Inserting error detection codes into information packets on a one-to-one basis, at a certain layer at which signal processing is performed earlier than at a physical layer

Problem: A packet error rate in a receiver needs to be effectively reduced.Solution to Problem: A transmitter 11 inserts error detection codes into information packets on one-to-one basis, at a certain layer at which signal processing is performed earlier than at a physical layer, to obtain first information packets. The transmitter 11 codes the first information packets at the physical layer to obtain second information packets, and transmits the second information packets. At the certain layer, the transmitter 11 generates parity packets by coding the information packets and inserts the error detection codes into the parity packets on one-to-one basis to obtain first parity packets. The transmitter codes the first parity packets at the physical layer to obtain second parity packets. The transmitter 11 transmits the second parity packets in accordance with a transmission request from each of one or more receivers.

TECHNICAL FIELD

The disclosure of Japanese Patent Application No. 2009-248021 filed on Oct. 28, 2009 including specification, drawings claims and abstract, and the disclosure of Japanese Patent Application No. 2010-35763 filed on Feb. 22, 2010 including specification, drawings claims and abstract are incorporated herein by reference in their entirety.

The present invention relates to a transmission method using parity packets, a transmitter and a repeater. For example, each of the transmission method, the transmitter and the repeater realizes improvement in reception quality at a time of retransmission by performing coding with use of LDPC Codes (Low Density Parity Check Codes) to generate the parity packets, and using the parity packets as data to be transmitted (retransmission data).

BACKGROUND ART

One of methods used by a transmitter to reliably transmit information to a receiver is a method of performing retransmission at a physical layer. The method of performing retransmission at the physical layer is technology that, even when the receiver cannot obtain information that has been transmitted, reliably provides the information to the receiver by transmitting some data that is based on the information again. When the number of retransmissions increases, data transmission efficiency decreases. Therefore, it is important to realize a retransmission method that can transmit information to the receiver while keeping the number of retransmissions small. Note that the following describes general retransmission. When the receiver cannot properly decode some information (or packets) received from the transmitter, the transmitter transmits data corresponding to the information (or packets) again in response to a retransmission request made by the receiver. However, the transmitter may transmit, to the receiver, data that is different from the initially transmitted information (or packets), in response to the retransmission request as long as the transmitted information (or packets) can be restored with use of the data. In the present Description, the retransmission includes a case where the transmitter transmits, in response to the retransmission request, data that is different data from information (or packets) initially transmitted to the receiver and is data with which the initially transmitted information (or packets) can be restored.

FIG. 27shows an exemplary retransmission method recited in Non Patent Literature 1. InFIG. 27, each Xi indicates information at a time point i, and each Pi indicates a parity at the time point i. When a coding rate is 1/2, a transmit sequence is composed of the information pieces Xi and the parities Pi. When the coding rate is 2/3, the transmit sequence is composed of bits excluding P2, X3, P6, X7, . . . , P2k+4, X3k+4, . . . (puncture), for example.

The transmitter initially transmits, to the receiver, the transmit sequence that is composed according to a method using the puncture at the coding rate of 2/3. Then, upon receiving a request from the receiver for retransmission, the transmitter transmits, to the receiver, bits that have not been initially transmitted (i.e. P2, X3, P6, X7, . . . , P2k+4, X3k+4, . . . ).

The receiver performs decoding at the coding rate of 1/2, with use of a received log likelihood ratio of the initially transmitted bits and a reception likelihood ratio of the retransmitted bits. In this case, the coding rate is lower at the time of the decoding for the retransmission than at the time of the initial decoding. Therefore, a packet error is less likely to occur at the time of retransmission.Non Patent Literature 1: J. Hagenauer, “Rate-compatible punctured convolutional codes (RCPC codes) and their applications”, IEEE Transaction on Communications, vol. 36, No. 4, April 1988Non Patent Literature 2: D. Chase, “Code combining-A maximum-likelihood decoding approach for combining an arbitrary number of noisy packet”, IEEE Transaction on Communications, vol. 33, No. 5, May 1985

However, according to the coding rate for the puncture, the number of codes having high error correcting ability is limited. Therefore, it is difficult to realize flexible design. Also, the above-mentioned retransmission method of Non Patent Literature 1 can be adopted in a unicast communication mode. However, it is effective, in many cases, to adopt another retransmission method that is different from the above-mentioned retransmission method in order to reliably reduce the possibility of packet error occurrence when a plurality of receivers make retransmission requests in a multicast communication mode.

In the method of performing retransmission at the physical layer, it is difficult to set flexible retransmission data. In the multicast communication mode, in particular, it is desirable to adopt a retransmission method that can reliably reduce a packet error rate by more flexibly setting retransmission data in accordance with the number of receivers that have made the retransmission requests.

Also, few suggestions are made for realizing a multicast relay method with use of a repeater when packets for the multicast (broadcast and MBMS (Multimedia Broadcast and Multicast Service)) are transmitted to terminals through the repeater. Therefore, a multicast retransmission method is desired that is used in the repeater and has fine data transfer efficiency.

In view of the above-described problems, the present invention has an aim to provide a transmitter and a transmission method using parity packets. Here, the transmission method and the transmitter make it possible to generate flexible retransmission data by generating the retransmission data in units of packets, and effectively reduce the packet error rate by the retransmission. The present invention also has an aim to provide a multicast retransmission method that has fine data transfer efficiency and is used in a repeater and a repeater for the multicast retransmission.

SUMMARY OF THE INVENTION

In order to achieve the above aim, a transmission method of the present invention is a transmission method of performing transmission with use of parity packets, the transmission method comprising: a first error detection code insertion step of inserting, at a certain layer, error detection codes into information packets on a one-to-one basis to obtain first information packets, the certain layer being a layer at which signal processing is performed earlier than at a first layer; a parity packet generation step of generating, at the certain layer, parity packets by coding the information packets; a second error detection code insertion step of inserting, at the certain layer, error detection codes into the parity packets on a one-to-one basis to obtain first parity packets; a first layer coding step of coding, at the first layer, the first information packets and the first parity packets to obtain second information packets and second parity packets, respectively, a transmission step of initially transmitting the second information packets; and a parity packet transmission step of transmitting the second parity packets to each of one or more receivers with reference to feedback information obtained from the receiver.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above-described transmission method using the parity packets, the parity packets are generated with use of the information packets at the layer at which signal processing is performed earlier than at the first layer, and the parity packets are retransmitted. Thus, flexible retransmission data can be generated. The packet error rate can be effectively reduced by retransmitting the parity packets.

In order to achieve the above aim, a repeater of the present invention receives a first packet group, and transmits the first packet group to a terminal device, the first packet group including a plurality of information packets and parity packets, the parity packets being generated by coding the information packets at a packet level, the repeater comprising: a first reception unit operable to receive the first packet group; a first transmission unit operable to transmit, to the terminal device, some packets of the received first packet group as a second packet group; a second reception unit operable to receive feedback information from the terminal device that has received the second packet group; and a second transmission unit operable, when the second reception unit receives the feedback information from the terminal device, to transmit, to the terminal device, one or more packets of the first packet group other than the packets included in the second packet group, as a third packet group.

Also, a communication method of the present invention is used in a repeater that receives a first packet group, and transmits the first packet group to a terminal device, the first packet group including a plurality of information packets and parity packets, the parity packets being generated by coding the information packets at a packet level, the communication method comprising: a first reception step of receiving the first packet group; a first transmission step of transmitting, to the terminal device, some packets of the received first packet group as a second packet group; a second reception step of receiving feedback information from the terminal device that has received the second packet group; and a second transmission step of, when the feedback information is received from the terminal device in the second reception step, transmitting, to the terminal device, one or more packets of the first packet group other than the packets included in the second packet group, as a third packet group.

According to the above-described repeater that uses the parity packets, the parity packets are generated with use of the information packets at the layer at which signal processing is performed earlier than at the first layer, and the parity packets are retransmitted. Thus, flexible retransmission data can be generated, and the packet error rate can be effectively reduced by retransmitting the parity packets. Also, it is possible to provide a multicast retransmission method that has fine data transfer efficiency and is used in the repeater.

DESCRIPTION OF EMBODIMENTS

One aspect of the present invention is a first transmission method of performing transmission with use of parity packets, the transmission method comprising: a first error detection code insertion step of inserting, at a certain layer, error detection codes into information packets on a one-to-one basis to obtain first information packets, the certain layer being a layer at which signal processing is performed earlier than at a first layer; a parity packet generation step of generating, at the certain layer, parity packets by coding the information packets; a second error detection code insertion step of inserting, at the certain layer, error detection codes into the parity packets on a one-to-one basis to obtain first parity packets; a first layer coding step of coding, at the first layer, the first information packets and the first parity packets to obtain second information packets and second parity packets, respectively, a transmission step of initially transmitting the second information packets; and a parity packet transmission step of transmitting the second parity packets to each of one or more receivers with reference to feedback information obtained from the receiver

One aspect of the present invention is a first transmitter that comprises a first error detection code insertion unit operable to insert, at a certain layer, error detection codes into information packets on a one-to-one basis to obtain first information packets, the certain layer being a layer at which signal processing is performed earlier than at a first layer; a parity packet generation unit operable to generate, at the certain layer, parity packets by coding the information packets; a second error detection code insertion unit operable to insert, at the certain layer, error detection codes into the parity packets on a one-to-one basis to obtain first parity packets; a first layer coding unit operable to code, at the first layer, the first information packets and the first parity packets to obtain second information packets and second parity packets, respectively, a transmission unit operable to initially transmit the second information packets; and a parity packet transmission unit operable to transmit the second parity packets to each of one or more receivers with reference to feedback information obtained from the receiver.

According to the above, the parity packets are generated with use of the information packets at the layer at which signal processing is performed earlier than at the first layer, and the parity packets are retransmitted. Thus, flexible retransmission data can be generated. The packet error rate can be effectively reduced by retransmitting the parity packets.

One aspect of the present invention which is a second transmission method that performs transmission with use of parity packets according to the first transmission method further comprises a determination step of determining, based on numbers of erroneous information packets in the one or more receivers, a coding rate of codes that are to be used for coding the information packets in the parity packet generation step, wherein in the parity packet generation step, the information packets are coded with use of the determined coding rate

According to the above, the coding rate of codes in the parity packet generation step can be changed based on the number of erroneous information packets in each of one or more receivers. Therefore, it is possible to reduce the amount of retransmission data. Thus, it is possible to realize both the improvement of the data transmission efficiency and the reduction of the packet error rate at the time of retransmission.

One aspect of the present invention which is a third transmission method that performs transmission with use of parity packets according to the first transmission method further comprises a first layer retransmission step of performing, at the first layer, retransmission based on erroneous information packets in each of the one or more receivers, with reference to the feedback information obtained from the receiver.

One aspect of the present invention which is a second transmitter according to the first transmitter further comprises a first layer retransmission unit operable to perform, at the first layer, retransmission based on erroneous information packets in each of the one or more receivers, with reference to the feedback information obtained from the receiver.

