemes of applying phase shift to
subcarriers;
FIG. 7 schematically illustrates a cyclic delay diversity precoding scheme;
FIG. 8 schematically illustrates using different codewords in different
retransmissions in a Hybrid automatic repeat and request (HARQ) scheme as one
embodiment according to the principles of the present invention;
FIG. 9 schematically illustrates a scheme for precoding a rank-2 space
frequency block code as another embodiment according to the principles of the
present invention;
FIG. 10 schematically illustrates a scheme for precoding a rank-2 space
frequency block code by applying different codewords in different
retransmissions in a HARQ scheme as another embodiment according to the
principles of the present invention; and
FIG. 11 schematically illustrates mapping of symbols to antennas for a
Space Frequency Block Code (SFBC) combined with frequency Switched
Transmit Diversity (FSTD) scheme as still another embodiment according to the
principles of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
FIG. 1 illustrates an Orthogonal Frequency Division Multiplexing (OFDM)
transceiver chain. In a communication system using OFDM technology, at
transmitter chain 110, control signals or data 111 is modulated by modulator 112
into a series of modulation symbols, that are subsequently serial-to-parallel
converted by Serial/Parallel (S/P) converter 113. Inverse Fast Fourier Transform
(IFFT) unit 114 is used to transfer the signals from frequency domain to time
domain into a plurality of OFDM symbols. Cyclic prefix (CP) or zero prefix (ZP)
is added to each OFDM symbol by CP insertion unit 116 to avoid or mitigate the
impact due to multipath fading. Consequently, the signal is transmitted by
transmitter (Tx) front end processing unit 117, such as an antenna (not shown), or
alternatively, by fixed wire or cable. At receiver chain 120, assuming perfect time
and frequency synchronization are achieved, the signal received by receiver (Rx)
front end processing unit 121 is processed by CP removal unit 122. Fast Fourier
Transform (FFT) unit 124 transfers the received signal from time domain to
frequency domain for further processing.
The total bandwidth in an OFDM system is divided into narrowband
frequency units called subcarriers. The number of subcarriers is equal to the
FFT/IFFT size N used in the OFDM system. In general, the number of
subcarriers used for data is less than N because some subcarriers at the edge of the
frequency spectrum are reserved as guard subcarriers. In general, no information
is transmitted on guard subcarriers.
In a communication link, a multi-path channel results in a
frequency-selective fading. Moreover, in a mobile wireless environment, the
channel also results in a time-varying fading. Therefore, in a wireless mobile
system employing OFDM based access, the overall system performance and
efficiency can be improved by using, in addition to time-domain scheduling,
frequency-selective multi-user scheduling. In a time-varying frequency-selective
mobile wireless channel, it is also possible to improve the reliability of the
channel by spreading and/or coding the information over the subcarriers.
In case of frequency-selective multi-user scheduling, a contiguous set of
subcarriers potentially experiencing an upfade is allocated for transmission to a
user. The total bandwidth is divided into subbands grouping multiple
contiguous subcarriers as shown in FIG. 2A where subcarriers f1, f2, f3 and f4 are
grouped into a subband for transmission to a user in frequency-selective
multi-user scheduling mode. In case of frequency-diversity transmission,
however, the allocated subcarriers are preferably uniformly distributed over the
whole spectrum. As shown in FIG. 2B, subcarriers f1, f5, f9 and f13 are grouped
into a subband for transmission. The frequency-selective multi-user scheduling
is generally beneficial for low mobility users for which the channel quality can be
tracked. But the channel quality generally can not be tracked for high mobility
users (particularly in a frequency-division-duplex system where the fading
between the downlink and uplink is independent) due to channel quality feedback
delays and hence the frequency diversity transmission mode is preferred.
Multiple Input Multiple Output (MIMO) schemes use multiple transmit
antennas and multiple receive antennas to improve the capacity and reliability of
a wireless communication channel. A MIMO system promises linear increase in
capacity with K where K is the minimum of number of transmit (M) and receive
antennas (N), i.e. K = min (M,N). A simplified example of a 4 x 4 MIMO
system is shown in FIG. 3. In this example, four different data streams are
transmitted separately from the four transmit antennas. The transmitted signals
are received at the four receive antennas. Some form of spatial signal
processing is performed on the received signals in order to recover the four data
streams. An example of spatial signal processing is vertical Bell Laboratories
Layered Space-Time (V-BLAST) which uses the successive interference
cancellation principle to recover the transmitted data streams. Other variants of
MIMO schemes include schemes that perform some kind of space-time coding
across the transmit antennas (e.g., diagonal Bell Laboratories Layered
Space-Time (D-BLAST)) and also beamforming schemes such as Spatial
Division multiple Access (SDMA).
The MIMO channel estimation consists of estimating the channel gain and
phase information for links from each of the transmit antennas to each of the
receive antennas. Therefore, the channel for M x N MIMO system consists of an
N x M matrix:
where aij represents the channel gain from transmit antenna j to receive
antenna i. In order to enable the estimations of the elements of the MIMO
channel matrix, separate pilots are transmitted from each of the transmit antennas.
An optional precoding protocol that employs a unitary pre-coding before
mapping the data streams to physical antennas is shown in FIGS. 5A and 5B.
The optional precoding creates a set of virtual antennas (VA) 171 before the
pre-coding. In this case, each of the codewords is potentially transmitted
through all the physical transmission antennas 172. Two examples of unitary
precoding matrices, P1 and P2 for the case of two transmission antennas 172 may
be:
Assuming modulation symbols S1 and S2 are transmitted at a given time
through stream 1 and stream 2 respectively. Then the modulation symbol T1
after precoding with matrix P1 in the example as shown in FIG. 5A and the
modulation symbol T2 after precoding with matrix P2 in the example as shown in
FIG. 5B can be respectively written as:

