JP3962711B2 - COMMUNICATION DEVICE, COMMUNICATION SYSTEM, AND COMMUNICATION METHOD - Google Patents

Description

  The present invention relates to a communication apparatus, a communication system, and a communication method for performing communication using a multicarrier method.

  In a system using an orthogonal frequency division multiplexing system, a transmitter firstly modulates information to be transmitted, arranges it in parallel on each subcarrier, and performs IFFT. Further, a guard interval (GI) for removing intersymbol interference is added, parallel-serial conversion is performed, digital / analog conversion is performed, and the data is transmitted to the outside.

  At this time, the method of assigning all subcarriers to the communication channel is the simplest and general regardless of the reception status of each terminal.

  In addition, a technique for determining a subcarrier to be used for each terminal in accordance with a reception status of each subcarrier in each terminal, that is, a frequency characteristic is known. A technique for determining a modulation scheme according to the frequency characteristics of each terminal is also known (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-247955

  In multicast communication, a method in which subcarriers to be used are fixed is known as in conventional broadcast broadcasting. Since the reception status differs for each terminal that receives information transmitted by multicast transmission, the reception quality at each terminal differs in a scheme in which multicarriers are fixed. That is, depending on the terminal, the reception quality is significantly deteriorated. Thus, it is difficult for all terminals belonging to the multicast group to receive data in a good state. Then, in some of the terminals of the provider, there is a problem that the reception quality is remarkably deteriorated depending on the reception status of the terminal even though there is a right to perform communication.

  The present invention has been made to solve the above problem, and by grasping the reception status of all terminals using multicast communication and determining subcarriers to be allocated to communication, all of the members belonging to the multicast group are determined. It is an object of the present invention to provide a communication device capable of data transmission so that a terminal can receive data in a more stable reception environment.

  In order to solve the above-described problems and achieve the object, the present invention provides a communication device that communicates with a plurality of terminal devices belonging to a multicast group using a multicarrier scheme, and communicates using the multicarrier scheme. A power detection unit that detects received signal power of each of the plurality of terminal devices in each of a plurality of subcarriers that can be used by the previous terminal device, and each subcarrier based on each received signal power detected by the power detection unit The minimum received signal power specifying means for specifying the minimum received signal power in the multi-carrier communication among the plurality of subcarriers that can be used by the destination terminal device based on the minimum received signal power Selecting means for selecting a subcarrier to be used in the process, and using the subcarrier selected by the selecting means Te, characterized in that a communication means for communicating with a plurality of terminal devices belonging to the multicast group.

  Since the communication apparatus according to the present invention selects a subcarrier to be allocated to communication based on the reception status of each terminal apparatus belonging to the multicast group, all terminals belonging to the multicast group can receive in a more stable reception environment. Data that can be sent.

  Embodiments of a communication apparatus, a communication system, and a communication method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 1 is a diagram showing an overall configuration of a communication system 1 including a base station 20 as a communication apparatus according to the present invention. The communication system 1 employs OFDM multicast communication. Here, multicast communication is different from broadcast communication in which information is transmitted to all terminals, and is specific information for one or more specified terminals that have a right to perform communication with respect to specific information. Is a method for transmitting.

  The multicast communication in the present invention is applied when specific information is transmitted from the base station 20 to specific mobile terminals 10a, 10b, 10c,... In a relatively narrow spot area 30 as shown in FIG. In addition, the spot areas 30 shown in FIG. 1 are scattered in the cellular area developed in a plane.

  FIG. 2 is a block diagram showing a functional configuration of the base station 20. The base station 20 includes a transmission side digital unit 100, a D / A conversion unit 110, a radio unit 150, a communication unit 160, an A / D conversion unit 210, a reception side digital unit 200, and a subcarrier allocation control unit. 170 and a terminal status storage device 172.

  Further, the transmission-side digital unit 100 includes a primary modulator 102, a subcarrier allocation unit 104, an inverse fast Fourier transform (IFFT) 106, a parallel / serial converter 107, a guard interval (GI) adding unit 108, have. The receiving-side digital unit 200 includes a GI removal unit 208, a serial / parallel converter 207, a fast Fourier transform (FFT) 206, a subcarrier selection unit 204, and a primary demodulator 202.

  The terminal status storage device 172 stores information related to subcarrier allocation in the transmission-side digital unit 100. Here, the allocation information is information indicating received signal power of each mobile terminal belonging to the multicarrier group. The terminal status storage device 172 acquires allocation information from the mobile terminal 10. The terminal status storage device 172 further stores PTh, which is a threshold used when the subcarrier allocation unit 104 allocates subcarriers.

