JP4635075B2 - Wireless communication apparatus and wireless communication method - Google Patents

Description

  The present invention relates to a radio communication apparatus and method capable of controlling radio resource allocation and transmission power for each radio resource when performing a plurality of radio communications simultaneously using the same radio resource.

  In recent years, as the demand for higher speeds for wireless communication has increased, many proposals have been made for realizing higher speeds by improving frequency utilization efficiency. In particular, attention is being focused on a technique called MIMO (Multiple Input Multiple Output) that simultaneously realizes a plurality of wireless communications using the same wireless resource.

  Among the MIMO technologies, there is a technology in which a plurality of wireless terminal devices called Spatial Division Multiple Access (SDMA) communicate simultaneously using a frequency band that is the same wireless resource. As one method for realizing SDMA, there is a technique in which a wireless communication apparatus multiplies a transmission signal transmitted to each wireless terminal apparatus by a complex number sequence orthogonal to each other and transmits it as a beam having directivity. As a result, it is possible to reduce the interference that the wireless terminal device signal receives from other signals when receiving the signal and to enjoy the spatial diversity effect.

  In order to maximize the communication efficiency, it is necessary for the wireless communication device to completely grasp the characteristics of the wireless communication channel (channel) for each wireless terminal device. However, in practice, since the channel status is constantly changing, even if transmission control is performed while grasping the characteristics of many wireless communication paths at the same time, the system performance is degraded. Therefore, the above embodiment is considered not practical.

  Therefore, a technique called random beam forming is a method that can obtain excellent characteristics by using multiuser diversity with a small amount of information without completely grasping the characteristics of the wireless communication channel for each wireless terminal device. Has been proposed (for example, Patent Document 1). The wireless communication device transmits a wireless channel estimation signal multiplied by an arbitrary complex number sequence to a plurality of wireless terminal devices. The wireless communication device is notified of the best complex number sequence in each wireless terminal device, the signal power to interference power ratio of the signal multiplied by the complex number sequence, and the equivalent wireless channel gain of the signal. Based on the notified information, the wireless communication device obtains a set of a wireless terminal device that exists in the wireless communication area and can communicate with the wireless communication device, and each complex number sequence (hereinafter, this process is referred to as a user selection process). .

  In a general random beamforming technique, transmission power is equally distributed to each complex number sequence. However, when the transmission power is equally distributed, the communication performance cannot be sufficiently improved due to the influence of the channel condition and interference between the transmission beams.

In order to perform appropriate transmission power allocation, a technique for increasing the system throughput performance by performing user selection processing and controlling the transmission power applied to each complex number sequence for the determined set has been proposed. (For example, Non-Patent Document 1).
JP 2006-333482 A “Random Beamforming for Spatial Multiplexing in Downlink Multiuser MIMO Systems”, Diego P. and Umberto S., 2005 IEEE 16th International Symposium on PIMRC.

  In the above-described technique, a transmission power applied to each complex number sequence is controlled after a set of a signal transmitted by multiplying each complex number sequence and a receiving wireless terminal device has already been selected. Therefore, the effect of controlling the transmission power is limited, and it has been difficult to realize a significant improvement in communication performance. Further, if the transmission power ratio is determined at the same time as the user selection, the communication performance can be improved. However, in this case, the calculation amount is remarkably increased.

  Simultaneously with the user selection, the transmission power is controlled while evaluating the system throughput with respect to the transmission power ratio in accordance with the amount of interference received by the wireless terminal device (received from signals corresponding to other complex sequences). An object of the present invention is to provide a wireless communication apparatus, a wireless communication method, and a wireless communication system that can improve system throughput without greatly increasing the amount of calculation by the above-described processing.

  In order to solve the above-described problem, the present invention provides a wireless communication apparatus capable of simultaneously communicating with a plurality of wireless terminals by multiplying a plurality of signal sequences by a plurality of different complex number sequences on the same frequency channel. And transmitting means for transmitting a measurement signal obtained by multiplying the complex number sequence to each wireless terminal, and a notification regarding the channel characteristics of each of the complex number sequences obtained by each wireless terminal using the measurement signal. Receiving means for receiving, selecting means for selecting one combination among combinations of the wireless terminal and the complex number sequence determined by selecting the complex number sequence for each wireless terminal; and Interference power calculation for calculating interference power received from the complex number sequence that is not selected as the combination by the wireless terminal using a notification regarding the channel characteristics And determining means for determining whether or not the interference power is smaller than a predetermined threshold, and when determining that the interference power is smaller than the threshold, change a transmission power ratio allocated to each of the wireless terminals. A transmission rate calculating means for calculating a transmission rate when communicating with the wireless terminal, a plurality of the combinations for communicating with the wireless terminals based on the transmission rates obtained for a plurality of the combinations and power ratios, and A wireless communication apparatus comprising: a determining unit configured to determine a transmission power ratio; and communicating with the wireless terminal using the combination determined by the determining unit and the transmission power ratio. I will provide a.

  In addition, by multiplying a plurality of signal sequences by a plurality of different complex number sequences on the same frequency channel with a plurality of wireless terminals, a wireless communication apparatus capable of simultaneous communication can multiply the complex number sequences. A transmission step of transmitting the obtained measurement signal to each wireless terminal; a reception step in which each of the wireless terminals receives a notification regarding the channel characteristics of each of the complex number sequences obtained using the measurement signal; and A selection step of selecting one combination from the combination of the wireless terminal and the complex number sequence determined by selecting the complex number sequence for the terminal, and the wireless terminal is selected as the combination An interference power calculation step of calculating interference power received from the complex number sequence using a notification regarding the channel characteristics; and A determination step for determining whether or not the interference power is smaller than a predetermined threshold; and if it is determined that the interference power is smaller than the threshold, the transmission power ratio assigned to each of the wireless terminals is changed to change the wireless terminal A transmission rate calculation step for calculating a transmission rate when communicating with each other, and a combination and a transmission power ratio for communicating with each wireless terminal based on the transmission rates calculated for a plurality of the combinations and power ratios. A wireless communication method characterized by comprising: a determining step for determining, and communicating with the wireless terminal using the combination and the transmission power ratio determined in the determining step.

