Receiver apparatus and communication method

Technical Field

0001The present invention relates to a reception apparatus and communication method used in a radio communication system that applies ARQ (Automatic Repeat Request).

Background Art

0002ARQ is used in a radio communication system that performs fast packet transmission ARQ to improve data reception performance.

0003ARQ is a method for automatically performing processing that a transmitting side retransmits a data unit (frame) in which an error is detected on a deceiving side. A system is disclosed where in a conventional ARQ system, a receiving side combines an already received packet and a retransmitted packet, and performs error correcting processing on the combined packet.

0004However, in the conventional ARQ system, since the receiving side combines all the retransmitted packets to perform error correcting processing, when propagation environments on a radio channel deteriorate and quality of a retransmitted packet deteriorates in retransmitting the packet, quality of the combined packet deteriorates and ARQ quality deteriorates.

0005<patcit id="pcit0001" dnum="WO9849796A2"><text>WO 98/49796 A2</text></patcit> relates to a method for transmitting packet switched data in a mobile communications system using an ARQ protocol. The document aims at allowing more effective signaling in ARQ protocols. In this regard, the document suggests repeatedly ordering a transmission of packets until the quality measured by the receiver from each packet exceeds a predetermined quality level. Thereby, the quality of each received transmission unit is independently checked.

0006If the quality of the transmission unit corresponds to a predetermined quality level, the received transmission unit is detected, deinterleaved and decoded. In case the received transmission unit is not of sufficient quality, same is stored for further processing. Subsequently, a retransmission request formed on the basis of the quality of the transmission units is sent. Upon receiving the retransmitted transmission unit, same is combined with the originally received transmission unit. Subsequently, the quality of the combined transmission unit is checked by comparing same with the predetermined quality level. In case the quality of the combined transmission unit does not correspond to the predetermined quality level, another retransmission request is transmitted. In case the quality level of the combined transmission unit is sufficient, the combined transmission unit is detected, deinterleaved and decoded.

0007<patcit id="pcit0002" dnum="US20020053058A1"><text>US 2002/0053058 A1</text></patcit> relates to a method for transmitting packet data to a receiver in a communication system using a Hybrid ARQ technique. According to the document, a first received packet is decoded in a receiver, if a buffer is empty. If it has been determined that an error has occurred during the encoding process, an index representative of how much the first received packet is damaged is compared to a predetermined threshold value. Subsequently, if the index is greater than or equal to the threshold value, the first received packet is stored in the buffer and the receiver requests to transmit a second additional packet encoded with a lower code rate. Otherwise, if the index is lower than the threshold value, the receiver requests to retransmit the first packet encoded with the same code rate.

0008<patcit id="pcit0003" dnum="EP1168703A2"><text>EP 1 168 703 A2</text></patcit> relates to packet transmission employing automatic repeat request (ARQ) in the environment of mobile communication. The document aims as improving the transmission performance by effectively utilizing the ACK/NACK signals in ARQ. According to the disclosed method, the receiver obtains reliability of a received packet when demodulating it at the reception end. Subsequently, it is reported from the reception end to the transmission end on the reliability of the received packet by utilizing the ACK/NACK signal. Thereafter, control of a transmission parameter is performed at the transmission end based on the ACK/NACK signals transmitted from the reception end. Thereby, the transmission end performs transmission parameter settings suitable to transmission situations according to the reliability of the received packet obtained at the reception end.

0009<patcit id="pcit0004" dnum="JP2001053728A"><text>JP 2001 053728 A</text></patcit> relates to a communication terminal and radio communication method, wherein it is aimed at appropriately judging the reliability of communication data in packet data communication and to reduce power consumption in a data retransmission processing. According to the document, this aim is achieved by calculating an SIR of a pilot symbol at a line quality estimating part, which is then compared to a preset threshold. In case the SIR is less than the threshold, a received data processing in a received data processing part is stopped by control of a reception processing control part. In addition, only the pilot symbol is transmitted from a transmitted data processing part by control of a transmission processing control part.

0010<patcit id="pcit0005" dnum="JP2001119426A"><text>JP 2001 119426 A</text></patcit> aims at providing an error control method by which the number of retransmitted packets can be reduced in a hybrid automatic request for retransmission (ARQ), where the ARQ and error correction coding are combined. The document further discloses a communication system comprising a transmitter and a receiver employing the error control method. The transmitter applies error correction coding to information, divides a code word obtained through the error correction coding into a plurality of packets and transmits the packets. The receiver measures the reliability of each received packet, makes a retransmission request to the transmitter and when the packet satisfies a prescribed condition on the basis of the reliability, synthesizes a plurality of the received packets including the retransmitted packet and decodes the code word obtained through the synthesis.