According to the above, the retransmission of the parity packets is performed in the first layer. Therefore, the number of retransmissions can be reduced.

One aspect of the present invention which is a fourth transmission method that performs transmission with use of parity packets according to the third transmission method further comprises a selection step of selecting, as a retransmission method, with reference to the feedback information obtained from each of the one or more receivers, one of (i) the transmission method of Claim1, (ii) a first layer retransmission method of performing, at the first layer, retransmission based on erroneous information packets in the receiver, and (iii) a combination of the transmission method of Claim1and the first layer retransmission method.

One aspect of the present invention which is a third transmitter according to the first transmitter further comprises a selection unit operable to select, as a retransmission method, with reference to the feedback information obtained from each of the one or more receivers, one of (i) the transmission method of Claim1, (ii) a first layer retransmission method of performing, at the first layer, retransmission based on erroneous information packets in the receiver, and (iii) a combination of the transmission method of Claim1and the first layer retransmission method.

According to the above, it is possible to realize improvement of the data reception quality and improvement of the data transfer efficiency.

According to one aspect of the present invention which is a fifth transmission method that performs transmission with use of parity packets according to the first transmission method, the first layer is a physical layer.

One aspect of the present invention is a first repeater that receives a first packet group, and transmits the first packet group to a terminal device, the first packet group including a plurality of information packets and parity packets, the parity packets being generated by coding the information packets at a packet level, the repeater comprising: a first reception unit operable to receive the first packet group; a first transmission unit operable to transmit, to the terminal device, some packets of the received first packet group as a second packet group; a second reception unit operable to receive feedback information from the terminal device that has received the second packet group; and a second transmission unit operable, when the second reception unit receives the feedback information from the terminal device, to transmit, to the terminal device, one or more packets of the first packet group other than the packets included in the second packet group, as a third packet group.

One aspect of the present invention is a first communication method used in a repeater that receives a first packet group, and transmits the first packet group to a terminal device, the first packet group including a plurality of information packets and parity packets, the parity packets being generated by coding the information packets at a packet level, the communication method comprising: a first reception step of receiving the first packet group; a first transmission step of transmitting, to the terminal device, some packets of the received first packet group as a second packet group; a second reception step of receiving feedback information from the terminal device that has received the second packet group; and a second transmission step of, when the feedback information is received from the terminal device in the second reception step, transmitting, to the terminal device, one or more packets of the first packet group other than the packets included in the second packet group, as a third packet group.

According to the above, the repeater transmits, from among the packet groups received by the terminal device, the first packet group first. When receiving the feedback information from the terminal device, the repeater transmits, as the third packet group, one or more packets of the first packet group other than the packets included in the second packet group. According to the above-stated structure, setting is made in the repeater such that the amount of information to be initially transmitted to the terminal device is smaller than the amount of the received packet group. In this way, the data transfer efficiency can be enhanced.

According to one aspect of the present invention which is a second repeater according to the first repeater, the first transmission unit transmits, as the second packet group, the information packets included in the first packet group, and the second transmission unit transmits, as the third packet group, some or all of the parity packets included in the first packet group.

According to one aspect of the present invention which is a second communication method of the first communication method, the first transmission step transmits, as the second packet group, the information packets included in the first packet group, and the second transmission step transmits, as the third packet group, some or all of the parity packets included in the first packet group.

According to the above, the repeater transmits the information packets first. In this way, processing in the terminal device can be reduced compared to a case where the parity packets are transmitted first. This is because when the information packets are transmitted first, the decoding at a packet level does not have to be executed while the decoding at a packet level needs to be executed when the parity packets are transmitted first.

According to one aspect of the present invention which is a third repeater according to the first repeater, the first transmission unit transmits, as the second packet group, one or more packets of the first packet group that have no error before decoding at a packet level is performed.

According to one aspect of the present invention which is a third communication method according to the first communication method, the first transmission step transmits, as the second packet group, one or more packets of the first packet group that have no error before decoding at a packet level is performed.

According to the above, the packets that have been received without an error before the decoding at a packet level (e.g. when the decoding at the physical layer is performed) is transmitted to the terminal device first. The erroneous packets can be restored by the decoding at a packet level without wasting time, after such transmission is performed and before the feedback information for the transmission is transmitted.

According to one aspect of the present invention which is a fourth repeater according to the third repeater, the first transmission unit transmits, as the second packet group, a number of packets that are equal to or greater than a predetermined number of packets, the predetermined number of packets being enough to restore, when received by the external terminal without an error and decoded at a packet level, original information of the information packets.

According to one aspect of the present invention which is a fourth communication method according to the third communication method, the first transmission step transmits, as the second packet group, a number of packets that are equal to or greater than a predetermined number of packets, the predetermined number of packets being enough to restore, when received by the external terminal without an error and decoded at a packet level, original information of the information packets.

According to the above, the terminal device receives the transmission data initially transmitted by the repeater. In this way, it is possible to increase the possibility of restoring information on which the transmission data is based, in the terminal device.

According to one aspect of the present invention that is a fifth repeater according to one of the third and fourth repeaters, the second transmission unit transmits, as the third packet group, a packet group including the one or more packets of the first packet group other than the packets included in the second packet group, the one or more packets being generated based on information restored by performing decoding at a packet level.

According to one aspect of the present invention which is a fifth transmission method according to the third and fourth transmission methods, the second transmission step transmits, as the third packet group, a packet group including the one or more packets of the first packet group other than the packets included in the second packet group, the one or more packets being generated based on information restored by performing decoding at a packet level.

One aspect of the present invention is a coder that generates third packets by: obtaining first packets and second packets, the first and second packets being respectively obtained by coding first information and second information at a packet level; extracting the first information and the second information respectively from the first packets and the second packets; and coding the first information and the second information at a packet level

One aspect of the present invention is a coding method that generates third packets by: obtaining first packets and second packets, the first and second packets being respectively obtained by coding first information and second information at a packet level; extracting the first information and the second information respectively from the first packets and the second packets; and coding the first information and the second information at a packet level.

The following describes embodiments of the present invention with reference to drawings.

First Embodiment

The following describes a first embodiment of the present invention with reference to drawings.

FIG. 1is a structural diagram of a communication apparatus11on a transmitting side (transmitter11) in the first embodiment.

The transmitter11includes a packet generation unit101, a packet data coding unit102, a physical layer error correction coding unit103, a modulation unit104, a transmission unit105, a transmission antenna106, a reception antenna107, a reception processing unit108and a transmission method determination unit109. Here, the packet generation unit101and the packet data coding unit102are functional units that function at a layer (e.g. application layer) at which signal processing is performed earlier than at the physical layer. Also, the physical layer error correction coding unit103, the modulation unit104and the transmission unit105are functional units that function at the physical layer.

The packet generation unit101receives information131and a control signal141as inputs. The packet generation unit101generates information packets132with use of the information131based on the control signal141, and outputs the generated information packets132to the packet data coding unit102. Here, the control signal141shows the transmission method (e.g. a coding rate of codes in the packet data coding unit102, a coding rate of error correction codes at the physical layer, a modulation method and whether or not retransmission data is to be transmitted or not). Note that the transmission method is not limited to the above-shown methods, and may be any method as long as the method includes information necessary for controlling processing in each of the units included in the transmitter11.

The packet data coding unit102receives the information packets132and the control signal141as inputs. The packet data coding unit102codes data of the information packets132based on the control signal141to obtain transmission packets133, and outputs the transmission packets133to the physical layer error correction coding unit103. Note that the packet generation unit101and the packet data coding unit102are described in detail later with reference toFIG. 2.

The physical layer error correction coding unit103receives transmission packets133and the control signal141as inputs. The physical layer error correction coding unit103codes data of the transmission packets133based on the coding rate of the error correction codes at the physical layer, for example, shown by the control signal141to obtain transmission data134, and outputs the transmission data134to the modulation unit104.

The modulation unit104receives the transmission data134and the control signal141as inputs. The modulation unit104modulates the transmission data134based on the modulation method shown by the control signal141to obtain a base band signal135, and outputs the resultant base band signal135to the transmission unit105.

The transmission unit105receives the base band signal135as an input. The transmission unit105performs processing (e.g. frequency conversion and amplification) on the base band signal135to obtain a transmission signal136, and outputs the resultant transmission signal136to the transmission antenna106. Then, the transmission antenna106outputs the transmission signal136. Note that the transmission signal136outputted from the transmission antenna106is received by a receiver with which the transmitter communicates.

The reception processing unit108A receives, as an input, a reception signal137received in the reception antenna107from the receiver. The reception processing unit108demodulates and decodes the reception signal137to obtain data138. Then, the reception processing unit108outputs the data138and feedback information139(received from the receiver) to a functional block (not depicted) and the transmission method determination unit109, respectively. Here, the feedback information139includes the following examples: information on packet numbers of erroneous packets, information on received signal strength indicator when the receiver receives a modulation signal transmitted by the transmitter11; Channel State Information (CSI); a packet error rate; a bit error rate; and information on a retransmission request. Note that the feedback information139is not limited to the above-described content.

The transmission method determination unit109receives, as inputs, the feedback information139and information140on a transmission method set by a user of the transmitter11. The transmission method determination unit109determines a transmission method (e.g. a coding rate of codes in a coding unit (parity packet generation unit)152, a coding rate of error correction codes at the physical layer, a modulation method and whether or not retransmission data is to be transmitted or not) with use of the feedback information139and the information140. Then, the transmission method determination unit109outputs the control signal141that is based on the determined content. As described in the above, the transmission method may be determined based on the feedback information received from the receiver. However, the transmission method does not necessarily have to be based on the feedback information received from the receiver. For example, when the transmitter recognizes a communication environment (e.g. communication traffic and a state of a channel), the transmission method determination unit109may determine the transmission method without referring to the feedback information received from the receiver.

FIG. 2is a structural diagram of the packet generation unit101and the packet data coding unit102shown inFIG. 1.

The packet generation unit101receives information131and the control signal141as inputs. The packet generation unit101generates the information packets132(e.g. information packets #1to #n) with use of the information131based on the number of bits composing packets and a method as to how control information (to be transmitted together with the information in the packets) is configured, for example. Then, the packet generation unit101outputs the generated information packets132to the packet data coding unit102.

As shown inFIG. 2, the packet data coding unit102includes an interleaving unit151, the coding unit152, an error detection code insertion unit153, a storage unit154, an error detection code insertion unit155and a selection unit156.

The interleaving unit151receives the information packets132as inputs. The interleaving unit151interleaves bits of the information packet132in units of bits or in units of sets of plural bits, for example, and outputs interleaved data171to the coding unit152.

