JP5202247B2 - COMMUNICATION SYSTEM, COMMUNICATION DEVICE, AND COMMUNICATION METHOD - Google Patents

Description

The present invention relates to a communication system , a communication apparatus, and a communication method using an OFDM scheme in a system having a master station and a plurality of slave stations.

  In recent years, orthogonal frequency division multiplexing (OFDM) modulation schemes have been applied in digital terrestrial television broadcasting and the like. The OFDM scheme has features such as high multipath tolerance and high band utilization efficiency because a plurality of transmission data is transmitted in parallel at low speed using a plurality of orthogonal subcarriers.

Patent Document 1 proposes a method of performing one-to-many simultaneous multiplex communication using an OFDM modulation signal as a transmission signal between a master station and a plurality of slave stations. According to the transmission method described in Patent Document 1, in data transmission from a master station to a slave station (hereinafter referred to as “downlink”), the master station performs data transmission by assigning a subcarrier to each slave station. Simultaneous multiplex communication with high bandwidth utilization efficiency is possible.
JP 2004-242059 A

  However, in Patent Document 1, band utilization efficiency is not considered for a multiplexing method of data transmission from a slave station to a master station (hereinafter referred to as “uplink”) and downlink transmission. As for the multiplexing of uplink and downlink transmission, the time division multiplexing method that divides and multiplexes in the time axis direction and the frequency division multiplex method that divides and multiplexes in the frequency axis direction are used. Low efficiency.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a communication method with better band utilization efficiency than time division multiplexing and frequency division multiplexing.

  In the present invention, in order to solve this problem, a master station divides orthogonal subcarriers in a communication band into a plurality of subcarrier groups and assigns them to a plurality of slave stations. The master station transmits an OFDM symbol for each slave station using the assigned subcarrier group. At the same time, each slave station transmits an OFDM symbol addressed to the master station in synchronization with the timing of this OFDM symbol. Each of the master station and each slave station divides the signal component transmitted by the known local station from the received signal component in order to cancel the transmission signal of the local station that has entered the transmission path.

More specifically, the communication system of the present invention is a communication system that performs communication between a master station and a plurality of slave stations using a signal having a plurality of subcarriers, wherein the master station includes the substations. Assigning means for allocating a carrier to each of the plurality of slave stations, and generating downlink signals to be transmitted to the plurality of slave stations by mapping transmission data addressed to the corresponding slave station to each of the plurality of subcarriers A downlink transmission means for transmitting the downlink signal to the plurality of slave stations;
An uplink receiving means for receiving uplink signals from the plurality of slave stations; and an uplink demodulation means for demodulating the received uplink signals, wherein each of the plurality of slave stations includes the downlink signal from the master station And transmitting to the parent station by mapping transmission data addressed to the parent station to subcarriers allocated from the parent station. Uplink transmission means for generating an uplink signal and transmitting the uplink signal to the master station;
A downlink signal from the master station to at least one slave station among the plurality of slave stations and an uplink signal from the one slave station to the master station are simultaneously transmitted on the same subcarrier, The uplink demodulation means performs demodulation processing on the signal after removing the signal component of the downlink signal corresponding to the subcarrier assigned to the at least one slave station from the received uplink signal, and The downlink demodulation means of the slave station performs demodulation processing on the signal after the signal component of the uplink signal is removed from the received downlink signal.

  According to the present invention, simultaneous multiplex communication with extremely high bandwidth utilization efficiency is possible by simultaneously performing uplink transmission and downlink transmission using a common orthogonal subcarrier.

  Hereinafter, the OFDM system of the present invention will be described in detail with reference to the drawings.

<Embodiment 1>
FIG. 1 is a block diagram showing a connection environment for the first to third embodiments of the present invention. FIG. 1 shows that the master station 401 and the slave stations 402 to 404 are connected by a common transmission line 405. In this embodiment, there are three slave stations, but the present invention is not limited to this, and can be applied to any number of stations. In this embodiment, it is assumed that the master station 401 and the slave stations 402 to 404 are connected by wire, but may be connected wirelessly. The operation clocks used in the master station 401 and the slave stations 402 to 404 are synchronized with sufficiently high accuracy by a high-precision oscillator. Further, the description will be made assuming that the signal transmission delay time between the master station 401 and the slave stations 402 to 404 is sufficiently small and can be ignored.

  First, the communication principle of the OFDM system in the present invention will be described.

  In the present embodiment, the subcarriers in the communication band are orthogonal to each other and are divided into three groups. Each subcarrier group is assigned to the slave stations 402 to 404.

  FIG. 2 is a diagram illustrating an example of assignment of the subcarrier group. In FIG. 2, a plurality of subcarriers included in the subcarrier group 501 are used for communication between a master station 401 and a slave station 402. A plurality of subcarriers included in the subcarrier group 502 are used for communication between the parent station 401 and the child station 403, and a plurality of subcarriers included in the subcarrier group 503 are included in the parent station 401 and the child station 403. Used for communication with station 404.

  The master station 401 generates transmission data for each slave station and transmits the transmission data to each slave station through the transmission path 405.

  FIG. 3 is a diagram showing a format of the OFDM symbol. As shown in FIG. 3, the format of the OFDM symbol includes an effective symbol 601 and a guard interval 602.

  For example, the master station 401 generates transmission data corresponding to the subcarrier group 501 for the slave station 402, maps it, converts it to an OFDM symbol, modulates it, and outputs it to the transmission line 405 in time series. . At the same time, the master station 401 performs the same processing as the transmission data for the slave station 402 on the transmission data for the slave station 403 and the transmission data for the slave station 404, and converts each OFDM symbol into The data is output to the transmission line 405.

  On the other hand, the slave station 402 maps the data for transmission to the master station 401 only to the subcarrier group 501, converts it into an OFDM symbol, further modulates it, and outputs it to the transmission path 405 continuously in time. At the same time, the slave station 403 and the slave station 404 similarly process the data for transmission to the master station 401 and output it to the transmission path 405.

  Here, in the slave stations 402 to 404, an OFDM symbol is generated in which the length of the effective symbol and the guard interval is equal to the OFDM symbol generated by the master station 401. Further, the slave stations 402 to 404 output OFDM symbols to the transmission path 405 in synchronization with the symbol timing of the master station 401.