Disclosure of Invention

0011It is an object of the present invention to provide a reception apparatus and communication method capable of preventing deterioration of ARQ performance even when radio channel quality deteriorates.

0012The object is achieved by determining a state of the radio channel quality in receiving a packet, and combining only a packet received in a state where the radio channel quality is good.

Brief Description of Drawings

0013<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG.1</figref> is a block diagram illustrating a configuration of a reception apparatus according to Embodiment 1 of the present invention;</li><li><figref idref="f0002">FIG.2</figref> is a view for specifically illustrating ARQ of Embodiment 1 of the present invention;</li><li><figref idref="f0003">FIG.3</figref> is a block diagram illustrating a configuration of a reception apparatus according to Embodiment 2 of the present invention;</li><li><figref idref="f0004">FIG. 4</figref> is a view for specifically illustrating ARQ of Embodiment 2 of the present invention;</li><li><figref idref="f0005">FIG.5</figref> is a block diagram illustrating a configuration of a reception apparatus according to Embodiment 3 of the present invention; and</li><li><figref idref="f0006">FIG.6</figref> is a view for specifically illustrating ARQ of Embodiment 3 of the present invention.</li></ul>

Best Mode for Carrying Out the Invention

0014Embodiments of the present invention will be described specifically below with reference to accompanying drawings.

0015<figref idref="f0001">FIG.1</figref> is a block diagram illustrating a configuration of a reception apparatus according to Embodiment 1 of the present invention. Reception apparatus 100 as illustrated in <figref idref="f0001">FIG.1</figref> has antenna 101, reception RF section 102, demodulation section 103, combining section 104, likelihood calculation section 105, combining determination section 106, switch 107, buffer 108, error correcting decoding section 109, error detection section 110, switch 111, modulation section 112 and transmission RF section 113.

0016Reception RF section 102 performs predetermined radio processing on a signal received in antenna 101, and outputs a baseband signal to demodulation section 103. Demodulation section 103 demodulates the output signal from reception RF section 102 to output to combining section 104 and likelihood calculation section 105.

0017Combining section 104 combines the output signal from demodulation section 103 and the signal stored in buffer 108, and outputs a combined signal to switch 107. Likelihood calculation section 105 calculates the likelihood of the output signal from demodulation section 103, and outputs information indicative of the likelihood to combining determination section 106.

0018Combining determination section 106 compares the likelihood calculated in likelihood calculation section 105 with a predetermined threshold Th1, and when the likelihood is more than the threshold Th1, closes switch 107. As a result, when the likelihood is more than the threshold Th1, the signal combined in combining section 104 is input to buffer 108 and error correcting decoding section 109. Meanwhile, when the likelihood is less than or equal to the threshold Th1, combining determination section 106 outputs a signal (NACK signal) of a command for requesting retransmission to modulation section 112. In this way, since it is possible to detect a packet received in a state where the radio channel quality deteriorates before error correcting decoding and to transmit a retransmission request command to a communicating party, it is possible to reduce a calculation amount in ARQ and further reduce power consumption.

0019Buffer 108 outputs a stored signal to combining section 104, and when receiving a new signal input via switch 107, overwrites and stores the signal.

0020Error correcting decoding section 109 performs error correcting decoding such as Viterbi decoding on a signal input via switch 107 to output to error detection section 110.

0021Error detection section 110 performs error detection (CRC decision) on an output signal of error correcting decoding section 109, and when detecting an error, outputs a signal (NACK signal) of a command for requesting retransmission to modulation section 112. Meanwhile, when an error is not detected, error detection section 110 deletes the signal stored in buffer 108, makes switch 111, and outputs a signal (ACK signal) of a command for requesting transmission of a new packet to modulation section 112. When an error is not detected as a result, received data output from error correcting decoding section 109 is output to an apparatus for performing post-processing, not shown.

0022Modulation section 112 modulates the NACK signal output from combining determination section 106 or error detection section 110, or the ACK signal output from error detection section 110 to output to transmission RF section 113. Transmission RF section 113 converts the output signal frommodulation section 112 into a radio-frequency signal, and the radio signal is transmitted from antenna 101.

0023ARQ will be described specifically below with reference to <figref idref="f0002">FIG.2</figref>.