The coding unit (parity packet generation unit)152receives the interleaved data171and the control signal141as inputs. The coding unit152generates parities by coding the interleaved data171based on the coding rate of codes or a coding method, for example, shown by the control signal141. The coding unit (parity packet generation unit)152generates parity packets172(e.g. parity packets #1to #m) with use of the generated parities, and outputs the generated parity packets172to the error detection code insertion unit153. Note that the coding unit152codes the interleaved data171with use of the following examples: LDPC (Low-Density Parity Check Codes); convolution codes; block codes; turbo codes; and Raptor codes. The coding method is not limited to the above-described codes. Also, examples of the LDPC codes include LDPC block codes and LDPC convolution codes.

The error detection code insertion unit153receives the parity packets172as inputs. The error detection code insertion unit153inserts CRC (Cyclic Redundancy Check), for example, into each of the parity packets172(e.g. parity packets #1to #m) in order to judge if a packet error occurs in the receiver. Then, the error detection code insertion unit153outputs parity packets173after the CRC insertion (e.g. parity packets #1to #m after the CRC insertion) into the storage unit154. Here, error detection codes other than the CRC may be used. For example, the error detection may be performed with the block codes (e.g. the LDPC codes).

The storage unit154receives the parity packets173after the CRC insertion as inputs and stores therein the parity packets173. The storage unit154receives the control signal141as an input. When the control signal141indicates transmission of the retransmission data, the storage unit154transmits, to the selection unit156, stored parity packets174after the CRC insertion.

The error detection code insertion unit155receives the parity packets132as inputs. The error detection code insertion unit155inserts the CRC (Cyclic Redundancy Check), for example, into each of the information packets132(e.g. information packets #1to #n) in order to judge whether or not the packet error occurs in the receiver. Then, the error detection code insertion unit155outputs information packets175(e.g. information packets #1to #n after the CRC insertion) to the selection unit156. Here, error detection codes other than the CRC may be used. For example, the error detection may be performed with the block codes (e.g. LDPC codes).

The selection unit156receives, as inputs, the parity packets174after the CRC insertion, the information packets175after the CRC insertion and control signal141. The selection unit156selects packets to be outputted based on the control signal141, and outputs the selected packets as the transmission packets133to the physical layer error correction coding unit103. Here, when the control signal141does not indicate transmission of the retransmission data, the selection unit156selects and outputs the information packets175after the CRC insertion. When the control signal141indicates the transmission of the retransmission data, the selection unit156selects and outputs the parity packets174after the CRC insertion. Processing such as coding and modulation at the physical layer is performed on the transmission packets133outputted from the selection unit156. Then, the transmission packets133are transmitted to the receiver.

FIG. 3shows an example of transmission operations of the transmitter11inFIG. 1. The following describes a relation between the layer at which signal processing is performed earlier than the physical layer (e.g. application layer) and the physical layer, and especially matters that relate to coding.

An information packet group201is a group of information packets inputted in the packet data coding unit102of the transmitter11. As shown inFIG. 3, the information packet group201is composed of information packets #1to #n.

The packet data coding unit102of the transmitter11receives information packets #1to #n as inputs. The packet data coding unit102generates the parity packets #1to #m by coding the information packets #1to #n. At a time of initial transmission, the packet data coding unit102outputs an information packet group202(information packets #1to #n). At a time of retransmission, the packet data coding unit102outputs a parity packet group203(parity packets #1to #m). Note that although the CRC is inserted into each of the information packets and the parity packets outputted from the packet data coding unit102, descriptions regarding the CRC is omitted here.

The following describes an exemplary case where the information packets #1to #n of the information packet group201and the information packets #1to #n of the information packet group202are identical. However, the structure of the information packets of the information packet group201and the structure of the information packets of the information packet group202do not have to be identical as long as all information pieces on the information packet group201are transmitted to a receiver without an error. Therefore, althoughFIG. 3shows an example where the number of bits composing the information packets of the information packet group201and the number of bits composing the information packets of the information packet group202are identical, it is possible that the number of bits composing the information packets of the information packet group201and the number of bits composing the information packets of the information packet group202are different.

Next, the physical layer error correction coding unit103generates an information packet group204(information packets #1to #n coded at the physical layer) by coding the information packet group202(information packets #1to #n) at the physical layer at the time of initial transmission. The information packet group204(information packets #1to #n coded at the physical layer) is transmitted from the transmitter11.

In this case, when an information packet error occurs in the receiver, the receiver makes a retransmission request to the transmitter11. At the time of retransmission, the physical layer error correction coding unit103generates a parity packet group205(parity packets #1to #m coded at the physical layer) by coding the parity packet group203(parity packets #1to #m) at the physical layer. The transmitter11transmits parity packet group205(parity packets #1to #m coded at the physical layer).

FIG. 4is a structural diagram of a communication apparatus31on a receiving side (receiver31) that communicates with the transmitter11inFIG. 1.

The receiver31includes a reception antenna301, a reception unit302, a communication method identifying unit303, a physical layer decoding unit304, an error detection unit305, a feedback information generation unit306, a transmission processing unit307, a transmission antenna308, a storage unit309and a packet decoding unit310.

The reception unit302A receives, as inputs, a reception signal331from the reception antenna301. The reception unit302performs, on the reception signal, processing such as frequency conversion and orthogonal demodulation. Then, the reception unit302outputs control information332included in the reception signal331to the communication method identifying unit303, and outputs reception data333to the physical layer decoding unit304. Note that a frame structure regarding the reception signal331includes, in addition to data symbol, a control symbol for transmitting: information on a modulation signal; information on the error detection codes at the physical layer; information on the coding rate of the error correction codes; information on codes used by the transmitter at a layer (e.g. application layer) at which signal processing is performed earlier than the physical layer; information on a coding rate of the codes; and information on whether data is retransmission data, for example. Note that the control symbol included in the frame structure is not limited to the above, and the frame structure may include some of the above control symbols or may include another control symbol.

The communication method identifying unit303receives the control information332as an input. The communication method identifying unit303extracts: information on a modulation signal; information on the error detection codes at the physical layer; information on the coding rate of the error correction codes; information on codes used by the transmitter at a layer (e.g. application layer) at which signal processing is performed earlier than the physical layer; information on a coding rate of the codes; and information on whether data is retransmission data, for example. The communication method identifying unit303outputs communication method information334including the extracted information pieces to each of the physical layer decoding unit304, the storage unit309and the packet decoding unit310.

The physical layer decoding unit304receives the reception data333and the communication method information334as inputs. The physical layer decoding unit304performs decoding at the physical layer based on information on the error correction codes at the physical layer and information on the coding rate of the error correction codes, for example, shown by the communication method information334. Then, the physical layer decoding unit304outputs the decoded data335to the error detection unit305.

The error detection unit305receives the decoded data335as an input. The error detection unit305performs error detection on the data335after the decoding in units of packets. The error detection unit305outputs the result of the error detection and data336of the packets to each of the feedback information generation unit306, the storage unit309and the packet decoding unit310.

The feedback information generation unit306receives, as inputs, the result of the error detection and the data336of the packets. The feedback information generation unit306determines whether or not to make a retransmission request based on the result of the error detection. The feedback information generation unit306generates information (information on numbers of erroneous packets and information on a retransmission request, for example) as feedback information337, and outputs the feedback information337to the transmission processing unit307. Note that the following shows an exemplary case where the transmitter determines the retransmission method (retransmission with use of the parity packet). However, the receiver may determine the retransmission method. In this case, the feedback information includes information on the retransmission method.

The transmission processing unit307receives the feedback information337and information338as inputs. The transmission processing unit307performs processing such as coding and modulation on the feedback information337and the information338to obtain a transmission signal339, and outputs the transmission signal339. The transmission signal339is outputted from the transmission antenna308. Note that the transmission signal339outputted from the transmission antenna308is received by a receiver with which the transmitter communicates.

The storage unit309receives the result of the error detection, the data336of the packets and the communication method information334as inputs. The storage unit309stores therein data of packets having no error, based on the result of the error detection. When the communication method information334indicates that data is retransmission data, the storage unit309outputs the data340of the stored packets to the packet decoding unit310.

The packet decoding unit310receives, as inputs, the result of the error detection, data336of the packets, data340of the packets and the communication method information33. When the communication method information334indicates that data is not retransmission data, the packet decoding unit310outputs, as packets341, the packets inputted by the error detection unit305without performing a decoding operation. When the communication method information334indicates that data is retransmission data, on the other hand, the packet decoding unit310performs decoding on both the data340of the packets, and a set of the retransmitted result of the error detection and the data336of the packets. Then, the packet decoding unit310outputs packets obtained as a result of the decoding, as the packets341.

The following describes the packet decoding unit310with reference toFIG. 5.FIG. 5is a structural diagram of the packet decoding unit310inFIG. 4. The packet decoding unit310includes an interleaving unit351and a decoding unit352.

The interleaving unit351receives, as inputs, the information packets371decoded at the physical layer and parity packets372decoded at the physical layer. Note that when the communication method information334indicates that data is not retransmission data, only the information packets371decoded at the physical layer are inputted in the interleaving unit351. When the communication method information334indicates that data is retransmission data, the interleaving unit351receives, as inputs, the information packets371decoded at the physical layer and the parity packets372decoded at the physical layer.

The interleaving unit351interleaves the information packets371decoded at the physical layer (e.g. the information packets #1to #N decoded at the physical layer) and the parity packet372decoded at the physical layer (e.g. parity packets #1to #M decoded at the physical layer). Then, the interleaving unit351outputs the interleaved data373(e.g. information packets each having a packet number and parity packets each having a packet number) to the decoding unit352. At this time, some of the information packets and some of the parity packets are missing while the other information packets and the other parity packets are not missing, as shown in one example inFIG. 5. Note that each XP inFIG. 5shows an information packet while each PP shows a parity packet.

The decoding unit352receives the interleaved data373as an input. When the communication method information334indicates that data is retransmission data, the decoding unit352obtains information packets374by restoring missing data with use of the information packets and the parity packets that are not missing. However, when some of the information packets are missing, a retransmission request is made. Note that when the communication method information334indicates that data is not retransmission data, the decoding unit352does not perform a particular decoding operation

FIG. 6Ashows an example of reception operations of the transmitter31inFIG. 4.

The receiver31receives the information packets (coded at the physical layer after the CRC insertion) initially transmitted by the transmitter11. The physical layer decoding unit304of the receiver31performs, at the physical layer, the error correction decoding on the received data to obtain the information packets #1to #n decoded at the physical layer. Then, the error detection unit305performs the error detection on the information packets #1to #n decoded at the physical layer.

When the result of the error detection by the error detection unit305indicates that no erroneous information packets exist, the receiver31does not make a retransmission request to the transmitter11.

FIG. 6Bshows another example of reception operations of the transmitter31inFIG. 4.

The receiver31receives the information packets (coded at the physical layer after the CRC insertion) initially transmitted by the transmitter11. The physical layer decoding unit304of the receiver31performs, at the physical layer, the error correction decoding on the received data to obtain the information packets #1to #n decoded at the physical layer. Then, the error detection unit305performs the error detection on the information packets #1to #n decoded at the physical layer.

