Title of Invention	BASE STATION, MOBILE STATION, AND POWER CONTROL METHOD
Abstract	A base station includes: means that derives a transmission power of a mobile station based on receive quality of an uplink pilot channel; means that reports the derived transmission power to the mobile station; and means that receives a control channel transmitted by the mobile station according to the reported information. Accordingly, irrespective of transmission power history over a past continuous time, the mobile station receives an instruction on the transmission power from the base station each time when transmitting a packet so as to be able to adjust the transmission power.

Title of Invention

BASE STATION, MOBILE STATION, AND POWER CONTROL METHOD

Abstract

A base station includes: means that derives a transmission power of a mobile station based on receive quality of an uplink pilot channel; means that reports the derived transmission power to the mobile station; and means that receives a control channel transmitted by the mobile station according to the reported information. Accordingly, irrespective of transmission power history over a past continuous time, the mobile station receives an instruction on the transmission power from the base station each time when transmitting a packet so as to be able to adjust the transmission power.

Full Text	-1- SPECIFICATION TITLE OF THE INVENTION BASE STATION, MOBILE STATION AND POWER CONTROL METHOD TECHNICAL FIELD The present invention generally relates to radio communication. More particularly, the present invention relates to a base station, a mobile station and a method for controlling transmission power of a shared control channel used for packet switching type communication. BACKGROUND ART In a mobile communication system such as IMT-2000, transmission power control is performed from the viewpoint of enlargement of circuit capacity and economy of battery of a mobile station and the like. For example, quality measurement of a channel is performed in a receiving side, and a transmission power control (TPC) bit is transmitted by a return channel (DPCCH, for example) such that the channel that is being received satisfies desired quality. As a result, the transmission power is updated by 1 dB, for example, and quality measurement and transmitting/receiving of the TPC bit are repeated, so that the transmission power can be gradually changed to be closer to an optimal value. That is, in a communication of a circuit switching scheme, an individual channel is assigned specifically to a mobile station, and the transmission power of the mobile station is gradually adjusted based on a temporally continuing history on the transmission power. Such transmission power control is described in a non- patent document 1, for example. [Non Patent document 1] Keiji Tachikawa, "W-CDMA -2- mobile communication scheme", MARUZEN, pp.126-128 DISCLOSURE OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION In a future mobile communication system, a packet switching type communication scheme is adopted in place of the conventional circuit switching type communication scheme. Radio resources of a packet form are shared by a plurality of users, and availability of the radio resources is properly scheduled in a base station. In such a mobile communication system, there is not only a mobile station to which the radio resources are actually assigned but also a mobile station that desires assignment but to which the resources are not yet assigned. In addition, such a situation arises in circuits of both of uplink and downlink. For causing a mobile station placed in various operation situations to operate properly, it is necessary that the shared control channel is transmitted well with a constant quality. Thus, it is necessary that the transmission power of the shared control channel is properly controlled. But, the above-mentioned transmission power control method of the circuit switching type cannot be used as it is, and a useful method is not yet established. An object of the present invention is to provide a base station, a mobile station and a power control method for controlling transmission power of a shared control channel using a method suitable for packet switching type communication. MEANS FOR SOLVING THE PROBLEM In the present invention, a base station, is used, that includes: means that derives a transmission power of a mobile station based on receive quality of an uplink pilot channel; means -3- that reports the derived transmission power to the mobile station; and means that receives a control channel transmitted by the mobile station according to the reported information. EFFECT OF THE INVENTION According to the present invention, transmission power of the shared control channel can be controlled using a method applicable to packet switching type communication. BRIEF DESCRIPTION OF THE DRAWINGS Fig.l shows a schematic block diagram of a base station according to an embodiment of the present invention; Fig.2 shows a schematic block diagram of a mobile station according to an embodiment of the present invention; Fig.3 is a flowchart showing a transmission power control method according to an embodiment of the present invention; Fig.4 is a diagram showing an example of correspondence relationship among CQI, MCS number and transmission power; Fig.5 is a diagram showing an example of correspondence relationship among CQI, MCS number and transmission power; Fig.6 is a diagram showing mapping examples of a pilot channel; Fig.7 is a diagram showing information items that are included in an uplink shared control channel; Fig.8 is a diagram showing a resource assignment example of an uplink shared data channel; Figs.9A-9D show a plurality of candidates considered when assigning a band; Fig.10 is a schematic diagram on operation -4- principle of AMC; Fig.11 is a flowchart showing a transmission power control method according to an embodiment of the present invention; Fig.12 is a diagram exemplary showing correspondence relationship between receive quality and transmission power; Fig.13 is a diagram showing information items included in a downlink shared control channel; Fig.14 is a diagram showing an example of power control according to an embodiment of the present invention; Fig.15 is a diagram showing radio resources and a unit of coding. Description of reference signs 11 modulation and coding unit 12 multiplexing unit 13 radio unit 14 transmission power determination unit 21 radio unit 23 demodulation and decoding unit 24 pilot channel processing unit PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION According to an embodiment of the present invention, relative or absolute power by which the mobile station needs to change its transmission power is derived based on relationship between receive quality of an uplink pilot channel and receive quality that a control channel needs to satisfy or a transmission power value of the pilot channel. Thus derived power is reported to the mobile station, so that uplink transmission power is properly controlled. Accordingly, without using the transmission power history over a past continuous time, the mobile station receives an instruction on -5- transmission power from the base station each time when sending a packet so as to be able to adjust the transmission power. When the mobile station has not yet received the instruction, an uplink pilot channel is transmitted after a procedure. In the procedure, a pilot channel and a transmission power is reported to the mobile station using a downlink, and the mobile station derives the transmission power based on an average propagation loss between the mobile station and the base station. The uplink pilot channel is transmitted using the derived power, and it is received by the base station. Accordingly, the base station can properly determine a transmission power of the mobile station of next time based on the pilot channel transmitted from the mobile station. The propagation loss may be derived from receive quality of a downlink pilot channel and the transmission power value. According to an embodiment of the present invention, the base station receives both or one of a first pilot channel in which a symbol mapping pattern is constant and a second pilot channel in which a symbol mapping pattern is variable. By preparing a plurality of kinds of uplink pilot channels, both of channel estimation accuracy and transmission efficiency of information can be considered. According to an embodiment of the present invention, the mobile station that is transmitting traffic data is caused to transmit the control channel using a power derived based on the uplink pilot channel. The mobile station that is not yet transmitting traffic data is caused to transmit the control channel using a power derived based on the average propagation loss. Since the number of -6- mobile stations that are transmitting traffic data is relatively small, efficiency of power control can be improved by applying the CQI based TPC only for the mobile stations. The base station may further includes means that determines a frequency chunk usable for the mobile station to transmit traffic data and determines a transmission power of the mobile station. The transmission power and the frequency chunk may be determined such that the transmission power exceeds a predetermined threshold and that more chunks are used. Accordingly, resources of the shared data channel can be easily and properly assigned. A base station according to an embodiment of the present invention includes means that transmits a common pilot channel; means that derives a plurality of transmission powers of a shared control channel based on receive quality of a plurality of common pilot channels reported by an uplink; and means that reports the shared control channel to a plurality of mobile stations using the derived transmission powers. The derived transmission powers may be separately reported to the mobile stations receiving traffic data. Accordingly, transmission power can be controlled for each mobile station. One of the derived transmission powers may be reported to the mobile stations that are receiving traffic data. Accordingly, the plurality of control stations can be controlled with a same transmission power. The transmission power may be a transmission power corresponding to a mobile station that reports the worst CQI among the plurality of mobile stations. The shared control channel may be reported to a mobile station that is not receiving traffic data using a predetermined transmission power. -7- Accordingly, transmission power control for the shared control channel can be performed also for mobile stations that desire only transmission of the uplink traffic data. The base station may include a coder for coding data for one or more mobile station as a unit, and the data for one or more mobile station may be transmitted using a same transmission power. By aligning the unit of coding with the range of data for which same transmission power control is performed, a combination of strength of error correction capability and excess or deficiency of transmission power can be properly set. For example, coding (decoding) can be simplified without excess or deficiency of power, and on the other hand, transmission power can be made large while error correction capability is high. [Embodiment 1] In a downlink, a common pilot channel is announced to all users from a base station, and a mobile station that desires downlink data communication reports receive quality of the common pilot channel to the base station, so that it can be expected that the base station determines a transmission power of the downlink shared control channel. However, in an uplink, the common pilot channel cannot be used. This embodiment is contrived in view of the problem. In the following, a transmission power control method for an uplink shared control channel in the packet switching type mobile communication system is described. Fig.1 shows a base station according to an embodiment of the present invention. The base station includes a modulation and coding unit 11 that performs multilevel modulation on data to be transmitted and performs channel coding, a multiplexing unit (MUX) 12 that multiplexes a -8- modulated signal and a pilot channel, and a radio unit (RF) 13 that converts an multiplexed signal to a signal format for transmitting from an antenna, and further includes a transmission power determination unit 14 that determines a transmission power of a mobile station based on information received from an upper apparatus of the