JP2008067171A - Radio communication system, base station, radio communication terminal and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control retransmission without reducing throughput as far as possible by preventing packet errors or useless retransmission during packet communication between a base station and a wireless communication terminal. <P>SOLUTION: The radio communication system is provided with a first error detection means which detects whether there are errors in a reception packet which is subjected to error correction processing after performing the error correction processing for the reception packet, a second error detection means which detects errors in the reception packet further subjected to error correction processing after the first error detection means, a second retransmission request means which requests for retransmission of the same packet as the reception packet to the sender according to the result of the second error correction, and a retransmission means which retransmits the same packet as the reception packet by the sender in response to the request. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

 The present invention relates to a wireless communication system, a base station, a wireless communication terminal, and a wireless communication method.

 In recent years, wireless communication systems that perform packet communication using OFDMA (Orthogonal Frequency Division Multiple Access) as a multiple access technology in addition to TDMA (Time Division Multiple Access) / TDD (Time Division Duplex) have become the next generation broadband mobiles. It is attracting attention as a communication system.

  In such a next-generation broadband mobile communication system, in order to maintain a high communication speed, H-ARQ (Hybrid) is used as an automatic retransmission control system that efficiently compensates for packet errors that occur in a radio section with a short control delay time. -Automatic Repeat reQuest) is adopted. Hereinafter, operations of the base station and the radio communication terminal regarding the H-ARQ will be described. In the following description, the base station is the transmitting side, the wireless communication terminal is the receiving side, and the packet combining type Type 1 method (Chase combining method) is exemplified as H-ARQ.

  First, the radio communication terminal performs error correction decoding processing on the received packet received from the base station, and then performs error detection on the received packet using a CRC (Cyclic Redundancy Check) code added to the received packet. Here, when an error is detected in the received packet, the wireless communication terminal stores the received packet in which the error is detected in a reception buffer provided therein, and sends a retransmission request signal (NACK: Negative ACKnowledgement) to the base station. ) Over the control channel. When receiving the NACK signal, the base station retransmits the packet requested for retransmission (that is, the same packet as the received packet in which an error is detected) to the wireless communication terminal at a predetermined timing.

 Then, the wireless communication terminal performs maximum ratio combining between the retransmission packet and the previous received packet (packet in which an error is detected) stored in the reception buffer, and performs error correction decoding processing on the retransmission packet that has been combined with the maximum ratio. In the same manner as described above, error detection is performed using a CRC code. Here, when an error is detected again in the retransmission packet, the same operation as described above is performed between the wireless communication terminal and the base station. Specifically, when an error is detected again in the retransmission packet, the maximum ratio combined data of the first received packet and the first retransmission packet is stored in the reception buffer, and when the second retransmission packet is received The maximum ratio combining between the maximum ratio combining data and the second retransmission packet is performed. When no CRC code error is detected in the received packet or retransmission packet, the wireless communication terminal transmits an ACK (ACKnowledgement) signal to the base station using the control channel, and the base station receives the ACK signal. The next packet is transmitted to the wireless communication terminal.

  According to such H-ARQ, since the maximum ratio combining of the received packet in which the previous error was detected and the retransmission packet is performed, a received signal with a high gain can be obtained. As a result, the desired wave SINR ( Since the signal to interference and noise ratio is improved, packet errors can be effectively compensated.

  The H-ARQ is a function mainly provided in the physical layer. As an automatic retransmission control method provided in the MAC (Media Access Control) layer, a Stop-and-wait method, a Go-back-N method, a Selective-repeat method. There is a MAC-ARQ such as a scheme.

In this MAC-ARQ, the stop-and-wait method is a method in which the transmitting side transmits a NACK signal or an ACK signal every time the transmitting side transmits one packet, and when the transmitting side receives the NACK signal, the transmitting side transmits the previous time. When the received packet is retransmitted and an ACK signal is received, the next packet is transmitted. The Go-back-N scheme is a scheme in which the transmitting side continuously transmits N packets, and when a retransmission request (NACK signal) is received from the receiving side, all packets after the packet requested for retransmission are retransmitted. It is. The selective-repeat scheme is a scheme in which, when the transmission side continuously transmits N packets and receives a retransmission request (NACK signal) from the reception side, only the packet requested for retransmission is retransmitted.
JP 2003-319464 A

 By the way, as described above, in H-ARQ, a received signal with a high gain can be obtained at the time of retransmission, so that a modulation method with a relatively high transmission rate can be used, thereby increasing the communication speed to the maximum. Yes. In addition, the number of data bits indicating the NACK signal or the ACK signal in the control signal is assigned to one bit of the frame header to suppress redundancy, thereby securing the payload portion and improving the throughput. The data bits indicating the NACK signal or the ACK signal are not used as CRC target data.

 Therefore, when H-ARQ is adopted, each communication bit may be inverted if the communication quality of the control channel deteriorates due to deterioration of the communication environment, but the data bit indicating whether it is a NACK signal or an ACK signal is 1 bit. Therefore, when this data bit is inverted, there is a possibility that the transmitting side may be mistaken for an ACK signal even though the receiving side has transmitted a NACK signal. In this case, there is a problem that a packet error occurs because the transmitting side transmits the next packet without performing retransmission. On the contrary, there is a possibility that the ACK signal is mistaken as a NACK signal, and in this case, useless retransmission occurs.

  The present invention has been made in view of the above-described circumstances, and in packet communication between a base station and a wireless communication terminal, retransmission control that prevents occurrence of packet errors or wasteful retransmission and reduces throughput as much as possible. The purpose is to do.

 In order to achieve the above object, according to the present invention, as a first means for solving a radio communication system, packet communication is performed between radio communication devices, and each of the radio communication devices determines whether or not there is an error in the received packet. In a communication system having an error detection means for detecting the error and a packet retransmission means for retransmitting the packet when the error is detected, the error correction process is performed on the received packet. A first error detecting means for detecting whether or not there is an error in the received packet; and a second error for detecting an error in the received packet that has undergone the error correction processing after the first error detecting means. Detection means; second retransmission request means for requesting retransmission of the same packet as the received packet to the transmission side according to the second error detection result; and transmission in response to the request There characterized in that it comprises a retransmission means for retransmitting the same packet as the received packet.