  FIG. 3 is a diagram schematically showing the data configuration of the terminal status storage device 172. As shown in FIG. The terminal status storage device 172 stores the received signal power value in each subcarrier in association with the terminal ID that identifies each mobile terminal.

  Subcarrier allocation control section 170 controls processing in subcarrier allocation section 104 based on information stored in terminal status storage device 172. The primary modulator 102 performs primary modulation on the digital data to be transmitted from the base station 20 and creates modulation symbols.

  Subcarrier allocation section 104 determines a subcarrier to which a multicast channel is allocated based on the control of subcarrier allocation control section 170. When the received signal power values of all mobile terminals belonging to the multicast group are stored in terminal status storage device 172, subcarrier allocation section 104 performs subcarrier allocation.

  IFFT 106 performs fast Fourier inverse transform on the transmission data received from subcarrier allocation section 104. The parallel / serial converter 107 rearranges the transmission data received from the IFFT 106 from parallel to serial.

  The GI adding unit 108 adds a guard interval to the transmission data received from the IFFT 106. Then, transmission data is transmitted to the mobile terminal 10 via the D / A conversion unit 110, the wireless unit 150, and the communication unit 160.

  Further, the GI removal unit 208 removes the guard interval from the reception data received from the mobile terminal 10 via the communication unit 160, the wireless unit 150, and the A / D conversion unit 210.

  The serial / parallel converter 207 rearranges serial reception data in parallel. The FFT 206 performs fast Fourier transform on the received data. Subcarrier selection section 204 selects a subcarrier based on the control of subcarrier allocation control section 170. The primary demodulator 202 performs primary demodulation on the received data.

  FIG. 4 is a diagram for explaining processing for determining subcarriers in multicast communication. In the communication system 1 according to the present embodiment, the subcarrier arrangement of the multicast communication channel is determined in consideration of the reception frequency characteristics of all mobile terminals belonging to the multicast group. At this time, the received signal power is particularly taken into consideration.

  The base station 20 receives the received signal power value of each subcarrier measured by the mobile terminal 10 until the multicast communication channel is established. And subcarrier arrangement | positioning is determined based on the received signal power value received from each subcarrier.

  For example, when the base station 20 receives the received signal power values as shown in FIG. 4 from the three mobile terminals 10a, 10b, and 10c, the frequency band in which the received signal power at each of the mobile terminals 10a, 10b, and 10c is relatively high. 410, 412, 414, and 416 are preferentially selected as subcarriers.

  On the other hand, the frequency band 400, 402, 404 having a relatively low received signal power in any of the mobile terminals 10a, 10b, 10c is determined as a frequency band that is not selected as a subcarrier as much as possible. Thus, subcarriers are determined based on received signal power in all mobile terminals belonging to the multicast group.

  Information is put on the subcarriers selected for multicast communication, and a known dummy signal is assigned to the subcarriers not selected.

  FIG. 5 is a block diagram illustrating a functional configuration of the mobile terminal 10. The functional configuration of the mobile terminal 10 is substantially the same as the functional configuration of the base station 20 described with reference to FIG. However, the mobile terminal 10 includes a subcarrier reception status estimation unit 180 and a reception status storage device 182 instead of the subcarrier allocation control unit 170 and the terminal status storage device 172 of the mobile terminal 10. The subcarrier reception status estimation unit 180 measures the received signal power of all N subcarriers and stores the received signal power in the reception status storage device 182 until communication with the base station 20 is established. Further, the mobile terminal 10 transmits the received signal power of each subcarrier stored in the reception status storage device 182 to the base station using the uplink.

  FIG. 6 is a flowchart showing subcarrier determination processing. 7 to 9 are diagrams for explaining the subcarrier determination processing.

  In the subcarrier determination process, the base station 20 first selects the minimum value for each subcarrier from the received signal power values stored in the terminal status storage device 172 (step S100). Then, the minimum received signal power value selected for each subcarrier is stored in the terminal status storage device 172.

  7 and 8 are diagrams for explaining processing for setting the minimum received signal power value for each subcarrier. As shown in FIG. 7, the received signal power in each portable terminal is different for each subcarrier. From this, the minimum received signal power value for each subcarrier is selected as shown in FIG.