When the result of the error detection by the error detection unit305indicates that erroneous packets exist, the receiver31makes a retransmission request to the transmitter11. When the retransmission request is made, the transmitter11transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion).

Then, the receiver31receives the parity packets #1to #m (coded at the physical layer after the CRC insertion). The physical layer decoding unit304of the receiver31performs, at the physical layer, the error correction decoding on the received data to obtain the parity packets #1to #m decoded at the physical layer. Then, the error detection unit305performs the error detection on the parity packets #1to #m decoded at the physical layer. Then, parity packets having no error, for example, are extracted.

Then, the packet decoding unit310obtains information packets #1to #n by decoding packets with use of the information packets having no error and parity packets having no error. Here, the information packets having no error are stored in the storage unit309. However, when the receiver31is unable to obtain all the information packets #1to #n, the receiver31makes another retransmission request in some cases.

<Communication Between Transmitter and Receiver>

FIG. 7shows an example of communication between the transmitter11shown inFIG. 1and the receiver31shown inFIG. 4.

The transmitter11inserts the CRC into each of the information packets #1to #n with use of the packet data coding unit102, and codes, at the physical layer, the information packets #1to #n after the CRC insertion with use of the physical layer error correction coding unit103. Then, the transmitter11transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). These packets are referred to as a packet group G1. At this time, the packet group G1does not include parity packets obtained by coding the information packets with use of the coding unit152shown inFIG. 2.

The receiver31receives the information packets #1to #n (coded at the physical layer after the CRC insertion). Then, the receiver31performs, on the information packets #1to #n, the decoding processing at the physical layer with use of the physical layer decoding unit304, and performs the error detection processing with use of the error detection unit305. Here, the receiver31transmits, to the transmitter11, feedback information including a retransmission request, when it is presumed that the erroneous information packets exist. At this time, the storage unit309of the receiver31stores therein the information packets having no error.

The transmitter11generates parity packets #1to #m by coding the information packets #1to #n, and inserts the CRC into each of the parity packets #1to #m, with use of the packet data coding unit102. The transmitter11codes, at the physical layer, the parity packets #1to #m after the CRC insertion with use of the physical layer error correction coding unit103. Then, the transmitter11transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion).

By the time when the transmitter11transmits the information packets #1to #n, the parity packets #1to #m after the CRC insertion have been generated by the packet data coding unit102shown inFIG. 2, and stored in the storage unit154. When the retransmission request is made, the packet data coding unit102outputs the parity packets #1to #m after the CRC insertion that have been stored in the storage unit154. The physical layer error correction coding unit103codes, at the physical layer, the parity packets #1to #m after the CRC insertion. Then, the parity packets #1to #m (coded at the physical layer after the CRC insertion) are transmitted.

The receiver31receives the parity packets #1to #m (coded at the physical layer after the CRC insertion). Then, the receiver31performs, on the parity packets #1to #m, the decoding processing at the physical layer with use of the physical layer decoding unit304, and the error detection processing with use of the error detection unit305. The packet decoding unit310obtains information packets by performing packet decoding processing on the information packets having no error and the parity packets having no error. Here, the information packets having no error are stored in the storage unit309.

According to the present embodiment, the receiver31generates the parity packets with use of the information packets at a layer at which signal processing is performed earlier than at the physical layer (generates retransmission data at a packet level), and retransmits the parity packets. Thus, flexible retransmission data can be generated. This makes it possible to effectively reduce the packet error rate by retransmitting the parity packets.

Second Embodiment

The following describes a second embodiment of the present invention with reference to drawings. A communication apparatus on a transmitting side (transmitter) in the second embodiment has, in addition to the functions of the transmitter11of the first embodiment, a function of changing the coding rate of the codes at a layer at which signal processing is performed earlier than at the physical layer (the number of parity packets to be retransmitted), in accordance with the number of erroneous packets. However, a communication apparatus on a receiving side (receiver) in each of the present embodiment and the third embodiment has the structures as shown inFIG. 4andFIG. 5. Such a receiver transmits, to the transmitter, feedback information including information on a retransmission request and information (e.g. the number of erroneous packets). Note that the same reference numerals are given to elements of the present embodiment that are substantially the same as the elements of the first embodiment. Since the descriptions thereof can be applied to the elements of the present embodiment, the descriptions are omitted or are kept brief.

The transmitter of the present embodiment includes a packet data coding unit102aand the transmission method determination unit109respectively having different functions from the packet data coding unit102and the transmission method determination unit109that are included in the transmitter11of the first embodiment. The following describes the packet data coding unit102aand the transmission method determination unit109.

The following describes the packet data coding unit102awith reference toFIG. 8.FIG. 8is a structural diagram of the packet generation unit101and the packet data coding unit102athat are included in the transmitter shown inFIG. 8.

The packet data coding unit102ais different from the packet data coding unit102in that the packet data coding unit102ahas a selection unit156ainstead of the selection unit156, does not include the storage unit154between the error detection code insertion unit153and the selection unit156a, and includes a storage unit154abetween the packet generation unit101and the interleaving unit151. The reasons for this are as follows. The transmitter determines the coding rate of codes in the coding unit152(the number of parity packets to be retransmitted) in accordance with the number of erroneous packets. It is difficult to determine the coding rate of the codes in the coding unit152before obtaining, from the receiver, the feedback information including the number of erroneous packets.

The storage unit154areceives the parity packets132as inputs. The storage unit154areceives the control signal141as an input. When the control signal141indicates transmission of the retransmission data (when the feedback information including the retransmission request is received from the receiver), the storage unit154aoutputs the stored information packets132ato the interleaving unit151.

The interleaving unit151interleaves bits composing the information packets132ain units of bits or in units of sets of plural bits, for example, in accordance with information regarding a interleaving method, for example, shown by the control signal141. The coding unit (parity packet generation unit)152generates the parity packets by coding interleaved data171based on the coding rate of codes or a coding method, for example, shown by the control signal141.

The selection unit156areceives, as inputs, the information packets175after the CRC insertion, the parity packets173after the CRC insertion and control signal141. Here, when the control signal141does not indicate transmission of retransmission data, the selection unit156aselects and outputs the information packets175after the CRC insertion. When the control signal141indicates the transmission of the retransmission data, the selection unit156aselects and outputs the parity packets173after the CRC insertion.

The following describes an example of determining the number of parity packets to be retransmitted (the coding rate of the codes in the coding unit152) with use of the transmission method determination unit109, with reference toFIG. 9.FIG. 9describes the example of determining the number of parity packets to be retransmitted with use of the transmission method determination unit109.

Suppose that the transmitter transmits information packets #1to #7to the receiver, and two information packets #2and #4from among the received information packets are missing in the receiver. In this case, the receiver transmits, to the transmitter, the feedback information including information such as the number of erroneous information packets and the retransmission request.

The transmission method determination unit109determines, as the number of parity packets to be retransmitted, a number (three or more in this example) that is larger than the number of erroneous information packets (two in this example) based on the number of erroneous information packets that is indicated by the feedback information139. Then, the transmission method determination unit109outputs the control signal141showing the coding rate of the codes in the coding unit152(corresponding to the number of parity packets to be retransmitted). Thus, the transmitter transmits three or more parity packets. Here, the number of bits composing the information packets and the number of bits composing the parity packets are identical.

The decoding operation by the packet decoding unit310of the receiver is equivalent, for example, to solving simultaneous equations with use of the Gauss elimination method. Therefore, when two information packets are missing, an unknown value exists that corresponds to the number of bits composing two information packets. In this case, the number of equations that is large enough to solve the number of bits composing the two information packets is necessary. Therefore, when the number of bits composing the information packets and the number of bits composing the parity packets are identical, it is necessary to transmit three or more parity packets. In addition, when the number of bits composing the information packets and the number of bits composing the parity packets are identical and L information packets are missing (L being an integer equal to or greater than one), it is necessary to transmit the number of parity packets that is equal to or greater than (L+1).

Note that the number of parity packets to be retransmitted (the coding rate of the codes in the coding unit152) may be determined so that the total number of bits composing parity packets to be retransmitted is greater than the total number of bits composing the erroneous information packets from among the information packets received by the receiver.

<Communication Between Transmitter and Receiver>

FIG. 10shows an example of communication between a communication apparatus12on a transmitting side (transmitter12) and a communication apparatus32on a receiving side (receiver32) in the present embodiment.

The transmitter12transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). These packets are referred to as a packet group G1. At this time, the packet group G1does not include parity packets that can be obtained by coding the information packets with use of the coding unit152shown inFIG. 8.

The receiver32receives the information packets #1to #n (coded at the physical layer after the CRC insertion). Then, the receiver32performs, on the information packets #1to #n, the decoding processing at the physical layer with use of the physical layer decoding unit304, and the error detection processing with use of the error detection unit305. Here, the receiver32transmits, to the transmitter12, feedback information including a retransmission request and the number of erroneous information packets, for example, when it is presumed that the erroneous information packets exist. At this time, the storage unit309of the receiver32stores therein the information packets having no error.

The transmitter12receives the feedback information. When the feedback information includes the retransmission request, the transmitter12determines, with use of the transmission method determination unit109, the coding rate of the codes in the coding unit152(the number of parity packets to be retransmitted) in accordance with the number of erroneous information packets included in the feedback information139. The transmitter12generates parity packets #1to #m by coding the information packets #1to #n at the determined coding rate of the codes with use of the coding unit152. Here, the information packets #1to #n are stored in the storage unit154a. The transmitter12inserts the CRC into each of the parity packets #1to #m with use of the error detection code insertion unit153, and codes, at the physical layer, the parity packets #1to #m after the CRC insertion with use of the physical layer error correction coding unit103. Then, the transmitter12transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion).

The receiver32receives the parity packets #1to #m (coded at the physical layer after the CRC insertion). The packet decoding unit310obtains information packets by performing packet decoding processing with use of the information packets having no error and the parity packet having no error. Here, the information packets having no error are stored in the storage unit309.

In the present embodiment, it is important that the transmitter12determines the coding rate of the codes in the coding unit152(the number of parity packets to be retransmitted) in accordance with the number of erroneous information packets. This is because since the number of missing information packets (the number of missing information bits) has been already known, the minimum required number of parity packets (number of parity bits) is clearly known. Even if the number of parity packets that is smaller than the minimum required number of parity packets is transmitted to the receiver32, the receiver32cannot restore the information packets. Accordingly, there is a merit that it is possible to reduce the possibility that the receiver32makes another retransmission request, by determining the coding rate of the codes in the coding unit152(the number of parity packets to be retransmitted) in accordance with the number of erroneous information packets.

According to the present embodiment, the transmitter12generates the parity packets with use of the information packets by changing the coding rate of the codes in the coding unit152(the number of parity packets to be retransmitted) in accordance with the number of erroneous information packets, and retransmits the parity packets. Thus, it is possible to reduce the possibility of packet error occurrence by the retransmission. Therefore, data reception quality can be improved. Also, the number of retransmissions can be reduced. Therefore, data transmission efficiency can be improved.