base station or from another mobile station or based on base station data. Fig.2 shows a mobile station according to an embodiment of the present invention. The mobile station includes a radio unit (RF) 21 that converts a signal format of a signal received by an antenna, a demultiplexing unit (DeMUX) 22 that demultiplexes a pilot channel and other channel from the received signal, a pilot channel processing unit 23 that performs channel estimation using the pilot channel and performs measurement of transmission loss and the like, and a demodulation and decoding unit 24 that demodulates the received data and performs error correction decoding. Fig. 3 shows a flowchart showing an uplink transmission power control method according to an embodiment of the present invention. In this embodiment, a shared control channel of a fixed information rate and a shared data channel of a variable rate are prepared as uplink channels. The transmission power control method described below can be used for both of the shared control channel and the shared data channel. Since the transmission rate of the shared control channel is constant, it is essential to control the transmission power of the mobile station for controlling receive quality of the shared control channel. On the other hand, for controlling receive quality of the shared data channel, there a choice of adjusting the transmission rate in addition to controlling the -9- transmission power of the mobile station. The transmission rate can be adjusted by changing the number of levels of the multilevel modulation or changing a coding rate of data. By the way, although the transmission rate of the shared control channel is fixed to be constant in this embodiment for simplifying explanation, the transmission rate of the shared control channel may be changed in another embodiment. In step 1, a downlink pilot channel is transmitted from the base station to the mobile station, and a transmission power Pt of the pilot channel is also transmitted via an annunciation channel or a broadcast channel (BCH). As indicated as step 2, the mobile station receives the downlink pilot channel and the transmission power for a period to calculate an average propagation loss L. The propagation loss L is mainly determined by distance variation and shadowing, and in general, the propagation loss L is not largely different between uplink and downlink when being averaged over a proper time. For example, by averaging the receive quality over a relatively long period such as a period of one or more frame, influence of instantaneous variation such as fading is removed. Fig.10 exemplary shows a relationship between instantaneous receive SIR and an average receive SIR. In this embodiment, although the receive quality is measured as SINR, it may be measured as SIR, or measured as other amount indicating quality. A target quality SIRt that the base station aims when the base station receives the uplink channel is represented as a following equation. SIRt = Pup+L-I0 [dB] In this equation, Pup indicates a transmission power (the control object at present) transmitted by the -10- mobile station, I0 indicates an interference power for an uplink channel observed at the base station. The propagation loss L is represented as a difference between the transmission power Pt in the base station and the receive power Pr in the mobile station. The annunciation channel announced from the base station includes the transmission power Pt at the base station, the uplink interference power ±o and the target quality SIRt. In step 3 of Fig.3, a pilot channel is transmitted from the mobile station to the base station. The transmission power at this time is a power that compensates for propagation loss calculated in step 2, and is not a power that compensates for instantaneous fading received on an uplink propagation route. In step 4, the base station measures a difference between the receive quality (receive SINR) of the received uplink pilot channel and the required quality (required SINR) expected for the pilot channel. The power indicated by the difference (power difference) indicates a power amount (relative power value) by which the mobile station needs to change its transmission power from the current value such that quality of channel received by the base station becomes the required quality. When deriving the power difference, the base station may use a table on receive SIR, required SIR, MCS number and power difference by which power should be changed from the current value. The MCS number specifies a combination of the number of levels of multilevel modulation and a coding rate. Fig.4 shows a table example defining a correspondence relationship among channel status information (CQI: Channel Quality Indicator) reported from the base station to the mobile station, MCS number and transmission power of the mobile -11- station. The channel status information is measured as SIR typically. In the example of Fig.4, MCS number and transmission power can be derived based on CQI (SIR) measured by the base station and reported from the base station. Fig.5 shows a table example that can be used in a case where MCS number, instead of the CQI information, is reported from the base station to the mobile station. Figs. 4 and 5 show merely examples of a table used for determining the transmission power, and the transmission power may be determined based on other correspondence relationship. In step 5, the base station reports, to the mobile station, the power difference by which the mobile station needs to change its transmission power from the current value using a downlink control channel. In step 6, the mobile station adjusts the transmission power based on the instructed information reported by the control channel. The adjusting amount in this case is different from one in control by TPC bit (not up and down by 1 dB), but is an amount for adjusting the current value to a target value at one time. In step 7, the control channel is transmitted using an adjusted transmission power. This transmission power is a value for compensating for not only the propagation loss but also minute variation such as fading. After that, by repeating the procedure from the step 3 to the step 7 or repeating the procedure of steps 7, 4 and 6 for each packet, an uplink transmission power suitable for the mobile station can be properly kept. However, in the repeated step 3, a pilot channel accompanying the uplink control channel is used. [Embodiment 2] In the second embodiment of the present -12- invention, processes in steps 3, 4 and 5 in Fig.3 are different. Since processes of other steps are the same, overlapping explanations are not provided. In step 3, the mobile station transmits a transmission power value of a pilot channel in addition to transmitting the pilot channel to the base station. In step 4, the base station measures receive quality (receive SINR) of the received pilot channel. The base station compares the receive quality and the required quality, and calculates a power value indicating the difference. A sum of the power value and the transmission power value indicates an absolute value of a power by which the mobile station transmits a channel such that quality of the channel received by the base station becomes the required quality. In the same way as the case of embodiment 1, the power (power difference) indicated as the difference indicates a power amount (relative power amount) by which the mobile station needs to change its transmission power from the current value such that quality of the channel received by the base station becomes the required quality. In step 5, one or both of the relative power value and the absolute power value is reported from the base station to the mobile station using a downlink. In step 6, the mobile station adjusts the transmission power according to the instructed information reported by the control channel. In step 7, the control channel is transmitted using the adjusted transmission power. After that, by repeating the procedure from the step 3 to the step 7 or repeating the procedure of steps 7, 4 and 6 for each packet, the uplink transmission power suitable for the mobile station can be -13- properly kept. [Embodiment 3] The pilot channel of the uplink is an individual pilot channel that is different for each mobile station and that is used for channel estimation, receive quality measurement, synchronization acquisition and the like for the uplink. For the purpose of precisely monitoring communication status that changes every moment, it is better to transmit many pilot channels. However, since the pilot channel is a known signal, the more the transmission amount of the pilot channel is, the more the transmission efficiency becomes lowered. In addition, it is not necessary to perform all of the channel estimation, receive quality measurement, synchronization acquisition for uplink with same frequency. From this viewpoint, in the third embodiment of the present invention, two types of uplink pilot channels are prepared, in which one is a reference pilot channel that does not necessarily accompany the shared control channel, and another one is a pilot channel for channel estimation that accompanies the shared data channel. The reference pilot channel may be used for channel estimation, receive quality measurement and synchronization acquisition for uplink, and it is similar to conventional one in terms of purpose of use. However, it is different from conventional one at least in the point that it is transmitted while transmission power control of the embodiments 1 and 2 are being performed such that the receive quality is kept. In addition, it is necessary to estimate the channel so as to compensate for the propagation route for demodulating the shared control channel. For that purpose, the reference pilot channel is transmitted accompanying the shared -14- control channel. On the other hand, for measuring uplink receive quality, the reference pilot channel may be transmitted independently without accompanying the shared control channel. However, the mapping position of the symbol is fixed beforehand as one kind. Fig.6(A) shows a situation in which the reference pilot channel accompanying the shared control channel and the independent reference pilot channel are transmitted. The pilot channel for channel estimation accompanies the shared data channel and is used for channel estimation. (B)-(D) in Fig.6 show examples of mapping of the pilot channel for channel estimation. Since the mobile station can move at various high and low speeds, there may be a case in which time variation of channel status is large depending on the mobile station. In this case, as shown in Figs.6(C) and (D) instead of Fig.6(B), man pilot channels for channel estimation are mapped in the time axis direction so that channel estimation accuracy for a user moving at high speed can be improved. For a mobile station that is not moving at high speed, by mapping the pilot channel for channel estimation as few as possible, transmission efficiency for information can be improved. Since the pilot channel for channel estimation is transmitted or not transmitted, it can be referred to as a pilot channel for capturing a reference pilot channel that is always being transmitted. According to the present embodiment, by providing a plurality of types of pilot channels and by adaptively mapping them according to use purpose or communication situation, channel estimation accurac and information transmission efficiency can be improved. [Embodiment 4] As mentioned above, in the mobile -15- communication system, there are not only a mobile station to which radio resources are actually assigned but also a mobile station that desires assignment but to which radio resources are not yet assigned. Such a situation occurs in both of uplink and downlink circuits. Therefore, the shared control channel includes information on these various statuses. Fig.7 shows information items that may be included in an uplink shared control channel. In the control information shown in four lines of (1)- (4), (1) and (2) indicate information on downlink data transmission by the shared data channel, and (3) and (4) indicate information on uplink data transmission by the shared data channel. The item (1) indicates information of a response transmitted by a mobile station when the mobile station that is actually performing downlink traffic data transmission receives a downlink shared data channel. When the mobile station can properly receive the downlink shared data channel, the mobile station returns an