  Next, the minimum received signal power value in each subcarrier is compared with the threshold value PTh, and the subcarrier indicating the minimum received signal power value equal to or higher than the threshold value PTh is selected (step S102). That is, a multicast channel is assigned to a subcarrier indicating a minimum received signal power value equal to or greater than the threshold value PTh. When N subcarriers are selected by the above processing (step S104, Yes), the subcarrier selection processing is completed.

  On the other hand, when the number of subcarriers selected in the above processing is less than N (step S104, No), the minimum received signal power not more than the threshold value PTh not selected in the above processing is extracted and rearranged in descending order (step S110). ).

  Next, the subcarrier having the largest minimum received signal power value is selected, and a multicast channel is assigned to the selected subcarrier (step S112). The selection of subcarriers is repeated until N subcarriers are selected (step S114, Yes). Thus, the subcarrier selection process is completed.

  Here, processing for selecting a subcarrier will be described. The subcarriers are selected in descending order of the minimum received signal power value. FIG. 9 is a diagram for explaining subcarrier selection processing in the present embodiment. As shown in FIG. 9, first, a subcarrier having a threshold value PTh or higher is selected as a multicast channel. Then, subcarriers having a threshold value PTh or less are selected by a difference between N and the number of subcarriers having a threshold value PTh or more.

  Thus, by setting the threshold value PTh in advance, it is possible to reduce the amount of processing when the received signal power values are rearranged in descending order. That is, the selection process can be performed efficiently.

  According to the communication system 1 according to the first embodiment, as described above, a subcarrier having a relatively high minimum received signal power value is selected as a multicast channel, so that a high-quality communication environment is provided to each mobile terminal. can do.

  Next, the communication system 1 according to the second embodiment will be described. The communication system 1 according to the second embodiment periodically performs subcarrier determination processing. In this regard, the communication system 1 according to the second embodiment is different from the communication system 1 according to the first embodiment that performs multicast communication using the determined subcarriers once the subcarriers are determined.

  FIG. 10 is a diagram for explaining subcarrier determination processing in the communication system 1 according to the second embodiment. In the communication system 1 according to the second embodiment, the subcarrier selection process is performed by four steps as shown in FIG.

  First, in section A, each mobile terminal measures the received signal power value in all subcarriers (step S200). Then, the time-averaged value is stored in the reception status storage device 182.

  Next, in section B, each mobile terminal transmits the minimum received signal power value for each subcarrier stored in the reception status storage device 182 to the base station 20 using the uplink (step S202). Then, the base station 20 updates the contents of the terminal status storage device 172 based on the received received signal power value.

  Next, in section C, the base station 20 uses the received signal power value for each subcarrier in each terminal stored in the terminal status storage device 172 to perform N by the subcarrier selection process described in the first embodiment. The number of subcarriers is selected (step S204).

  Next, in the section D, the base station 20 notifies the determined subcarrier number to all mobile terminals performing multicast communication (step S206).

  The above four steps are set as one unit of the subcarrier selection period T, and the subcarrier selection period T is repeated. The subcarrier selection period T is preferably a time interval corresponding to a constant multiple of one frame length transmitted by multicast communication, for example.

  At the time when the subcarrier determination process is performed, since a subcarrier having a large minimum received signal power is selected, a high-quality communication environment can be provided to each mobile terminal. However, the frequency characteristic of each subcarrier varies with the passage of time or the movement of the mobile terminal of the transmission destination. Therefore, even if subcarriers determined by the subcarrier selection process according to the first embodiment are used, it is not always possible to continue to provide a high-quality communication environment. On the other hand, in the communication system 1 according to the second embodiment, as described above, since the subcarrier selection process is performed periodically, it is possible to always provide a high-quality communication environment to each mobile terminal. it can.

  Next, the communication system 1 according to the third embodiment will be described. In the communication system 1 according to the third embodiment, when a new mobile terminal joins a multicast group, a subcarrier is selected in consideration of a received signal power value in the newly joined mobile terminal. In this respect, the communication system 1 according to the third embodiment is different from the communication system 1 according to another embodiment.

  FIG. 11 is a diagram for explaining subcarrier determination processing when a new mobile terminal joins a multicast group in the communication system according to the third embodiment.

  First, in the first period 501, the base station 20 recognizes the joining terminal X (step S210). Here, the first cycle 501 corresponds to one cycle of the subcarrier selection cycle T described in the second embodiment.

  Next, in the second cycle 502, the base station 20 notifies each mobile terminal of the multicast group of the subcarrier selected in the first cycle 501 (step S212). The base station 20 further notifies the terminal status storage device 172. A column for the subscriber terminal X is added (step S214).