  FIG. 4 is a diagram showing an example of a time / frequency arrangement of transmission / reception signals in the present invention. As can be seen from the transmission signal arrangement of each station on the time axis in the upper part of FIG. 4, the symbol timings of the transmission signals of the master station 401 and the slave stations 402 to 404 are synchronized. Then, the receiving units of the master station 401 and the slave stations 402 to 404 receive a signal that is the sum of the received signal from the other station and the received signal received by wrapping around the transmission signal of the own station.

  As shown in the lower part of FIG. 4, the DFT (Discrete Fourier Transform) processing section in each station is set to a section that does not include symbol boundaries, so that the subcarriers of the transmission signals of each station can be orthogonalized. . Each station can implement a transmission signal canceller having a relatively simple configuration that performs subtraction processing on the transmission signal component of the own station from the frequency analysis result during demodulation processing of the OFDM scheme. Therefore, the signal transmitted by each station can be demodulated without interfering with each other. As a result, it is possible to increase the transmission band by adopting the configuration of this OFDM method as compared with the case where downlink and uplink transmissions are multiplexed by time division or frequency division.

  The configuration of the master station 401 and the slave stations 402 to 404 that execute the operations shown in the above flow will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a diagram illustrating an internal functional block of the master station 401 in the first embodiment. First, the carrier allocation control unit 108 allocates a plurality of orthogonal subcarrier groups obtained by dividing subcarriers in a communication band planned in advance to each of a plurality of slave stations.

  The control data generation unit 122 generates transmission data addressed to the slave stations 402 to 404 and sends the transmission data to the transmission data buffers 101 to 103 of the corresponding slave stations.

  The transmission data addressed to the assigned slave station is mapped by symbol mappers 104 to 106 and output to transmission carrier selection section 107. For example, the symbol mappers 104 to 106 map transmission data on a complex plane by 64QAM or the like.

  The transmission carrier selection unit 107 rearranges the data based on the instruction from the carrier allocation control unit 108 so that the mapped data is multiplexed on a predetermined subcarrier.

  The selector 109 selects any one of the downlink preamble data 111, the null data 112, and the data output from the transmission carrier selection unit 107 based on an instruction from the transmission data control unit 110, and sends it to an IDFT unit (Inverse Discrete Fourier Transform unit) 113. Output. The null data 112 is used when the transmission output in one symbol period is made no signal.

  The IDFT unit 113 performs inverse discrete Fourier transform (IDFT) processing on the input data on the frequency axis, and generates an effective symbol on the time axis.

  A GI (Gird Interval) adding unit 114 generates an OFDM symbol by adding a guard interval to an effective symbol, and outputs the OFDM symbol to the transmitting unit 115.

  Heretofore, the downlink symbol generating means for performing operations from mapping of transmission data to outputting of OFDM symbols to the transmission unit has been described.

  The transmission unit 115 serving as a downlink transmission unit performs D / A conversion processing, orthogonal modulation, and frequency conversion on the generated OFDM symbol based on the clock signal of the clock generation unit 116 that supplies the clock, and the transmission path 405 in FIG. Transmit as the upper downlink signal.

  In this way, the transmission unit 115 continuously transmits the downlink signal in time based on the timing signal output from the timing generation unit 117.

  On the other hand, the receiving unit 118 serving as an uplink receiving unit receives uplink signals transmitted from the slave stations 402 to 404. However, actually, the signal output from the downlink transmission unit 115 wraps around to the reception unit 118 of the own station. This is because the transmission path between the transmission unit and the reception unit does not have a duplexer that separates upstream and downstream signals. Therefore, the upstream receiving unit 118 receives a sum signal that is the sum of the downstream signal and the upstream signal. In the following, the transmission path between the transmission unit and the reception unit is referred to as a wraparound transmission path.

  The received sum signal is subjected to frequency conversion processing, orthogonal demodulation processing, and A / D conversion processing based on the clock signal output from the clock generation unit 116, and is output to the symbol timing detection unit 119 and the GI removal unit 120.

  The symbol timing detection unit 119 detects the symbol timing of the uplink preamble symbol and outputs it to the timing error calculation unit 121.

  The timing error calculation unit 121 calculates a timing error between the timing signal output from the timing generation unit 117 and the uplink symbol timing. Here, when the timing error is greater than or equal to a predetermined value (first threshold), the timing error calculation unit 121 determines that a symbol timing detection error has occurred in the slave station, and generates the control data from the transmission data control unit 110. This is notified to the unit 122.

  The control data generation unit 122 generates data for controlling the slave station such as an uplink preamble transmission command that is a signal for instructing each slave station to transmit an uplink preamble, and a stop command for stopping transmission. For example, when an output from the timing error calculation unit 121 is received, a timing change command is generated, and the timing change command is transmitted to the slave station where the timing detection error has occurred. The timing change command is input to the transmission data, mapped, output from the selector 109 under the control of the transmission data control unit 110, and transmitted to the corresponding slave station.

  GI removal section 120 removes the guard interval from the received signal based on the timing signal output from timing generation section 117 and outputs the effective symbol to DFT section 123.

  The DFT unit (discrete Fourier transform unit) 123 performs DFT processing on the effective symbol and outputs the result to the transmission signal removal unit 124.

  The transmission signal removal unit 124 performs subtraction processing for the wraparound downlink signal component. Here, the wraparound downlink signal component refers to a signal component that wraps around to the receiving section of the own station among the downlink signals transmitted by the own station.

  FIG. 6 is a diagram illustrating an internal configuration example of the first transmission signal removal unit 124. The transmission signal removing unit 124 is a transmission signal removing unit for removing a downlink signal transmitted by the own station. The transmission signal removal unit 124 includes a first transmission data switching unit 301, a first reception data switching unit 302, a first complex division unit 303, a first characteristic storage unit 304, and a first complex multiplication unit 305. The first subtracting unit 306 is configured.

  The output of the selector 109 is also input to the transmission data switching unit 301. When transmitting a downlink preamble symbol, transmission data switching section 301 outputs the output of selector 109 to complex division section 303. When transmitting downlink data symbols, the output of the selector 109 is output to the complex multiplier 305. One of the purposes of transmitting the downlink preamble symbol is to obtain the transmission path characteristic of the wraparound transmission path by transmitting from the downlink transmission unit.