Third Embodiment

The following describes a third embodiment of the present invention with reference to drawings. The above second embodiment describes the change in the coding rate of the codes in the coding unit152in the unicast communication mode. The third embodiment describes the change in the coding rate of the codes in a multicast communication mode. Note that a description of the broadcast that relates to the present embodiment can be substantially the same as a description of the multicast. Note that the same reference numerals are provided to elements of the present embodiment that are substantially the same as the elements of the first and second embodiments. Since the descriptions thereof can be applied to the elements of the present embodiment, the descriptions are omitted or are kept brief.

The transmitter of the present embodiment includes a transmission method determination unit109bhaving different functions from the functions of the transmission method determination unit109of the transmitter in the second embodiment. The following describes the transmission method determination unit109b.

FIG. 11is a structural diagram of the transmission method determination unit109bof the transmitter. The transmission method determination unit109bincludes a retransmission requesting terminal number count unit501, a terminal packet error number collecting unit502, a retransmission packet number determination unit503and a transmission method information generation unit504. The following describes a function relating in particular to determination of the number of parity packets to be retransmitted from among functions of the transmission method determination unit109b.

The retransmission requesting terminal number count unit501receives the feedback information139as an input. The retransmission requesting terminal number count unit501counts the number of receivers that make transmission requests, based on the request information for retransmission, for example, included in the feedback information139received from each of the receivers. Then, the retransmission requesting terminal number count unit501outputs, to the retransmission packet number determination unit503, retransmission requesting terminal number information531showing a counted value.

The terminal packet error number collecting unit502receives the feedback information139as an input. The terminal packet error number collecting unit502collects information on the number of erroneous information packets, for example, included in the feedback information139received from each of the receivers. The terminal packet error number collecting unit502outputs, to the retransmission packet number determination unit503, terminal packet error number information532showing the number of erroneous information packets in each of the receivers.

The retransmission packet number determination unit503receives, as inputs, the retransmission requesting terminal number information531and the terminal packet error number information532. The retransmission packet number determination unit503determines the number of parity packets to be retransmitted (the coding rate of the codes in the coding unit152), and outputs, to the transmission method information generation unit504, retransmission parity packet number information (the coding rate of the codes in the coding unit152)533indicating the number of parity packets to be retransmitted (the coding rate of the codes in the coding unit152).

The transmission method information generation unit504receives, as inputs, the retransmission parity packet number information533and another transmission method information534. The transmission method information generation unit504outputs the control signal141including these information pieces.

Note that a concrete example of determining the number of parity packets to be retransmitted with use of the transmission method determination unit139bis described later with reference toFIG. 14.

<Communication Between Transmitter and Receiver>

FIG. 12shows a conceptual diagram of the multicast communication. A base station (transmitter) S simultaneously transmits the same information to each of a plurality of terminals (receivers) T1to Tn. Then, each of the terminals T1to Tn transmits, to the base station S, the feedback information including the request information for retransmission, information on the number of erroneous information packets and indexes of the erroneous information packets, for example.

FIG. 13shows an example of communication among the transmitter13and communication apparatuses33A,33B and33C on a receiving side (receivers33A,33B and33C) in the present embodiment. Note that the transmitter13corresponds to the base station S shown inFIG. 12, and the receivers33A,33B and33C correspond to terminals T1to Tn shown inFIG. 12.

The transmitter13simultaneously transmits the same information packets to each of the receivers33A,33B and33C. Here, the transmitter13transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). These packets are collectively referred to as a packet group G1. At this time, the packet group G1does not include parity packets that can be obtained by coding the information packets with use of the coding unit152shown inFIG. 8.

The receiver33A receives information packets #1to #n (coded at the physical layer after the CRC insertion), and transmits, to the transmitter13, the feedback information including, for example, the retransmission request and the number of erroneous information packets, when it is presumed that the erroneous information packets exist.

Each of the receivers33B and33C receives information packets #1to #n (coded at the physical layer after the CRC insertion), and transmits, to the transmitter13, the feedback information including, for example, the retransmission request and the number of erroneous information packets, when it is presumed that the erroneous information packets exist.

The transmitter13receives the feedback information from each of the receivers33A,33B and33C. The transmitter13transmits the parity packets when the feedback information includes the retransmission request. Suppose that many receivers receive the information packets from the transmitter13(not depicted inFIG. 13). The transmitter13counts the number of receivers that have made the retransmission requests, with use of the retransmission requesting terminal number count unit501. The transmitter13collects the number of erroneous information packets in each of the receivers, with use of the terminal packet error number collecting unit502. Then, the retransmission packet number determination unit503determines the coding rate of the codes in the coding unit152(the number of parity packets to be retransmitted) in accordance with the number of erroneous information packets in each of the receivers. The transmitter13generates parity packets #1to #m by coding the information packets #1to #n at the determined coding rate of the codes with use of the coding unit152. Here, the information packets #1to #n are stored in the storage unit154a. The transmitter13inserts the CRC into each of the parity packets #1to #m with use of the error detection code insertion unit153, and codes, at the physical layer, the parity packets #1to #m after the CRC insertion with use of the physical layer error correction coding unit103. Then, the transmitter13transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion).

Each of the receivers33A,33B and33C receives the parity packets #1to #m (coded at the physical layer after the CRC insertion). Each of the receivers33A,33B and33C obtains information packets by performing packet decoding processing on the information packets having no error and the parity packets having no error. Here, the information packets having no error are stored in the storage unit309.

<Concrete Example of Determining Number of Parity Packets to be Retransmitted>

FIG. 14describes a concrete example of determining the number of parity packets to be retransmitted with use of the transmission method determination unit109b.

Suppose that: the transmitter13transmits information packets #1to #7to each of the receivers33A,33B and33C; and three packets #2, #5and #7, two packets #1, #2and three packets #3, #4and #6are missing in the receivers33A,33B and33C respectively. As with the descriptions given ofFIG. 9, when the number of bits composing the information packets and the number of bits composing the parity packets to be retransmitted are identical, the transmitter13retransmits four or more parity packets, three or more parity packets and four or more parity packets to the receivers33A,33B and33C, respectively. In this way, all the receivers33A,33B and33C can obtain all the information packets as a result of the retransmission. Therefore, if the transmitter13retransmits four (that is larger by one than the maximum number of the numbers of erroneous information packets in the receivers33A,33band33C) or more parity packets, all of the receivers33A,33B and33C are possibly able to obtain all the information packets. Thus, the transmitter13determines the number of parity packets to be retransmitted (the total number of bits composing the parity packets to be retransmitted).

Note that the number of parity packets (the coding rate of the codes in the coding unit152) to be retransmitted may be determined so that the total number of bits composing parity packets to be retransmitted is greater than the total number of bits composing the erroneous information packets in the receiver having the maximum number of erroneous information packets from among the receivers.

According to the present embodiment, the transmitter can estimate the number of erroneous information packets in each of the receivers. Also, the transmitter can estimate the coding rate of the codes in the coding unit152(the number of parity packets to be retransmitted). Here, the coding rate can reduce the packet error rate at the time of the retransmission to each of the receivers. Therefore, the packet error rate of the information packets can be reduced after the retransmission in as many receivers as possible.

Note that the following example is possible. A threshold value is provided for the number of receivers that have made retransmission requests. When the number of receivers that have made the retransmission requests is equal to or greater than a first threshold value, the transmitter performs retransmission with use of the parity packets. When the number of receivers that have made the retransmission requests is equal to or smaller than a second threshold value, the transmitter performs retransmission at the physical layer (conventional retransmission). Then, when the number of receivers is equal to or smaller than the first threshold value and is equal to or greater than the second threshold value, the transmitter judges which type of retransmission methods should be adopted in accordance with an error state of the packets in each of the receivers.

Note that when the number of receivers (in each of which the packet error occurs) is small, the coding rate of the codes in the coding unit152is increased (the number of parity packets to be retransmitted is reduced). When the number of receivers in which the packet error occurs is large, the coding rate of the codes in the coding unit152is reduced (the number of parity packets to be retransmitted is increased). Thus, it is possible to realize both the improvement of the data transmission efficiency and the reduction of the packet error rate at the time of retransmission.

Fourth Embodiment

The following describes a fourth embodiment of the present invention with reference to drawings. A communication apparatus on a transmitting side (transmitter) in the fourth embodiment reduces the number of retransmissions by performing retransmission at the physical layer as well as the retransmission with use of the parity packets as described in the first embodiment. Note that the same reference numerals are provided to elements of the present embodiment that are substantially the same as the elements of the first embodiment. Since the descriptions thereof can be applied to the elements of the present embodiment, the descriptions are omitted or are kept brief.

The transmitter of the present embodiment has a physical layer error correction coding unit103chaving different functions from the functions of the physical layer error correction coding unit103included in the transmitter11of the first embodiment. The following describes the physical layer error correction coding unit103c.

FIG. 15is a structural diagram of the physical layer error correction coding unit103cand the modulation unit104included in the transmitter. The physical layer error correction coding unit103cincludes a coding unit701, a storage unit702and a selection unit703.

The coding unit701receives the transmission packet133and the control signal141as inputs. The coding unit701codes data of the transmission packets133based on the coding rate of the error correction codes at the physical layer, for example, shown by the control signal141, and outputs coded data731to each of the storage unit702and the selection unit703.

The storage unit702receives the coded data731as an input. The storage unit702receives the control signal141as an input. When the control signal141indicates transmission of the retransmission data, the storage unit702outputs, as retransmission data732, the coded data stored therein to the selection unit703. Here, the coded data that has been outputted from the storage unit702as retransmission data is coded data of the information packet corresponding to the information packet having an erroneous packet number in the receiver.

The election unit703receives, as inputs, the coded data731, the retransmission data732and the control signal141. When the control signal141does not indicate transmission of the retransmission data, the selection unit703selects and outputs the coded data731to the modulation unit104as the transmission data134. When the control signal141indicates transmission of the retransmission data, the selection unit703selects and outputs the retransmission data732(the coded data corresponding to the packet number of each of the erroneous information packets in the receiver) to the modulation unit104as the transmission data134. Also, the selection unit703selects and outputs the coded data731(the coded data of the parity packets) to the modulation unit104as the transmission data134.

The modulation unit (mapping unit)104receives the transmission data134and the control signal141as inputs. The modulation unit104modulates the transmission data134based on the modulation method shown by the control signal141, and outputs the base band signal135obtained by the modulation.

FIG. 16is a structural diagram of a communication apparatus34on a receiving side (receiver34) in the present embodiment. The receiver34shown inFIG. 16is different from the receiver31shown inFIG. 4in that the receiver34has a function for supporting retransmission at the physical layer. That is, the reception unit34includes a physical layer decoding unit304chaving different functions from the functions of the physical layer decoding unit304of the receiver31shown in FIG.31. The receiver34further includes a storage unit315.