  According to the present invention, the system throughput can be improved without greatly increasing the amount of calculation.

  Embodiments of the present invention will be described in detail with reference to the drawings. Hereinafter, the same reference numerals are given to the same components, and duplicate descriptions are omitted.

(First embodiment)
A wireless communication system according to the first embodiment will be described.

FIG. 1 is a diagram illustrating an outline of a wireless communication system according to the present embodiment. A base station (hereinafter referred to as BS) 100, which is a wireless communication device connected to a network (not shown), and a wireless terminal (hereinafter referred to as MS) that are present in the wireless communication area and can be carried by a plurality of users. (Description) Wireless communication with 200 is performed. At this time, wireless communication between the BS 100 and the plurality of MSs 200 can be simultaneously performed using the same wireless resource (frequency band). The radio resource management is all performed by the BS 100.

A region surrounded by a broken line in FIG. 1A indicates a region where the BS 100 performs communication.

Beam 1 in FIG. 1 (b) indicates a beam that is not multiplied by a complex number sequence.

Both the beam 2 and the beam 3 in FIG. 1C are beams having directivity obtained by multiplying a complex number series. Each beam uses the same frequency band and is multiplied by a different complex number sequence.

  Although FIG. 1 shows an example in which three MSs 200 exist in the wireless communication area, the number of MSs 200 may be an arbitrary number. The number of directional beams to be formed depends on the number of antennas that the BS 100 has.

  FIG. 2 is a diagram showing a configuration of the MS 200 belonging to the wireless communication system of the present embodiment.

  The MS 200 includes a control unit 210, a transmission signal generation unit 220, a control signal generation unit 221, a selection unit 222, a transmission processing unit 223, a transmission antenna 224, a reception antenna 225, a reception processing unit 226, a separation unit 227, and a reception data demodulation unit 228. A control data demodulating unit 229 and a wireless communication path measuring unit 230.

  In FIG. 2, one transmission antenna 224 and one reception antenna 225 are described, but any number may be used.

  The receiving antenna 225 receives the radio signal transmitted by the BS 100. The received radio signal is output to the reception processing unit 226.

The reception processing unit 226 generates a reception signal by predetermined reception processing of power amplification, band limitation, down-conversion, orthogonal demodulation, and A / D conversion for the input radio signal. The generated reception signal is output to separation section 227.

  The separation unit 227 separates the input reception signal into a reception data signal, a reception control signal, and a wireless channel measurement signal. The reception data signal is output to reception data demodulation section 228. The reception control signal is output to the control data demodulator 229. The wireless channel measurement signal is output to the wireless channel measurement unit 230.

  The reception data demodulator 228 demodulates the input reception data signal by a predetermined demodulation method corresponding to a predetermined modulation process. Also, the received data is decoded by a predetermined error correction method and a decoding method corresponding to the coding rate. The decoded received data is output to control unit 210.

  The control data demodulation unit 229 demodulates the input reception control signal by a predetermined demodulation method corresponding to a predetermined modulation process. Moreover, it decodes as control data by the decoding method corresponding to a predetermined error correction method and coding rate. The decoded control data is output to the control unit 210.

  The wireless channel measurement unit 230 uses the input wireless channel measurement signal to measure the state of the wireless channel under conditions that do not depend on the complex number series and conditions corresponding to each complex number series, and Output. In addition, an equivalent gain corresponding to each complex number sequence (gain resulting from multiplication of the complex number sequence) is measured, and the result is output to the control unit 210. As an index indicating the state of the wireless communication path, signal power-to-noise power ratio (SNR), signal power-to-interference and noise power ratio (SINR), and the like can be given.

  Further, the transmission signal generation unit 220 performs error correction coding on the transmission data input from the control unit 210 using a predetermined method and coding rate. In addition, a transmission signal is generated by modulation using a predetermined modulation method, and is input to the selection unit 222.

  The control signal generation unit 221 performs error correction coding on the input control data using a predetermined method and coding rate. As an example of the control data, the measurement result of the state of the wireless communication path can be cited. Further, the control data is modulated by a predetermined modulation method to generate a control signal and input to the selection unit 222.

  The selection unit 222 selects each of the input transmission signal and control signal based on the control of the control unit 210 and inputs the selected transmission signal and control signal to the transmission processing unit 223. The transmission processing unit 223 generates a radio signal for the input signal by predetermined transmission processing such as D / A conversion, orthogonal modulation, up-conversion, band limitation, and power amplification. The generated radio signal is transmitted from the transmission antenna 224 to the BS 100.

  FIG. 3 is a diagram illustrating a configuration of the BS 100 belonging to the wireless communication system of the present embodiment.

  The BS 100 belonging to the wireless communication system of the present embodiment includes a control unit 120, a transmission signal generation unit 121, a wireless channel measurement signal generation unit 122, a control signal generation unit 123, a known signal generation unit 124, a first selection unit 125, A complex series multiplication unit 126, a second selection unit 127, a transmission processing unit 128, a transmission antenna 129, a reception antenna 130, a reception processing unit 131, a separation unit 132, a reception data demodulation unit 133, and a control data demodulation unit 134 are provided.

  Although FIG. 3 shows an example in which three transmission antennas 129 and one reception antenna 130 are provided, any number may be used.