  On the other hand, in the second period 502, the joining terminal X measures the received signal power (step S200). The subsequent processing of the joining terminal X in the second period 502 is the same as the processing of the mobile terminal 10 described with reference to FIG. 10 in the second embodiment.

  In the third period 503, the base station 20 receives the received signal power value from each mobile terminal of the multicast group including the subscribed terminal X. Based on this, a subcarrier is selected (step S216).

  Thus, in the communication system 1 according to the third embodiment, when a joining terminal is detected, subcarriers are determined based on received signal power at mobile terminals in the multicast group including the joining terminal from the next subcarrier selection cycle. You can choose. Therefore, it is possible to always select an appropriate subcarrier for mobile terminals belonging to the multicast group at the time of provision.

  FIG. 12 is a diagram for explaining the subcarrier determination process when the mobile terminal leaves the multicast group in the communication system according to the third embodiment.

  In the first period 511, the base station 20 recognizes the withdrawal terminal Y (step S220). Specifically, when the base station 20 does not receive a predetermined reception signal power value from a predetermined mobile terminal, the base station 20 recognizes the mobile terminal as a withdrawal terminal.

  Then, in the second cycle, the base station 20 deletes the column of the withdrawal terminal Y in the terminal status storage device 172 (step S224). In the third cycle 513, the base station 20 receives from the mobile terminal other than the withdrawal terminal Y. Receive the signal power value. Based on this, a subcarrier is selected (step S226).

  In addition, the process in the base station 20 and the portable terminal 10 other than this is the same as the process in the base station 20 and the portable terminal 10 with respect to the subscription terminal X demonstrated in FIG.

  As described above, in the communication system 1 according to the second embodiment, when the leaving terminal Y is detected, the subcarrier can be selected based on the received signal power in the terminal other than the leaving terminal from the next subcarrier selection period. Therefore, it is possible to always select an appropriate subcarrier for mobile terminals belonging to the multicast group at the time of provision.

  As described above, according to the communication system 1 according to the second embodiment, even when multicast communication joins and leaves frequently, reflection and deletion of reception statuses from terminals that have joined and withdrawn by a simple method can be performed. Since this can be realized, it is possible to always select an appropriate subcarrier for mobile terminals belonging to the multicast group.

  FIG. 13 is a diagram illustrating an overall configuration of the communication system 1 according to the fourth embodiment. In the communication system 1 according to the fourth embodiment, spot areas 30 for performing multicast communication are scattered in the mobile communication cells 40 using the multicarrier scheme. Here, the cell 40 for mobile communication is arranged in a plane.

  Further, the communication system 1 according to the fourth embodiment performs communication using orthogonal frequency division multiplexing (OFDM) and combining OFDM by code spreading multiplexing, that is, code division multiplexing (CDM). Thereby, it is possible to provide a system with high frequency utilization efficiency.

  Note that in OFDM without CDM, subcarriers assigned for multicast communication cannot be used for other communications, but in the fourth embodiment, by assigning one spreading code for multicast communication, Communication with a spot area in a cell as shown in FIG. 13 becomes possible.

  FIG. 14 is a block diagram of a functional configuration of the transmission-side digital unit 100 of the base station 20 according to the fourth embodiment. In the fourth embodiment, diffusion in the time axis direction is used. The transmission-side digital unit 100 includes a serial / parallel converter 103 and a spreading code generator 105 in addition to the functional configuration of the transmission-side digital unit 100 described in the first embodiment.

  The primary modulator 102 performs primary modulation such as QPSK modulation on transmission data to create a modulation symbol. Thereafter, the serial / parallel converter 103 rearranges the transmission data in parallel. The modulation symbols are spread in the time axis direction by being multiplied by the spread code by the spread code generator 105. Each of the spread chips arranged in parallel in M is assigned to a subcarrier in subcarrier allocating section 104.

  FIG. 15 is a block diagram of a functional configuration of the receiving-side digital unit 200 of the mobile terminal 10 according to the fourth embodiment. The receiving-side digital unit 200 includes a parallel / serial converter 203, a spreading code generator 205, and an adder 201 in addition to the functional configuration of the receiving-side digital unit 200 described in the first embodiment.

  The subcarrier selection unit 204 extracts M signals from the N FFTed signals, and the M signals are multiplied by the spreading code obtained by the spreading code generator 205. Further, despreading is performed by adding in time by the adder 201, and a primary modulation symbol is obtained. Then, these symbols are subjected to parallel / serial conversion by the parallel / serial converter 203 and sent to the primary demodulator.