0024In <figref idref="f0002">FIG.2</figref>, it is assumed that reception apparatus 100 first receives new packet 201. In reception apparatus 100, likelihood calculation section 105 calculates the likelihood of packet 201, and combining determination section 106 compares the likelihood with the threshold Th1. When the likelihood is less than or equal to the threshold Th1 as a result of comparison, reception apparatus 100 determines that packet 201 is received in a state where the radio channel quality deteriorates, does not perform error correcting decoding and error detection on packet 201, and transmits NACK signal 251 to a transmission apparatus of the communicating party.

0025Next, reception apparatus 100 receives retransmitted packet 202, likelihood calculation section 105 calculates the likelihood of packet 202, and combining determination section 106 compares the likelihood with the threshold Th1. When the likelihood is more than the threshold Th1 as a result of comparison, reception apparatus 100 stores packet 202 in buffer 108, error correcting decoding section 109 performs error correcting decoding on packet 202, and error detection section 110 performs error detection on the packet. When an error is detected (CRC=NG) as a result, reception section 100 transmits NACK signal 252 to the transmission apparatus of the communicating party.

0026Then, reception apparatus 100 receives retransmittedpacket 203, likelihood calculation section 105 calculates the likelihood of packet 203, and combining determination section 106 compares the likelihood with the threshold Th1. When the likelihood is more than the threshold Th1 as a result of comparison, reception apparatus 100 stores a combined packet (202+203) inbuffer 108, error correcting decoding section 109 performs error correcting decoding on the combined packet (202+203), and error detection section 110 performs error detection on the packet. When an error is detected (CRC=NG) as a result, reception section 100 transmits NACK signal 253 to the transmission apparatus of the communicating party.

0027Next, reception apparatus 100 receives retransmitted packet 204, likelihood calculation section 105 calculates the likelihood of packet 204, and combining determination section 106 compares the likelihood with the threshold Th1. When the likelihood is more than the threshold Th1 as · a result of comparison, reception apparatus 100 stores a combined packet (202+203+204) in buffer 108, error correcting decoding section 109 performs error correcting decoding on the combined packet (202+203+204), and error detection section 110 performs error detection on the packet. When an error is not detected (CRC=OK) as a result, reception section 100 deletes the content of buffer 108, and transmits ACK signal 254 to the transmission apparatus of the communicating party.

0028In this way, the likelihood of a demodulated received packet is compared with a predetermined threshold, a state of radio channel quality in receiving the packet is thus determined, and a packet received in a state where the radio channel quality is good is only combined, whereby it is possible to prevent the quality of the combined packet from deteriorating and to further prevent the performance of ARQ from deteriorating.

0029In addition, this Embodiment describes the threshold Th1 used in the combining determination section as a predetermined value, but the present invention is not limited to the foregoing, and the threshold Th1 may be controlled variably. For example, it may be possible that an error rate is detected, and the threshold Th1 is determined so as to keep the error rate at a constant value.

(Embodiment 1)

0030<figref idref="f0003">FIG.3</figref> is a block diagram illustrating a configuration of a reception apparatus according to Embodiment 2 of the present invention. In reception apparatus 300 as illustrated in <figref idref="f0003">FIG.3</figref>, sections common to reception apparatus 100 as illustrated in <figref idref="f0001">FIG.1</figref> are assigned the same reference numerals to omit descriptions thereof.

0031Reception apparatus 300 as illustrated in <figref idref="f0003">FIG.3</figref> further has switch 301 and buffer 302 as compared with <figref idref="f0001">FIG.1</figref>. In reception apparatus 300 as illustrated in <figref idref="f0003">FIG.3</figref>, the function of combining determination section 303 is different from that of combining determination section 106 in <figref idref="f0001">FIG.1</figref>.

0032Demodulation section 103 demodulates an output signal from reception RF section 102 to output to combining section 104. Combining section 104 combines the output signal from demodulation section 103 and a signal stored in buffer 108, and outputs a combined signal to likelihood calculation section 105 and switch 107. Likelihood calculation section 105 calculates the likelihood of the signal combined in combining section 104, and outputs information indicative of the likelihood to switch 301 and combining determination section 303.

0033Buffer 302 outputs the stored likelihood information to combining determination section 303, while overwriting and storing likelihood information when receiving the new likelihood information input via switch 301.