  Note that a plurality of transmission signal generation units 121 and transmission processing units 128 are provided corresponding to the number of transmission antennas 129 of the BS 100.

  The control unit 120 controls operations of the transmission signal generation unit 121, the wireless channel measurement signal generation unit 122, the known signal generation unit 124, the first selection unit 125, the complex number series multiplication unit 126, and the second selection unit 127. Specific processing will be described later with reference to the flowcharts of FIGS.

  The transmission signal generation unit 121 performs error correction coding on the transmission data input from the control unit 120 using a predetermined method and coding rate. Further, a transmission signal is generated by modulation according to a predetermined modulation method and input to the first selection unit 125.

  The wireless channel measurement signal generator 122 generates a signal corresponding to a predetermined pattern for wireless channel measurement and inputs the signal to the first selection unit 125 and the second selection unit 127. Similarly, the known signal generation unit 124 generates a signal corresponding to a predetermined pattern so that the communication partner (corresponding to the MS 200 in the present embodiment) estimates the characteristics of the wireless communication path, and the first selection unit 125. And input to the second selection unit 127.

  The control signal generation unit 123 performs error correction coding on the control data (an identifier of the communication partner MS 200 that transmits the transmission data) input from the control unit 120 using a predetermined method and coding rate. Further, a control signal is generated by a predetermined modulation method and input to the second selection unit 127.

  The first selection unit 125 selects each of the input transmission signal, radio channel measurement signal, and known signal based on the control of the control unit 120, and outputs the selected signal to the complex number series multiplication unit 126.

  The complex number series multiplying unit 126 multiplies each of the input signals by different complex number series generated based on the control of the control unit 120 and orthogonal to each other. The sequence length of the generated complex number sequence corresponds to the number of transmitting antennas, and the number of sequences corresponds to the number of input signals.

  The second selection unit 127 selects a signal multiplied by the input complex number sequence, a radio channel measurement signal, a known signal, and a control signal based on the control of the control unit 120 and inputs them to the transmission processing unit 128. To do.

  The transmission processing unit 128 generates a radio signal for the input signal by predetermined transmission processing such as D / A conversion, quadrature modulation, up-conversion, band limitation, and power amplification. The generated radio signal is transmitted from the transmission antenna 129.

  A radio signal received by the receiving antenna 130 is input to the reception processing unit 131.

  The reception processing unit 131 generates a reception signal by predetermined reception processing such as power amplification, band limitation, down-conversion, orthogonal demodulation, A / D conversion, and the like for the input radio signal. The generated reception signal is input to the separation unit 132.

  The separation unit 132 separates the input reception signal into a reception data signal and a reception control signal. The received data signal is input to the received data demodulator 133. The reception control signal is input to the control data demodulator 134.

  The reception data demodulator 133 demodulates the input reception data signal by a predetermined demodulation method corresponding to a predetermined modulation process. Further, it is decoded as received data by a decoding method corresponding to a predetermined error correction method and coding rate, and is output to the control unit 120.

  The control data demodulator 134 demodulates the input reception control signal by a predetermined demodulation method corresponding to a predetermined modulation process. Further, it is decoded as control data by a decoding method corresponding to a predetermined error correction method and coding rate, and the control data is output to the control unit 120.

  FIG. 4 is a sequence diagram illustrating signals communicated between the MS 100 and the BS 200 in the wireless communication system according to the present embodiment. A broken line arrow indicates a signal that is multiplied by a complex number series, and a solid line arrow indicates a signal that is not multiplied by a complex number series.

  In the wireless communication system of this embodiment, the BS 100 transmits a wireless communication path measurement signal. At this time, the BS 100 performs radio communication path measurement signals multiplied by different complex number sequences each orthogonal to a predetermined number of transmission antennas or a predetermined number equal to or less than the number of transmission antennas, and wireless communication not multiplied by complex number sequences. Transmit the signal for road measurement.

  First, BS 100 transmits a radio channel measurement signal to MS 200 (ST10). Receiving the wireless channel measurement signal, each MS 200 measures the state of the wireless channel (ST11) and notifies the BS 100 of the measurement result (ST12). The state of the wireless channel to be measured is the SNR measured from the wireless channel measurement signal not multiplied by the complex number sequence and each complex number sequence measured from the wireless channel measurement signal multiplied by the complex number sequence. Represents an equivalent gain (gain obtained by multiplying a complex number sequence).

  Next, the BS 100 performs a user selection process for selecting the MS 200 that performs radio communication using the complex number sequence and the complex number sequence applied to the radio communication for the MS 200 based on the measurement result of the state of the radio communication path notified from the MS 200 ( ST13). The selection result is notified to each MS 200 via the control data (ST14a). In addition, transmission data is transmitted to selected MS 200 using the selected complex number sequence (ST14b). Next, the user selection process, control data transmission, and transmission data transmission are repeated a predetermined number of times (ST15). Thereafter, the process again proceeds to processing (ST16) for transmitting a wireless channel measurement signal. Note that the radio channel measurement signal transmitted in ST16 is preferably multiplied by a complex number sequence different from the complex number sequence used in ST10.

  FIG. 5 is a diagram illustrating a configuration of the control unit 120 of the BS 100 according to the wireless communication system of the present embodiment.

  The control unit 120 of the wireless communication apparatus of the present embodiment includes an upper layer I / F 111, a transmission / reception data buffer 112, a user selection unit 113, a transmission parameter storage unit 114, a transmission parameter setting unit 115, a complex number series setting unit 116, a communication path state A measurement result storage unit 117 is provided.

  The upper layer I / F 111 inputs / outputs data to be transmitted from the upper layer to each MS 200 and data received from the MS 200.