The storage unit315receives reception data333as an input. Note that the reception data333relates to the log likelihood ratio as an input. The storage unit315receives the communication method information334as an input. When the communication method information334indicates that data is retransmission data, the storage unit315outputs stored data346to the physical layer decoding unit304c.

The physical layer decoding unit304creceives, as inputs, the reception data333, the data346and the communication method information334. When the communication method information334indicates that data is not retransmission data, the physical layer decoding unit304cdecodes the reception data333of the information packets, and outputs decoded data307to the error detection unit305. When the communication method information334indicates that data is retransmission data, on the other hand, the physical layer decoding unit304cperforms decoding processing with use of the reception data333of the information packets and data346of the information packets to obtain decoded data335, and outputs the decoded data335to the error detection unit305. The physical layer decoding unit304calso decodes the reception data333of the parity packets, and outputs decoded data307to the error detection unit305.

<Communication Between Transmitter and Receiver>

FIG. 17shows an example of communication between the transmitter14and the receiver34in the present embodiment.

The transmitter14transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). These packets are collectively referred to as a packet group G1. At this time, the packet group G1does not include parity packets that can be obtained by coding the information packets with use of the coding unit152shown inFIG. 2.

The receiver34receives the information packets #1to #n (coded at the physical layer after the CRC insertion). Then, the receiver34performs, on the information packets #1to #n, the decoding processing at the physical layer with use of the physical layer decoding unit304c, and the error detection processing with use of the error detection unit305. In the following, the receiver34transmits, to the transmitter14, the feedback information including, for example, a retransmission request and packet numbers of the erroneous information packets #2and #5, when it is supposed that that packets #2and #5are erroneous.

The transmitter14receives the feedback information. When the feedback information includes the retransmission request, the transmitter14transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion) together with the information packets #2and #5whose packet numbers are packet numbers of erroneous information packets. Here, the information packets #2and #5have been coded at the physical layer after the CRC insertion, and stored in the storage unit702.

The receiver34receives the parity packets #1to #m (coded at the physical layer after the CRC insertion) as well as the information packets #2and #5(coded at the physical layer after the CRC insertion). The receiver34performs, on the data346stored in the storage unit315and the reception data333of the information packets #2and #5, decoding processing at the physical layer the with use of the physical layer decoding unit304c, and the error detection with use of the error detection unit305. The receiver34performs, on the parity packets #1to #m (coded at the physical layer after the CRC insertion), the decoding processing at the physical layer with use of the physical layer decoding unit304c, and the error detection processing with use of the error detection unit305. Then, the receiver34obtains the information packets by performing decoding processing with use of the information packets having no error and the parity packets having no error, with use of the packet decoding unit310.

According to the present embodiment, even when the packet error occurs in the receiver34, it is possible to greatly reduce the possibility that the receiver34makes a retransmission request, by performing both the retransmission with use of the parity packets and the retransmission at the physical layer. Note that the number of parity packets to be retransmitted (the coding rate of the codes in the coding unit152) may be changed in accordance with the number of erroneous packets, as described in the second and third embodiments.

Note that it is possible to combine the retransmission method described in the fourth embodiment (combination of the retransmission with use of the parity packets and the retransmission at the physical layer) and the retransmission methods described in the first to third embodiments (retransmission method of performing retransmission with use of the parity packets). In this case, the number of erroneous information packets is important. Therefore, it is preferable that the transmitter selects one method from among the retransmission method described in the fourth embodiment and the retransmission methods described in the first to third embodiments in accordance with the number of erroneous information packets. When the number of erroneous information packets is large, it is preferable to select the retransmission method described in the fourth embodiment in order to reduce the possibility of packet error occurrence after the retransmission. When the number of erroneous information packets is small, on the other hand, it is preferable to select the retransmission method described in the first to third embodiments. It is natural that when the number of erroneous information packets is small, it is possible to select a conventional retransmission method called “chase combining” (shown in the Non Patent Literature 2), that is, the retransmission method of retransmitting the erroneous packets at the physical layer. Note that selection methods and criteria for selecting the retransmission method described in the fourth embodiment and the retransmission methods described in the first to third embodiments are not limited to the above-state methods and criteria.

Fifth Embodiment

The following describes a fifth embodiment of the present invention with reference to drawings. A communication apparatus on a transmitting side (transmitter) in the fifth embodiment is different from the transmitter of the fourth embodiment in a retransmission structure at the physical layer. However, a communication apparatus on a receiving side (receiver) in the fifth embodiment has a structure shown inFIG. 16. Note that the same reference numerals are provided to elements of the present embodiment that are substantially the same as the elements of the first to fourth embodiments. Since the descriptions thereof can be applied to the elements of the present embodiment, the descriptions are omitted or are kept brief.

The transmitter of the present embodiment has a physical layer error correction coding unit103dhaving different functions from the functions of the physical layer error correction coding unit103cincluded in the transmitter of the fourth embodiment. The following describes the physical layer error correction coding unit103d.

FIG. 18is a structural diagram showing the physical layer error correction coding unit103dand the modulation unit104included in the transmitter. The physical layer error correction coding unit103dincludes the coding unit701, a puncture unit711, a storage unit702dand a selection unit703d.

The puncture unit711receives the coded data731as an input. The puncture unit711determines bits that are not to be transmitted, in accordance with a certain standard. The puncture unit711outputs, to the selection unit703, coded data741of bits other than the determined bits that are not to be transmitted (hereinafter, also referred to as “coded data after the puncture” in some cases). The puncture unit711also outputs, to the storage unit702d, coded data742of the determined bits (hereinafter, also referred to as “thinned data” in some cases).

The storage unit702receives thinned data742as an input and stores the thinned data742. The storage unit702dreceives the control signal141as an input. When the control signal141indicates transmission of the retransmission data, the storage unit702doutputs the thinned data stored therein to the selection unit703as the retransmission data743(seeFIG. 27). Here, the thinned data that has been outputted from the storage unit702das retransmission data is thinned data relating to packet numbers of the erroneous information packets.

The selection unit703dreceives, as inputs, the coded data741after the puncture, the retransmission data743and the control signal141. When the control signal141does not indicate transmission of the retransmission data, the selection unit703dselects and outputs the coded data741after the puncture as the transmission data134. When the control signal141indicates transmission of the retransmission data, on the other hand, the selection unit703dselects and outputs the retransmission data732(thinned data relating to packet numbers of the erroneous information packets in the receiver) to the modulation unit104as the transmission data134. Also, the selection unit703dselects and outputs the coded data731(relating to the parity packets) after the puncture to the modulation unit104as the transmission data134.

<Communication Between Transmitter and Receiver>

FIG. 19shows an example of communication between the transmitter15and the receiver35in the present embodiment.

As shown inFIG. 19, the transmitter15transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). These packets are collectively referred to as a packet group G1. At this time, the packet group G1does not include parity packets that can be obtained by coding the information packets with use of the coding unit152of the packet data coding unit102shown inFIG. 2.

The receiver35receives the information packets #1to #n (coded at the physical layer after the CRC insertion). Then, the receiver35performs, on the information packets #1to #n (coded at the physical layer after the CRC insertion), the decoding processing at the physical layer with use of the physical layer decoding unit304c, and the error detection processing with use of the error detection unit305. In the following, the receiver35transmits, to the transmitter15, the feedback information including, for example, a retransmission request and packet numbers of the erroneous information packets #2and #5, when it is presumed that packets #2and #5are erroneous.

When the transmitter15receives the feedback information including the retransmission request from the receiver35, the transmitter14transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion) as well as bits relating to the information packets #2and #5(stored in the storage unit702d) whose packet numbers are packet numbers of erroneous information packets. Here, the bits relating to the information packets are bits punctured (not transmitted) at the time of the transmission of the information packets #2and #5at the physical layer.

The receiver35receives the parity packets #1to #m (coded at the physical layer after the CRC insertion) as well as data of bits relating to the information packets #2and #5(coded at the physical layer after the CRC insertion). The receiver35performs, on the data346stored in the storage unit315and the reception data333relating to the information packets #2and #5, decoding processing at the physical layer with use of the physical layer decoding unit304c, and the error detection processing with use of the error detection unit305. The receiver35also performs, on the parity packets #1to #m (coded at the physical layer after the CRC insertion), the decoding processing with use of the physical layer decoding unit304c, and the error detection processing with use of the error detection unit305. Then, the receiver35obtains the information packets by performing the packet decoding processing on the information packets having no error and the parity packets having no error, with use of the packet decoding unit310.

According to the present embodiment, even when the packet error occurs in the receiver35, it is possible to greatly reduce the possibility that the receiver35makes a retransmission request, by performing both the retransmission with use of the parity packets and the retransmission at the physical layer. Note that the number of parity packets to be retransmitted (the coding rate of the codes in the coding unit152) may be changed in accordance with the number of erroneous packets, as described in the second and third embodiments.

Note that it is possible to combine the retransmission method described in the fifth embodiment (combination of the retransmission with use of the parity packets and the retransmission at the physical layer) and the retransmission method described in the first to third embodiments (retransmission method of performing retransmission with use of the parity packets). In this case, the number of erroneous information packets is important. Therefore, it is preferable that the transmitter selects a retransmission method from among the retransmission method described in the fifth embodiment and the retransmission methods described in the first to third embodiments in accordance with the number of erroneous information packets. When the number of erroneous information packets is large, it is preferable to select the retransmission method described in the fifth embodiment in order to reduce the possibility of packet error occurrence after the retransmission. When the number of erroneous information packets is small, on the other hand, it is preferable to select the retransmission method described in the first to third embodiments. It is natural that when the number of erroneous information packets is small, it is possible to select a conventional retransmission method (Incremental redundancy) of transmitting bits punctured (not transmitted) at the time of initial transmission of the erroneous packets at the physical layer (shown in Non Patent Literature 1) (FIG. 27). Note that selection methods and criteria for selecting the retransmission method described in the fifth embodiment and the retransmission methods described in the first to third embodiments are not limited to the above-stated methods and criteria. Also, the method of performing retransmission at the physical layer may be switched to the retransmission method described in the fourth embodiment.

Sixth Embodiment

The following describes a sixth embodiment of the present invention with reference to drawings. The present embodiment relates to a method of configuring packets to be retransmitted in a communication apparatus on a transmitting side (transmitter).

<Method of Configuring Packets to be Retransmitted>

FIG. 20shows an example of a frame structure at the time of retransmission in the transmitter of the present embodiment. Note that the transmitter has structures shown inFIGS. 1 and 2.

The transmitter16transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). In this case, suppose that the data amount of each of the information packets #1to #n before the CRC insertion is 128 bytes, for example.

Then, the transmitter16transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion), when it is presumed that a communication apparatus36on a receiving side (receiver36) has made a retransmission request. In this case, the transmitter16generates the parity packets such that a size of one parity packet before the CRC insertion is smaller than a size of one information packet before the CRC insertion in order to maintain reception quality at the time of retransmission. For example, the data amount of one parity packet before the CRC insertion is 64 bytes.