 Further, according to the present invention, as the second solving means relating to the radio communication system, the first solving means includes scheduling means for determining the transmission order of the packets, and retransmits the transmission packet using the retransmission means. When transmission is performed, the transmission unit determines the transmission order of the transmission packets, and retransmits the transmission packets using the retransmission unit.

 Further, in the present invention, as a third solving means relating to a wireless communication system, in the first or second solving means, the packet communication is communicated between wireless communication devices by an OFDMA method, and the packet communication is communicated. A channel allocating unit for allocating a communication channel for performing retransmission, and when retransmitting the transmission packet using the retransmission unit, the channel allocating unit is different from the communication channel that transmitted the packet before the retransmission. A communication channel is assigned to retransmission of a packet using the retransmission means.

 Further, in the present invention, as a fourth solving means relating to a radio communication system, in any one of the first to third solving means, the packet communication is communicated between radio communication devices by an OFDMA method, and the packet When the communication includes a modulation scheme determining means for determining a modulation scheme for performing communication, and the retransmission means retransmits the transmission packet, the modulation scheme determination means transmits the packet before the retransmission. A modulation scheme for retransmission of a packet using the retransmission means is determined so that a modulation scheme different from the modulation scheme described above is obtained.

 In the present invention, as a fifth solving means relating to the radio communication system, in the fourth solving means, the modulation scheme determining means determines the modulation determined at the time of retransmission of the packet using the retransmission means. The method is characterized in that the method is determined so as to be a modulation method having a lower transmission rate than the modulation method in which the packet is transmitted before the retransmission.

 On the other hand, in the present invention, as a first solving means related to the base station, after performing packet communication and performing error correction processing on the received packet, whether or not the received packet subjected to the error correction processing has an error is determined. First error detecting means for detecting, second error detecting means for detecting an error of the received packet subjected to the error correction processing after the first error detecting means, and the second error detecting In response to a request for retransmission of the packet from a wireless communication terminal having retransmission request means for requesting retransmission of the same packet as the received packet according to the result, the same packet as the received packet is retransmitted Retransmission means is provided.

 In the present invention, as the second solving means for the base station, the first solving means includes scheduling means for determining the transmission order of the packets, and retransmits the transmission packet using the retransmission means. When performing the transmission, the transmission packet transmission order is determined by the scheduling unit, and the retransmission packet is retransmitted using the retransmission unit.

 Further, in the present invention, as a third solving means relating to a base station, in the first or second solving means, the packet communication is communicated between the base station and the wireless communication terminal by an OFDMA method, In the case where a packet allocating means for allocating a communication channel for performing packet communication and retransmitting the transmission packet using the retransmitting means, the channel allocating means transmits the packet before the retransmission. A communication channel different from the channel is assigned to retransmission of a packet using the retransmission means.

 Further, in the present invention, as a fourth solving means relating to the base station, in any one of the first to third solving means, the packet communication is performed between the base station and the wireless communication terminal using the OFDMA method. And a modulation scheme determining means for determining a modulation scheme in which the packet communication communicates, and when retransmitting the transmission packet using the retransmission means, the modulation scheme determining means The modulation scheme for retransmission of the packet using the retransmission means is determined so that the modulation scheme is different from the modulation scheme for transmitting the packet.

 Further, in the present invention, as a fifth solving means relating to a base station, in the fourth solving means, the modulation scheme determining means determines the modulation scheme to be determined when retransmitting a packet using the retransmission means. Is determined to be a modulation scheme having a lower transmission rate than the modulation scheme that transmitted the packet before the retransmission.

 On the other hand, in the present invention, as a first solving means for the wireless communication terminal, whether or not there is an error in the received packet after performing packet communication and performing error correction processing on the received packet, First error detecting means for detecting the error, second error detecting means for detecting an error in the received packet subjected to the error correction processing after the first error detecting means, and the second error It further comprises retransmission request means for requesting the base station to retransmit the same packet as the received packet according to the detection result.

 Further, in the present invention, as means for solving the wireless communication method, when packet communication is performed between wireless communication devices, each of the wireless communication devices detects whether there is an error in the received packet, and when the error is detected In the communication method for retransmitting the packet, after the error correction process is performed on the received packet, the first step of detecting whether the received packet subjected to the error correction process has an error; After the step, a second step of detecting an error of the received packet that has been subjected to the error correction processing, and a retransmission of the same packet as the received packet to the transmitting side according to the error detection result of the second step A third step of making a request and a fourth step in which the transmitting side retransmits the same packet as the received packet in response to the request.

  According to the present invention, in packet communication between a base station and a radio communication terminal, it is possible to prevent occurrence of a packet error and useless retransmission processing, and to perform retransmission control without reducing throughput.

 Hereinafter, a wireless communication system, a base station, a wireless communication terminal, and a wireless communication method according to an embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the radio communication system of this embodiment includes a base station CS, a radio communication terminal PS, and a network (not shown). The base station CS and the radio communication terminal PS are time division multiple access (TDMA), time division. Communication is performed using orthogonal frequency division multiple access (OFDMA) in addition to duplex (TDD) as a multiple access technique. A plurality of base stations CS are provided at fixed distance intervals, and perform radio communication by performing multiple connections with a plurality of radio communication terminals PS. Hereinafter, a case where the base station CS is the transmitting side and the wireless communication terminal PS is the receiving side will be described as an example.

 As is well known, OFDMA means that all subcarriers in an orthogonal relationship are shared by all radio communication terminals PS, a group of arbitrary subcarriers is positioned as one group, and one or each radio communication terminal PS This technique realizes multiple access by adaptively assigning a plurality of groups. In the wireless communication system of this embodiment, the above-described OFDMA technology is further combined with a time division multiple access (TDMA) and time division duplex (TDD) technology. That is, each group is divided into uplink and downlink in the time axis direction as TDD, and the uplink and downlink are further divided into four TDMA slots. In this embodiment, one unit obtained by dividing each group as a TDMA slot in the time axis direction is called a subchannel. FIG. 2 shows the relationship among frequencies, TDMA slots, and subchannels in the wireless communication system of this embodiment. The vertical axis represents frequency and the horizontal axis represents time. As shown in FIG. 2, 112 subchannels obtained by multiplying 28 frequency directions and 4 time axis directions (4 slots) are allocated for uplink and downlink, respectively.