  The transmission / reception data buffer 112 stores transmission / reception data input from an upper layer.

  The user selection unit 113 performs user selection processing with reference to the communication path state measurement result storage unit 117, the transmission parameter storage unit 114, and the like. Specific processing contents will be described later.

  The transmission parameter storage unit 114 stores SINR, modulation scheme, and coding rate in association with each other.

  The transmission parameter setting unit 115 generates first control data for notifying the MS 200 of the selection result using the result of the user selection process. Further, with reference to the transmission parameter storage unit 114, transmission parameters (in this embodiment, modulation scheme and coding rate) to be applied to the wireless communication with the selected MS 200 are determined. Further, second control data for notifying the result is generated.

  Complex number sequence setting section 116 determines a predetermined number of mutually orthogonal complex number sequences equal to or less than the number of transmission antennas or the number of transmission antennas, and includes a radio channel measurement signal multiplied by the determined complex number sequence. Control to transmit a wireless channel measurement signal.

  The communication channel state measurement result storage unit 117 stores the user (each MS 200), the SNR, and the gain in a corresponding state. The wireless communication path state measurement result notified from each MS 200 is received, and the measurement result is stored. As shown in FIG. 5, the configuration example of the channel state measurement result storage unit 117 includes the user, the SNR obtained from the channel measurement signal not multiplied by the complex number sequence, and the equivalent gain (gain 1) of each complex number sequence. To gain N) are stored in a corresponding state. M is the number of MSs 200 that perform radio communication with the BS 100, and N is the number of transmission antennas held by the BS 100 or a predetermined number equal to or less than the number of transmission antennas.

  FIG. 6 is a flowchart showing processing of the control unit 120 of the wireless communication apparatus according to the present embodiment.

In the control unit 120 of the wireless communication apparatus according to the present embodiment, first, the complex number sequence setting unit 116 determines a predetermined number of complex number sequences orthogonal to each other that are equal to or less than the number of transmission antennas or the number of transmission antennas (ST301). . Control is performed to transmit a wireless channel measurement signal including the wireless channel measurement signal multiplied by the determined complex number sequence (ST302). The wireless channel measurement signal is transmitted with transmission power that is equal to each complex number sequence.

  The wireless communication path state measurement result notified from each MS 200 is received, and the measurement result is stored in communication path state measurement result storage section 117 (ST303). The configuration of the channel state measurement result storage unit 117 is as shown in FIG. 5, where M is the number of MSs 200 that perform radio communication with the BS, and N is a predetermined number of transmission antennas or less than the number of transmission antennas. It is a predetermined number. Subsequently, the user selection unit 113 performs user selection processing with reference to the communication path state measurement result storage unit 117, the transmission parameter storage unit 114, and the like (ST304). Although details will be described later, in this case, selection of a complex number sequence to be used and a partner radio terminal that performs radio communication using the complex number sequence is performed.

  Next, transmission parameter setting section 115 uses the result of the user selection process to generate first control data for notifying MS 200 of the selection result (ST305). Further, with reference to the transmission parameter storage unit 114, transmission parameters (in this embodiment, modulation scheme and coding rate) to be applied to the wireless communication with the selected MS 200 are determined. Also, second control data for notifying BS 100 of the determined result is generated (ST306).

  The transmission parameter setting unit 115 inputs the first control data to the control signal generation unit 123. As a result, the first control data is transmitted without being multiplied by the complex number sequence. Furthermore, together with the transmission data corresponding to each MS 200 input from the upper layer via the upper layer I / F 111 and stored in the transmission / reception data buffer 112, the second control data is collected as transmission data to generate a transmission signal. Input to the unit 121. Through the above processing, the second control data is transmitted after being multiplied by the complex number sequence. Thereafter, control unit 120 determines whether to end control due to various factors (ST309). If it is determined that the control process is to be terminated (ST309, Yes), the control is terminated. When control is continued (ST309, No), it is determined whether or not a predetermined period has passed (ST310). When the predetermined period has passed (ST310, Yes), a new complex number sequence is determined. (ST301). If it has not elapsed (ST310, No), the process proceeds to the user selection process again (ST304).

  FIG. 7 is a flowchart showing in detail the user selection process (ST304) among the processes performed by the control unit 120 shown in FIG.

  First, parameters TPUT_max, P, and Q are initialized (ST401). TPUT_max is a parameter for storing the maximum throughput (transmission rate) in the selection process. P is a parameter for storing the number of complex number sequences in the selection process, and Q is a parameter for storing the number of complex number sequences used for wireless communication.

  Next, reference complex number series selection processing is performed (ST402). Although details will be described later, here, a complex number sequence serving as a reference in subsequent processing and an MS 200 (user) that is a counterpart wireless terminal that performs wireless communication using the complex number sequence are selected.

  Next, it is determined whether the value of the parameter P has reached a predetermined number (Ntx) equal to or less than the number of transmission antennas or the number of transmission antennas (ST403). If it has been reached (ST403, Yes), it is determined whether the end condition of this process is satisfied (ST405).

  If not reached (ST403, No), a new complex number sequence is added (ST404). Although details will be described later, here, for the combination of the complex number sequence serving as a reference and the counterpart MS 200 (user) that performs radio communication, a different complex number sequence and a partner radio that performs radio communication using the complex number sequence are used. Processing for determining whether a combination of MS 200 (user) as a terminal can be selected is performed. Next, it is determined whether the end condition of this process is satisfied (ST405).

  In ST405, the condition is satisfied by comparing with a predetermined end condition, for example, whether or not a predetermined number of processes have been performed and whether or not a throughput (transmission rate) equal to or greater than a predetermined value is obtained. If YES, the process ends. If not satisfied, the process returns to the reference complex number series selection process (ST402).