transmitted via antenna 1 and antenna 2, respectively, when precoding is done
using precoding matrix P1 as shown in FIG. 4A. Similarly, the symbols
T vill be transmitted via antenna 1 and antenna
2, respectively, when precoding is done using precoding matrix P2 as shown in
FIG. 4B. It should be noted that precoding is done on an OFDM subcarrier level
before the IFFT operation as illustrated in FIGS. 4A and 4B.
In a pre-coded MIMO system, inverse operations are performed at the
receiver to recover the transmitted symbols. The received symbols are
multiplied with the inverse precoding matrices. The inverse precoding matrices
are given as:
It should be noted that the inverse of a unitary precoding matrix can
simply be obtained by taking the complex conjugate transpose of the pre-coding
matrix. The transmitted symbols are decoded by multiplying the received
symbol vector with the inverse pre-coding matrices. Therefore, the transmitted
symbols are given as:

A downlink physical channel corresponds to a set of resource elements
carrying information originating from higher layers. First, a plurality of
information bits are coded with a plurality of code words to generate a plurality of

We described a precoding approach that applies to both transmit diversity
and MIMO spatial multiplexing. A composite precoder is constructed based on
a unitary precoder such as Fourier matrix precoder multiplied with another
unitary precoder representing a transmit diversity scheme such as cyclic delay-
diversity. It should be noted that the principles of the current invention also
applies to the cases of non-unitary precoding or unitary precoders other than
Fourier matrix precoder.

Multiple Fourier matrices can be defined by introducing a shift parameter
(g/G) in the Fourier matrix. The entry of the multiple Fourier matrices is given
by:
A set of four 2x2 Fourier matrices can be defined by taking G=4, and g=0.
1, 2 and 3, and are written as:

A cyclic delay diversity scheme can be implemented in the frequency
domain with a phase shift of e"Plk applied to subcarrier k transmitted from the
i-th transmission antenna. The angle p, is given as:

where D, is the cyclic delay in samples applied from the i-th antenna. It
should be noted that other functions can be used to derive the frequency domain
phase shift. The phase shift may be kept constant for a group of subcarriers.
As shown in FIG. 6A, phase shift is constant over subband (SB) 1,Q2 is
constant SB2, and so on. It is also possible to allow the phase shift to vary from
one group of subcarriers to the next. As shown in FIG. 6B, the phase shift varies
from 2x/N to 2n over a frequency range from subcarrier 1 to subcarrier 512.
The cyclic delay diversity can be seen as precoding with the following
precoding matrix for the case of four transmission antennas:

FIG. 7 schematically illustrates a transmitter provided with the CDD
precoding scheme using the above precoding matrix. It can be noted that the
same symbol with antenna and frequency (subcarrier) dependent phase shifts are
transmitted from multiple antenna. No phase shift is applied for the symbol
transmitted from the first antenna.
In 3GPP RANI contribution Rl-073096, "Text Proposal for 36.211
regarding CDD Design", published in June 2007, Orlando, USA, a joint proposal
is depicted that includes both small and large delay CDD.
For zero-delay and small-delay CDD, precoding for spatial multiplexing
shall be performed according to the following equation:

where the precoding matrix w(i) is of size P x v, P is the number of
antenna ports, v is the number of layers, the matrix D(i) is a diagonal matrix

Note that these values apply only when transmit diversity is not
configured for transmission rank 1.
For spatial multiplexing, the values of w(i) shall be selected among the
precoder elements in the codebook configured in the Node B and the UE. Node
B can further confine the precoder selection in the UE to a subset of the elements
in the codebook using codebook subset restriction. According to TS 36.211.
version 1.1.0, the configured codebook shall be equal to
Table 2. Note that the number of layers v is equal to the transmission rank p
in case of spatial multiplexing.