acknowledgement (ACK) to the base station, and when the mobile station cannot properly receive the downlink shared data channel, the mobile station returns a negative acknowledgement (NACK) to the base station. The item (2) indicates CQI information reported, to the base station, by the mobile station that is not currently performing downlink traffic data transmission but wants to perform data transmission in the future. The mobile station that desires to perform the uplink data transmission measures receive quality of a pilot channel included in the annunciation channel, and reports the measurement result as the CQI information to the base station to request scheduling of next time. The item (3) indicates information -16- accompanying the uplink shared data channel transmitted by the mobile station that is actually performing uplink traffic data transmission. This accompanying information is used for demodulation of shared data channel in the base station, for example. More particularly, the accompanying information may include modulation scheme, transport block size, retransmission control information, and identifier of the mobile station and the like. The modulation scheme is information for specifying a scheme such as QPSK, 16 QAM and the like, and it may be represented as a number of levels of multilevel modulation. The retransmission control information may include, for example, a process number for specifying a position of a packet in hybrid ARQ (HARQ), a redundancy format of a retransmitted bit, a new data indicator indicating whether a packet is new data or a retransmitted packet, or the like. The item (4) indicates information reported to the base station by a mobile station that is currently not performing traffic data transmission but desires to perform data transmission in the future. This information may include information on a transmission power or a buffer status of the mobile station. For example, transmission power information may include information indicating how large a power is by which the mobile station transmits the shared control channel, information (maximum transmission power) indicating how large the power is at the maximum by which the mobile station can transmit it, or the like. The buffer status may be represented as a data amount (a filling factor of a buffer) stored in a transmission buffer of the mobile station. For example, the larger the data amount is, the larger the priority of the scheduling may be set. In the present embodiment, the base -17- satiation determines which of the items (l)-(4) corresponds to transmission contents of the shared control channel. As a result, as to a mobile station ((1), (3)) that is actually performing traffic data transmission, the transmission power of the uplink shared control channel is controlled by the method described in the embodiment 1 or 2. That is, the base station measures receive quality of a pilot channel received from the mobile station, and determines and reports the transmission power of the mobile station according to the quality, so that the mobile station transmits the uplink shared control channel according to the reported information (this transmission power control method is to be referred to as "CQI based TPC" for the sake of convenience). On the other hand, as to a mobile station ((2), (4)) that is not currently performing uplink traffic data transmission but desires to perform the data transmission in the future, the transmission power of the uplink shared control channel is controlled by the method described in steps 2 and 3 in Fig.3. That is, the mobile station receives the pilot channel and the annunciation channel for a period so as to calculate an average propagation loss, so that the uplink shared control channel is transmitted to compensate for the propagation loss and compensate for interference power at the base station (this transmission power control method is to be referred to as "slow TPC" for the sake of convenience). Since the transmission power is adaptively changed at every moment in the CQI based TPC, calculation load for determining it is large. Therefore, if control of the transmission power of the uplink shared control channel is performed based on the CQI based TPC for all of the mobile stations, there is a fear that calculation load and delay in -18- the base station become very large. On the other hand, as to the uplink shared control channel for the mobile station, corresponding to (2) and (4), that is not yet performing traffic data transmission, the importance is lower than that corresponding to (1) and (3). For example, when the acknowledgement (ACK) of retransmission control is erroneously determined, useless traffic increases to exert a bad influence on the system. But, even though the buffer status of the mobile station is erroneously determined, large bad effect does not arise. In addition, there is a possibility that the number of mobile stations related to (2) and (4) becomes far larger than that of mobile stations related to (1) and (3). From this viewpoint, in the present embodiment, the CQI based TPC is performed for the mobile stations related to (1) and (3), so that accurate transmission power control that can address instantaneous fading variation is performed. Then, slow TPC is performed for the mobile stations related to (2) and (4) in which instantaneous fading is not compensated for, and slow transmission power control is performed such that signal quality is maintained averagely. Accordingly, the CQI based TPC described in embodiments 1 and 2 can be efficiently used. [Embodiment 5] Fig.8 indicates a radio resource assignment example for an uplink shared data channel according to a fifth embodiment of the present invention. Each procedure shown in Fig.8 is executed in the base station. In the present embodiment, there is a mobile station that is actually transmitting traffic data using an uplink shared data channel. This mobile station transmits the uplink shared control channel or the pilot channel or the like including the information item -19- of (3) shown in Fig.7 in the embodiment 4. The base station receives the pilot channel transmitted from the mobile station, and the flow of Fig.8 goes to step 10. In step 10, receive quality of the pilot channel is measured as CQI information. In step 12, a band of the uplink shared data channel for the mobile station is determined based on the measured CQI information and the transmission power information received from the mobile station. In the present embodiment, the usable band is divided into a plurality of frequency blocks each including one or more sub-carrier. Typically, the present invention is used for a radio communication system of an orthogonal frequency division multiplexing (OFDM) scheme. The frequency block is also referred to as a frequency chunk or simply a chunk. One or more frequency chunk may be used as various references such as a unit of resource assignment, a unit of retransmission, or a unit of coding. In the present embodiment, one frequency chunk is set as a unit of resource assignment. Figs.9A-9D show a plurality of candidates considered when assigning a band. The lateral axis of each figure corresponds to frequency f, and the vertical axis corresponds to power P. As shown in Fig.9A, a band of 10 MHz is divided to four frequency chunks of 2.5MHz. In step 12 of Fig.8, resources are determined such that the power becomes greater than a power threshold Pth derived from the transmission power information of the mobile station and that a band as wide as possible is kept (the band is determined such that the transmission power per one chunk is equal to or greater than the threshold and that the band occupies a wider transmission bandwidth.) For example, as to -20- transmission power of the mobile station reported from the mobile station, assuming that relationship between the power threshold Pth and the frequency chunk becomes each of ones in Fig.9. In this case, in the resource assignments shown in Figs.9A and 9B, since the power is less than the threshold, these two candidates are excluded. Although each of Figs.9C and 9D exceeds the threshold of the power, since the one shown in Fig.9C occupies a wider frequency band, it is determined to be an optimal resource assignment method. In step 14 of Fig.8, a MCS number corresponding to the power determined in step 12 is selected. In step 16, information on the MCS number derived in step 14, the band (information for specifying frequency chunk) determined in step 12 and transmission power and the like is reported to the mobile station via the downlink shared control channel. Accordingly, the mobile station can properly transmit the uplink shared data channel. According to the present embodiment, as shown in Fig.10, an adaptive modulation and coding (AMC) scheme is adopted for addressing instantaneous fading, and the MCS number is adaptively updated for each TTI in the example shown in the figure. By adopting AMC in addition to the slow TPC for bringing the average receive SIR close to a target value, transmission quality of the uplink shared data channel can be improved. [Embodiment 6] Uplink transmission power control is described in the first to fifth embodiments, and a transmission power control method for a downlink shared control channel is described in the sixth embodiment of the present invention. Fig.11 is a flowchart showing a transmission power control -21- method according to an embodiment of the present invention. As shown in step 112, the base station transmits a common pilot channel to mobile stations under the base station. The common pilot channel is different from the pilot channel that is transmitted by each mobile station via an uplink in that the common pilot channel is commonly transmitted to all of the mobile stations. In step 114, the mobile station measures receive signal quality as CQI information based on the received common pilot channel. The mobile station performing downlink data transmission reports the measured CQI information to the base station using the uplink shared control channel in step 116. In step 118, the base station determines a transmission power of the downlink shared control channel based on the reported CQI information. Correspondence relationship between CQI information and transmission power shown in Fig.12 is prepared beforehand. In step 120, the base station transmits the downlink shared control channel using the determined power in step 118. Accordingly, the transmission power of the downlink shared control channel can be determined based on the CQI information measured in the mobile station (this method is to be referred to as "CQI based downlink TPC" for the sake of convenience). Fig.13 indicates information items that may be included in the downlink shared control channel. These information items are largely classified as control information on downlink (left column) and control information on uplink (right column). In addition, as shown in the left side of the figure, the control information is largely classified as one on physical layer (upper side) and one on layer 2 (L2) (lower side). The control information on the downlink may include demodulation -22- information, scheduling information and retransmission control information (HARQ). The demodulation information may include chunk assignment information, data modulation information and transport block size information. The chunk assignment information is information for specifying a frequency chunk to be assigned to the downlink shared data channel to the mobile station. The data modulation information is information for specifying a modulation scheme applied to the shared data channel, and it may be specified by the MCS number. The transport block size information indicates the number of bits that are transmitted, and can be associated with coding rate, and may be specified by the MCS number. The scheduling information may include identification information for identifying the mobile station. The retransmission control information may include a process number of a transmitted packet, information indicating redundancy format, and a new data indicator. The new data indicator is an indicator that indicates whether a packet is a new packet or a retransmitted packet. The control information on the uplink may include a transmission power control bit, a transmission timing control bit, a response bit of a contention-based channel, scheduling information and retransmission control information (HARQ) and the like. The transmission power control bit and the transmission timing control bit