  The output of the DFT unit 123 is input to the reception data switching unit 302. Received data switching section 302 outputs the output of DFT section 123 to complex division section 303 when transmitting a downlink preamble symbol, and outputs the output of DFT section 123 to complex multiplication section 305 when transmitting a downlink data symbol.

  The complex division unit 303 performs a first complex transmission line from the transmission unit 115 to the reception unit 118 by performing complex division on the DFT output of the wraparound downlink preamble symbol from the downlink transmission unit to the uplink reception unit of the local station by the downlink preamble data. Estimate the characteristic value. Here, the wraparound downlink preamble symbol refers to a symbol in which the downlink preamble symbol from the downlink transmission unit wraps around the uplink reception unit 118 via the wraparound transmission path.

  The characteristic storage unit 304 subsequently holds the output of the complex division unit 303 as a first transmission path characteristic value related to the sneak transmission path from the downlink transmission unit to the uplink reception unit. Here, the master station may transmit a plurality of downlink preamble symbols, and average the transmission path characteristics estimated by each wraparound downlink preamble symbol to improve the estimation accuracy of the transmission path characteristic values. In this case, the characteristic storage unit 304 averages the transmission path characteristic value output from the complex division unit 303 when receiving the wraparound downlink preamble symbol in the symbol direction, and thereafter holds the averaged value as the first transmission path characteristic value. To do.

  The complex multiplier 305 estimates the wraparound downlink signal component by performing complex multiplication on the data output from the selector 109 by the first transmission path characteristic value, and outputs the estimated signal to the subtractor 306.

The subtracting unit 306 removes the wraparound downlink signal component by subtracting the output of the complex multiplier 305 from the DFT output of the downlink data symbol.
Through the above operation, the transmission signal removal unit 124 removes the wraparound downlink signal component from the reception signal, and outputs the signal from which the component of the wraparound downlink signal is removed to the reception signal equalization unit 125.

  The reception signal equalization unit 125 performs equalization processing on the uplink reception signal. The equalization processing of the uplink reception signal is performed by estimating the transmission path characteristics from the slave station to the master station using the uplink preamble symbol from the transmitter 211 of the slave station.

  The reception carrier selection unit 126 separates the received data after reception signal equalization based on the control of the carrier allocation control unit 108 and outputs the data to the symbol demappers 127 to 129.

  The symbol demappers 127 to 129 perform demapping processing such as 64QAM, and demodulate the received data 130 to 132 from the slave stations 402 to 404.

  The uplink demodulation means for demodulating the reception signal through the GI removal unit 120, the DFT unit 123, the transmission signal removal unit 124, the reception signal equalization unit 125, the reception carrier selection unit 126, and the symbol demappers 127 to 129 has been described above. .

  FIG. 7 is a diagram illustrating the internal configuration and operation of the slave stations 402 to 404. The carrier allocation control unit 208 allocates a subcarrier group in the communication band planned by the master station as addressed to the master station.

  The symbol mapper 202 maps the transmission data output from the master station 401 data transmission buffer 201 on the complex plane using, for example, 64QAM and outputs the mapping data to the selector 203.

  The selector 203 selects any one of the uplink preamble data 205, the null data 206, and the data output from the symbol mapper 202 based on an instruction from the transmission data control unit 204 and outputs the selected data to the IDFT unit 209.

  Based on the control of the carrier allocation control unit 208, the transmission carrier selection unit 207 rearranges the data so that the transmission data is multiplexed into the assigned subcarrier group.

  The IDFT unit 209 performs an inverse discrete Fourier transform process on the input data to generate an effective symbol.

  GI adding section 210 generates an OFDM symbol by adding a guard interval to an effective symbol, and outputs the OFDM symbol to transmitting section 211.

  Transmitting section 211, which is an uplink transmitting means, performs D / A conversion processing, orthogonal modulation processing, and frequency conversion processing based on the clock signal output from clock generation section 212, and transmits the OFDM symbol as an upstream signal on the transmission path. . Here, based on the timing signal output from the timing generation unit 213, the transmission unit 211 continuously transmits uplink signals addressed to the master station in terms of time.

  The receiving unit 214 serving as a downlink receiving unit performs frequency conversion processing, orthogonal demodulation processing, and A / D conversion processing on the received signal based on the clock signal output from the clock generation unit 212, and performs a symbol timing detection unit 215 and a GI removal unit. To 216.

  The symbol timing detection unit 215 detects the symbol timing of the downlink preamble symbol and outputs the detection signal to the timing generation unit 213.

  The timing generation unit 213 generates a timing signal synchronized with the symbol timing of the downlink preamble symbol, and outputs the timing signal to the transmission unit 211 and the GI removal unit 216.

  GI removal section 216 removes the guard interval from the received signal based on the timing signal output from timing generation section 213, and outputs the effective symbol of the removed signal to DFT section 217.

  The DFT unit 217 performs DFT processing on the effective symbol and outputs the processed signal to the transmission signal removal unit 218.

  The second transmission signal removing unit 218, which is a transmission signal removing unit for removing the uplink signal transmitted by the own station, performs a subtraction process on the wraparound uplink signal component, and receives the data after the subtraction process as a reception signal equalization unit To 219. Here, the wraparound uplink signal refers to a signal component that wraps around the reception unit of the own station among the uplink signals transmitted by the own station. The transmission signal removal unit 218 has the same configuration and operation as the first transmission signal removal unit 124 of the master station 401 described in FIG. As a configuration of the slave station corresponding to FIG. 3, the second transmission signal removal unit includes a second transmission data switching unit, a second reception data switching unit, a second complex division unit, a second characteristic storage unit, The second complex multiplication unit and the second subtraction unit 306 are configured (not shown). However, the difference is that the master station estimates the channel characteristics by the wraparound transmission path during downlink preamble transmission, whereas the slave station estimates the channel characteristics by the wraparound transmission path at uplink preamble transmission. Yes.

  The reception signal equalization unit 219 performs equalization processing of the downlink reception signal. The downlink received signal equalization process is performed by estimating the transmission path characteristics from the master station to the slave station using the downlink preamble symbol. In addition, reception carrier selection section 220 separates received data of the allocated subcarrier group from the data after reception signal equalization based on control of carrier allocation control section 208 and outputs the separated data to symbol demapper 221.