0034Combining determination section 303 compares the likelihood (hereinafter referred to as "current likelihood") calculated in likelihood calculation section 105 with the likelihood (hereinafter referred to as "last likelihood") stored in buffer 302, and when the current likelihood is more than the last likelihood, makes switches 107 and 301. Meanwhile, when the current likelihood is less than or equal to the last likelihood, combining determination section 303 outputs a signal (NACK signal) of a command for requesting retransmission to modulation section 112. As a result, when the current likelihood is more than the last likelihood, the information indicative of the likelihood calculated in likelihood calculation section 105 is input to buffer 302, and the signal combined in combining section 104 is input to buffer 108 and error correcting decoding section 109.

0035When an error is not detected, error detection section 110 deletes the signal stored in buffer 108 and the likelihood information stored in buffer 302, closes switch 111, and outputs a signal (ACK signal) of a command for requesting transmission of a new packet to modulation section 112.

0036ARQ in this Embodiment will be described specifically below with reference to <figref idref="f0004">FIG.4</figref>.

0037In <figref idref="f0004">FIG.4</figref>, it is assumed that reception apparatus 300 first receives new packet 401. In reception apparatus 300, likelihood calculation section 105 calculates the likelihood of packet 401. At this point, since the last likelihood is not present, reception apparatus 300 stores the current likelihood in buffer 301, and stores packet 4.01 in buffer 108, error correcting decoding section 110 performs error correcting decoding on packet 401, and error detection section 110 performs error detection on the packet. As a result, when an error is detected (CRC=NG), reception apparatus 300 transmits NACK signal 451 to a transmission apparatus of the communicating party.

0038Next, reception apparatus 300 receives retransmitted packet 402, likelihood calculation section 105 calculates the likelihood of a combined packet (401+402), and combining determination section 303 compares the current likelihood with the last likelihood. As a result of comparison, when the current likelihood is more than the last likelihood, reception apparatus 300 stores the current likelihood in buffer 302, and stores the combined packet (401+402) in buffer 108, error correcting decoding section 109 performs error correcting decoding on the combined packet (401+402), and error detection section 110 performs error detection on the packet. As a result, when an error is detected (CRC=NG), reception apparatus 300 transmits NACK signal 452 to the transmission apparatus of the communicating party.

0039Then, reception apparatus 300 receives retransmitted packet 403, combining section 104 combines the combined packet (401+402) and packet 403, likelihood calculation section 105 calculates the likelihood of combined packet (401+402+403), and combining determination section 303 compares the current likelihood with the last likelihood. As a result of comparison, when the current likelihood is less that or equal to the last likelihood, reception apparatus 300 determines that packet 403 is received in a state where the radio channel quality deteriorates, does not perform error correcting decoding and error detection on the combined packet (401+402+403), and transmits NACK signal 453 to the transmission apparatus of the communicating party.

0040Next, reception apparatus 300 receives retransmitted packet 404, combining section combines the combined packet (401+402) and packet 404, likelihood calculation section 105 calculates the likelihood of combined packet (401+402+404), and combining determinationsection303comparesthecurrentlikelihood with the last likelihood. As a result of comparison, when the current likelihood is more than the last likelihood, reception apparatus 300 stores the current likelihood in buffer 302 and further stores the combined packet (401+402+404) in buffer 108, error correcting decoding section 109 performs error correcting decoding on the combined packet (401+402+404), and error detection section 110 performs error detection on the packet.. As a result, when an error is not detected (CRC=OK), reception apparatus 300 deletes the content of buffer 108 and buffer 302, and transmits ACK signal 454 to the transmission apparatus of the communicating party.

0041In this way, the current likelihood is compared with the last likelihood to determine a state of radio channel quality in receiving the packet, and a packet received in a state where the radio channel quality is good is only combined, whereby it is possible to prevent the quality of the combined packet from deteriorating and to further prevent the performance of ARQ from deteriorating.

(Embodiment 2)

0042<figref idref="f0005">FIG.5</figref> is a block diagram illustrating a configuration of a reception apparatus according to Embodiment 2 of the present invention. In reception apparatus 500 as illustrated in <figref idref="f0005">FIG.5</figref>, sections common to reception apparatus 100 as illustrated in <figref idref="f0001">FIG.1</figref> are assigned the same reference numerals to omit descriptions thereof.

0043As compared to <figref idref="f0001">FIG.1</figref>, reception apparatus 500 as illustrated in <figref idref="f0005">FIG.5</figref> has the configuration with likelihood calculation section 105 and combining determination section 106 eliminated and SIR measurement section 501 and SIR determination section 502 added.

0044Demodulation section 103 outputs a desired signal level and interfering signal level measured during demodulation to SIR measurement section 501.