indicate a transmission power and a transmission timing when transmitting the uplink shared data channel, and these are determined and reported in scheduling by the base station. The contention-based channel is a channel that may be transmitted from the mobile station to the base station without scheduling, and that is a channel that may cause contention between -23- the mobile station and another mobile station. The contention-based channel may be a fast access channel and the like that includes a reservation packet for requesting scheduling of the shared data channel, traffic data of small size or control data. The control information includes response information (ACK/NACK), as response contents, indicating whether the contention-based channel that is transmitted from the mobile station is properly received by the base station. The scheduling information may include identification information of the mobile station, chunk assignment information, data modulation information and transport block size and the like. These are similar to those described for the downlink, but these are different in that these are information on the uplink. The retransmission control information (HARQ) includes information (ACK/NACK) indicating whether information transmitted from the mobile station to the base station is properly received by the base station. The mobile station that receives the control information on the downlink (left side) actually receives traffic data using the downlink shared data channel. Therefore, since the number of that kind of mobile stations is the maximum number of users that can be assigned at most, the number of the mobile stations is not enormous. Therefore, the power of the downlink shared control channel may be controlled using the CQI based downlink TPC for each mobile station. Alternatively, "CQI based downlink TPC" for a mobile station corresponding to the worst CQI among a plurality of mobile stations may be applied to other mobile stations. On the other hand, mobile stations that receive control information on uplink (right side) include mobile stations that desire to transmit traffic data using the uplink -24- shared data channel currently or in the future. In the mobile stations, as to mobile stations that receives control information on the downlink, power control using the CQI based downlink TPC may be performed for each mobile station like the case of downlink, or "CQI based TPC" for a mobile station corresponding to bad CQI may be similarly applied to other mobile stations. However, there may be many mobile stations (including mobile stations desiring only uplink data transmission) that do not receive downlink traffic data currently or in the future. In addition, since it is not necessary that such mobile stations report receive quality of a received pilot channel to the base station as CQI information, it is difficult to perform CQI based downlink TPC. In the present embodiment, as to such mobile station, the shared control channel is transmitted using a power that is fixed to be a constant value. Fig.14 shows an example of power control according to the present embodiment. In this example, users #l-#3 among five users are receiving downlink traffic data. Therefore, the downlink shared control channel for the user #1 may be controlled by the CQI based downlink TPC, and the transmission power is indicated as Pi. For the users #2 and #3, in the same way, they may be controlled by the CQI based downlink TPC separately, and the transmission powers are represented as P2 and P3 respectively. Alternatively, transmission power control for a mobile station that reports the worst CQI among the three users may be applied to other mobile stations. The transmission power Pa (a=l,2 or 3) in this case is made common to the users #1 - #3. In addition, in the example shown in the figure, the remaining users #4 and #5 in the five users do not receive downlink traffic data, so that the downlink shared control channel for these -25- mobile stations is transmitted using a fixed power PFIX. By the way, data transmitted from a transmitter is coded, modulated, mapped to radio resources, converted to a transmission symbol (OFDM symbol, for example), and transmitted. Coding is performed for providing error correction capability. Convolution coding or turbo coding or the like may be performed. The unit for performing coding may be a chunk, or data of a plurality of chunks may be coded as a whole. As for the present embodiment, it is desirable that coding is performed in units of data for which same transmission power control is performed. For example, when the transmission power control is performed for each user, it is desirable that coding is also performed for each user. When transmission power control is performed for three users as a whole, it is desirable that coding is performed for three users as a whole. For example, in a situation described with reference to Fig.14, assuming that resources of three users of users #1, #2 and #3 are assigned as shown in Fig.15(1). One chunk is assigned to the user #1, three chunks are assigned to the user #2, and four chunks are assigned to the user #3. Coding is performed for each user, and each of three ranges of data each enclosed with a thick line is coded separately. As to these pieces of data, three users are controlled by "CQI based downlink TPC" separately, and transmission powers are represented as Pi, P2 and P3 respectively. Fig. 15(2) also shows a situation in which coding and power control are performed for each user, but assignment of chunk is different. In the example shown in Fig.15(3), data of three users are coded as a whole, and a control method (CQI based downlink TPC) for one of the users is applied to other users. The transmission power -26- is indicated as Pα (α=l,2 or 3), and is transmission power for a user that reports the worst CQI. By the way, the user number and the unit for bringing together in coding are merely examples, and various numbers may be adopted. Generally, the larger the unit for coding is, the higher error correction ability becomes, but calculation load tends to increase. Therefore, in the example shown in Fig.15(1), calculation load for coding and decoding is small, and transmission power is optimally controlled without excess or deficiency. On the other hand, in the example shown in Fig.15(3), although calculation load for coding and decoding becomes large, large error correction ability can be expected, and in addition, since power becomes excessive for two users of the three users, improvement of data can be expected. From the viewpoint for simplifying processes and strengthening improvement of quality, it is desirable to adopt same power control to data included in one unit of coding like the present embodiment. The present application claims priority based on Japanese patent application No.2005-174395, filed in the JPO on June 14, 2005 and Japanese patent application No.2005-241902, filed in the JPO on August 23, 2005, and the entire contents of them are incorporated herein by reference. -27- CLAIMS 1. A base station comprising: means that derives a transmission power of a mobile station based on receive quality of an uplink pilot channel; means that reports the derived transmission power to the mobile station; and means that receives a control channel transmitted by the mobile station according to the reported information. 2. The base station as claimed in claim 1, wherein the base station derives a relative power amount by which the mobile station needs to change a transmission power based on relationship between the receive quality of the uplink pilot channel and receive quality that the control channel needs to satisfy. 3. The base station as claimed in claim 1, wherein the base station derives an absolute power amount to which the mobile station needs to change a transmission power based on relationship between the receive quality of the uplink pilot channel and a transmission power value of the pilot channel. 4. The base station as claimed in claim 1, -28- wherein the base station reports a pilot channel and the transmission power using a downlink, and receives the uplink pilot channel that is transmitted with a power derived by the mobile station based on an average propagation loss between the mobile station and the base station. 5. The base station as claimed in claim 4, wherein the propagation loss is derived from the receive quality and the transmission power value of the pilot channel of the downlink. 6. The base station as claimed in claim 1, wherein the base station receives both or one of a first pilot channel in which a symbol mapping pattern is constant and a second pilot channel in which a symbol mapping pattern is variable. 7. The base station as claimed in claim 4, wherein the base station causes the mobile station that is transmitting traffic data to transmit the control channel using a power derived based on the uplink pilot channel, and causes the mobile station that is not yet transmitting traffic data to transmit the control channel using a power derived based on the average propagation loss. -29- 8. The base station as claimed in claim 1, the base station further comprising: means that determines a frequency chunk usable for the mobile station to transmit traffic data and determines a transmission power of the mobile station. 9. The base station as claimed in claim 8, wherein the transmission power and the frequency chunk are determined such that the transmission power exceeds a predetermined threshold and that more chunks are used. 10. A base station comprising: means that transmits a common pilot channel; means that derives a plurality of transmission powers of a shared control channel based on receive quality of a plurality of common pilot channels reported by an uplink; and means that reports the shared control channel to a plurality of mobile stations using the derived transmission powers. 11. The base station as claimed in claim 10, -30- wherein the base station reports the derived transmission powers separately to the mobile stations receiving traffic data. 12. The base station as claimed in claim 10, wherein the base station reports one of the derived transmission powers to the mobile stations that are receiving traffic data. 13. The base station as claimed in claim 10, wherein the base station reports the shared control channel, using a predetermined transmission power, to a mobile station that is not receiving traffic data. 14. The base station as claimed in claim 10, the base station comprising a coder for coding data for one or more mobile station as a unit, wherein the data for one or more mobile station is transmitted using a same transmission power. 15. A mobile station comprising: means that receives a transmission power using a downlink when a base station derives the transmission power by which the mobile station needs -31- to change based on receive quality of an uplink pilot channel; and means that changes its transmission power based on reported information to transmit a control channel. 16. The mobile station as claimed in claim 15, wherein the mobile station receives a pilot channel and the transmission power value using the downlink; derives a transmission power based on an average propagation loss between the mobile station and the base station; and transmits the uplink pilot channel using the derived transmission power. 17. The mobile station as claimed in claim 15, wherein the mobile station transmits both or one of a first pilot channel in which a symbol mapping pattern is constant and a second pilot channel in which a symbol mapping pattern is variable. 18. A power control method, wherein: a base station derives a transmission power by which a mobile station needs to change based on receive quality of an uplink pilot channel, reports the derived transmission power to the mobile station, and -32- the mobile station changes its transmission power according to the reported information to transmit a control channel. A base station includes: means that derives a transmission power of a mobile station based on receive quality of an uplink pilot channel; means that reports the derived transmission power to the mobile station; and means that receives a control channel transmitted by the mobile station according to the reported information. Accordingly, irrespective of transmission power history over a past continuous time, the mobile station receives an instruction on the transmission power from the base station each time when transmitting a packet so as to be able to adjust the transmission power.