  The symbol demapper 221 performs demapping processing such as 64QAM, and demodulates the received data 222 from the master station 401. When the received data is control data such as an uplink preamble transmission command, the information is notified to the transmission data control unit 204, and the transmission data control unit 204 controls the selector 203 based on the information. . For example, when an uplink preamble symbol transmission command is received from the master station 401, the transmission data control unit 204 performs control so that the uplink preamble data 205 is output from the selector 203.

  The downlink demodulation means for demodulating the reception signal has been described above through the GI removal unit 216, DFT unit 217, transmission signal removal unit 218, reception signal equalization unit 219, reception carrier selection unit 220, and symbol demapper 221. Next, in order to start transmission in the OFDM transmission method of the present invention, it is necessary for the master station 401 and the slave stations 402 to 404 to synchronize the transmission timing and to estimate the second transmission path characteristic by wraparound. is there.

  FIG. 8 is a flowchart showing the overall operation of the master station 401 and the slave stations 402 to 404.

  In step S800, the carrier allocation control unit 108 of the master station 401 allocates a plurality of orthogonal subcarrier groups obtained by dividing subcarriers in the communication band planned in advance to each of the plurality of slave stations.

  In step S801, the clock generation unit 116 of the master station 401 generates a timing signal that is high (hereinafter referred to as “H”) for each OFDM symbol length. This timing signal is used as a transmission timing signal for the downlink signal.

  In step S802, based on this timing signal, transmission section 115 of base station 401 sets an arbitrary section that does not include the symbol boundary of the transmission signal as a demodulation DFT processing section.

  In step S803, transmitting section 115 of base station 401 outputs a downlink preamble symbol to transmission path 405 in synchronization with the timing signal. The downlink preamble symbol is a symbol in which a known data pattern is placed on all subcarriers, and is prepared for the signal processing circuit in each slave station to synchronize with the master station.

  In step S804, the transmission signal removal unit 124 of the master station 401 uses the downlink preamble symbol received by wrapping as described in the operation of the transmission signal removal unit 124 in FIGS. Estimate the characteristics.

  In step S805, since the transmission signal removal unit 124 of the master station 401 can estimate the wraparound downlink signal component after the next symbol, the subtraction removal of the wraparound downlink signal component is performed at the time of demodulation of the reception signal after step S804. I do.

  On the other hand, the following operations are performed on the slave station side.

  In step S806, the symbol timing detection unit 215 of the slave stations 402 to 404 detects the downlink symbol timing using the downlink preamble symbol received by the reception unit 214.

  In step S807, the timing generation unit 213 of the slave stations 402 to 404 generates a timing signal synchronized with the symbol timing detected by the symbol timing detection unit 215. This timing signal is used as an upstream signal transmission timing signal thereafter.

  In step S808, the DFT units 217 of the slave stations 402 to 404 set an arbitrary section that does not include the symbol boundary of the transmission signal as a demodulated DFT processing section based on this timing signal.

  In step S809, the reception signal equalization unit 219 of the transmission signal removal unit 218 of each of the slave stations 402 to 404 estimates downlink transmission path characteristics using the downlink preamble symbol.

  Subsequently, the following steps are performed on the master station 401 side.

  In step S810, the downlink transmission unit 115 of the master station 401 stops transmission of the downlink preamble symbol. Note that downlink preamble symbols are transmitted for a period sufficient for the slave stations 402 to 404 to execute steps S806 to S809.

  In step S811, the downlink transmission unit 115 of the parent station 401 transmits an uplink preamble transmission command generated by the control data generation unit 122, thereby transmitting an uplink preamble symbol to one of the child stations 402 to 404. Send the command.

  Upon receiving the uplink preamble symbol transmission command in step S812, the transmission unit 211 of the slave station (here, the slave station 402) transmits the uplink preamble symbol to the transmission path 405 in synchronization with the timing signal generated in step S807. Output.

  In step S813, the complex division unit in the transmission signal removal unit 218 of the slave station 402 performs complex division on the DFT output of the uplink preamble symbol by the uplink preamble data, thereby causing a wraparound transmission path characteristic from the transmission unit 211 to the reception unit 214. Estimate

  In step S814, since the subtraction unit in the transmission signal removal unit 218 of the slave station 402 can estimate the wraparound reception component of the transmission signal, the wraparound signal component from the reception signal is obtained in the reception signal demodulation after step S813. Perform subtraction removal.

  In step S815, the symbol timing detection unit 119 of the master station 401 detects the uplink symbol timing using this uplink preamble symbol.

  In step S816, the timing error calculation unit 121 of the parent station 401 calculates a timing error between the symbol timing and the parent station timing signal generated by the timing generation unit 117.

  If the timing error is greater than or equal to the first threshold value in step S817, the timing error calculation unit 121 sends a message to that effect to the transmission data control unit 110. The transmission data control unit 110 generates a timing change command, transmits the timing change command to the slave station 402 from the transmission unit 115, and returns to step S803. If the timing error is less than or equal to the first threshold, the process proceeds to step S819.

  In step S818, when receiving the timing change command from the parent station 401, the receiving unit 214 of the slave station 402 determines that the detection of the downlink symbol timing has failed, and sends a message to that effect to the symbol timing detecting unit, step S806. Return to.

  In step S819, the complex division unit in the transmission signal removal unit 124 of the master station 401 performs complex division on the DFT output of the uplink preamble symbol by the uplink preamble data, so that the wraparound channel characteristics from the transmission unit 115 to the reception unit 118 are obtained. Estimate

  In step S820, transmission data control section 110 of parent station 401 generates a transmission stop instruction, and transmission section 115 transmits an uplink preamble symbol transmission stop instruction to slave station 402.

  In step S821, the receiving unit 214 of the slave station 402 receives the transmission stop command and stops transmission of the uplink preamble symbol.

  As a result of the above operation, the master station 401 and the slave station 402 are in a state in which the transmission timing is synchronized and the wraparound received signal can be canceled.

  Thereafter, in step S822, the master station 401 performs the same processing in steps S812 to S821 for the slave stations 403 and 404 as well.