 In the wireless communication system of the present embodiment, as shown in FIG. 2, the most subchannel in the frequency direction (number 1 in FIG. 2) is used as a control channel (CCH) among all the subchannels, and the remaining subchannels are used. The channel is used as a traffic subchannel (TCH). Then, the base station CS and the radio communication terminal PS that perform radio communication include all of the traffic subchannels belonging to each of the uplink and downlink (in this case, 108 subchannels of 27 × 4 slots excluding CCH). Any one or more traffic subchannels are assigned. The same traffic subchannel is assigned to the uplink and downlink traffic subchannels as communication channels.

  FIG. 3 is a block diagram showing the main configuration of the base station CS and the radio communication terminal PS in the present embodiment. As shown in FIG. 3, the base station CS includes a QoS (Quality Of Service) control unit 1, a scheduler 2, a communication management unit 3, a bandwidth allocation unit 4, and a MAC-PDU (Media Access Control-Protocol Data Unit) construction unit 5. PHY-PDU (PHYsical-Protocol Data Unit) construction unit 6, error correction coding unit 7, modulation unit 8, transmission unit 9, reception unit 10, demodulation unit 11, error correction decoding unit 12, PHY-PDU analysis unit 13 A retransmission control unit 14 and a data reconstruction unit 15. The PHY-PDU analysis unit 13 includes an H-ARQ response determination unit 13a and a MAC-ARQ response determination unit 13b. The retransmission control unit 14 includes an H-ARQ control unit 14a and a MAC-ARQ control unit 14b. I have.

 In the base station CS, a QoS (Quality Of Service) control unit 1, a scheduler 2, a communication management unit 3, a bandwidth allocation unit 4, a MAC-PDU construction unit 5, a PHY-PDU construction unit 6, a PHY-PDU analysis unit 13 The retransmission control unit 14 and the data reconstruction unit 15 are functional components of the MAC (Media Access Control) layer. Also, the error correction coding unit 7, the modulation unit 8, the transmission unit 9, the reception unit 10, and the demodulation unit The unit 11 and the error correction decoding unit 12 are functional components of the physical layer. In FIG. 3, the configuration of the upper layer of the MAC layer is omitted.

 The QoS control unit 1 assigns priority to data (payload) input from the upper layer based on the user priority of the application operating in the upper layer and the wireless communication terminal PS connected to the communication, and a packet including the data That is, the scheduler 2 is controlled so as to assign transmission / reception timing of (ie, MAC-PDU).

 The scheduler 2 performs flow control of the MAC-PDU input from the QoS control unit 1, and under the control of the QoS control unit 1, the service class assigned to the wireless communication terminal PS to be connected and the base station The transmission order of packets to be transmitted is determined based on the queue state of packets (MAC-PDU) between the CS and the radio communication terminal PS. Further, the scheduler 2 determines the transmission order of retransmission packets based on an instruction from the retransmission control unit 14. The communication management unit 3 assigns a packet coding rate and a modulation method according to the communication quality with the wireless communication terminal PS connected for communication.

 The bandwidth allocating unit 4 assigns each packet based on the priority information from the QoS control unit 1, the information on the transmission data amount from the scheduler 2, the information on the communicable bandwidth, and the modulation method information from the communication management unit 3. The subchannel to be assigned is determined. This subchannel allocation information is called MAP information. The MAC-PDU constructing unit 5 appends a MAC header and a CRC code to the packet input from the scheduler 2 via the band allocating unit 4 to construct a MAC-PDU, and outputs the MAC-PDU to the PHY-PDU constructing unit 6.

  The PHY-PDU constructing unit 6 adds a physical layer header including control information such as MAP information, a coding rate, and a modulation method to the MAC-PDU output from the scheduler 2 at a predetermined timing (downlink slot). In addition, a PHY-PDU to be transmitted to the downlink, that is, the radio communication terminal PS is constructed, and a bit string of the PHY-PDU is output to the error correction encoding unit 7. The error correction coding unit 7 is, for example, an FEC (Forward Error Correction) encoder, and adds an error correction code, which is redundant information, to the bit string of the PHY-PDU based on the coding rate assigned by the communication management unit 3 And output to the modulation unit 8.

 FIG. 4 is a schematic configuration diagram of the modulation unit 8. As shown in FIG. 4, the modulation unit 8 includes an interleaver 8a, a serial-parallel conversion unit 8b, a digital modulation unit 8c, an IFFT (Inverse Fast Fourier Transform) unit 8d, and a GI (Guard Interval) addition unit 8e.

 The interleaver 8a performs an interleaving process on the bit string of the PHY-PDU to which the error correction code is added by the error correction encoding unit 7. The serial-parallel conversion unit 8b divides the bit sequence of the PHY-PDU after the interleaving process in units of bits for each subcarrier included in the subchannel allocated by the band allocation unit 4, and outputs the divided bit sequence to the digital modulation unit 8c. . The digital modulation units 8c are provided in the same number as the subcarriers, digitally modulate the bit data divided for each subcarrier using the subcarrier corresponding to the bit data, and output the modulation signal to the IFFT unit 8d To do. Each digital modulator 8c uses a modulation scheme assigned by the communication manager 3, such as BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), 64QAM, or the like. Perform digital modulation.

 The IFFT unit 8d generates an OFDM signal by performing inverse Fourier transform and orthogonal multiplexing on the modulation signal input from each digital modulation unit 8c, and outputs the OFDM signal to the GI adding unit 8e. The GI adding unit 8e adds a guard interval (GI) to the OFDM signal input from the IFFT unit 8d and outputs the signal to the transmitting unit 9.

 Returning to FIG. 3, the description will be continued. The transmission unit 9 converts the OFDM signal input from the GI addition unit 8e into an RF signal and transmits the RF signal to the radio communication terminal PS. The receiving unit 10 receives an RF signal transmitted from the radio communication terminal PS, converts the frequency of the RF signal into an OFDM signal, and outputs the signal to the demodulation unit 11.