Full Text

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SPECIFICATION
TITLE OF THE INVENTION
BASE STATION, MOBILE STATION AND POWER
CONTROL METHOD
TECHNICAL FIELD
The present invention generally relates to
radio communication. More particularly, the present
invention relates to a base station, a mobile
station and a method for controlling transmission
power of a shared control channel used for packet
switching type communication.
BACKGROUND ART
In a mobile communication system such as
IMT-2000, transmission power control is performed
from the viewpoint of enlargement of circuit
capacity and economy of battery of a mobile station
and the like. For example, quality measurement of a
channel is performed in a receiving side, and a
transmission power control (TPC) bit is transmitted
by a return channel (DPCCH, for example) such that
the channel that is being received satisfies desired
quality. As a result, the transmission power is
updated by 1 dB, for example, and quality
measurement and transmitting/receiving of the TPC
bit are repeated, so that the transmission power can
be gradually changed to be closer to an optimal
value. That is, in a communication of a circuit
switching scheme, an individual channel is assigned
specifically to a mobile station, and the
transmission power of the mobile station is
gradually adjusted based on a temporally continuing
history on the transmission power. Such
transmission power control is described in a non-
patent document 1, for example.
[Non Patent document 1] Keiji Tachikawa, "W-CDMA

-2-
mobile communication scheme", MARUZEN, pp.126-128
DISCLOSURE OF THE INVENTION
PROBLEM TO BE SOLVED BY THE INVENTION
In a future mobile communication system, a
packet switching type communication scheme is
adopted in place of the conventional circuit
switching type communication scheme. Radio
resources of a packet form are shared by a plurality
of users, and availability of the radio resources is
properly scheduled in a base station. In such a
mobile communication system, there is not only a
mobile station to which the radio resources are
actually assigned but also a mobile station that
desires assignment but to which the resources are
not yet assigned. In addition, such a situation
arises in circuits of both of uplink and downlink.
For causing a mobile station placed in various
operation situations to operate properly, it is
necessary that the shared control channel is
transmitted well with a constant quality. Thus, it
is necessary that the transmission power of the
shared control channel is properly controlled. But,
the above-mentioned transmission power control
method of the circuit switching type cannot be used
as it is, and a useful method is not yet established.
An object of the present invention is to
provide a base station, a mobile station and a power
control method for controlling transmission power of
a shared control channel using a method suitable for
packet switching type communication.
MEANS FOR SOLVING THE PROBLEM
In the present invention, a base station,
is used, that includes: means that derives a
transmission power of a mobile station based on
receive quality of an uplink pilot channel; means

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that reports the derived transmission power to the
mobile station; and means that receives a control
channel transmitted by the mobile station according
to the reported information.
EFFECT OF THE INVENTION
According to the present invention,
transmission power of the shared control channel can
be controlled using a method applicable to packet
switching type communication.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.l shows a schematic block diagram of a
base station according to an embodiment of the
present invention;
Fig.2 shows a schematic block diagram of a
mobile station according to an embodiment of the
present invention;
Fig.3 is a flowchart showing a
transmission power control method according to an
embodiment of the present invention;
Fig.4 is a diagram showing an example of
correspondence relationship among CQI, MCS number
and transmission power;
Fig.5 is a diagram showing an example of
correspondence relationship among CQI, MCS number
and transmission power;
Fig.6 is a diagram showing mapping
examples of a pilot channel;
Fig.7 is a diagram showing information
items that are included in an uplink shared control
channel;
Fig.8 is a diagram showing a resource
assignment example of an uplink shared data channel;
Figs.9A-9D show a plurality of candidates
considered when assigning a band;
Fig.10 is a schematic diagram on operation

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principle of AMC;
Fig.11 is a flowchart showing a
transmission power control method according to an
embodiment of the present invention;
Fig.12 is a diagram exemplary showing
correspondence relationship between receive quality
and transmission power;
Fig.13 is a diagram showing information
items included in a downlink shared control channel;
Fig.14 is a diagram showing an example of
power control according to an embodiment of the
present invention;
Fig.15 is a diagram showing radio
resources and a unit of coding.
Description of reference signs
11 modulation and coding unit
12 multiplexing unit
13 radio unit
14 transmission power determination unit
21 radio unit

23 demodulation and decoding unit
24 pilot channel processing unit
PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION
According to an embodiment of the present
invention, relative or absolute power by which the
mobile station needs to change its transmission
power is derived based on relationship between
receive quality of an uplink pilot channel and
receive quality that a control channel needs to
satisfy or a transmission power value of the pilot
channel. Thus derived power is reported to the
mobile station, so that uplink transmission power is
properly controlled. Accordingly, without using the
transmission power history over a past continuous
time, the mobile station receives an instruction on

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transmission power from the base station each time
when sending a packet so as to be able to adjust the
transmission power.
When the mobile station has not yet
received the instruction, an uplink pilot channel is
transmitted after a procedure. In the procedure, a
pilot channel and a transmission power is reported
to the mobile station using a downlink, and the
mobile station derives the transmission power based
on an average propagation loss between the mobile
station and the base station. The uplink pilot
channel is transmitted using the derived power, and
it is received by the base station. Accordingly,
the base station can properly determine a
transmission power of the mobile station of next
time based on the pilot channel transmitted from the
mobile station.
The propagation loss may be derived from
receive quality of a downlink pilot channel and the
transmission power value.
According to an embodiment of the present
invention, the base station receives both or one of
a first pilot channel in which a symbol mapping
pattern is constant and a second pilot channel in
which a symbol mapping pattern is variable. By
preparing a plurality of kinds of uplink pilot
channels, both of channel estimation accuracy and
transmission efficiency of information can be
considered.
According to an embodiment of the present
invention, the mobile station that is transmitting
traffic data is caused to transmit the control
channel using a power derived based on the uplink
pilot channel. The mobile station that is not yet
transmitting traffic data is caused to transmit the
control channel using a power derived based on the
average propagation loss. Since the number of

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mobile stations that are transmitting traffic data
is relatively small, efficiency of power control can
be improved by applying the CQI based TPC only for
the mobile stations.
The base station may further includes
means that determines a frequency chunk usable for
the mobile station to transmit traffic data and
determines a transmission power of the mobile
station. The transmission power and the frequency
chunk may be determined such that the transmission
power exceeds a predetermined threshold and that
more chunks are used. Accordingly, resources of the
shared data channel can be easily and properly
assigned.
A base station according to an embodiment
of the present invention includes means that
transmits a common pilot channel; means that derives
a plurality of transmission powers of a shared
control channel based on receive quality of a
plurality of common pilot channels reported by an
uplink; and means that reports the shared control
channel to a plurality of mobile stations using the
derived transmission powers.
The derived transmission powers may be
separately reported to the mobile stations receiving
traffic data. Accordingly, transmission power can
be controlled for each mobile station. One of the
derived transmission powers may be reported to the
mobile stations that are receiving traffic data.
Accordingly, the plurality of control stations can
be controlled with a same transmission power. The
transmission power may be a transmission power
corresponding to a mobile station that reports the
worst CQI among the plurality of mobile stations.
The shared control channel may be reported
to a mobile station that is not receiving traffic
data using a predetermined transmission power.

-7-
Accordingly, transmission power control for the
shared control channel can be performed also for
mobile stations that desire only transmission of the
uplink traffic data.
The base station may include a coder for
coding data for one or more mobile station as a unit,
and the data for one or more mobile station may be
transmitted using a same transmission power. By
aligning the unit of coding with the range of data
for which same transmission power control is
performed, a combination of strength of error
correction capability and excess or deficiency of
transmission power can be properly set. For example,
coding (decoding) can be simplified without excess
or deficiency of power, and on the other hand,
transmission power can be made large while error
correction capability is high.
[Embodiment 1]
In a downlink, a common pilot channel is
announced to all users from a base station, and a
mobile station that desires downlink data
communication reports receive quality of the common
pilot channel to the base station, so that it can be
expected that the base station determines a
transmission power of the downlink shared control
channel. However, in an uplink, the common pilot
channel cannot be used. This embodiment is
contrived in view of the problem. In the following,
a transmission power control method for an uplink
shared control channel in the packet switching type
mobile communication system is described.
Fig.1 shows a base station according to an
embodiment of the present invention. The base
station includes a modulation and coding unit 11
that performs multilevel modulation on data to be
transmitted and performs channel coding, a
multiplexing unit (MUX) 12 that multiplexes a

-8-
modulated signal and a pilot channel, and a radio
unit (RF) 13 that converts an multiplexed signal to
a signal format for transmitting from an antenna,
and further includes a transmission power
determination unit 14 that determines a transmission
power of a mobile station based on information
received from an upper apparatus of the base station
or from another mobile station or based on base
station data.
Fig.2 shows a mobile station according to
an embodiment of the present invention. The mobile
station includes a radio unit (RF) 21 that converts
a signal format of a signal received by an antenna,
a demultiplexing unit (DeMUX) 22 that demultiplexes
a pilot channel and other channel from the received
signal, a pilot channel processing unit 23 that
performs channel estimation using the pilot channel
and performs measurement of transmission loss and
the like, and a demodulation and decoding unit 24
that demodulates the received data and performs
error correction decoding.
Fig. 3 shows a flowchart showing an uplink
transmission power control method according to an
embodiment of the present invention. In this
embodiment, a shared control channel of a fixed
information rate and a shared data channel of a
variable rate are prepared as uplink channels. The
transmission power control method described below
can be used for both of the shared control channel
and the shared data channel. Since the transmission
rate of the shared control channel is constant, it
is essential to control the transmission power of
the mobile station for controlling receive quality
of the shared control channel. On the other hand,
for controlling receive quality of the shared data
channel, there a choice of adjusting the
transmission rate in addition to controlling the

-9-
transmission power of the mobile station. The
transmission rate can be adjusted by changing the
number of levels of the multilevel modulation or
changing a coding rate of data. By the way,
although the transmission rate of the shared control
channel is fixed to be constant in this embodiment
for simplifying explanation, the transmission rate
of the shared control channel may be changed in
another embodiment.
In step 1, a downlink pilot channel is
transmitted from the base station to the mobile
station, and a transmission power Pt of the pilot
channel is also transmitted via an annunciation
channel or a broadcast channel (BCH).
As indicated as step 2, the mobile station
receives the downlink pilot channel and the
transmission power for a period to calculate an
average propagation loss L. The propagation loss L
is mainly determined by distance variation and
shadowing, and in general, the propagation loss L is
not largely different between uplink and downlink
when being averaged over a proper time. For example,
by averaging the receive quality over a relatively
long period such as a period of one or more frame,
influence of instantaneous variation such as fading
is removed. Fig.10 exemplary shows a relationship
between instantaneous receive SIR and an average
receive SIR. In this embodiment, although the
receive quality is measured as SINR, it may be
measured as SIR, or measured as other amount
indicating quality. A target quality SIRt that the
base station aims when the base station receives the
uplink channel is represented as a following
equation.
SIRt = Pup+L-I0 [dB]
In this equation, Pup indicates a transmission power
(the control object at present) transmitted by the