  In step S823, the transmission unit 115 of the parent station 401 transmits a data transmission start command to the child stations 402 to 404.

  In steps S824 and S825, data transmission by OFDM between the master station 401 and the slave stations 402 to 404 is started.

  FIG. 9 is a diagram showing main timing signals and transmission signal timings of the master station 401 and the slave stations 402 to 404. This timing diagram shows the timing when the operation of the flow shown in FIG. 8 is performed using the above-described configuration of the master station 401 and the slave stations 402 to 404.

  In FIG. 9, the timing signal 901 of the parent station 401 is a timing signal output from the timing generation unit 117 of the parent station 401. A transmission signal 902 of the parent station 401 is a transmission signal output from the transmission unit 115 of the parent station 401. Transmitter 115 outputs an OFDM symbol to transmission path 405 in synchronization with timing signal 901.

  The timing signals 903 of the slave stations 402 to 404 are timing signals output from the timing generator 213 by the slave stations 402 to 404. The timing generation unit 213 generates and outputs a timing signal synchronized with the symbol timing of the downlink preamble symbol.

  Transmission signals 904 of the slave stations 402 to 404 are transmission signals output from the transmission unit 211 of the slave stations 402 to 404. Transmitting section 211 outputs an OFDM symbol to transmission path 405 in synchronization with timing signal 903.

  As described above, the transmission timing of each station is synchronized and the transmission signal component of the own station can be removed by the configuration and operation shown in FIGS. 5, 6 and 8, and the OFDM transmission system according to the present invention can be performed. Become. As a result, the band utilization efficiency can be further improved as compared with the conventional OFDM system, and the transmission rate of data transmitted from each station can be increased. In addition, it is possible to realize a flexible system according to the application, such as increasing error tolerance by allocating an increase in transmission band to an error correction code while keeping the net transmission rate of data transmitted by each station. .

  In the present embodiment, the subcarriers are divided into the three groups shown in FIG. 2 and assigned to the slave stations 402 to 404. However, the present invention is not limited to this.

  FIG. 10 is a diagram showing a case where arbitrary subcarriers are grouped and assigned to the slave stations 402 to 404 as shown in the groups 1901 to 1903. In this case as well, the method of the present invention can be similarly applied. In this case, more efficient transmission can be performed by determining the subcarrier grouping and assignment to the slave stations 402 to 404 according to the transmission path characteristics.

  In the first embodiment, as illustrated in FIG. 4, the frequency intensity of the signals transmitted from the master station 401 and the slave stations 402 to 404 has been described as being the same. However, the present invention is not limited to this. Absent.

  For example, FIG. 11 is a diagram illustrating a case where the frequency intensity of the transmission signal of the master station 401 is set larger than that of the slave stations 402 to 404. Then, it is possible to perform flexible transmission according to the application, for example, by using 256QAM or the like as a downlink communication modulation system to increase the transmission band of downlink communication. In the present embodiment, as illustrated in FIG. 4, the case where each station uses subcarriers in the communication band at the same frequency intensity has been described as an example.

  FIG. 12 is a diagram illustrating a case where only specific subcarriers in the communication band are not used. In this case, as shown in FIG. 12, the subcarriers may be divided into groups equal to or larger than the number of slave stations, and a subcarrier group (2301) not used may be set.

  FIG. 13 shows a case where only the master station 401 or the slave stations 402 to 404 occupy a single subcarrier group having a single carrier other than the subcarrier groups (501 to 503) having a plurality of subcarriers. FIG. Needless to say, this case can also be applied to this embodiment.

  As described above, in the first embodiment, the downlink signal from the master station to the slave station and the uplink signal to the master station are transmitted simultaneously and by the same subcarrier group. The master station includes a transmission signal removing unit that subtracts and removes the component of the downlink signal transmitted from the own station to the one slave station from the uplink signal received by the uplink demodulating unit. On the other hand, the slave station includes a transmission signal removal unit that subtracts and removes the component of the uplink signal transmitted by the local station from the downlink signal received by the downlink demodulation unit. By adopting this configuration, simultaneous multiplex communication with extremely high bandwidth utilization efficiency becomes possible.

  In the first embodiment, the master station 401 includes a characteristic transmission signal removal unit. That is, the transmission signal removal unit performs complex division on the downlink preamble symbol transmitted from the downlink transmission unit and received from the wraparound transmission path by the known downlink preamble symbol. Then, the transmission path characteristic between the downlink transmission unit and the uplink reception unit is estimated, and a value obtained by averaging the estimated transmission path characteristic output from the complex division unit with the number of downlink preamble symbols is used as the transmission path characteristic value. Remember. Furthermore, the signal component due to the wraparound of the downlink signal addressed to the slave station is estimated by performing complex multiplication of the transmission data addressed to the slave station and the transmission path characteristic value. Finally, the influence of the wraparound is removed by subtracting the signal component estimated by the complex multiplier from the received sum signal of the downlink. This transmission signal removing means enables high-precision demodulation at the master station.

  On the other hand, in the first embodiment, the transmission signal removal means in the slave station also has a characteristic transmission signal removal unit, similar to the parent station. First, the uplink preamble symbol transmitted from the uplink transmission unit and received from the wraparound transmission path is complex-divided by a known uplink preamble symbol. Then, the transmission path characteristic between the uplink transmission unit and the downlink reception means is estimated, and the value obtained by averaging the output of the transmission path characteristic estimated from the complex division unit with the number of uplink preamble symbols is transmitted to the second transmission. Stored as a road characteristic value. Further, by multiplying the transmission data addressed to the master station by the transmission path characteristic value, the signal component due to the wraparound of the uplink signal addressed to the master station is estimated. Finally, the influence of the wraparound is removed by subtracting the signal component estimated by the complex multiplier from the received sum signal of the uplink. This transmission signal removal unit enables highly accurate demodulation at the slave station.

<Embodiment 2>
Application of the present invention requires an oscillator with extremely high oscillation accuracy at each station, but it is also possible to use a voltage controlled oscillator as an operation clock for the slave stations 402 to 404. The specific embodiment will be described below. In the present embodiment, a subcarrier group is provided for the master station 401 to transmit pilot data. The slave stations 402 to 404 perform clock synchronization control using the pilot data.