It is possible to reduce the number of bits (to be eliminated) of the retransmission data by making the size of each of the parity packets #1to #m before the CRC insertion smaller than the size of each of the information packets #1to #n before the CRC insertion as described in the above. Thus, it is possible to obtain an effect that the packet error is highly likely to be prevented at the time of first retransmission.

Note that the above-stated data amount of one information packet and the data amount of one parity packet are merely examples. Therefore, any data amount is possible as long as the data amount of one parity packet is smaller than the data amount of one information packet.

Also, the present embodiment can be combined with any of the other embodiments. For example, it is possible to adopt the method of transmitting (retransmitting) the parity packets or the method of making the number of bits composing the parity packets smaller than the number of bits composing the information packets. Also, in a case where the parity packets are transmitted (retransmitted) a plurality of times, a method may be adopted of decreasing the number of bits composing the parity packets as the number of retransmissions increases.

Seventh Embodiment

The following describes a seventh embodiment of the present invention with reference to drawings. The present embodiment relates to a method of configuring packets to be retransmitted in a communication apparatus on a transmitting side (transmitter) when the parity packets are retransmitted a plurality of times. Note that the same reference numerals are provided to elements of the present embodiment that are the same as the elements of the first embodiment. Since the descriptions thereof can be applied to the elements of the present embodiment, the descriptions are omitted or are kept brief.

The transmitter of the present embodiment includes a packet data coding unit102fhaving different functions from the functions of the packet data coding unit102of the transmitter11of the first embodiment, and the transmission method determination unit109outputs the control signal141including the retransmission number information showing how many times the retransmission has been performed. The following describes the packet data coding unit102f.

FIG. 21is a structural diagram of the packet generation unit101and the packet data coding unit102fof the transmitter. The following describes how the packet data coding unit102fis different from the packet data coding unit102shown inFIG. 2. The packet data coding unit102fhas a coding unit152finstead of the coding unit152. The packet data coding unit102fdoes not have the storage unit154between the error detection code insertion unit153and a selection unit156f. Instead, the packet data coding unit102fhas a storage unit154fbetween the coding unit152fand the error detection code insertion unit153. The reasons for these is to decrease the size of one parity packet each time the transmitter of the present embodiment performs retransmission with use of the parity packet, in a case where the transmitter performs retransmission a plurality of times.

The coding unit152freceives the interleaved data171and the control signal141as inputs. The coding unit152fgenerates parities by coding the interleaved data171based on the coding rate of codes or the coding method, for example, shown by the control signal141, and outputs the generated parities172fto the storage unit154f.

The storage unit154freceives the parities172fas inputs and stores therein the parities172. The storage unit154freceives the control signal141as an input. When the control signal141indicates transmission of the retransmission data, the storage unit154fgenerates parity packets with use of the parities based on the retransmission number information shown by the control signal141such that the size of one parity packet decreases as the number of retransmissions increases. The storage unit154foutputs the generated parity packets172to the error detection code insertion unit153. Here, the size of one parity packet before the CRC insertion at the time of the first retransmission should be equal to or larger than the size of the one information packet before the CRC, for example.

<Method of Configuring Packets to be Retransmitted>

FIG. 22shows a concrete example of a frame structure at the time of retransmission in a communication apparatus on a transmitting side (transmitter) in the present embodiment.

The following describes the concrete example.

A transmitter17transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). In this case, suppose that the amount of data composing each of the information packets #1to #n before the CRC insertion is 128 bytes, for example.

Then, the transmitter17generates parity packets with use of the parities stored in the storage unit154fof the packet data coding unit102f, and transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion), when it is presumed that a communication apparatus37on a receiving side (receiver37) has made a retransmission request. In this case, the size of one parity packet before the CRC insertion at the time of initial transmission should be 128 bytes which is equal to the size of one information packet before the CRC.

Then, the transmitter17generates parity packets with use of the parities stored in the storage unit154fof the packet data coding unit102, and transmits the parity packets #1to #h (coded at the physical layer after the CRC insertion), when it is presumed that the receiver37has made a retransmission request. In this case, it is important that the size of one parity packet before the CRC insertion at the time of the second retransmission is smaller than the size of one parity packet before the CRC insertion at the time of the first retransmission. The size of one parity packet before the CRC insertion at the time of the second retransmission is 64 bytes, for example, that is smaller than the size of one parity packet before the CRC insertion at the time of the first retransmission.

The following describes another concrete example.

The transmitter17transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). In this case, suppose that the amount of data composing each of the information packets #1to #n before the CRC insertion is 128 bytes, for example.

Then, the transmitter17transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion), when it is presumed that the receiver37has made a retransmission request. In this case, the size of one parity packet before the CRC insertion at the time of the first retransmission is 64 bytes that is smaller than the size of one information packet before the CRC insertion.

Then, the transmitter17retransmits the parity packets (coded at the physical layer after the CRC insertion), when it is presumed that the receiver37has made a retransmission request. In this case, it is important that the size of one parity packet before the CRC insertion at the time of the second retransmission is smaller than the size of one parity packet before the CRC insertion at the time of the first retransmission. The size of one parity packet before the CRC insertion at the time of the second retransmission is 32 bytes, for example, that is smaller than the size of one parity packet before the CRC insertion at the time of the first retransmission.

Note that the above-stated data amount of one information packet and the data amount of one parity packet at the time of each of the first and second retransmissions are merely examples. Therefore, any data amount is possible as long as the data amount of one parity packet at the time of the second retransmission is smaller than the data amount of one parity packet at the time of the first retransmission.

Thus, the number of bits (to be eliminated) of the transmission data can be reduced by making the size of one packet smaller as the number of retransmissions increases as described in the above. This improves the reception quality.

Eighth Embodiment

The following describes an eighth embodiment of the present invention with reference to drawings. The present embodiment relates to a method of configuring packets to be retransmitted in a communication apparatus on a transmitting side (transmitter) in a case of alternately performing retransmission with use of the parity packets and retransmission with use of the information packets. Note that the same reference numerals are provided to elements of the present embodiment that are substantially the same as the elements of the first to seventh embodiments. Since the descriptions thereof can be applied to the elements of the present embodiment, the descriptions are omitted or are kept brief.

A transmitter of the present embodiment has a packet data coding unit102ghaving different functions from the functions of the packet data coding unit102fof the transmitter of the seventh embodiment. The transmission method determination unit109outputs the control signal141including retransmission number information showing how many times the retransmission has been performed, as described in the seventh embodiment. The following describes the packet data coding unit102g.

FIG. 23is a structural diagram of the packet generation unit101and the packet data coding unit102gin the transmitter. The following shows how the packet data coding unit102gis different from the packet data coding unit102fshown inFIG. 21. The packet data coding unit102ghas a selection unit156ginstead of the selection unit156, and further includes a storage unit161and a selection unit162. The reason for these is to retransmit the information packets at a layer at which signal processing is performed earlier than at the physical layer (e.g. application layer) in the transmitter of the present invention. Note that when the control signal141indicates transmission of the retransmission data and the retransmission number shown by the retransmission number information of the control signal141is an odd number, the storage unit154foutputs the parity packets172.

The storage unit161receives the information packets132as inputs. The storage unit161receives the control signal141as an input. In a case where: the control signal141indicates transmission of the retransmission data; and the retransmission number shown by the retransmission number information of the control signal141is an even number, the storage unit161reconfigures the stored information packets so that the size of one information packet decreases as the retransmission number increases, and outputs information packets132g.

The selection unit162receives the information packets132, the information packets132gand the control signal141as inputs. When the control signal141does not indicate transmission of the retransmission data, the selection unit162selects and outputs the information packet132to the error detection code insertion unit155as the information packet132G. In a case where: the control signal141indicates transmission of the retransmission data; and the retransmission number shown by the retransmission number information of the control signal141is an even number, on the other hand, the selection unit162selects and outputs the information packets132gto the error detection code insertion unit155as the information packet132G.

The selection unit156greceives, as inputs, the information packets175after the CRC insertion, the parity packets173after the CRC insertion and the control signal141. In a case where (1) the control signal141does not indicate transmission of the retransmission data or (2): the control signal141indicates transmission of the retransmission data; and the retransmission number shown by the retransmission number information of the control signal141is an even number, the selection unit156gselects and outputs the information packets175after the CRC insertion. In a case where: the control signal141indicates transmission of the retransmission data; and the retransmission number shown by the retransmission number information of the control signal141is an odd number, on the other hand, the selection unit156gselects and outputs the parity packets173after the CRC insertion.

<Method of Configuring Packets to be Retransmitted>

FIG. 24shows an example of a frame structure at the time of retransmission in a communication apparatus on a transmitting side (transmitter) in the present embodiment.

The following describes the concrete example.

A transmitter18transmits the information packets (coded at the physical layer after the CRC insertion). In this case, suppose that the amount of data composing each of the information packets #1to #n before the CRC insertion is 128 bytes, for example.

Then, the transmitter18transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion), when it is presumed that a communication apparatus38on a receiving side (receiver38) has made a retransmission request. In this case, the size of one parity packet before the CRC insertion should be 128 bytes which is equal to the size of one information packet before the CRC insertion at the time of the initial transmission.

The transmitter18transmits information packets #1to #k (coded at the physical layer after the CRC insertion) with use of the information packets stored in the storage unit161of the packet data coding unit102g, when it is presumed that the receiver38has made the retransmission request. In this case, it is important that the size of one information packet before the CRC insertion at the time of the second retransmission is smaller than the size of one information packet before the CRC insertion at the time of the initial transmission. Thus, the size of one information packet before the CRC insertion at the time of the second retransmission is 64 bytes, for example, which is smaller than the size of one information packet before the CRC insertion at the time of the initial transmission.

The following describes another concrete example.

The transmitter18transmits the information packets #1to #n (coded at the physical layer after the CRC insertion). In this case, suppose that the amount of data composing each of the information packets #1to #n before the CRC insertion is 128 bytes, for example.

Then, the transmitter18transmits the parity packets #1to #m (coded at the physical layer after the CRC insertion), when it is presumed that the receiver38has made a retransmission request. In this case, the size of one parity packet before the CRC insertion should be 64 bytes which is smaller than the size of one information packet before the CRC insertion at the time of the initial transmission.

The transmitter18transmits information packets #1to #k (coded at the physical layer after the CRC insertion) with use of the information packets stored in the storage unit161of the packet data coding unit102g, when it is presumed that the receiver38has made the retransmission request. In this case, it is important that the size of one information packet before the CRC insertion at the time of the second retransmission is smaller than the size of one information packet before the CRC insertion at the time of the initial transmission. Thus, the size of one information packet before the CRC insertion at the time of the second retransmission is, for example, 64 bytes which is smaller than the size of one information packet before the CRC insertion at the time of the initial transmission.

Note that the above-stated data amount of one information packet at the time of the initial transmission, and the data amount of one parity packet at the time of each of the initial and second retransmissions are merely examples. Therefore, any data amount is possible as long as the data amount of one information packet at the time of the second retransmission is smaller than the data amount of one information packet at the time of the initial transmission.