-10-
mobile station, I0 indicates an interference power
for an uplink channel observed at the base station.
The propagation loss L is represented as a
difference between the transmission power Pt in the
base station and the receive power Pr in the mobile
station. The annunciation channel announced from
the base station includes the transmission power Pt
at the base station, the uplink interference power
±o and the target quality SIRt.
In step 3 of Fig.3, a pilot channel is
transmitted from the mobile station to the base
station. The transmission power at this time is a
power that compensates for propagation loss
calculated in step 2, and is not a power that
compensates for instantaneous fading received on an
uplink propagation route.
In step 4, the base station measures a
difference between the receive quality (receive
SINR) of the received uplink pilot channel and the
required quality (required SINR) expected for the
pilot channel. The power indicated by the
difference (power difference) indicates a power
amount (relative power value) by which the mobile
station needs to change its transmission power from
the current value such that quality of channel
received by the base station becomes the required
quality. When deriving the power difference, the
base station may use a table on receive SIR,
required SIR, MCS number and power difference by
which power should be changed from the current value.
The MCS number specifies a combination of the number
of levels of multilevel modulation and a coding rate.
Fig.4 shows a table example defining a
correspondence relationship among channel status
information (CQI: Channel Quality Indicator)
reported from the base station to the mobile station,
MCS number and transmission power of the mobile

-11-
station. The channel status information is measured
as SIR typically. In the example of Fig.4, MCS
number and transmission power can be derived based
on CQI (SIR) measured by the base station and
reported from the base station. Fig.5 shows a table
example that can be used in a case where MCS number,
instead of the CQI information, is reported from the
base station to the mobile station. Figs. 4 and 5
show merely examples of a table used for determining
the transmission power, and the transmission power
may be determined based on other correspondence
relationship.
In step 5, the base station reports, to
the mobile station, the power difference by which
the mobile station needs to change its transmission
power from the current value using a downlink
control channel.
In step 6, the mobile station adjusts the
transmission power based on the instructed
information reported by the control channel. The
adjusting amount in this case is different from one
in control by TPC bit (not up and down by 1 dB), but
is an amount for adjusting the current value to a
target value at one time.
In step 7, the control channel is
transmitted using an adjusted transmission power.
This transmission power is a value for compensating
for not only the propagation loss but also minute
variation such as fading. After that, by repeating
the procedure from the step 3 to the step 7 or
repeating the procedure of steps 7, 4 and 6 for each
packet, an uplink transmission power suitable for
the mobile station can be properly kept. However,
in the repeated step 3, a pilot channel accompanying
the uplink control channel is used.
[Embodiment 2]
In the second embodiment of the present

-12-
invention, processes in steps 3, 4 and 5 in Fig.3
are different. Since processes of other steps are
the same, overlapping explanations are not provided.
In step 3, the mobile station transmits a
transmission power value of a pilot channel in
addition to transmitting the pilot channel to the
base station.
In step 4, the base station measures
receive quality (receive SINR) of the received pilot
channel. The base station compares the receive
quality and the required quality, and calculates a
power value indicating the difference. A sum of the
power value and the transmission power value
indicates an absolute value of a power by which the
mobile station transmits a channel such that quality
of the channel received by the base station becomes
the required quality. In the same way as the case
of embodiment 1, the power (power difference)
indicated as the difference indicates a power amount
(relative power amount) by which the mobile station
needs to change its transmission power from the
current value such that quality of the channel
received by the base station becomes the required
quality.
In step 5, one or both of the relative
power value and the absolute power value is reported
from the base station to the mobile station using a
downlink.
In step 6, the mobile station adjusts the
transmission power according to the instructed
information reported by the control channel.
In step 7, the control channel is
transmitted using the adjusted transmission power.
After that, by repeating the procedure from the step
3 to the step 7 or repeating the procedure of steps
7, 4 and 6 for each packet, the uplink transmission
power suitable for the mobile station can be

-13-
properly kept.
[Embodiment 3]
The pilot channel of the uplink is an
individual pilot channel that is different for each
mobile station and that is used for channel
estimation, receive quality measurement,
synchronization acquisition and the like for the
uplink. For the purpose of precisely monitoring
communication status that changes every moment, it
is better to transmit many pilot channels. However,
since the pilot channel is a known signal, the more
the transmission amount of the pilot channel is, the
more the transmission efficiency becomes lowered.
In addition, it is not necessary to perform all of
the channel estimation, receive quality measurement,
synchronization acquisition for uplink with same
frequency.
From this viewpoint, in the third
embodiment of the present invention, two types of
uplink pilot channels are prepared, in which one is
a reference pilot channel that does not necessarily
accompany the shared control channel, and another
one is a pilot channel for channel estimation that
accompanies the shared data channel.
The reference pilot channel may be used
for channel estimation, receive quality measurement
and synchronization acquisition for uplink, and it
is similar to conventional one in terms of purpose
of use. However, it is different from conventional
one at least in the point that it is transmitted
while transmission power control of the embodiments
1 and 2 are being performed such that the receive
quality is kept. In addition, it is necessary to
estimate the channel so as to compensate for the
propagation route for demodulating the shared
control channel. For that purpose, the reference
pilot channel is transmitted accompanying the shared

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control channel. On the other hand, for measuring
uplink receive quality, the reference pilot channel
may be transmitted independently without
accompanying the shared control channel. However,
the mapping position of the symbol is fixed
beforehand as one kind. Fig.6(A) shows a situation
in which the reference pilot channel accompanying
the shared control channel and the independent
reference pilot channel are transmitted.
The pilot channel for channel estimation
accompanies the shared data channel and is used for
channel estimation. (B)-(D) in Fig.6 show examples
of mapping of the pilot channel for channel
estimation. Since the mobile station can move at
various high and low speeds, there may be a case in
which time variation of channel status is large
depending on the mobile station. In this case, as
shown in Figs.6(C) and (D) instead of Fig.6(B), man
pilot channels for channel estimation are mapped in
the time axis direction so that channel estimation
accuracy for a user moving at high speed can be
improved. For a mobile station that is not moving
at high speed, by mapping the pilot channel for
channel estimation as few as possible, transmission
efficiency for information can be improved. Since
the pilot channel for channel estimation is
transmitted or not transmitted, it can be referred
to as a pilot channel for capturing a reference
pilot channel that is always being transmitted.
According to the present embodiment, by providing a
plurality of types of pilot channels and by
adaptively mapping them according to use purpose or
communication situation, channel estimation accurac
and information transmission efficiency can be
improved.
[Embodiment 4]
As mentioned above, in the mobile

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communication system, there are not only a mobile
station to which radio resources are actually
assigned but also a mobile station that desires
assignment but to which radio resources are not yet
assigned. Such a situation occurs in both of uplink
and downlink circuits. Therefore, the shared
control channel includes information on these
various statuses.
Fig.7 shows information items that may be
included in an uplink shared control channel. In
the control information shown in four lines of (1)-
(4), (1) and (2) indicate information on downlink
data transmission by the shared data channel, and
(3) and (4) indicate information on uplink data
transmission by the shared data channel.
The item (1) indicates information of a
response transmitted by a mobile station when the
mobile station that is actually performing downlink
traffic data transmission receives a downlink shared
data channel. When the mobile station can properly
receive the downlink shared data channel, the mobile
station returns an acknowledgement (ACK) to the base
station, and when the mobile station cannot properly
receive the downlink shared data channel, the mobile
station returns a negative acknowledgement (NACK) to
the base station.
The item (2) indicates CQI information
reported, to the base station, by the mobile station
that is not currently performing downlink traffic
data transmission but wants to perform data
transmission in the future. The mobile station that
desires to perform the uplink data transmission
measures receive quality of a pilot channel included
in the annunciation channel, and reports the
measurement result as the CQI information to the
base station to request scheduling of next time.
The item (3) indicates information

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accompanying the uplink shared data channel
transmitted by the mobile station that is actually
performing uplink traffic data transmission. This
accompanying information is used for demodulation of
shared data channel in the base station, for example.
More particularly, the accompanying information may
include modulation scheme, transport block size,
retransmission control information, and identifier
of the mobile station and the like. The modulation
scheme is information for specifying a scheme such
as QPSK, 16 QAM and the like, and it may be
represented as a number of levels of multilevel
modulation. The retransmission control information
may include, for example, a process number for
specifying a position of a packet in hybrid ARQ
(HARQ), a redundancy format of a retransmitted bit,
a new data indicator indicating whether a packet is
new data or a retransmitted packet, or the like.
The item (4) indicates information
reported to the base station by a mobile station
that is currently not performing traffic data
transmission but desires to perform data
transmission in the future. This information may
include information on a transmission power or a
buffer status of the mobile station. For example,
transmission power information may include
information indicating how large a power is by which
the mobile station transmits the shared control
channel, information (maximum transmission power)
indicating how large the power is at the maximum by
which the mobile station can transmit it, or the
like. The buffer status may be represented as a
data amount (a filling factor of a buffer) stored in
a transmission buffer of the mobile station. For
example, the larger the data amount is, the larger
the priority of the scheduling may be set.
In the present embodiment, the base