  FIG. 14 is a diagram illustrating an example of group assignment according to the second embodiment. In FIG. 14, subcarrier groups 1001 to 1003 are subcarrier groups used for communicating with each of the master station 401 and the slave stations 402 to 404. The subcarrier group 1004 is used only by the master station 401 and is a group for transmitting pilot subcarriers.

  FIG. 15 is a block diagram showing the master station 401 in this embodiment. Regarding the configuration and operation of the master station 401 and the slave stations 402 to 404, blocks different from the configuration of the first embodiment will be described. Other blocks are the same as those in the first embodiment.

  In FIG. 15, pilot data 1101 is composed of a first known data pattern. Pilot data 1101 is input to transmission carrier selection section 107, and data rearrangement is performed so as to be carried on a predetermined subcarrier.

  FIG. 16 is a block diagram illustrating a configuration of a slave station in the second embodiment. In FIG. 16, the clock generation unit 1201 includes a voltage controlled oscillator, and is controlled so that its oscillation frequency is synchronized with the clock frequency of the master station 401 according to the output of the synchronization control unit 1203. Pilot extraction section 1202 in FIG. 16 extracts only the subcarrier data in which pilot data is multiplexed from the output of DFT section 217 based on an instruction from carrier allocation control section 208 and outputs the extracted data to synchronization control section 1203. The synchronization control unit 1203 controls the clock generation unit 1201 based on the extracted pilot data.

  FIG. 17 is a diagram illustrating a configuration example of the synchronization control unit 1203. In the complex multiplier 1303 of FIG. 17, the extracted pilot data is complex-multiplied with the complex conjugate data of the pilot data one symbol before output by the delay unit 1301 and the complex conjugate unit 1302. Since the multiplication result has a declination proportional to the clock frequency deviation, the multiplication result is averaged by the average calculation unit 1304, and then the declination is calculated by the arctan unit 1305, and the clock generation unit is determined according to this value. 1201 is controlled. At this time, it is also possible to perform more accurate clock synchronization control by calculating the symbol timing deviation amount of the pilot data for each symbol and adding the calculation result as control information of the clock generation unit 1201. .

  In the second embodiment, as shown in FIG. 14, by providing a pilot subcarrier group used only by the master station 401, the slave stations 402 to 404 can perform clock synchronization control using all pilot subcarriers of the same subcarrier group. It is.

  FIG. 18 is a diagram illustrating an example in which pilot subcarriers are provided in each subcarrier group using the example of FIG. Hereinafter, the subcarrier group assignment shown in FIG. 14 is referred to as assignment 1, and the subcarrier group assignment shown in FIG. 18 is referred to as assignment 2.

  In allocation 2, the slave stations 402 to 404 cannot perform clock synchronization control using pilot subcarriers of subcarrier groups used by other slave stations. Therefore, the allocation 2 has a problem that the clock synchronization accuracy is lowered as compared with the allocation 1 according to the second embodiment. Further, in order to obtain clock synchronization accuracy equivalent to that of allocation 1, it is necessary to provide the same number of pilot subcarriers as the number of pilot subcarriers of allocation 1 in each group. In this case, there arises a problem that the downstream transmission band is lowered more than necessary. In order to improve this, it is proposed in Embodiment 2 of the allocation 1 that clock synchronization control that effectively uses the frequency band is performed to avoid a decrease in the downlink transmission band.

  Since allocation 1 provides a pilot subcarrier group that only the master station 401 transmits, compared to allocation 2, the transmission band of the slave stations 402 to 404 is reduced by the number of pilot subcarriers. Therefore, allocation 1 and allocation 2 may be selected according to the necessity of the upstream transmission band.

  In Embodiment 2, the master station assigns at least one subcarrier group in the subcarrier group as a subcarrier group in which only the master station transmits. The master station uses this subcarrier to transmit a pilot carrier, which is a known data pattern, to the slave station. With this configuration, the slave station can use the pilot carrier, and there is an effect of providing synchronization with higher accuracy than in the first embodiment.

In the second embodiment, in the slave station, the downlink demodulator extracts a pilot carrier from the master station, and controls the clock generator of the slave station based on the extracted carrier. By adopting this configuration, there is an effect that synchronization with higher accuracy can be realized as compared with synchronization using only the timing symbols of the first embodiment.
<Embodiment 3>
In the third embodiment, in addition to the second embodiment, a subcarrier group is provided for the slave stations 402 to 404 to transmit pilot data having the second known data pattern. FIG. 19 shows an example of group assignment of this embodiment.

  FIG. 19 is a diagram illustrating an example of group assignment according to the third embodiment. In FIG. 19, groups 1501 to 1503 indicate subcarrier groups used for communicating with each of the master station 401 and the slave stations 402 to 404. The group 1504 is a group used only by the master station 401 and for transmitting pilot subcarriers. Groups 1505 to 1507 are groups used only by the slave stations 402 to 404 to transmit pilot carriers.

  FIG. 20 is a block diagram illustrating a configuration of the master station 401 according to the third embodiment. Regarding the configuration and operation of the master station 401, a block different from the configurations of the first and second embodiments will be described. Other blocks are the same as those described in the configurations of the first and second embodiments.

  In FIG. 20, null data 1601 is input to the transmission carrier selection unit 107, and the data is rearranged in a form in which data is not multiplexed for groups 1505-1507.

  FIG. 21 is a diagram illustrating a detailed configuration example of the phase tracking units 1602 to 1604 as phase tracking means for performing phase control of the subcarrier group. In FIG. 20, a pilot separation unit 1701 separates a pilot carrier and a data carrier based on an instruction from the carrier allocation control unit 108. The first complex division unit 1703 performs complex division between the pilot carrier and the known uplink pilot data 1702 to calculate a phase rotation component caused by phase noise. An average calculation unit 1704 performs an in-phase rotation component averaging process, and a first complex multiplication unit 1705 performs complex multiplication of the average calculation result and a data carrier. With the above operation, it is possible to correct the phase noise component generated in the slave stations 402 to 404.

  FIG. 22 is a diagram illustrating the configuration of the slave stations 402 to 404 according to the present embodiment. The reception signal equalization unit 2001 of the slave stations 402 to 404 according to the third embodiment notifies the synchronization control unit 2003 of the transmission path characteristic values of pilot groups transmitted by other slave stations.