According to TS 36.211, version 8.2.0, For transmission on two antenna
ports, p e {0,l}, the precoding matrix W(i) for zero, small, and large-delay CDD
shall be selected from Table 3 or a subset thereof.

For transmission on four antenna ports, p e {0,1,2,3}, the precoding matrix
w for zero, small, and large-delay CDD shall be selected from Table 4 or a
subset thereof. The quantity w>s] denotes the matrix defined by the columns
given by the set {.?} from the expression wn = i-2unu"/u"u„ where / is the
4x4 identity matrix and the vector u„ is given by Table 4.

For large-delay CDD, the precoding for spatial multiplexing shall be
performed according to the following equation:

where the precoding matrix W{i) is of size Pxu, P is the number of
antenna ports, v is the number of layers, the quantity £)(/) is a diagonal matrix
for support of large cyclic delay diversity, and U is a fixed matrix. The
For spatial multiplexing, the values of w(i) shall be selected among the
precoder elements in the codebook configured in the Node B and the UE. Node
B can further confine the precoder selection in the UE to a subset of the elements
in the codebook using codebook subset restriction. The configured codebook
shall be equal to Table 3 and Table 4. Note that the number of layers v is equal
to the transmission rank p in case of spatial multiplexing.
Furthermore, a codeword cycling method is proposed for the large delay
equation, y(i)= D(i)-W(i)-U . x(i), so that W(i) is cyclically selected as one of
the codeword in either the codebook in Table 3 for two antenna ports, and in
Table 4 for four antenna ports, or a subset of the codebooks. It is proposed that
the codeword changes either every subcarrier, or every v subcarriers, where v is
the transmission rank.
In a first embodiment according to the principles of the present invention,
we propose to perform codeword cycling in the large delay CDD method
y(i) = W(i)-D(i)-U-x(i) for every resource block (RB) or every integer number of
RBs. For LTE system one RB consists of twelve subcarriers. Therefore, the
codeword W(i) is selected according to W(i) = Ck, where k is given by

non-negative integer and 12 is the number of subcarriers in a RB. Furthermore.
Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding
codebooks defined in Table 3 for two antenna ports, and in Table 4 for four
antenna ports, or a subset thereof, and N is the codebook size or the size of the
subset. Also note that mod(x) is a modulo operation and [x] is a ceiling
operation.
In a second embodiment according to the principles of the present
invention, we propose to perform codeword cycling in the small delay CDD
method y(i)= D(i)-W(i)-x(i) for every q subcarriers. Therefore, the codeword
W(i) is selected according to W(i) = Ck, where k is given by

non-negative integer. Examples of q value include q = 1, or q - u where v
is the transmission rank, or q = 12m (cycle every m RBs) where m > 0 is a
non-negative number and 12 is the number of subcarriers in a RB. Furthermore.
Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding
codebooks defined in Table 3 for two antenna ports, and in Table 4 for four
antenna ports, or a subset thereof, and N is the codebook size or the size of the
subset. Also note that mod(x) is a modulo operation and [x] is a ceiling
operation.
In a third embodiment according to the principles of the present invention,
we propose to perform codeword cycling in a uniform small and large delay CDD
method as given by:

Table 6. Therefore, the codeword W(i) is selected according to
w(i) = Ck, where k is given by:

non-negative integer. Examples of q value include q = 1, or q = v where v
is the transmission rank, or q = 12m (cycle every m RBs) where m>0 is a
non-negative number and 12 is the number of subcarriers in a RB. Furthermore.
Ck denotes the k-th codeword in the single-user MIMO (SU-MIMO) precoding
codebooks defined in Table 3 for two antenna ports, and in Table 4 for four
antenna ports, or a subset thereof, and N is the codebook size or the size ot the
subset. Also note that mod(x) is a modulo operation and [x] is a ceiling
operation.