 The demodulator 11 demodulates the OFDM signal (that is, the received signal) input from the receiver 10. Specifically, the demodulator 11 demodulates the received signal by performing reverse processing on the modulator 8. That is, the demodulator 11 first removes the guard interval from the received signal and performs FFT processing to divide it into modulated signals for each subcarrier, and then performs digital demodulation on each modulated signal and obtains it by the demodulation. The bit data is subjected to parallel-serial conversion and deinterleaver processing to reconstruct a bit string. This reconstructed bit string is a bit string indicating the PHY-PDU received from the radio communication terminal PS.

 The error correction decoding unit 12 is, for example, an FEC decoder, performs error correction decoding on the bit string of the received PHY-PDU input from the demodulation unit 11, and outputs the error corrected bit string to the PHY-PDU analysis unit 13. . The PHY-PDU analysis unit 13 analyzes the bit string of the received PHY-PDU, extracts various control information included in the physical layer header and MAC header, extracts the payload that is data information, and the like, and also extracts the MAC-PDU. The data is extracted and output to the data reconstruction unit 15. In the present embodiment, the H-ARQ response determination unit 13a and the MAC-ARQ response determination unit 13b among the functional elements in the PHY-PDU analysis unit 13 will be described.

 As a result of analysis of the received PHY-PDU, the H-ARQ response determination unit 13a determines whether the received PHY-PDU is an ACK signal or NACK signal related to H-ARQ, and uses the determination result as the H-ARQ of the retransmission control unit 14. It outputs to the control part 14a. Further, as a result of analyzing the received PHY-PDU, the MAC-ARQ response determining unit 13b determines whether the received PHY-PDU is an ACK signal or a NACK signal related to MAC-ARQ, and uses the determination result as the MAC of the retransmission control unit 14. -Output to ARQ control unit 14b.

 When the received PHY-PDU is a NACK signal related to H-ARQ based on the determination result of the H-ARQ response determination unit 13a, the H-ARQ control unit 14a receives a packet (MAC -PDU) is retransmitted by the H-ARQ method, the scheduler 2 is controlled. Further, when the received PHY-PDU is an ACK signal related to H-ARQ, the H-ARQ control unit 14a wirelessly transmits the next packet (MAC-PDU) based on the determination result of the H-ARQ response determination unit 13a. The scheduler 2 is controlled to transmit to the communication terminal PS.

 When the received PHY-PDU is a NACK signal related to MAC-ARQ based on the determination result of the MAC-ARQ response determination unit 13b, the MAC-ARQ control unit 14b receives a packet (MAC -PDU) is retransmitted by the MAC-ARQ method, the scheduler 2 is controlled. Further, based on the determination result of the MAC-ARQ response determination unit 13b, the MAC-ARQ control unit 14b wirelessly communicates the next packet (MAC-PDU) when the received PHY-PDU is an ACK signal related to MAC-ARQ. The scheduler 2 is controlled to transmit to the terminal PS.

 Here, retransmission in the H-ARQ scheme means that a retransmission packet is transmitted with the same subchannel, modulation scheme and coding rate as when a CRC error detected packet is transmitted on the receiving side, that is, the radio communication terminal PS. It is a way to do. The reason for this is that retransmission control using H-ARQ performs maximum ratio combining of a packet in which a CRC error is detected on the receiving side and the retransmission packet, so that the retransmission packet has the same subchannel (that is, frequency band) as the previously transmitted packet. This is because it is necessary to use a modulation scheme and a coding rate. On the other hand, retransmission by the MAC-ARQ method is a method of retransmitting a previously transmitted packet. When retransmitting a retransmitted packet, the subchannel may be changed or the modulation method may be changed with respect to the previous transmission. it can.

  The data reconstruction unit 15 rearranges the order of one group of MAC-PDUs input from the PHY-PDU analysis unit 13, and then removes the MAC header and CRC code of each MAC-PDU for the one group. The upper layer data (payload) is output to the upper layer.

  Next, the configuration of the wireless communication terminal PS will be described. As shown in FIG. 1, the radio communication terminal PS includes a receiving unit 20, a demodulating unit 21, a maximum ratio combining unit 22, an error correction decoding unit 23, a receiving buffer 24, a CRC detecting unit 25, an H-ARQ retransmission request unit 26, PHY-PDU analysis unit 27, data reconstruction unit 28, data order determination unit 29, MAC-ARQ retransmission request unit 30, MAC-PDU construction unit 31, PHY-PDU construction unit 32, error correction coding unit 33, modulation unit 34 and a transmission unit 35. In addition, the PHY-PDU analysis unit 27 includes a retransmission method change detection unit 27a.

 The reception unit 20 receives the RF signal transmitted from the transmission unit 7 of the base station CS, converts the frequency of the RF signal into an OFDMA signal, and outputs the OFDM signal to the demodulation unit 21. Since the demodulator 21 is the same component as the demodulator 11 of the base station CS, the description is omitted.

 The maximum ratio combining unit 22 includes the bit string indicating the received PHY-PDU (retransmitted PHY-PDU) input from the demodulating unit 21 and the received PHY-PDU in which the previous CRC error stored in the reception buffer 24 is detected. The maximum ratio combining with the bit string is performed, and the maximum ratio combining bit string is output to the error correction decoding unit 23 and the reception buffer 24. When a PHY-PDU other than the retransmission PHY-PDU is received, the maximum ratio combining unit 22 outputs the received PHY-PDU to the error correction decoding unit 23 and the reception buffer 24 without performing the maximum ratio combining.

 Since the error correction decoding unit 23 is the same component as the error correction decoding unit 12 of the base station CS, description thereof is omitted. The reception buffer 24 stores the received PHY-PDU (that is, the PHY-PDU in which a CRC error is detected) input from the maximum ratio combining unit 22 in response to a request from the CRC detection unit 25, while the maximum ratio combining unit 22 In response to the request, the stored received PHY-PDU is output to the maximum ratio combining unit 22. The CRC detection unit 25 performs CRC error detection of the received PHY-PDU that has been error-corrected and decoded by the error correction decoding unit 23, and requests a reception buffer 24 to store the received PHY-PDU when a CRC error is detected. At the same time, it notifies the H-ARQ retransmission request unit 26 that a CRC error has been detected. Also, the CRC detection unit 25 outputs the received PHY-PDU to the PHY-PDU analysis unit 27.