  FIG. 8 is a flowchart showing in detail the reference complex number sequence selection process (ST402) among the processes performed by the control unit 120 shown in FIG.

  According to FIG. 8, in the reference complex number sequence selection process, a combination of MS200 (user), which is a counterpart wireless terminal that performs wireless communication using a predetermined reference, for example, an arbitrary complex number sequence and complex number sequence, A combination of MS 200 (user), which is a radio terminal of the other party that performs radio communication using a complex number sequence and a complex number sequence having an equivalent gain of (ST501). The parameter P is set to 1 (ST502), and the communication quality (signal power to interference and noise power ratio: SINR in this embodiment) is calculated from the equivalent gain for the selected combination (ST503).

The signal power to interference and noise power ratio (SINR) described above can be obtained from Equation 1. Here, k is the number of the MS 100, m is the number of the complex number sequence, and M is a value indicating the number of the complex number sequence.

  Based on the communication quality, the transmission parameter storage unit 114 is referred to calculate the throughput (transmission rate) in the selected combination, and this is stored as TPUT_new (ST504). Subsequently, the value of TPUT_new is stored in TPUT_max (ST505), the parameter Q is set to 1 (ST506), and the selected complex number sequence and the combination of MS200 (user) that is a counterpart radio terminal that performs radio communication using the complex number sequence Is stored (ST507), and the process ends.

  FIG. 9 is a flowchart showing in detail an additional complex number sequence selection process (ST404) among the processes performed by the control unit 120 shown in FIG.

  In the additional complex number sequence selection processing, wireless communication is performed using P complex number sequences and the complex number sequences from the complex number sequences stored in the reference complex number sequence processing based on a predetermined criterion. The combination candidate of the MS 200 that is the other party's wireless terminal performing the selection is selected (ST601).

  Corresponds to the amount of interference from radio communication performed using an additional complex sequence for MS 200 that performs radio communication using a reference complex sequence, that is, an equivalent gain for the additional complex sequence of MS 200 that performs radio communication using a reference complex sequence. The amount is compared with a predetermined threshold value (TH (INT) 1), and it is determined whether or not the interference amount is smaller than the threshold value. Similarly, the amount of interference from wireless communication performed using the reference complex number sequence for MS 200 that performs wireless communication using the additional complex number sequence, that is, the equivalent gain for the reference complex number sequence of MS 200 that performs wireless communication using the additional complex number sequence Is compared with a predetermined threshold value (TH (INT) 2) determined in advance to determine whether or not the interference amount is smaller than the threshold value (ST602).

  If either one of the interference amounts is smaller than each predetermined threshold (ST602, Yes), a transmission power control process is performed (ST603).

  When both interference amounts are equal to or greater than the respective predetermined threshold values (ST602, No), the communication quality (in this embodiment, the signal is related to each of the combination selected in the above and the combination selected in the reference complex sequence selection process). Power-to-interference and noise power ratio (SINR) is calculated (ST604).

The signal power to interference and noise power ratio (SINR) described above can be obtained from Equation 2. Here, k is the number of the MS 100, m is the number of the complex number sequence, and M is a value indicating the number of the complex number sequence.

  Next, based on each communication quality, the transmission parameter storage unit 114 is referred to calculate the throughput (transmission rate) in the combination, and this is stored as TPUT_new (ST605).

  Next, TPUT_new and TPUT_max are compared (ST606). If TPUT_new is greater than TPUT_max (ST606, Yes), the value of TPUT_new is stored in TPUT_max (ST607), the parameter Q is set to P + 1 (ST608), and the reference complex number The complex number sequence stored in the sequence selection process and the combination of the partner radio terminal MS 200 that performs radio communication using the complex number sequence and the other party performing radio communication using the selected P complex number sequences and complex number sequences The combination of MS 200 that is the destination wireless terminal is stored (ST609).

  Subsequently, all combinations are selected, and it is determined whether or not processing such as comparison between TPUT_new and TPUT_max as described above has been performed (ST610). When an unselected combination remains (ST610, No), a process of selecting a combination candidate of MS 200 (user) that is a counterpart wireless terminal that performs wireless communication using P complex number sequences and complex number sequences Migrate to When all combinations are selected (ST610, Yes), the parameter P is set to P + 1 (ST611), and the value of the parameter P reaches the predetermined number (Ntx) that is equal to or less than the number of transmission antennas or the number of transmission antennas. Is determined (ST612).

  If it has arrived (ST612, Yes), this process ends. If not reached (ST612, No), the process proceeds to a process of selecting a combination candidate of MS 200 (user) that is a counterpart wireless terminal that performs wireless communication using P complex number sequences and complex number sequences. In this case, since the value of the parameter P is increased by 1, a new combination corresponding to the value of P is selected.

  In addition, when there are a plurality of additional complex number sequences, that is, when P> 1, from the wireless communication performed using any one additional complex number sequence for the MS 200 that performs wireless communication using the reference complex number sequence. Use either method to compare whether the amount of interference is smaller than a predetermined threshold or whether the amount of interference from wireless communication performed using all additional complex sequences is smaller than a predetermined threshold. Similarly, is the amount of interference from wireless communication performed using the reference complex number sequence for the MS 200 performing wireless communication using any one additional complex number sequence smaller than a predetermined threshold? Or the amount of interference from wireless communication performed using the reference complex number sequence for the MS 200 performing wireless communication using all the additional complex number sequences is greater than a predetermined threshold Whether smaller, it is possible to compare either way.

  FIG. 10 is a flowchart showing in detail a transmission power control process (ST603) performed by control section 120 shown in FIG.