for uniform small and large delay CDD. Furthermore, we propose to
select these codewords in such a way that Wl{i)=Ck for t = \,...,T, where Q
denotes the k, -th codeword in the codebook of the precoding codebook defined
in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or a subset
thereof, and such that the choice of Ck is independent for each retransmission.
i.e, for the t-th transmission, Q can be any of the N codewords, regardless of
which codeword is used in the previous transmissions. FIG.8 illustrates how the
different codewords are used in different re-transmissions.
In a fifth embodiment according to the principles of the present invention,
we propose to add a pre-coding process, denoted by matrix w(i) where / is the
subcarrier index, at the output of the rank-2 space frequency block code (SFBC)
block given by:
and this precoded rank-2 method is illustrated in FIG. 9. And the overall
transmit signal is given by:
where we used the notation A(i) to emphasize the fact that the rank-2
SFBC transmission matrix is a function of the subcarrier index. That is,

In addition, note that Sj to S4 are generated from the same codeword.
One way to choose the codeword is to choose the w(i) according to the
precoding matrix index (PMI) in the feedback, and W{i) belongs the codebook
defined in Table 3 for two antenna ports, and in Table 4 for four antenna ports, or
a subset thereof.
Another way to choose the codeword is to choose W(i) as an arbitrary
unitary matrix that varies every q subcarriers, where q > 0 is an arbitrary
non-negative integer. Therefore, the codeword W{i) is selected according to
w{i)=Ck, where k is given by:

include q = \, or q = o where v is the transmission rank, or q = \2m (cycle
every m RBs) where m>0 is a non-negative number and 12 is the number of
subcarriers in a RB. Furthermore, Ck denotes the k-th codeword in the
single-user MIMO (SU-MIMO) precoding codebook defined in Table 3 for two
antenna ports, and in Table 4 for four antenna ports, or a subset thereof, and A'
is the codebook size or the size of the subset. Also note that mod(x) is a
modulo operation and \x~\ is a ceiling operation.
In a sixth embodiment according to the principles of the present invention,
we propose to apply different codewords for different retransmission in a Hybrid
automatic repeat-request (HARQ) system that uses the rank-2 SFBC transmission.
Let there be T re-transmissions in the HARQ system, and let
W\{j\W2{i),---,Wr{i) be the codeword used for these T retransmissions, the
transmit signal for each retransmission is then given by:

Furthermore, we propose to select these codewords in such a way that
W, (/) =Cki for / = 1,..., T , where Ck denotes the k, -th codeword in the
codebook of the precoding codebook defined in Table 3 for two antenna ports.
and in Table 4 for four antenna ports, or a subset thereof, and such that the choice
of Cki is independent for each retransmission, i.e, for the t-th transmission, Ccan be any of the N codewords, regardless of which codeword is used in the
previous transmissions. FIG. 10 illustrates how the different codewords are used
in different re-transmissions.
In a seventh embodiment according to the principles of the present
invention, we propose a scheme where mapping of symbols to antennas is
changed on repeated symbols as shown in FIG. 11. In this example we assumed
that four symbols 5,, S2, S3 and S4 are transmitted with one repetition over
eight subcarriers, or two groups of subcarriers in two subframes, with four
subcarriers in each group. In the first four subcarriers, symbols S, and S2 are
transmitted on antennas ports ANTO and ANT1, while symbols S^ and S4 are
transmitted on antennas ports ANT2 and ANT3. On repetition in the last four
subcarriers, the symbols 5, and S2 are transmitted on antennas ports ANT2 and
ANT3 while symbols 53 and S4 are transmitted on antennas ports ANTO and
ANT1. This proposed mapping results in greater diversity gain compared to the
transmission where mapping does not change on repetition. This diversity gains
stems from the fact that after one repetition all the four symbols are transmitted
from all the four transmit antennas.
In the proposed mapping scheme, the transmission matrix 7j shown
below is used for initial transmission:

where T-,j represents symbol transmitted on the ith antenna and the jth
subcarrier ox jth time slot (i=J,2,3,4, j=J,2,3,4) for the case of 4-Tx antennas.
When the same symbols are repeated, a different mapping matrix T2 shown
below is used for transmission:

Note that the principles of the present invention may be applied to
decoding information received from a transmitter. In this case, since the
selection of precoding matrices is a function of time (subframe number) and
frequency (subcarrier number), the receiver can simply observe the subframe
number and subcarrier number, and use the same function to figure out the
precoder matrix. The dependence of the precoding matrix selection on
frequency is explicit from Equations (13) and (14). The dependence of the
precoding matrix selection on time is explicit in the HARQ transmission scheme.
While the present invention has been shown and described in connection
with the preferred embodiments, it will be apparent to those skilled in the art that
modifications and variations can be made without departing from the spirit and
scope of the invention as defined by the appended claims.
WE CLAIM
1. A method for transmission in a communication system, the method comprising:
encoding a plurality of information bits to generate a plurality of coded bits;
scrambling the plurality coded bits to generate a plurality of scrambled bits;
modulating the plurality of scrambled bits to generate a plurality of modulation symbols;
mapping the plurality of modulation symbols onto the subcarriers in at least one transmission
layer of a transmission resource;
precoding the modulation symbols by using a precoding matrix of which codewords of a
codebook are changed every subcarriers.
2. An apparatus for transmission in a communication system, the method comprising:
means for encoding a plurality of information bits to generate a plurality of coded bits;
means for scrambling the plurality coded bits to generate a plurality of scrambled bits;
means for modulating the plurality of scrambled bits to generate a plurality of modulation
symbols;
means for mapping the plurality of modulation symbols onto the subcarriers in at least one
transmission layer of a transmission resource;
means for precoding the modulation symbols by using a precoding matrix of which codewords of
a codebook precoding matrix are changed every subcarriers.
3. The method of claim 1 apparatus of claim 2, wherein a index of the codeword is determined by
performing a modulo operation, subband index mod a size of the codebook.
4. The method of claim 1 or apparatus of claim 2, wherein the codewords are used for precoding
the modulation symbols corresponding to an i-th subcarrier being established by:

where Ck is the k-th codeword in the set of codewords, with the index k being established by:

where q is a certain positive integer, and N is the size of the codewords; and
transmitting the precoded symbols via a plurality of transmission antennas.
5. The method of claim 1 or apparatus of claim 2, comprised of the precoded symbols
corresponding to the i-th subcarrier being established by:

with:
x(i) being a block of modulation symbols corresponding to the i-th subcarrier and
where v is the number of transmission layers;
U being a certain fixed matrix and the elements of U being established by for
m = 0, l,...,v-1, and n = 0,1,...,v-1; and
D(i) being a diagonal matrix for supporting large delay cyclic delay diversity.
6. The method of claim 1 or apparatus of claim 2, comprised of the precoded symbols
corresponding to the i-th subcarrier being established by:

with:
x(i) being a block of modulation symbols corresponding to the i-th subcarrier and
where v is the number of transmission layers; and
D(i) being a diagonal matrix for supporting small delay cyclic delay diversity.

In this invention, several open-loop solutions that encompass the small
delay CDD codeword cycling, codeword cycling between different
re-transmissions of both small and large delay CDD are proposed. In addition, an
open-loop codeword cycling method for SFBC+FSTD scheme, as well as its
extension to SFBC+FSTD based HARQ, are proposed. In one method, a
plurality of information bits are encoded, scrambled and modulated to generate a
plurality of modulation symbols. The plurality of modulation symbols are
mapped onto the subcarriers in at least one transmission layer of a transmission
resource. The modulation symbols are then precoded by using a matrix for
cyclic delay diversity and a set of codewords from a certain codebook to generate
a plurality of precoded symbols. The codewords are cycled for every a certain
number of subcarriers. Finally, the precoded symbols are transmitted via a
plurality of transmission antennas.

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http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=F39akCiGJyL6sZNwjl4nXQ==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

272903

Indian Patent Application Number

4453/KOLNP/2009

PG Journal Number

19/2016

Publication Date

06-May-2016

Grant Date

02-May-2016

Date of Filing

22-Dec-2009

Name of Patentee

SAMSUNG ELECTRONICS CO. LTD.

Applicant Address

416, MAETAN-DONG, YEONGTONG-GU, SUWON-SI, GYEONGGI-DO, 442-742 REPUBLIC OF KOREA

Inventors:

#	Inventor's Name	Inventor's Address
1	KHAN, FAROOQ	820 SADDLEBROOK DRIVE, ALLEN, COLLIN COUNTRY, TX 75002, UNITED STATES OF AMERICA
2	DING, YINONG	4556 PEBBLE BROOK LANE, PLANO, TX 75093, UNITED STATES OF AMERICA
3	ZHANG, JIANZHONG	504 RENFRO CT., IRVING, TX 75063 UNITED STATES OF AMERICA
4	VAN RENSBURG, CORNELIUS	16500 LAUDER LANE, APT. 20103, DALLAS, TX 75248 UNITED STATES OF AMERICA

PCT International Classification Number

H04B 7/02,H04B 7/06

PCT International Application Number

PCT/KR2008/003646

PCT International Filing date

2008-06-25

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	60/929,376	2007-06-25	U.S.A.
2	12/155,319	2008-06-02	U.S.A.