-17-
satiation determines which of the items (l)-(4)
corresponds to transmission contents of the shared
control channel. As a result, as to a mobile
station ((1), (3)) that is actually performing
traffic data transmission, the transmission power of
the uplink shared control channel is controlled by
the method described in the embodiment 1 or 2. That
is, the base station measures receive quality of a
pilot channel received from the mobile station, and
determines and reports the transmission power of the
mobile station according to the quality, so that the
mobile station transmits the uplink shared control
channel according to the reported information (this
transmission power control method is to be referred
to as "CQI based TPC" for the sake of convenience).
On the other hand, as to a mobile station
((2), (4)) that is not currently performing uplink
traffic data transmission but desires to perform the
data transmission in the future, the transmission
power of the uplink shared control channel is
controlled by the method described in steps 2 and 3
in Fig.3. That is, the mobile station receives the
pilot channel and the annunciation channel for a
period so as to calculate an average propagation
loss, so that the uplink shared control channel is
transmitted to compensate for the propagation loss
and compensate for interference power at the base
station (this transmission power control method is
to be referred to as "slow TPC" for the sake of
convenience).
Since the transmission power is adaptively
changed at every moment in the CQI based TPC,
calculation load for determining it is large.
Therefore, if control of the transmission power of
the uplink shared control channel is performed based
on the CQI based TPC for all of the mobile stations,
there is a fear that calculation load and delay in

-18-
the base station become very large. On the other
hand, as to the uplink shared control channel for
the mobile station, corresponding to (2) and (4),
that is not yet performing traffic data transmission,
the importance is lower than that corresponding to
(1) and (3). For example, when the acknowledgement
(ACK) of retransmission control is erroneously
determined, useless traffic increases to exert a bad
influence on the system. But, even though the
buffer status of the mobile station is erroneously
determined, large bad effect does not arise. In
addition, there is a possibility that the number of
mobile stations related to (2) and (4) becomes far
larger than that of mobile stations related to (1)
and (3). From this viewpoint, in the present
embodiment, the CQI based TPC is performed for the
mobile stations related to (1) and (3), so that
accurate transmission power control that can address
instantaneous fading variation is performed. Then,
slow TPC is performed for the mobile stations
related to (2) and (4) in which instantaneous fading
is not compensated for, and slow transmission power
control is performed such that signal quality is
maintained averagely. Accordingly, the CQI based
TPC described in embodiments 1 and 2 can be
efficiently used.
[Embodiment 5]
Fig.8 indicates a radio resource
assignment example for an uplink shared data channel
according to a fifth embodiment of the present
invention. Each procedure shown in Fig.8 is
executed in the base station. In the present
embodiment, there is a mobile station that is
actually transmitting traffic data using an uplink
shared data channel. This mobile station transmits
the uplink shared control channel or the pilot
channel or the like including the information item

-19-
of (3) shown in Fig.7 in the embodiment 4. The base
station receives the pilot channel transmitted from
the mobile station, and the flow of Fig.8 goes to
step 10.
In step 10, receive quality of the pilot
channel is measured as CQI information.
In step 12, a band of the uplink shared
data channel for the mobile station is determined
based on the measured CQI information and the
transmission power information received from the
mobile station. In the present embodiment, the
usable band is divided into a plurality of frequency
blocks each including one or more sub-carrier.
Typically, the present invention is used for a radio
communication system of an orthogonal frequency
division multiplexing (OFDM) scheme. The frequency
block is also referred to as a frequency chunk or
simply a chunk. One or more frequency chunk may be
used as various references such as a unit of
resource assignment, a unit of retransmission, or a
unit of coding. In the present embodiment, one
frequency chunk is set as a unit of resource
assignment.
Figs.9A-9D show a plurality of candidates
considered when assigning a band. The lateral axis
of each figure corresponds to frequency f, and the
vertical axis corresponds to power P. As shown in
Fig.9A, a band of 10 MHz is divided to four
frequency chunks of 2.5MHz. In step 12 of Fig.8,
resources are determined such that the power becomes
greater than a power threshold Pth derived from the
transmission power information of the mobile station
and that a band as wide as possible is kept (the
band is determined such that the transmission power
per one chunk is equal to or greater than the
threshold and that the band occupies a wider
transmission bandwidth.) For example, as to

-20-
transmission power of the mobile station reported
from the mobile station, assuming that relationship
between the power threshold Pth and the frequency
chunk becomes each of ones in Fig.9. In this case,
in the resource assignments shown in Figs.9A and 9B,
since the power is less than the threshold, these
two candidates are excluded. Although each of
Figs.9C and 9D exceeds the threshold of the power,
since the one shown in Fig.9C occupies a wider
frequency band, it is determined to be an optimal
resource assignment method.
In step 14 of Fig.8, a MCS number
corresponding to the power determined in step 12 is
selected.
In step 16, information on the MCS number
derived in step 14, the band (information for
specifying frequency chunk) determined in step 12
and transmission power and the like is reported to
the mobile station via the downlink shared control
channel. Accordingly, the mobile station can
properly transmit the uplink shared data channel.
According to the present embodiment, as shown in
Fig.10, an adaptive modulation and coding (AMC)
scheme is adopted for addressing instantaneous
fading, and the MCS number is adaptively updated for
each TTI in the example shown in the figure. By
adopting AMC in addition to the slow TPC for
bringing the average receive SIR close to a target
value, transmission quality of the uplink shared
data channel can be improved.
[Embodiment 6]
Uplink transmission power control is
described in the first to fifth embodiments, and a
transmission power control method for a downlink
shared control channel is described in the sixth
embodiment of the present invention. Fig.11 is a
flowchart showing a transmission power control

-21-
method according to an embodiment of the present
invention. As shown in step 112, the base station
transmits a common pilot channel to mobile stations
under the base station. The common pilot channel is
different from the pilot channel that is transmitted
by each mobile station via an uplink in that the
common pilot channel is commonly transmitted to all
of the mobile stations. In step 114, the mobile
station measures receive signal quality as CQI
information based on the received common pilot
channel. The mobile station performing downlink
data transmission reports the measured CQI
information to the base station using the uplink
shared control channel in step 116. In step 118,
the base station determines a transmission power of
the downlink shared control channel based on the
reported CQI information. Correspondence
relationship between CQI information and
transmission power shown in Fig.12 is prepared
beforehand. In step 120, the base station transmits
the downlink shared control channel using the
determined power in step 118. Accordingly, the
transmission power of the downlink shared control
channel can be determined based on the CQI
information measured in the mobile station (this
method is to be referred to as "CQI based downlink
TPC" for the sake of convenience).
Fig.13 indicates information items that
may be included in the downlink shared control
channel. These information items are largely
classified as control information on downlink (left
column) and control information on uplink (right
column). In addition, as shown in the left side of
the figure, the control information is largely
classified as one on physical layer (upper side) and
one on layer 2 (L2) (lower side). The control
information on the downlink may include demodulation

-22-
information, scheduling information and
retransmission control information (HARQ). The
demodulation information may include chunk
assignment information, data modulation information
and transport block size information. The chunk
assignment information is information for specifying
a frequency chunk to be assigned to the downlink
shared data channel to the mobile station. The data
modulation information is information for specifying
a modulation scheme applied to the shared data
channel, and it may be specified by the MCS number.
The transport block size information indicates the
number of bits that are transmitted, and can be
associated with coding rate, and may be specified by
the MCS number. The scheduling information may
include identification information for identifying
the mobile station. The retransmission control
information may include a process number of a
transmitted packet, information indicating
redundancy format, and a new data indicator. The
new data indicator is an indicator that indicates
whether a packet is a new packet or a retransmitted
packet.
The control information on the uplink may
include a transmission power control bit, a
transmission timing control bit, a response bit of a
contention-based channel, scheduling information and
retransmission control information (HARQ) and the
like. The transmission power control bit and the
transmission timing control bit indicate a
transmission power and a transmission timing when
transmitting the uplink shared data channel, and
these are determined and reported in scheduling by
the base station. The contention-based channel is a
channel that may be transmitted from the mobile
station to the base station without scheduling, and
that is a channel that may cause contention between

-23-
the mobile station and another mobile station. The
contention-based channel may be a fast access
channel and the like that includes a reservation
packet for requesting scheduling of the shared data
channel, traffic data of small size or control data.
The control information includes response
information (ACK/NACK), as response contents,
indicating whether the contention-based channel that
is transmitted from the mobile station is properly
received by the base station. The scheduling
information may include identification information
of the mobile station, chunk assignment information,
data modulation information and transport block size
and the like. These are similar to those described
for the downlink, but these are different in that
these are information on the uplink. The
retransmission control information (HARQ) includes
information (ACK/NACK) indicating whether
information transmitted from the mobile station to
the base station is properly received by the base
station.
The mobile station that receives the
control information on the downlink (left side)
actually receives traffic data using the downlink
shared data channel. Therefore, since the number of
that kind of mobile stations is the maximum number
of users that can be assigned at most, the number of
the mobile stations is not enormous. Therefore, the
power of the downlink shared control channel may be
controlled using the CQI based downlink TPC for each
mobile station. Alternatively, "CQI based downlink
TPC" for a mobile station corresponding to the worst
CQI among a plurality of mobile stations may be
applied to other mobile stations. On the other hand,
mobile stations that receive control information on
uplink (right side) include mobile stations that
desire to transmit traffic data using the uplink