  Pilot extraction section 2002 extracts pilot carriers transmitted from other child stations in addition to the pilot carriers transmitted from parent station 401, and outputs the extracted pilot carriers to synchronization control section 2003.

  FIG. 23 is a diagram illustrating an internal configuration example of the synchronization control unit 2003. The pilot data extracted in FIG. 23 is complex-multiplied by the second complex multiplier 2103 with the complex conjugate data of the pilot data one symbol before output from the delay unit 2101 and the complex conjugate unit 2102. The multiplication result is separated for each group by the group separation unit 2104. The pilot data received from the master station is input to the addition average calculation unit 2107, and the pilot data received from other slave stations is input to the weighting calculation unit 2105.

  Weighting calculation section 2105 weights the pilot data according to the transmission path loss amount of each group output from absolute value calculation section 2106 and outputs the result to addition average calculation section 2107. The absolute value calculation unit 2106 calculates the absolute value of the transmission line characteristic value input from the reception signal equalization unit 2001 to obtain the transmission line loss amount. Thereafter, the pilot data received from the master station 401 and the other slave stations is calculated by the arithmetic mean calculator 2107 and sent to the arctan calculator 2108. The arctan calculation unit 2108 calculates a declination from the addition average, and the declination is used as synchronization control information for the clock generation unit 1201.

  In order to enable the operations of the slave stations 402 to 404, in this embodiment, the slave stations 402 to 404 need to demodulate pilot carriers from other slave stations.

  FIG. 24 is a diagram illustrating operations of the master station 401 and the slave stations 402 to 404 in the present embodiment. The operation flow shown in FIG. 24 is performed after step S822 in the operation flow of FIG. 8 shown in the first embodiment.

  In step S1801, the transmission unit 115 of the parent station 401 transmits a pilot transmission command to the child station 402.

  In step S1802, the receiving unit 214 of the slave station 402 receives this pilot transmission command. As a result, the IDFT unit 209 converts the pilot data into OFDM symbols on the time axis only for the assigned pilot group, and the transmission unit 211 performs orthogonal frequency modulation on the OFDM symbols and transmits them.

  In step S1803 and step S1804, the reception unit 214 of the slave station 403 and the slave station 404 receives the transmission signal, and the reception signal equalization unit 2001 transmits the pilot group transmitted from the slave station 402 using the pilot data. Estimate road characteristics.

  In step S1805, the received signal equalization unit 125 of the master station 401 performs equalization processing by performing complex multiplication of the inverse characteristics of the transmission path characteristics on the pilot groups transmitted from the subsequent slave stations 402. Thereafter, the transmission unit 115 of the parent station 401 transmits a pilot stop command to the child station 402.

  In step S1806, the reception unit 214 of the slave station 402 receives this pilot stop command, and the transmission unit 211 stops transmission of the pilot signal.

  In Steps S1807 to S1818, thereafter, the same operation is performed for all the slave stations by the master station 401, and each slave station estimates the transmission path characteristics with the other slave stations.

  Through the above operation, the slave stations 402 to 404 can perform synchronization control using pilot carriers from other slave stations.

  As described above, the configuration using the pilot carriers of the master station 401 and the slave stations 402 to 404 in the third embodiment enables the master station 401 to correct the phase noise component generated in the slave stations 402 to 404. Become. Further, since the slave stations 402 to 404 perform clock synchronization control using not only pilot carriers from the master station 401 but also pilot carriers transmitted from other slave stations, the synchronization accuracy can be improved. Further, in the third embodiment, pilot carriers received from other slave stations are weighted according to transmission path characteristics and used as synchronization control information. As a result, even when the transmission path characteristics between the slave stations are not good, flexible synchronization control that is less susceptible to the influence can be performed, and the communication system of the OFDM system in which the third embodiment is more reliable than the second embodiment. Can provide.

  In the third embodiment, at least one subcarrier group is assigned as a subcarrier group to be transmitted only by a child station in the parent station, and the parent station transmits null data in a subcarrier group to which only the child station transmits. . The slave station is configured to transmit a pilot carrier having a known data pattern to the master station using a group in which only this slave station transmits. By using this pilot carrier, there is an effect of providing phase control that cannot be realized in the second embodiment.

  In the third embodiment, the master station extracts the pilot carrier from the slave station and includes a phase tracking loop, thereby realizing phase control of each subcarrier using the pilot carrier. As a result, not only clock synchronization but also the phase of each subcarrier can be controlled with high accuracy.

Diagram showing connection environment block The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (1) Diagram showing the structure of an OFDM symbol The figure which shows the time and frequency arrangement | positioning of the transmission / reception signal in this invention The figure which shows the block of the main | base station 401 in Embodiment 1. FIG. The figure which shows the block of the transmission signal removal part 124 The figure which shows the block of the substations 402-404 in Embodiment 1. The figure which shows the operation | movement flow in Embodiment 1. The figure which shows the timing of the signal in Embodiment 1. The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (2) The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (3) FIG. 4 shows an example of subcarrier group allocation frequency arrangement (4) The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (5) The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (6). The figure which shows the block of the main | base station 401 in Embodiment 2. FIG. The figure which shows the block of the substations 402-404 in Embodiment 2. The figure which shows the block of the synchronous control part 1203 The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (7) The figure which shows the example of a subcarrier group allocation frequency arrangement | positioning (8). The figure which shows the block of the master station 401 in Embodiment 3. The figure which shows the block of the phase tracking parts 1601-1603 The figure which shows the block of the substations 402-404 in Embodiment 3. The figure which shows the block of the synchronous control part 2003 Operation Flow Diagram in Embodiment 3

Explanation of symbols

101-103 Transmission data
104 to 106 Symbol mapper 107 Transmission carrier selection unit 108 Carrier allocation control unit 109 Selector 110 Transmission data control unit 111 Downstream preamble data 112 Null data 113 IDFT unit 114 GI addition unit 115 Transmission unit 116 Clock generation unit 117 Timing generation unit 118 Reception unit 119 Symbol timing generation unit 120 GI removal unit 121 Timing error calculation unit 122 Control data generation unit 123 DFT unit 124 Transmission signal removal unit 125 Reception signal equalization unit 126 Reception carrier selection unit 127 to 129 Symbol demapper 130 to 132 Reception data