 When notified from the CRC detection unit 25 that a CRC error has been detected in the received PHY-PDU, the H-ARQ retransmission request unit 26 generates a PHY-PDU indicating a NACK signal related to H-ARQ, The NACK signal is transmitted to the base station CS via the modulation unit 34 and the transmission unit 35 using the ACK channel. Further, when the CRC detection unit 25 notifies that the CRC error is not detected in the received PHY-PDU, the H-ARQ retransmission request unit 26 generates a PHY-PDU indicating an ACK signal related to H-ARQ. The ACK signal is transmitted to the base station CS via the modulation unit 34 and the transmission unit 35 using the ACK channel.

 The PHY-PDU analysis unit 27 is the same as the PHY-PDU analysis unit 13 of the base station CS. Here, the retransmission method change detection unit 27a which is a characteristic functional element on the reception side will be described. When the retransmission method change detection unit 27a detects that the retransmission control method has been changed from H-ARQ to MAC-ARQ as a result of the analysis of the received PHY-PDU, the maximum ratio combining unit 22, the reception buffer 24, and the CRC detection unit 25, and requests to stop the operation of the H-ARQ retransmission request unit 26. The retransmission scheme change detection unit 27a detects that the modulation scheme identifier (MI: Modulation Indicator) has changed during retransmission in the control information included in the received PHY-PDU, so that the retransmission scheme has been changed. Detect that.

 In the stopped state, the maximum ratio combining unit 22 and the CRC detecting unit 25 only pass the received PHY-PDU, and the receiving buffer 24 and the H-ARQ retransmission requesting unit 26 temporarily suspend the operation. That is, the characteristic operation of H-ARQ is not performed.

 Since the data reconstruction unit 28 is the same component as the data reconstruction unit 15 of the base station CS, the description thereof is omitted. The data order determination unit 29 detects the packet error by determining the order of one group of MAC-PDUs received from the base station CS, and notifies the MAC-ARQ retransmission request unit 30 of the detection result. When a packet error is detected based on the packet error detection result, the MAC-ARQ retransmission request unit 30 generates a MAC-PDU indicating a NACK signal related to MAC-ARQ, and uses the ACK channel to generate a PHY- The NACK signal is transmitted to the base station CS via the PDU construction unit 32, the error correction coding unit 33, the modulation unit 34, and the transmission unit 35. Further, the MAC-ARQ retransmission request unit 30 generates a MAC-PDU indicating an ACK signal related to MAC-ARQ based on the detection result of the packet error, and uses the ACK channel. Then, the ACK signal is transmitted to the base station CS via the PHY-PDU construction unit 32, the error correction coding unit 33, the modulation unit 34, and the transmission unit 35.

 The MAC-PDU construction unit 31, the PHY-PDU construction unit 32, the error correction coding unit 33, the modulation unit 34, and the transmission unit 35 are the MAC-PDU construction unit 5, the PHY-PDU construction unit 6, and the error in the base station CS. Since the components are the same as those of the correction encoding unit 7, the modulation unit 8, and the transmission unit 9, the description thereof is omitted.

 In FIG. 3, for convenience of explanation, the case where the base station CS is assumed to be the transmitting side and the wireless communication terminal PS is assumed to be the receiving side is illustrated. However, since the wireless communication is bidirectional, the base station CS A component of the terminal PS is provided, and the wireless communication terminal PS includes a component of the base station CS. However, since the QoS control unit 1, the scheduler 2, the communication management unit 3, and the bandwidth allocation unit 4 in the base station CS are components unique to the base station CS, the radio communication terminal PS does not include them. For this reason, when the transmitting side is the radio communication terminal PS, the base station CS notifies the radio communication terminal PS of the assignment of subchannels, modulation schemes and coding rates to be used at the time of retransmission.

 Next, a communication operation between the base station CS and the radio communication terminal PS in the radio communication system configured as described above will be described with reference to the sequence chart of FIG. In the following description, it is assumed that the base station CS is the transmitting side and the radio communication terminal PS is the receiving side. Further, it is assumed that four packets from the base station CS to MAC-PDU1 (PHY-PDU1) to MAC-PDU4 (PHY-PDU4) are transmitted to the radio communication terminal PS as a data set for one group.

 In FIG. 5, first, the base station CS transmits the PHY-PDU 1 via the transmission unit 9 using the subchannel, modulation scheme, and coding rate that are scheduled in advance when establishing a communication connection with the radio communication terminal PS. Transmit to the radio communication terminal PS (step S1). The radio communication terminal PS receives the PHY-PDU 1 via the receiving unit 20, and the PHY-PDU 1 is demodulated by the demodulating unit 21 and then output to the maximum ratio combining unit 22. At this time, since the PHY-PDU 1 is not a retransmission packet, the PHY-PDU 1 is input to the CRC detection unit 25 via the error correction decoding unit 23 without being subjected to maximum ratio combining.

 Here, assuming that the CRC detection unit 25 performs CRC error detection of the PHY-PDU 1 and no CRC error is detected, the H-ARQ retransmission request unit 26 includes a PHY-PDU indicating an ACK signal related to H-ARQ. And transmits the ACK signal to the base station CS via the modulation unit 34 and the transmission unit 35 using the ACK channel (step S2). On the other hand, the PHY-PDU 1 is input to the data reconstruction unit 28 via the PHY-PDU analysis unit 27.

 The base station CS receives the ACK signal related to the H-ARQ from the radio communication terminal PS via the reception unit 10, and the ACK signal is received from the PHY-PDU analysis unit 13 via the demodulation unit 11 and the error correction decoding unit 12. Is input. In this PHY-PDU analysis unit 13, the H-ARQ response determination unit 13a determines that the received PHY-PDU is an ACK signal related to H-ARQ as a result of analysis of the received PHY-PDU indicating the ACK signal. The determination result is output to the H-ARQ control unit 14a of the retransmission control unit 14. Based on the determination result of the H-ARQ response determination unit 14a, the H-ARQ control unit 14a transmits the next packet (MAC-PDU2) to the radio communication terminal PS because the received PHY-PDU is an ACK signal related to H-ARQ. The scheduler 2 is controlled to transmit to Thereby, the base station CS transmits the next packet (MAC-PDU2) on the predetermined downlink subchannel as the PHY-PDU2 to the radio communication terminal PS (step S3).