  In the transmission power control process, first, the transmission power ratio of each of the P additional complex number sequences with respect to the reference complex number sequence is selected (ST701). At this time, it is preferable to determine a selection range (for example, −10 dB to +10 dB) in advance. Subsequently, the communication quality (signal power-to-interference and noise power ratio: SINR in this embodiment) of the reference in the case of the transmission power ratio selected in ST701 and the selected P additional complex number sequences is calculated from the equivalent gain. (ST702). Based on the calculated communication quality, the transmission parameter storage unit 114 is referred to calculate a throughput (transmission rate), and this is stored as TPUT_new (ST703). Subsequently, TPUT_new is compared with TPUT_max (ST704).

  When TPUT_new is greater than TPUT_max (ST704, Yes), the value of TPUT_new is stored in TPUT_max (ST705). The parameter Q is set to P + 1 (ST706), and the combination of the MS200 (user) that is a radio terminal using the complex number sequence and the complex number sequence stored in the reference complex number sequence selection process, and the selected P number And a combination of MS 200 (user) that is a counterpart wireless terminal that performs wireless communication using the complex number sequence and complex number sequence (ST707). Further, the transmission power ratio of each of the P additional complex number sequences with respect to the reference complex number sequence is stored (ST708).

  Subsequently, it is determined whether or not the above comparison processing or the like has been performed for all transmission power ratios in a transmission power ratio selection range in a predetermined range (ST709). If the unexecuted transmission power ratio is not left (ST709, Yes), the process is terminated. If the unimplemented transmission power ratio is left (ST709, No), the reference complex sequence again. The process proceeds to processing (ST701) for selecting the transmission power ratio of each of the P additional complex number sequences.

  In this case, a transmission power ratio that is different from the previously selected transmission power ratio is selected. At this time, it is preferable to determine a selection step (for example, 1 dB) in advance. Therefore, according to the above example, when one additional complex number sequence is considered, since the range of −10 dB to +10 dB is selected in 1 dB steps, a total of 11 selections are performed.

  It should be noted that any transmission power control method can be applied in the transmission power control process performed by the control unit 120 of the wireless communication apparatus of the present embodiment.

  In the above-described processing, transmission is performed only when the condition that the amount of interference from wireless communication performed using another complex number sequence with respect to MS 200 performing wireless communication using each complex number sequence is smaller than a predetermined threshold is satisfied. Control is performed to perform power control.

In general, as the SINR (communication quality) increases, the throughput (transmission speed) increases, but the relationship is not a simple proportional relationship. When the SINR value is small, the throughput improvement rate with respect to the increase in SINR is large. Conversely, when the SINR value is large, the throughput improvement rate with respect to the SINR increase tends to be small. Therefore, the total throughput can be improved by reducing the transmission power of signals corresponding to complex number sequences having a large SINR and increasing the transmission power of signals corresponding to other complex number sequences.

  Therefore, in this embodiment, when there is a signal corresponding to a complex number sequence whose interference amount is smaller than a predetermined threshold in ST602 of FIG. 9 during the user selection process, the transmission power control process is simultaneously performed. Therefore, system performance such as system throughput can be efficiently increased by performing the user selection process and the transmission power control process at the same time without significantly increasing the calculation amount of the user selection process.

  In the above embodiment, the communication is performed with the MS 200 using the combination of the complex number sequence and the user that maximizes the throughput (transmission rate) and the transmission power ratio. ) Is not limited to a mode in which communication is performed only when the maximum is taken. For example, a maximum value of a transmission rate that should be satisfied with one MS 200 is determined in advance, and communication is performed by appropriately selecting from a combination of a complex number sequence and a user that does not exceed the maximum value and a transmission power ratio. You may make it do. In addition, when it is preferable to communicate with as many MSs 200 as possible, various changes may be made, such as preferentially selecting a combination that increases the number of MSs 200 that perform communication.

(Second Embodiment)
The second embodiment of the present invention will be described in detail below.

  FIG. 11 is a flowchart illustrating processing in which the control unit 120 of the wireless communication apparatus according to the present embodiment performs user selection. The operation example described in FIG. 9 is different in the process of comparing the interference amount with a predetermined threshold value.

  A combination candidate of MS 200 (user) that is a counterpart wireless terminal that performs wireless communication using P additional complex number sequences and complex number sequences is selected (ST801). Next, the amount of interference from the wireless communication performed using the additional complex number sequence for the MS 200 that performs wireless communication using the reference complex number sequence, that is, the gain for the additional complex number sequence of the MS 200 that performs the wireless communication using the reference complex number sequence. The corresponding amount is compared with a predetermined threshold value (TH (INT) 1) (ST802). When the amount of interference is smaller than the threshold (ST802, Yes), the first transmission power control is performed (ST803). The first transmission power control is the same as the transmission power control process shown in FIG. 10, except that the transmission power ratio of each of the P additional complex sequences to the reference complex sequence is relative to the reference complex sequence. This means that control is performed so that only the transmission power ratio in a range that becomes smaller is selected in step 701.

  Also, the amount of interference from wireless communication performed using the reference complex number sequence for MS 200 that performs wireless communication using the additional complex number sequence is compared with a predetermined threshold (TH (INT) 2) and the comparison. (ST804). When the amount of interference is smaller than the threshold (ST804, Yes), second transmission power control is performed (ST805). The second transmission power control means that the transmission power ratio of each of the P additional complex sequences with respect to the reference complex number sequence is controlled only within a range in which the transmission power with respect to the reference complex number sequence becomes relatively large.

  Communication quality is calculated for each of the selected combination and the combination selected in the reference complex sequence selection process (ST806). Next, based on the communication quality, the transmission parameter storage unit 114 is referred to calculate the throughput (transmission rate) in the combination, and this is stored as TPUT_new (ST807).