Claims (11)

A communication system that performs communication between a master station and a plurality of slave stations using a communication method having a plurality of subcarriers ,
The master station is
Allocating means for allocating the subcarrier to each of the plurality of slave stations;
Downlink transmission for generating a downlink signal to be transmitted to the plurality of slave stations by mapping transmission data addressed to the corresponding slave station to each of the plurality of subcarriers, and transmitting the downlink signal to the plurality of slave stations Means,
Uplink reception means for receiving uplink signals from the plurality of slave stations;
Uplink demodulating means for demodulating the received uplink signal ;
With
Each of the plurality of slave stations is
Downlink receiving means for receiving the downlink signal from the master station;
Downlink demodulating means for demodulating the received downlink signal;
An uplink transmission means for generating an uplink signal to be transmitted to the master station by mapping transmission data addressed to the master station to a subcarrier assigned by the master station, and transmitting the uplink signal to the master station; ,
Wherein the upstream signal from the master station to the parent station from the downlink signal and said one slave station to at least one child station of the plurality of slave stations is transmitted simultaneously in the same sub-carrier, the uplink The demodulating means performs demodulation processing on the signal after the signal component of the downlink signal corresponding to the subcarrier assigned to the at least one slave station is removed from the received uplink signal, and the at least one slave station The downlink demodulation means performs demodulation processing on the signal after removing the signal component of the uplink signal from the received downlink signal,
A communication system characterized by the above.   In a communication system having a plurality of subcarriers, a communication device that communicates with one or more devices using the assigned subcarriers,
  Based on the subcarrier allocation, a transmission signal to be transmitted to the one or more devices is generated by mapping transmission data to each of the plurality of subcarriers, and the transmission signal is transmitted to the one or more devices. A transmission means for transmitting;
  Receiving means for receiving signals from the one or more devices;
  Demodulation means for demodulating the received signal;
  With
  Simultaneously in the same subcarrier, the transmitting means transmits the transmission signal to one or more devices, the receiving means receives the received signal from the device, and the demodulating means is assigned to the device. A demodulation process is performed on the signal after the signal component of the transmission signal corresponding to the subcarrier is removed from the reception signal.
  A communication device.   The demodulating means includes
    Transmission path estimation means for estimating a transmission path of a signal transmitted from the transmission means and received by the reception means by using a known preamble symbol and outputting a transmission path estimation value;
    Signal component estimation means for estimating the signal component by complex multiplication of the transmission path estimation value and the transmission signal;
  The communication apparatus according to claim 2, further comprising:   The transmission path estimation means performs complex division on a component corresponding to the preamble symbol of a signal transmitted from the transmission means and received by the reception means by the preamble symbol, and complex division for a plurality of the preamble symbols The average of the results is taken as the transmission line estimation value,
  The communication apparatus according to claim 3.   The signal component estimation means estimates the signal component by complex-multiplying the transmission signal with the transmission path estimation value for the subcarrier that receives the reception signal from the one or more devices.
  The communication apparatus according to claim 3 or 4, wherein   In the subcarrier allocation, at least one subcarrier is allocated such that only one device transmits,
  The demodulation means estimates a phase rotation of a signal received from the one device based on a signal received on a subcarrier assigned to the one device only;
  The communication device according to any one of claims 2 to 5, wherein:   A clock generation unit for supplying a clock to the transmission unit and the reception unit;
  In the subcarrier allocation, at least one subcarrier is allocated so that only one device performs transmission, and the clock generation unit is based on a signal received by a subcarrier allocated only to the one device. Controlled,
  The communication apparatus according to claim 6.   A signal received on a subcarrier assigned to only one device includes a known data pattern,
  The communication apparatus according to claim 6 or 7, wherein   An allocation means for determining allocation of the subcarriers;
  The communication device according to claim 2, wherein the communication device is a device. A communication method for performing communication between a master station and a plurality of slave stations using a communication method having a plurality of subcarriers ,
In the master station,
An assigning unit assigning the subcarrier to each of the plurality of slave stations;
A downlink transmission unit generates a downlink signal to be transmitted to the plurality of slave stations by mapping transmission data addressed to the corresponding slave station to each of the plurality of subcarriers, and the downlink signal is transmitted to the plurality of slave stations. Sending to
An uplink receiving means for receiving uplink signals from the plurality of slave stations;
An uplink demodulation means for demodulating the received uplink signal ;
Run
In each of the plurality of slave stations,
A downlink receiving means for receiving the downlink signal from the master station;
Downlink demodulation means, the step of demodulating said received downlink signal,
A step of generating an uplink signal to be transmitted to the parent station by mapping transmission data addressed to the parent station to a subcarrier assigned by the parent station, and transmitting the uplink signal to the parent station and,
Run
Wherein the upstream signal from the master station to the parent station from the downlink signal and said one slave station to at least one child station of the plurality of slave stations is transmitted simultaneously in the same sub-carrier, the uplink The demodulating means performs demodulation processing on the signal after the signal component of the downlink signal corresponding to the subcarrier assigned to the at least one slave station is removed from the received uplink signal, and the at least one slave station The downlink demodulation means performs demodulation processing on the signal after removing the signal component of the uplink signal from the received downlink signal,
A communication method characterized by the above.   In a communication system having a plurality of subcarriers, a communication method in a communication device that performs communication with one or more devices using the assigned subcarriers,
  A transmission means generates a transmission signal to be transmitted to the one or more devices by mapping transmission data to each of the plurality of subcarriers based on the allocation of the subcarriers, and transmits the transmission signal to the one of the plurality of subcarriers. A transmission step for transmitting to the above devices;
  A receiving step in which receiving means receives signals from the one or more devices;
  A demodulation step in which the demodulation means demodulates the received signal;
  With
  Simultaneously in the same subcarrier, the transmission signal is transmitted to one or more devices in the transmission step, and the reception signal is received from the device in the reception step. The demodulation step is a sub-assignment assigned to the device. Demodulating the signal after removing the signal component of the transmission signal corresponding to the carrier from the reception signal,
  A communication method characterized by the above.

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