 The radio communication terminal PS receives the PHY-PDU 2 via the receiving unit 20, and the PHY-PDU 2 is demodulated by the demodulating unit 21 and then output to the maximum ratio combining unit 22. At this time, since the PHY-PDU 2 is not a retransmission packet, the PHY-PDU 2 is input to the CRC detection unit 25 via the error correction decoding unit 23 without being subjected to maximum ratio combining.

 Here, assuming that the CRC detection unit 25 performs CRC error detection of the PHY-PDU 2 and a CRC error is detected, the H-ARQ retransmission request unit 26 transmits a PHY-PDU indicating a NACK signal related to H-ARQ. The NACK signal is generated and transmitted to the base station CS via the modulator 34 and the transmitter 35 using the ACK channel (step S4). At this time, the reception buffer 24 stores the PHY-PDU 2 in which a CRC error is detected in response to a request from the CRC detection unit 25. In this case, the PHY-PDU 2 in which the CRC error is detected is not sent to the PHY-PDU analysis unit 27, which is an upper layer.

 The base station CS receives the NACK signal related to the H-ARQ from the radio communication terminal PS via the reception unit 10, and the NACK signal is received from the PHY-PDU analysis unit 13 via the demodulation unit 11 and the error correction decoding unit 12. Is input. In the PHY-PDU analysis unit 13, the H-ARQ response determination unit 13a determines that the received PHY-PDU is a NACK signal related to H-ARQ as a result of analysis of the received PHY-PDU indicating the NACK signal. The determination result is output to the H-ARQ control unit 14a of the retransmission control unit 14. Based on the determination result of the H-ARQ response determination unit 13a, the H-ARQ control unit 14a receives a packet (MAC) that has been requested to be retransmitted from the radio communication terminal PS because the received PHY-PDU is a NACK signal related to H-ARQ. -Schedule 2 is controlled to retransmit PDU2) by the H-ARQ method. Thereby, the base station CS transmits a retransmission packet (MAC-PDU2) as a retransmission PHY-PDU2 to the radio communication terminal PS in a predetermined downlink slot (step S5). Here, the same subchannel, modulation scheme, and coding rate as the PHY-PDU 2 in which the previous CRC error was detected are used for transmission of the retransmission PHY-PDU 2.

 The radio communication terminal PS receives the retransmission PHY-PDU 2 via the reception unit 20, and the retransmission PHY-PDU 2 is demodulated by the demodulation unit 21 and then output to the maximum ratio combining unit 22. Here, the maximum ratio combining unit 22 performs maximum ratio combining between the retransmission PHY-PDU 2 and the PHY-PDU 2 in which the previous CRC error stored in the reception buffer 24 is detected, and error correction decoding is performed on the maximum ratio combining bit string. Output to the unit 23 and the reception buffer 24. Here, assuming that the CRC detection unit 25 performs CRC error detection of the maximum ratio combined bit string and no CRC error is detected, the H-ARQ retransmission request unit 26 includes a PHY signal indicating an ACK signal related to H-ARQ. A PDU is generated, and the ACK signal is transmitted to the base station CS via the modulation unit 34 and the transmission unit 35 using the ACK channel (step S6). On the other hand, the maximum ratio combined bit string of the retransmission PHY-PDU 2 is input to the data reconstruction unit 28 via the PHY-PDU analysis unit 27.

 When receiving the ACK signal from the radio communication terminal PS, the base station CS transmits the next packet (MAC-PDU3) to the radio communication terminal PS as a PHY-PDU3 in a predetermined downlink slot, as in step S3. Step S7). Then, similarly to step S4, the wireless communication terminal PS assumes that a CRC error has been detected in the received PHY-PDU 3 and has transmitted a NACK signal to the base station CS (step S8).

 In this step S8, it is assumed that the communication quality of the ACK channel deteriorates and the data bit indicating the NACK signal is inverted, that is, the NACK signal is erroneously recognized as an ACK signal in the base station CS. In this case, the base station CS transmits the next packet (MAC-PDU4) to the radio communication terminal PS as a PHY-PDU4 in a predetermined downlink slot, similarly to step S3 (step S9).

 In the radio communication terminal PS, the received PHY-PDU 4 is not a retransmission packet, and is input to the CRC detection unit 25 without being subjected to maximum ratio combining. Here, assuming that the CRC detection unit 25 performs CRC error detection of the received PHY-PDU 4 and no CRC error is detected, the H-ARQ retransmission request unit 26 includes a PHY- that indicates an ACK signal related to H-ARQ. A PDU is generated, and the ACK signal is transmitted to the base station CS via the modulation unit 34 and the transmission unit 35 using the ACK channel (step S10).

 On the other hand, the received PHY-PDU 4 is input to the data reconstruction unit 28 via the PHY-PDU analysis unit 27. Therefore, at this time, the data reconstruction unit 28 receives four packets of MAC-PDU1, MAC-PDU2, MAC-PDU3 and MAC-PDU4 including an error, and rearranges the order of one group of the MAC-PDU. When MAC is performed, a state in which the MAC-PDU 3 is lost, that is, a packet error occurs.

 The data order determination unit 29 detects the packet error by determining the order of the MAC-PDUs for one group, and notifies the MAC-ARQ retransmission request unit 30 of the detection result (step S11). Based on the detection result of the packet error, the MAC-ARQ retransmission request unit 30 generates a MAC-PDU indicating a NACK signal (MAC-PDU3 retransmission request) related to MAC-ARQ when a packet error is detected, The NACK signal related to the MAC-ARQ is transmitted to the base station CS through the PHY-PDU construction unit 32, the error correction coding unit 33, the modulation unit 34, and the transmission unit 35 using the ACK channel (step S12).