  The configuration and processing of the communication system 1 according to the fourth embodiment other than those described above are the same as the configuration and processing of the communication system 1 according to the first embodiment.

  Specific examples of combining OFDM and code division multiplexing (CDM) include multicarrier CDMA and multicarrier DS-CDMA. By combining these schemes with the procedure for performing multicast communication described in the first to third embodiments, effective subcarrier selection can be performed in consideration of the reception environment of all terminals performing multicast communication. it can. In addition, spot areas for performing multicast communication can be interspersed in the cells arranged in a plane.

  Next, the communication system 1 according to the fifth embodiment will be described. The communication system 1 according to the fifth embodiment performs communication using orthogonal frequency division multiplexing (OFDM) and combining OFDM by code spreading multiplexing, that is, code division multiplexing (CDM). This is the same as the communication system 1 according to the fourth embodiment. Note that the communication system 1 according to the fifth embodiment uses spreading in the frequency direction. In this respect, the communication system 1 according to the fifth embodiment is different from the communication system 1 according to the fourth embodiment.

  FIG. 16 is a block diagram of a functional configuration of the transmission-side digital unit 100 of the base station 20 according to the fifth embodiment. The transmission-side digital unit 100 according to the fifth embodiment includes a serial / parallel converter 103, a spreading code generator 105, and a copy unit 101 in addition to the functional configuration of the transmission-side digital unit 100 according to the first embodiment. ing.

  The serial / parallel converter 103 rearranges the modulation symbols output from the primary modulator 102 in parallel. At this time, the number K to be arranged in parallel is K = M / SF. Here, M is the number of subcarriers used in communication (M <N, N: total number of subcarriers), and SF is the spreading factor. The modulation symbols arranged in parallel are copied with the same value by SF for each symbol and multiplied by a spreading code. This is repeated for K symbols, and is assigned to subcarriers by the subcarrier allocation unit 104. Thereby, information from the user is diffused in the frequency axis direction.

  FIG. 17 is a block diagram of a functional configuration of the receiving-side digital unit 200 of the mobile terminal 10 according to the fifth embodiment. The receiving-side digital unit 200 according to the fifth embodiment includes a parallel / serial converter 203, a spreading code generator 205, and an adder 201 in addition to the functional configuration of the receiving-side digital unit 200 according to the first embodiment. ing.

  The subcarrier selection unit 204 extracts M signals from N post-FFT signals. The extracted M signals are despread by multiplying each SF by a spreading code and adding in the subcarrier direction. Thereby, a primary modulation symbol is obtained. Further, the parallel / serial converter 203 performs parallel / serial conversion on the primary modulation symbol. Then, the primary demodulator 202 demodulates to obtain digital data.

  Further, the configuration and processing other than those described above in the communication system 1 according to the fifth embodiment are the same as the configuration and processing of the communication system 1 according to the fourth embodiment.

  As described above, the present invention has been described using the embodiment, but various changes or improvements can be added to the above embodiment.

  As described above, the communication device according to the present invention is useful for a communication device that communicates with a plurality of terminal devices, and is particularly suitable for a communication device using a multicarrier system.

1 is a diagram illustrating an overall configuration of a communication system 1. FIG. 2 is a block diagram showing a functional configuration of a base station 20. FIG. It is a figure which shows typically the data structure of the terminal status memory | storage device 172. FIG. It is a figure for demonstrating the process which determines the subcarrier in multicast communication. 2 is a block diagram showing a functional configuration of a mobile terminal 10. FIG. It is a flowchart which shows a subcarrier determination process. It is a figure for demonstrating a subcarrier determination process. It is a figure for demonstrating a subcarrier determination process. It is a figure for demonstrating a subcarrier determination process. FIG. 10 is a diagram for explaining subcarrier determination processing in the communication system according to the second embodiment. FIG. 12 is a diagram for explaining subcarrier determination processing when a new mobile terminal joins a multicast group in the communication system according to the third embodiment. FIG. 10 is a diagram for explaining subcarrier determination processing when a mobile terminal leaves a multicast group in the communication system according to the third embodiment. FIG. 7 is a diagram illustrating an overall configuration of a communication system 1 according to a fourth embodiment. FIG. 9 is a block diagram illustrating a functional configuration of a transmission-side digital unit 100 of a base station 20 according to a fourth embodiment. FIG. 10 is a block diagram illustrating a functional configuration of a reception-side digital unit 200 of a mobile terminal 10 according to a fourth embodiment. FIG. 10 is a block diagram illustrating a functional configuration of a transmission-side digital unit 100 of a base station 20 according to a fifth embodiment. FIG. 10 is a block diagram illustrating a functional configuration of a reception-side digital unit 200 of a mobile terminal 10 according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Communication system 10 Portable terminal 20 Base station 30 Spot area 40 Cell 100 Transmission side digital part 101 Copy part 102 Secondary modulator 103 Parallel converter 104 Subcarrier allocation part 105 Spreading code generator 107 Parallel / serial converter 108 GI addition part DESCRIPTION OF SYMBOLS 110 D / A conversion part 150 Radio | wireless part 160 Communication part 170 Subcarrier allocation control part 172 Terminal condition memory | storage device 180 Subcarrier reception condition estimation part 182 Reception condition memory | storage device 200 Reception side digital part 201 Adder 202 Primary demodulator 203 Serial Converter 204 Subcarrier selection unit 205 Spreading code generator 207 Serial / parallel converter 208 GI removal unit 210 A / D conversion unit