  Next, TPUT_new is compared with TPUT_max (ST808). If TPUT_new is greater than TPUT_max (ST808, Yes), the value of TPUT_new is stored in TPUT_max (ST809), the parameter Q is set to P + 1 (ST810), and the reference complex number The complex number sequence stored in the sequence selection process and the combination of the partner radio terminal MS 200 that performs radio communication using the complex number sequence and the other party performing radio communication using the selected P complex number sequences and complex number sequences The combination of MS 200 that is the destination wireless terminal is stored (ST811).

  Subsequently, all combinations are selected, and it is determined whether or not processing such as comparison between TPUT_new and TPUT_max as described above has been performed (ST812). When an unselected combination remains (ST812, No), a process of selecting a combination candidate of MS 200 (user) that is a counterpart wireless terminal that performs wireless communication using P complex number sequences and complex number sequences Migrate to When all combinations are selected (ST812, Yes), the parameter P is set to P + 1 (ST813), and the value of the parameter P reaches the predetermined number (Ntx) that is equal to or less than the number of transmission antennas or the number of transmission antennas. (ST814).

  If it has been reached (ST814, Yes), this process is terminated. If not reached (ST814, No), the process proceeds to processing for selecting a combination candidate of MS 200 (user), which is a counterpart wireless terminal that performs wireless communication using P complex numbers and complex numbers. In this case, since the value of the parameter P is increased by 1, a new combination corresponding to the value of P is selected.

  The threshold values TH (INT1) and TH (INT2) are predetermined constants. The amount of calculation for performing transmission power control can be controlled by the magnitude of the values of TH (INT1) and TH (INT2).

  In addition, the operation example shown in FIG. 11 includes a process of comparing two interference amounts with a predetermined threshold in ST802 and ST804, but only one of them is compared to perform the first transmission power control. Or you may make it operate | move so that only either one of 2nd transmission power control may be implemented.

  As described above, by selecting the transmission power ratio only within a range where the throughput is likely to increase according to the amount of interference, the calculation amount is further reduced, and the user selection process and the transmission power control process are efficiently performed simultaneously. be able to.

(Third embodiment)
Hereinafter, the third embodiment of the present invention will be described in detail. The radio communication system according to the present embodiment is different from the operation example described in FIG. 9 in that a predetermined threshold value to be compared with the interference amount is made more specific.

  FIG. 12 is a flowchart illustrating processing in which the control unit 120 of the BS 100 according to the present embodiment selects a user.

  A combination candidate of MS 200 (user), which is a counterpart wireless terminal that performs wireless communication using P additional complex number sequences and complex number sequences, is selected (ST901).

  Amount of interference from wireless communication performed using an additional complex number sequence for MS 200 performing wireless communication using a reference complex number sequence (an amount corresponding to an equivalent gain for an additional complex number sequence of MS 200 performing wireless communication using a reference complex number sequence ) Is compared with the SNR notified from the MS 200 that performs wireless communication using the reference complex number sequence and a value determined by a predetermined offset (α1), more specifically, 1 / SNR × α1. Then, it is determined whether or not the amount of interference is smaller than the above value (ST902). Similarly, the amount of interference from radio communication performed using the reference complex number sequence for MS 200 performing radio communication using the additional complex number sequence, that is, the equivalent gain for the reference complex number sequence of MS 200 performing radio communication using the additional complex number sequence Is a value determined by the SNR notified from the MS 200 that performs wireless communication using the additional complex number sequence and a predetermined offset (α2), more specifically, 1 / SNR × Compared with α2, it operates to confirm whether or not the amount of interference is smaller than the above value.

  Note that, as described with reference to FIG. 11, the operation example can be modified so that the process of comparing each interference amount and the above value is performed separately.

  FIG. 13 is a diagram illustrating an example of predetermined threshold values (TH (INT) 1 and TH (INT) 2) to be compared with the interference amount. A value of α in the predetermined threshold, 1 / SNR × α1 and 1 / SNR × α2 described in FIG. 12 will be described. FIGS. 13A, 13B and 13C all show the relationship between SNR and α.

  In FIG. 13A, the value of α is defined as an arbitrary fixed value (1 in the example of FIG. 13) in any SNR value. In this case, transmission power control is performed with a relatively high probability under a condition with a low SNR, and transmission power control is performed with a relatively low probability under a condition with a high SNR.

  In FIG. 13B, in any SNR value, the value of α is defined as a value (1/100 in the example of FIG. 13) obtained by multiplying the SNR by an arbitrary fixed value. In this case, the probability of performing transmission power control is constant regardless of the SNR value.

  In FIG. 13C, in each SNR value, the value of α is defined as an arbitrary fixed value different from each other. In this case, it is preferable to set the value of α in consideration of the probability of performing transmission power control and the throughput improvement amount according to the SNR value.

  In FIG. 13, the value of α is not separately described as α1 and α2, but α1 and α2 can also be defined independently.

  According to the radio communication system of the present embodiment, the probability that transmission power control is performed and the relationship between the increased throughput and the increase in throughput are dependent on SNR, and the throughput is improved while the probability of performing transmission power control is kept low. Thus, it is possible to perform a more effective transmission power control process.

In addition, this invention is not limited to said embodiment as it is, You may modify | change and implement a component in the implementation stage in the range which does not deviate from the summary.