 The base station CS receives the NACK signal related to the MAC-ARQ from the radio communication terminal PS via the reception unit 10, and the NACK signal is received from the PHY-PDU analysis unit 13 via the demodulation unit 11 and the error correction decoding unit 12. Is input. In the PHY-PDU analysis unit 13, the MAC-ARQ response determination unit 13b determines that the received PHY-PDU is a NACK signal related to MAC-ARQ as a result of analysis of the received PHY-PDU indicating the NACK signal. The determination result is output to the MAC-ARQ control unit 14b of the retransmission control unit 14. Based on the determination result of the MAC-ARQ response determination unit 13b, the MAC-ARQ control unit 14b receives a packet (MAC) for which a retransmission request has been received from the radio communication terminal PS because the received PHY-PDU is a NACK signal related to MAC-ARQ. The scheduler 2 is controlled to retransmit the -PDU3) by the MAC-ARQ method (step S13).

 In retransmission using the MAC-ARQ scheme, the scheduler 2 assigns downlink slots so as to delay the transmission timing of the retransmission packet (MAC-PDU 3) by a predetermined time (specifically, wait for the traffic queue in order). I do. Further, the bandwidth allocating unit 4 allocates a subchannel different from the previous transmission of the MAC-PDU 3 to the retransmission packet, and the communication management unit 3 allocates a modulation scheme having a low transmission rate to the retransmission packet.

 As described above, by delaying the transmission timing of the retransmission packet (MAC-PDU3), communication quality improvement (time diversity effect) over time can be expected. Therefore, successful reception of the retransmission packet and successful reception of the NACK signal The possibility increases. Further, by using the MAC-ARQ method, a modulation method different from the previous transmission of the MAC-PDU 3 can be used. Therefore, a modulation method having a low transmission rate (that is, strong against deterioration in communication quality) is used as a retransmission packet. By allocating, it can be expected that the retransmission packet is successfully received and the NACK signal is successfully received.

 Furthermore, by assigning a subchannel different from the previous transmission of MAC-PDU 3, it is possible to expect an improvement in communication quality (frequency diversity effect), improving the possibility of successful reception of retransmission packets and successful reception of NACK signals. Can contribute. Thus, when allocating a subchannel different from the previous transmission of MAC-PDU 3, after the base station CS receives a bandwidth allocation request from the radio communication terminal PS, the base station CS performs uplink carrier sense and performs SINR. It is desirable to preferentially assign subchannels having a high value.

 That is, if it is assumed that the uplink reception level is the same among users by uplink transmission output control, it can be considered that the reception level is the same between subchannels. Therefore, a subchannel with a high SINR aggregated for each subchannel is considered to have a low interference level (good communication quality). From the above, subchannels with high SINR are preferentially assigned to retransmission packets. At the time of SINR measurement, SINR aggregated in units of subchannels is used for determination without being aware of the user. In addition, SINR uses an average value for a certain period, and old SINR is not used.

 Then, the base station CS transmits a control PHY-PDU to which a physical layer header including control information such as MAP information indicating a subchannel for a retransmission packet determined as described above and a coding rate and a modulation scheme is added. It is constructed and transmitted to the radio communication terminal PS (step S14).

 In the wireless communication terminal PS, the retransmission scheme change detection unit 27a detects that the retransmission control scheme has been changed from H-ARQ to MAC-ARQ as a result of the analysis of the control PHY-PDU received in step S14. The maximum ratio combining unit 22, the reception buffer 24, the CRC detecting unit 25, and the H-ARQ retransmission requesting unit 26 are requested to shift to an operation stop state (step S15).

 Then, when the transmission timing of the retransmission packet (MAC-PDU3) arrives, the base station CS wirelessly transmits the MAC-PDU3 (PHY-PDU3) using the subchannel determined in step S13 and the modulation scheme having a low transmission rate. Transmit to the communication terminal PS (step S16). In the radio communication terminal PS, the maximum ratio combining unit 22, the reception buffer 24, the CRC detection unit 25, and the H-ARQ retransmission request unit 26 are in an operation stop state, so that the received PHY-PDU 3 is characteristic of H-ARQ. The data is input to the data order determination unit 29 via the PHY-PDU analysis unit 27 and the data reconstruction unit 28 without being subjected to any special processing.

 Here, when it is assumed that the PHY-PDU 3 has been successfully received and the retransmitted MAC-PDU 3 is successfully grouped with the MAC-PDU 1, MAC-PDU 2, and MAC-PDU 4 already received, the data order determination is performed. The unit 29 notifies the MAC-ARQ retransmission request unit 30 that no packet error has been detected (step S17). The MAC-ARQ retransmission request unit 30 generates a MAC-PDU indicating an ACK signal related to MAC-ARQ, and uses the ACK channel to generate a PHY-PDU construction unit 32, an error correction encoding unit 33, a modulation unit 34, and a transmission unit. An ACK signal related to the MAC-ARQ is transmitted to the base station CS via 35 (step S18). Then, the MAC-PDU1 to MAC-PDU4 that have been successfully grouped and rearranged without any packet error as described above are output to the upper layer (step S19).

 As described above, according to the wireless communication system including the base station CS and the wireless communication terminal PS in the present embodiment, by performing retransmission control using H-ARQ at first, A certain high communication speed, efficient packet error compensation is realized, and when packet quality occurs due to degradation of communication quality, switching to MAC-ARQ, retransmission packet transmission timing delay, subchannel change, modulation method It is possible to prevent the occurrence of a packet error by lowering the transmission rate and increasing the accuracy of successful reception of retransmission packets.

 In the above embodiment, when MAC-ARQ is used, the transmission timing delay of the retransmission packet, the change of the subchannel, and the reduction of the transmission rate of the modulation method are performed simultaneously. Even if only this is performed, the improvement in communication quality over time can be expected, so that there is an effect of preventing the occurrence of a packet error. However, in order to more reliably prevent the occurrence of packet errors, it is desirable to simultaneously change the subchannel and lower the modulation rate as in the above embodiment.

 In addition, when a packet error occurs while using H-ARQ, a configuration may be adopted in which retransmission is performed using H-ARQ with a time delay without using MAC-ARQ. Even with such a configuration, improvement in communication quality over time can be expected. However, in this case, since retransmission is performed using H-ARQ, the subchannel and the modulation scheme cannot be changed.

 In the above-described embodiment, the case where orthogonal frequency division multiple access (OFDMA) is employed in addition to time division multiple access (TDMA) and time division duplex (TDD) as the wireless communication system has been described as an example. The present wireless communication system is not limited to this, and any wireless communication system that uses H-ARQ for retransmission control can be applied.