-24-
shared data channel currently or in the future. In
the mobile stations, as to mobile stations that
receives control information on the downlink, power
control using the CQI based downlink TPC may be
performed for each mobile station like the case of
downlink, or "CQI based TPC" for a mobile station
corresponding to bad CQI may be similarly applied to
other mobile stations. However, there may be many
mobile stations (including mobile stations desiring
only uplink data transmission) that do not receive
downlink traffic data currently or in the future.
In addition, since it is not necessary that such
mobile stations report receive quality of a received
pilot channel to the base station as CQI information,
it is difficult to perform CQI based downlink TPC.
In the present embodiment, as to such mobile station,
the shared control channel is transmitted using a
power that is fixed to be a constant value.
Fig.14 shows an example of power control
according to the present embodiment. In this
example, users #l-#3 among five users are receiving
downlink traffic data. Therefore, the downlink
shared control channel for the user #1 may be
controlled by the CQI based downlink TPC, and the
transmission power is indicated as Pi. For the
users #2 and #3, in the same way, they may be
controlled by the CQI based downlink TPC separately,
and the transmission powers are represented as P2
and P3 respectively. Alternatively, transmission
power control for a mobile station that reports the
worst CQI among the three users may be applied to
other mobile stations. The transmission power Pa
(a=l,2 or 3) in this case is made common to the
users #1 - #3. In addition, in the example shown in
the figure, the remaining users #4 and #5 in the
five users do not receive downlink traffic data, so
that the downlink shared control channel for these

-25-
mobile stations is transmitted using a fixed power
PFIX.
By the way, data transmitted from a
transmitter is coded, modulated, mapped to radio
resources, converted to a transmission symbol (OFDM
symbol, for example), and transmitted. Coding is
performed for providing error correction capability.
Convolution coding or turbo coding or the like may
be performed. The unit for performing coding may be
a chunk, or data of a plurality of chunks may be
coded as a whole. As for the present embodiment, it
is desirable that coding is performed in units of
data for which same transmission power control is
performed. For example, when the transmission power
control is performed for each user, it is desirable
that coding is also performed for each user. When
transmission power control is performed for three
users as a whole, it is desirable that coding is
performed for three users as a whole.
For example, in a situation described with
reference to Fig.14, assuming that resources of
three users of users #1, #2 and #3 are assigned as
shown in Fig.15(1). One chunk is assigned to the
user #1, three chunks are assigned to the user #2,
and four chunks are assigned to the user #3. Coding
is performed for each user, and each of three ranges
of data each enclosed with a thick line is coded
separately. As to these pieces of data, three users
are controlled by "CQI based downlink TPC"
separately, and transmission powers are represented
as Pi, P2 and P3 respectively. Fig. 15(2) also shows
a situation in which coding and power control are
performed for each user, but assignment of chunk is
different. In the example shown in Fig.15(3), data
of three users are coded as a whole, and a control
method (CQI based downlink TPC) for one of the users
is applied to other users. The transmission power

-26-
is indicated as Pα (α=l,2 or 3), and is transmission
power for a user that reports the worst CQI. By the
way, the user number and the unit for bringing
together in coding are merely examples, and various
numbers may be adopted. Generally, the larger the
unit for coding is, the higher error correction
ability becomes, but calculation load tends to
increase. Therefore, in the example shown in
Fig.15(1), calculation load for coding and decoding
is small, and transmission power is optimally
controlled without excess or deficiency. On the
other hand, in the example shown in Fig.15(3),
although calculation load for coding and decoding
becomes large, large error correction ability can be
expected, and in addition, since power becomes
excessive for two users of the three users,
improvement of data can be expected. From the
viewpoint for simplifying processes and
strengthening improvement of quality, it is
desirable to adopt same power control to data
included in one unit of coding like the present
embodiment.
The present application claims priority
based on Japanese patent application No.2005-174395,
filed in the JPO on June 14, 2005 and Japanese
patent application No.2005-241902, filed in the JPO
on August 23, 2005, and the entire contents of them
are incorporated herein by reference.

-27-
CLAIMS
1. A base station comprising:
means that derives a transmission power of
a mobile station based on receive quality of an
uplink pilot channel;
means that reports the derived
transmission power to the mobile station; and
means that receives a control channel
transmitted by the mobile station according to the
reported information.
2. The base station as claimed in claim 1,
wherein the base station derives a relative power
amount by which the mobile station needs to change a
transmission power based on relationship between the
receive quality of the uplink pilot channel and
receive quality that the control channel needs to
satisfy.
3. The base station as claimed in claim 1,
wherein the base station derives an absolute power
amount to which the mobile station needs to change a
transmission power based on relationship between the
receive quality of the uplink pilot channel and a
transmission power value of the pilot channel.
4. The base station as claimed in claim 1,

-28-
wherein the base station reports a pilot channel and
the transmission power using a downlink, and
receives the uplink pilot channel that is
transmitted with a power derived by the mobile
station based on an average propagation loss between
the mobile station and the base station.
5. The base station as claimed in claim 4,
wherein the propagation loss is derived from the
receive quality and the transmission power value of
the pilot channel of the downlink.
6. The base station as claimed in claim 1,
wherein the base station receives both or one of a
first pilot channel in which a symbol mapping
pattern is constant and a second pilot channel in
which a symbol mapping pattern is variable.
7. The base station as claimed in claim 4,
wherein the base station causes the mobile station
that is transmitting traffic data to transmit the
control channel using a power derived based on the
uplink pilot channel, and
causes the mobile station that is not yet
transmitting traffic data to transmit the control
channel using a power derived based on the average
propagation loss.

-29-
8. The base station as claimed in claim 1,
the base station further comprising:
means that determines a frequency chunk
usable for the mobile station to transmit traffic
data and determines a transmission power of the
mobile station.
9. The base station as claimed in claim 8,
wherein the transmission power and the frequency
chunk are determined such that the transmission
power exceeds a predetermined threshold and that
more chunks are used.
10. A base station comprising:
means that transmits a common pilot
channel;
means that derives a plurality of
transmission powers of a shared control channel
based on receive quality of a plurality of common
pilot channels reported by an uplink; and
means that reports the shared control
channel to a plurality of mobile stations using the
derived transmission powers.
11. The base station as claimed in claim 10,

-30-
wherein the base station reports the derived
transmission powers separately to the mobile
stations receiving traffic data.
12. The base station as claimed in claim
10, wherein the base station reports one of the
derived transmission powers to the mobile stations
that are receiving traffic data.
13. The base station as claimed in claim
10, wherein the base station reports the shared
control channel, using a predetermined transmission
power, to a mobile station that is not receiving
traffic data.
14. The base station as claimed in claim
10, the base station comprising a coder for coding
data for one or more mobile station as a unit,
wherein the data for one or more mobile station is
transmitted using a same transmission power.
15. A mobile station comprising:
means that receives a transmission power
using a downlink when a base station derives the
transmission power by which the mobile station needs

-31-
to change based on receive quality of an uplink
pilot channel; and
means that changes its transmission power
based on reported information to transmit a control
channel.
16. The mobile station as claimed in claim
15, wherein the mobile station receives a pilot
channel and the transmission power value using the
downlink;
derives a transmission power based on an
average propagation loss between the mobile station
and the base station; and
transmits the uplink pilot channel using
the derived transmission power.
17. The mobile station as claimed in claim
15, wherein the mobile station transmits both or one
of a first pilot channel in which a symbol mapping
pattern is constant and a second pilot channel in
which a symbol mapping pattern is variable.
18. A power control method, wherein:
a base station derives a transmission
power by which a mobile station needs to change
based on receive quality of an uplink pilot channel,
reports the derived transmission power to
the mobile station, and

-32-
the mobile station changes its
transmission power according to the reported
information to transmit a control channel.

A base station includes: means that
derives a transmission power of a mobile station
based on receive quality of an uplink pilot channel;
means that reports the derived transmission power to
the mobile station; and means that receives a
control channel transmitted by the mobile station
according to the reported information. Accordingly,
irrespective of transmission power history over a
past continuous time, the mobile station receives an
instruction on the transmission power from the base
station each time when transmitting a packet so as
to be able to adjust the transmission power.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=f/sdEWXai9m9rFCAcClLPA==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

270544

Indian Patent Application Number

4824/KOLNP/2007

PG Journal Number

01/2016

Publication Date

01-Jan-2016

Grant Date

30-Dec-2015

Date of Filing

11-Dec-2007

Name of Patentee

NTT DOCOMO, INC.

Applicant Address

11-1, NAGATACHO 2-CHOME CHIYODA-KU, TOKYO

Inventors:

#	Inventor's Name	Inventor's Address
1	ATARASHI HIROYUKI	C/O INTELLECTUAL PROPERTY DEPARTMENT, NTT DOCOMO, INC., SANNO PARK TOWER, 11-1, NAGATACHO 2-CHOME, CHIYODA-KU, TOKYO 100-6150
2	HIGUCHI KENICHI	C/O INTELLECTUAL PROPERTY DEPARTMENT, NTT DOCOMO, INC., SANNO PARK TOWER, 11-1, NAGATACHO 2-CHOME, CHIYODA-KU, TOKYO 100-6150
3	SAWAHASHI MAMORU	C/O INTELLECTUAL PROPERTY DEPARTMENT, NTT DOCOMO, INC., SANNO PARK TOWER, 11-1, NAGATACHO 2-CHOME, CHIYODA-KU, TOKYO 100-6150

PCT International Classification Number

H04B 7/26, H04B 1/04

PCT International Application Number

PCT/JP2006/311874

PCT International Filing date

2006-06-13

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2005-241902	2005-08-23	Japan
2	2005-174395	2005-06-14	Japan