The figure which shows the outline | summary of the radio | wireless communications system of this embodiment. The figure which shows the structure of the radio | wireless terminal (MS) of the radio | wireless communications system of 1st Embodiment. The figure which shows the structure of the base station (BS) of the radio | wireless communications system of 1st Embodiment. The sequence diagram which shows communication of the radio | wireless terminal and base station in the radio | wireless communications system of 1st Embodiment. The figure which shows the structure of the control part of the base station which concerns on the radio | wireless communications system of 1st Embodiment. 3 is a flowchart illustrating processing of the wireless communication system according to the first embodiment. The flowchart which shows the user selection process of the radio | wireless communications system of 1st Embodiment. 5 is a flowchart showing processing for selecting a reference complex number sequence by the wireless communication system according to the first embodiment. 5 is a flowchart illustrating processing for selecting an additional complex number sequence by the wireless communication system according to the first embodiment. The flowchart which shows the process which the radio | wireless communications system of 1st Embodiment controls transmission power. 9 is a flowchart illustrating processing for selecting an additional complex number sequence in the wireless communication system according to the second embodiment. 9 is a flowchart showing processing for selecting an additional complex number sequence in the wireless communication system according to the third embodiment. The figure which shows the example of (alpha) used in the user selection process of the radio | wireless communications system of 3rd Embodiment.

Explanation of symbols

100 ... BS (base station)
110: Control unit 111: Upper layer I / F
112 ... Transmission / reception data buffer 113 ... User selection unit 114 ... Transmission parameter storage unit 1140 ... LUT
115 ... Transmission parameter setting unit 116 ... Complex number sequence setting unit 117 ... Channel state measurement result storage unit 120 ... Control unit 121 ... Transmission signal generation unit 122 ... For wireless channel measurement Signal generation unit 123 ... control signal generation unit 124 ... known signal generation unit 125 ... first selection unit 126 ... complex number series multiplication unit 127 ... second selection unit 128 ... transmission Processing unit 129 ... Transmission antenna 130 ... Reception antenna 131 ... Reception processing unit 132 ... Separation unit 133 ... Reception data demodulation unit 134 ... Control data demodulation unit 200 ... MS (wireless) Terminal)
210 ... Control unit 220 ... Transmission signal generation unit 221 ... Control signal generation unit 222 ... Selection unit 223 ... Transmission processing unit 224 ... Transmission antenna 225 ... Reception antenna 226 ... Reception processing unit 227 ... separation unit 228 ... reception data demodulation unit 229 ... control data demodulation unit 230 ... wireless channel measurement unit

Claims (7)

In a wireless communication device capable of simultaneous communication by multiplying a plurality of signal sequences on a same frequency channel with a plurality of different complex number sequences between a plurality of wireless terminals,
Transmitting means for transmitting a measurement signal obtained by multiplying the complex number sequence to each wireless terminal;
Receiving means for each wireless terminal to receive a notification regarding the channel characteristics of each of the complex number sequences obtained using the measurement signal;
Selection means for selecting one combination from among the combinations of the wireless terminal and the complex number sequence determined by selecting the complex number sequence for each wireless terminal;
Interference power calculating means for calculating interference power received from the complex number sequence that is not selected as the combination by the wireless terminal using a notification regarding the channel characteristics;
Determining means for determining whether the interference power is smaller than a predetermined threshold;
If it is determined that the interference power is smaller than the threshold, transmission rate calculation means for calculating a transmission rate when communicating with the wireless terminal by changing a transmission power ratio assigned to each of the wireless terminals;
Determining means for determining the combination and the transmission power ratio for communicating with each wireless terminal based on the transmission rates obtained for a plurality of the combinations and power ratios;
Have
A wireless communication apparatus that communicates with the wireless terminal using the combination and the transmission power ratio determined by the determining means.
The transmission rate calculation means obtains the transmission rate when the ratio is changed to the transmission power ratio in which the ratio of transmission power allocated to the complex number sequence for which the interference power is determined to be smaller than the threshold is reduced. The wireless communication apparatus according to claim 1, wherein:
3. The determination unit according to claim 1, wherein the determination unit calculates a ratio between received power and noise power using a notification related to the channel characteristic, and makes a determination according to the threshold value determined by an inverse number of the ratio. Wireless communication device.
4. The wireless communication apparatus according to claim 3, wherein the determination unit uses a value obtained by multiplying the inverse by a predetermined fixed value as the threshold value.
4. The wireless communication apparatus according to claim 3, wherein the determination unit uses a value obtained by multiplying the reciprocal by a predetermined value that increases as the ratio increases.
The transmission rate calculation means calculates the transmission rate when equal power is allocated to each wireless terminal for the combination in which the interference power is determined to be larger than the threshold. The wireless communication apparatus according to any one of claims 1 to 5.
In a wireless communication device capable of simultaneous communication by multiplying a plurality of signal sequences on a same frequency channel with a plurality of different complex number sequences between a plurality of wireless terminals,
Transmitting a measurement signal obtained by multiplying the complex number sequence to each wireless terminal;
Each of the wireless terminals receives a notification regarding the channel characteristics of each of the complex number sequences obtained using the measurement signal;
A selection step of selecting one combination from the combination of the wireless terminal and the complex number sequence, which is determined by selecting the complex number sequence for each wireless terminal;
An interference power calculation step of calculating interference power received from the complex number sequence that is not selected as the combination by the wireless terminal using a notification regarding the channel characteristics;
A determination step of determining whether the interference power is smaller than a predetermined threshold;
If it is determined that the interference power is smaller than the threshold, a transmission rate calculation step for calculating a transmission rate when communicating with the wireless terminal by changing a transmission power ratio assigned to each of the wireless terminals;
Based on the transmission rates calculated for a plurality of the combinations and power ratios, a determination step for determining the combinations and the transmission power ratios for communicating with the wireless terminals;
Have
A wireless communication method comprising communicating with the wireless terminal using the combination and the transmission power ratio determined in the determining step.

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