0045SIR measurement section 501 measures a ratio (SIR) of the desired signal level to the interfering signal level, and outputs information indicative of SIR to SIR determination section 502.

0046SIR determination section 502 compares SIR measured in SIR measurement section 501 with a predetermined threshold Th2, and when SIR is more than the threshold Th2, makes switch 107, while outputting a signal (NACK signal) of a command for requesting retransmission to modulation section 112 when SIR is less than or equal to the threshold Th2. As a result, when SIR is more than the threshold Th2, the signal combined in combining section 104 is input to buffer 108 and error correcting decoding section 109.

0047ARQ in this Embodiment will be described specifically below with reference to <figref idref="f0006">FIG.6</figref>.

0048In <figref idref="f0006">FIG.6</figref>, it is assumed that reception apparatus 500 first receives new packet 601. In reception apparatus 500, SIR measurement section 501 measures SIR (Signal to Interference Ratio) of packet 601, and SIR determination section 502 compares SIR with the threshold Th2. As a result of comparison, when SIR is more than the threshold Th2, reception apparatus 500 stores packet 601 in buffer 108, error correcting decoding section 109 performs error correcting decoding on packet 601, and error detection section 110 performs error detection on the packet. When an error is detected (CRC=NG) as a result, reception section 500 transmits NACK signal 651 to the transmission apparatus of the communicating party.

0049Next, reception apparatus 500 receives retransmitted packet 602, combining section 104 combines packet 601 and packet 602, SIR measurement section 501 measures SIR of packet 602, and SIR determination section 502 compares SIR with the threshold Th2. As a result of comparison, when SIR is more than the threshold Th2, reception apparatus 500 stores the combined packet (601+602) in buffer 108, error correcting decoding section 109 performs error correcting decoding on the combined packet (601+602), and error detection section 110 performs error detection on the packet. When an error is detected (CRC=NG) as a result, reception section 500 transmits NACK signal 652 to the transmission apparatus of the communicating party.

0050Then, reception apparatus 500 receives retransmitted packet 603, combining section 104 combines the combined packet (601+602) and packet 603, SIR measurement section 501 measures SIR of packet 603, and SIR determination section 502 compares SIR of packet 603 with the threshold Th2. As a result of comparison, when SIR is equal to or less than the threshold Th2, reception apparatus 500 determines that packet 603 is received in a state where the radio channel quality deteriorates, does not perform error correcting decoding and error detection on the combined packet (601+602+603), and transmits NACK signal 653 to the transmission apparatus of the communicating party.

0051Next, reception apparatus 500 receives retransmitted packet 604, combining section 104 combines the combined packet (601+602) and packet 604, SIR measurement section 501 measures SIR of packet 604, and SIR determination section 502 compares SIR of packet 604 with the threshold Th2. As a result of comparison, when SIR is more than the threshold Th2, reception apparatus 500 stores the combined packet (601+602+604) in buffer 108, error correcting decoding section 109 performs error correcting decoding on the combined packet (601+602+604), and error detection section 110 performs error detection on the packet. As a result, when an error is not detected (CRC=OK), reception apparatus 500 deletes the content of buffer 108, and transmits ACK signal 654 to the transmission apparatus of the communicating party.

0052In this way, SIR is compared with a threshold to determine a state of radio channel quality in receiving the packet, and a packet received in a state where the radio channel quality is good is only combined, whereby it is possible to prevent the quality of the combined packet from deteriorating and to further prevent the performance of ARQ from deteriorating.

0053In addition, this Embodiment describes the threshold Th2 used in the combining determination section as a predetermined value, but the present invention is not limited to the foregoing, and the threshold Th2 may be controlled variably. For example, it may be possible that an error rate is detected, and the threshold Th2 is determined so as to keep the error rate at a constant value.

0054Further, the above-mentioned Embodiments are capable of being combined as appropriate. For example, a reception apparatus may calculate SIR of a second combined packet obtained by combining an earlier combined first combined packet and received packet, select a received packet such that SIR of the second combined packet is more than SIR of the first combined packet, and perform error detection on the combined packet resulting from combining of the selected packet.

0055As is apparent from the foregoing, according to the present invention, by determining a state of radio channel quality in receiving a packet and combining a packet received in a state where the radio channel quality is good is only combined, it is possible to prevent the quality of the combined packet from deteriorating and to further prevent the performance of ARQ from deteriorating.

Industrial Applicability

0056The present invention is suitable for use in a communication terminal apparatus and base station apparatus in a radio communication system that applies ARQ (Automatic Repeat Request).