Claims (10)

A communication device that communicates with a plurality of terminal devices belonging to a multicast group using a multicarrier scheme,
Power detection means for detecting the received signal power of each of the plurality of terminal devices in each of a plurality of subcarriers that can be used for a communication destination terminal device that communicates using the multicarrier scheme;
Based on each received signal power detected by the power detecting means, minimum received signal power specifying means for specifying the minimum received signal power in each subcarrier;
Selection means for selecting, based on the minimum received signal power, a subcarrier to be used in the multicarrier communication from among a plurality of subcarriers that can be used by the terminal device of the transmission destination;
A communication device comprising: communication means for communicating with a plurality of terminal devices belonging to the multicast group using the subcarrier selected by the selection means.   2. The communication apparatus according to claim 1, wherein the selection unit selects a predetermined number of subcarriers in order from the subcarrier having the smallest minimum received signal power. The reception status detection means detects the reception status every time a fixed period elapses,
3. The communication apparatus according to claim 1, wherein the selection unit selects a subcarrier each time the reception status detection unit detects the reception status. A multicast group management means for detecting a newly joined terminal device newly joined to the multicast group;
4. The reception status detection unit further detects a reception status of the new subscription terminal device when the multicast group management unit detects the new subscription terminal device. The communication device according to item. A multicast group management means for detecting a withdrawal terminal device withdrawn from the multicast group;
5. The reception status detection unit does not detect the reception status of the withdrawal terminal device when the multicast group management unit detects the withdrawal terminal device. 6. Communication equipment.   The multicast group detection unit detects the terminal device as a withdrawal terminal device when a predetermined time has passed without the reception status detection unit detecting a reception status from the predetermined terminal device. The communication device according to claim 5. A communication system comprising a plurality of terminal devices belonging to a multicast group using a multicarrier scheme, and a communication device that communicates with the terminal devices,
The communication device
Power detection means for detecting the received signal power of each of the plurality of terminal devices in each of a plurality of subcarriers that can be used for a communication destination terminal device that communicates using the multicarrier scheme;
Based on each received signal power detected by the power detecting means, minimum received signal power specifying means for specifying the minimum received signal power in each subcarrier;
Selection means for selecting, based on the minimum received signal power, a subcarrier to be used in the multicarrier communication from among a plurality of subcarriers that can be used by the terminal device of the transmission destination;
A communication unit comprising: a communication unit that communicates with a plurality of terminal devices belonging to the multicast group using the subcarrier selected by the selection unit.   The communication system according to claim 7, wherein the selection unit selects a predetermined number of subcarriers in order from the subcarrier having the smallest minimum received signal power. A communication method for communicating with a plurality of terminal devices belonging to a multicast group using a multicarrier scheme,
A power detection step of detecting received signal power of each of the plurality of terminal devices in each of a plurality of subcarriers that can be used for a communication destination terminal device that communicates using the multicarrier scheme;
A minimum received signal power specifying step for specifying a minimum received signal power in each subcarrier based on each received signal power detected in the power detecting step;
A selection step of selecting a subcarrier to be used in the communication of the multicarrier scheme from among a plurality of subcarriers that can be used by the terminal device of the transmission destination based on the minimum received signal power;
And a communication step of communicating with a plurality of terminal devices belonging to the multicast group using the subcarrier selected in the selection step.   The communication method according to claim 9, wherein, in the selection step, a predetermined number of subcarriers are selected in order from the subcarrier having the smallest minimum received signal power.

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