1 is a schematic configuration diagram of a wireless communication system in an embodiment of the present invention. It is a schematic diagram which shows the relationship between the subchannel and slot of the radio | wireless communications system in one Embodiment of this invention. FIG. 2 is a configuration block diagram of a base station CS and a radio communication terminal PS in an embodiment of the present invention. It is a block diagram of the configuration of the modulation unit 8 in an embodiment of the present invention. It is a sequence chart of the radio | wireless communications system in one Embodiment of this invention.

Explanation of symbols

 CS ... base station, PS ... wireless communication terminal, 1 ... QoS control unit, 2 ... scheduler, 3 ... communication management unit, 4 ... bandwidth allocation unit, 5, 31 ... MAC-PDU construction unit, 6, 32 ... PHY-PDU Construction unit 7, 33 ... Error correction coding unit, 8, 34 ... Modulation unit, 9, 35 ... Transmission unit, 10, 20 ... Reception unit, 11, 21 ... Demodulation unit, 12, 23 ... Error correction decoding unit, DESCRIPTION OF SYMBOLS 13, 27 ... PHY-PDU analysis part, 13a ... H-ARQ response determination part, 13b ... MAC-ARQ response determination part, 14 ... Retransmission control part, 14a ... H-ARQ control part, 14b ... MAC-ARQ control part, DESCRIPTION OF SYMBOLS 15, 28 ... Data reconstruction part, 22 ... Maximum ratio synthetic | combination part, 24 ... Receive buffer, 25 ... CRC detection part, 26 ... H-ARQ retransmission request part, 27a ... Retransmission scheme change detection part, 29 ... Data order determination part 30 ... MAC-ARQ retransmission request part

Claims (12)

Packet communication is performed between wireless communication devices, and each of the wireless communication devices detects an error in the received packet, and packet retransmission for retransmitting the packet when the error is detected In a communication system comprising means,
First error detection means for detecting whether or not there is an error in the received packet that has been subjected to the error correction process after the error correction process has been performed on the received packet;
After the first error detection means, second error detection means for detecting an error of the received packet further subjected to the error correction processing;
Second retransmission request means for requesting the transmitter to retransmit the same packet as the received packet according to the second error detection result;
Retransmission means for retransmitting the same packet as the received packet in response to the request;
A wireless communication system comprising: Scheduling means for determining a transmission order of the packets;
When retransmitting the transmission packet using the retransmission means,
Determining the transmission order of the transmission packets by the scheduling means, and retransmitting the transmission packets using the retransmission means;
The communication system according to claim 1. The packet communication is communicated between the wireless communication devices by the OFDMA method,
Channel allocating means for allocating a communication channel in which the packet communication communicates;
When retransmitting the transmission packet using the retransmission means,
The channel allocation means allocates a communication channel different from the communication channel that transmitted the packet before the retransmission to the retransmission of the packet using the retransmission means;
The communication system according to claim 1 or 2. The packet communication is communicated between the wireless communication devices by the OFDMA method,
A modulation scheme determining means for determining a modulation scheme in which the packet communication communicates;
When retransmitting the transmission packet using the retransmission means,
The modulation scheme determining means determines a modulation scheme for retransmission of a packet using the retransmission means so that the modulation scheme is different from the modulation scheme that transmitted the packet before the retransmission;
The communication system according to any one of claims 1 to 3. The modulation scheme determining means sets the modulation scheme determined at the time of packet retransmission using the retransmission means to be a modulation scheme having a transmission rate lower than the modulation scheme that transmitted the packet before the retransmission. decide,
The communication system according to claim 4. Perform packet communication,
After performing error correction processing on the received packet, first error detecting means for detecting whether or not the received packet subjected to the error correction processing has an error; and after the first error detecting means, Second error detecting means for detecting an error in the received packet subjected to error correction processing; and retransmission request means for requesting retransmission of the same packet as the received packet according to the second error detection result. Resending means for retransmitting the same packet as the received packet in response to a request for retransmission of the packet from the wireless communication terminal provided,
A base station comprising: Scheduling means for determining a transmission order of the packets;
When retransmitting the transmission packet using the retransmission means,
Determining the transmission order of the transmission packets by the scheduling means, and retransmitting the transmission packets using the retransmission means;
The base station according to claim 6. The packet communication is communicated between the base station and the wireless communication terminal by the OFDMA method,
Channel allocating means for allocating a communication channel in which the packet communication communicates;
When retransmitting the transmission packet using the retransmission means,
The channel allocation means allocates a communication channel different from the communication channel that transmitted the packet before the retransmission to the retransmission of the packet using the retransmission means;
The base station according to claim 6 or 7, wherein The packet communication is communicated between the base station and the wireless communication terminal by the OFDMA method,
A modulation scheme determining means for determining a modulation scheme in which the packet communication communicates;
When retransmitting the transmission packet using the retransmission means,
The modulation scheme determining means determines a modulation scheme for retransmission of a packet using the retransmission means so that the modulation scheme is different from the modulation scheme that transmitted the packet before the retransmission;
The base station according to claim 6, wherein the base station is a base station. The modulation scheme determining means sets the modulation scheme determined at the time of packet retransmission using the retransmission means to be a modulation scheme having a transmission rate lower than the modulation scheme that transmitted the packet before the retransmission. decide,
The base station according to claim 9. Perform packet communication,
First error detection means for detecting whether or not there is an error in the received packet that has been subjected to the error correction process after the error correction process has been performed on the received packet;
After the first error detection means, second error detection means for detecting an error of the received packet further subjected to the error correction processing;
Retransmission request means for requesting the base station to retransmit the same packet as the received packet according to the second error detection result;
A wireless communication terminal comprising: In a communication method in which packet communication is performed between wireless communication devices, each of the wireless communication devices detects whether there is an error in the received packet, and when the error is detected, the packet is retransmitted.
A first step of detecting whether or not there is an error in the received packet after the error correction processing is performed on the received packet;
After the first step, a second step of detecting an error of the received packet subjected to the error correction process;
A third step of requesting the transmitter to retransmit the same packet as the received packet according to the error detection result of the second step;
A fourth step in which the sender resends the same packet as the received packet in response to the request;
A wireless communication method comprising:

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