Thus, the number of bits (to be eliminated) of the transmission data can be reduced by making the size of one packet to be retransmitted smaller as described in the above. This improves the reception quality.

Ninth Embodiment

The following describes a ninth embodiment of the present invention with reference to drawings. The present embodiment relates to a method for selecting a retransmission method.

FIG. 25is a flowchart showing an example of how to select a retransmission method pertaining to the present embodiment.

In order to reduce processing delay, for example, the transmission method determination unit may make setting, in view of a state of control processing such as the processing delay and a calculation size, such that the ARQ (Automatic repeat-request) is not changed. When the processing delay is not likely to occur or transmission efficiency is desired to be increased, on the other hand, the ARQ is changed. Therefore, the transmission method determination unit makes a selection as to whether the ARQ is changed or not (Step S101). When the ARQ is not changed as a result of the selection (S101: NO), the transmission method determination unit selects one of: the retransmission at the physical layer; the retransmission with use of the parity packet; and a combination of these retransmissions, as the retransmission method to be executed at the time of retransmission (Step S102).

When the ARQ is changed as a result of the selection (S101: YES), the transmission method determination unit judges whether or not communication to be performed is the multicast communication (Step S103). When the judgment is negative (S103: NO), the transmission method determination unit selects the retransmission with use of the physical layer as the retransmission method to be executed at the time of the retransmission (S104). When the judgment is positive (S103: YES), on the other hand, processing proceeds to Step S105. Note that it is possible to select, at this time, the retransmission with use of the parity packets as the retransmission method to be executed at the time of the retransmission.

The transmission method determination unit judges whether or not to determine the retransmission method in view of the state of control processing such as the processing delay and a calculation size (Step S105). When determining the retransmission method (S105: YES), the transmission method determination unit selects the retransmission with use of the parity packets as the retransmission method to be executed at the time of the retransmission (Step S106). When not determining the retransmission method (S105: NO), the transmission method determination unit judges whether or not the number of packets to be transmitted is equal to or greater than a threshold value (Step S107).

When the number of packets to be transmitted is smaller than the threshold value (S107:NO), the transmission method determination unit selects the retransmission at the physical layer as the retransmission method to be executed at the time of the retransmission (Step S108). This is because when the number of bits to be transmitted is small, the amount of retransmission data itself is small. Therefore, improvement of the transmission efficiency of data is small even if the retransmission with use of the parity packets is adopted. When the number of bits to be transmitted is equal to or greater than the threshold value (S107: YES), processing proceeds to Step S109. Note that it is possible to select, at this time, the retransmission with use of the parity packets as the retransmission method to be executed at the time of the retransmission.

The transmission method determination unit judges whether or not to determine the retransmission method in view of the state of control processing such as the processing delay and the calculation size (Step S109). When determining the retransmission method (S109: YES), the transmission method determination unit selects the retransmission with use of the parity packets as the retransmission method to be executed at the time of the retransmission (Step S110). When not determining the retransmission method (S109: NO), the transmission method determination unit judges whether or not the number of erroneous packets to be transmitted is equal to or greater than a threshold value (Step S111).

When the number of erroneous packets is equal to or smaller than the threshold value (S111: YES), the transmission method determination unit selects the retransmission with use of the parity packets (Step S112). When the number of erroneous packets is equal to or greater than the threshold value (S111: NO), on the other hand, the transmission method determination unit selects the combination of the retransmission at the physical layer and the retransmission with use of the parity packets as the retransmission method to be executed at the time of the retransmission (Step S113).

As described in the above, there is a merit that it is possible to realize both the improvement of the data reception quality and the improvement of the data transmission efficiency, by selecting one of (1) the retransmission at the physical layer, (2) the retransmission with use of the parity packets and (3) the combination of these retransmissions. Note that criterion for selecting the retransmission method to be executed at the time of the retransmission is not limited to the method shown inFIG. 25. Although the example is given of the case where one of the retransmission methods is selected in the above, it is possible to make a selection that the retransmission is not performed.

Also, when the retransmission is performed in the multicast communication mode as shown inFIG. 12, the transmitter initially transmits the same information packets to each of a plurality of receivers. The transmitter receives, form each of the receivers, the feedback information including the information relating to the packet error occurrence. In this case, there are two possible patterns.

A case <1> is a case where the number of erroneous information packets in each of the receivers A, B and C is close to one another as shown in the following. For example, the number of erroneous information packets in a receiver A, the number of erroneous information packets in a receiver B and the number of erroneous information packets in a receiver C are three, two and three, respectively.

A case <2> is a case where the number of erroneous information packets in each of the receivers is not close to one another as shown in the following. For example, the number of erroneous information packets in the receiver A, the number of erroneous information packets in the receiver B, the number of erroneous information packets in the receiver C and the number of erroneous information packets D are three, three, three and five, respectively.

In the case <1>, the number of parity packets to be transmitted can be easily calculated at the time of the retransmission. Thus, selection of the retransmission with use of the parity packets is highly likely to be prioritized (seeFIG. 14and the description for the same for the explanations on the number of parity packets to be retransmitted). However, when the number of erroneous information packets is large in all of the receivers, it is highly likely to combine the retransmission at the physical layer and the retransmission with use of the parity packets.

In the case <2>, the receiver having the large number of erroneous information packets is specified. In the above case <2>, the receiver having the large number of erroneous information packets is the receiver D. Then, the transmitter extracts the erroneous information packets at the receiver D, generates, for the extracted information packets, the retransmission data to be retransmitted at the physical layer, and retransmits the generated retransmission data. However, it is not necessary to retransmit all the erroneous information packets at the physical layer. Thus, since it is assumed that the number of erroneous information packets in each of the receivers is identical, the transmitter transmits four or more parity packets. Thus, it is highly likely that the packet error does not occur at the time of the retransmission in all the receivers. It is presumed in the above case that the number of bits composing the information packets and the number of bits composing the parity packets are identical.

In a case where: the number of terminals is large; and a terminal exists that has the outstandingly large number of erroneous packets, the transmitter may exceptionally perform, at the physical layer, the retransmission to the terminal with use of the information packets as described in the case <2>. However, when the number of terminals is large, it is difficult to dynamically select a terminal to which the exceptional retransmission is performed. Therefore, it is preferable to provide a threshold value for the number of erroneous packets, and to retransmit, at the physical layer, the information packets to the terminals in each of which the number of packet error is larger than the threshold value. However, when the number of terminals (in each of which the number of packet errors is larger than the threshold value) is large, the retransmission at the physical layer needs to be performed for all the information packets in some cases. In this case, since the data transmission efficiency decreases as the parity packets are transmitted, the transmitter does not have to transmit the parity packets. In order to make sure that the packets are transmitted to all the terminals at once without an error, the parity packets may be transmitted. This selection depends on request condition of a communication system.

The following describes one example with reference toFIG. 26. Suppose that the transmitter transmits the information packets #1to #7and that three information packets, three information packets, three information packets and five information packets are missing in the receivers A, B, C and D, respectively. That is, suppose that the number of missing information packets in the receiver D is larger than the number of missing information packets in each of the receivers A, B and C. Suppose also that the number of bits composing the information packets and the number of bits composing the parity packets are identical. In this case, when the number of parity packets to be retransmitted is determined in accordance with the same rules as the rules described inFIG. 14, it is necessary to determine the number of parity packets to be retransmitted based on the receiver D. In this case, it is necessary to retransmit six or more parity packets. However, such number of parity packets is an amount of redundant retransmission data for each of the receivers A, B and C. In this case, it is possible to adopt the following method. According to the method, the number of parity packets to be retransmitted is four, and two information packets are transmitted to the receiver D. In this case, it is possible to obtain a merit in terms of data transmission efficiency by using the hybrid ARQ at the physical layer for the information packets to be transmitted to the receiver D.

As described in the above, it is possible to obtain especially an effect of reducing the number of retransmissions by adopting the retransmission method of selecting one of: the retransmission at the physical layer; the retransmission with use of the parity packets; and the combination of these transmissions. Therefore, it is possible to obtain an effect of improving the data transmission efficiency.

Tenth Embodiment

The following describes a tenth embodiment of the present invention with reference to drawings. The tenth embodiment describes details of the coding method (coding method at a packet level) at a layer at which signal processing is performed earlier than at the physical layer.

FIG. 28shows an example of coding methods at a layer at which signal processing is performed earlier than at the physical layer. InFIG. 28, the coding rate of the error correction codes is 2/3, and the size of data of one packet (excluding control information and information on error detection codes etc.) is 512 bits.

InFIG. 28, in the coding processing at a layer at which signal processing is performed earlier than at the physical layer (coding at a packet level), parities are generated by interleaving the information packets #1to #8and then coding the information packets #1to #8. Some of generated parities that correspond to 512 bits compose a group as one parity packet. Here, since the coding rate is 2/3, the number of parity packets is four. That is, parity packets #1to #4are generated. Therefore, the information packets described in the other embodiments correspond to the information packets #1to #8inFIG. 28. The parity packets correspond to the parity packets #1to #4inFIG. 29. Note that the size of the parity packet is 512 bits which is the same as the size of the information packet for simplifying the descriptions. However, one parity packet does not have to have the same size as the size of the information packet.

FIG. 29shows an example of coding methods at a layer at which signal processing is performed earlier than at the physical layer, which is different from what is shown inFIG. 28. That is, the transmitter may execute the coding at a layer at which signal processing is performed earlier than at the physical layer with use of the coding method shown inFIG. 29instead of the coding method shown inFIG. 28. InFIG. 29, the information packets #1to #512are original information packets. A size of data of each of these information packets (excluding the control information and information on the error detection code etc.) is 512 bits. Then, each of the information packets #k (k=1, 2, . . . , 511 and 512) is divided into eight to generate the sub information packets #k−1, #k−2, . . . , and #k−8.

Therefore, when the coding is performed in accordance with the coding method shown inFIG. 29, the information packets described in the other embodiments correspond to the information packets #1to #512shown inFIG. 29. The parity packets correspond to parity packets #n−1, #n−2, . . . , and #n−m (n=1, 2, 3, 4, 5, 6, 7 and 8) shown inFIG. 30. In this case, although one information packet is 512 bits, one parity packet does not necessarily have to be 512 bits.

Note that each of the sub information packets obtained as a result of the division may be one packet inFIG. 29.

Also, as described in the other embodiments, the error correction codes are inserted into the information packets and the parity packets. The error correction coding is performed on the information packets and the parity packets at the physical layer.

Eleventh Embodiment

The following describes an eleventh embodiment of the present invention with reference to drawings. The eleventh embodiment describes details of multicast relay/retransmission method in a repeater.

FIG. 31shows a relationship between a base station (or an access point), repeaters and terminals in the present embodiment. As shown inFIG. 31, the base station transmits the same packet group3400(hereinafter, referred to as packet group #A) to a plurality of terminals. In this case, the base station either directly transmits the packet group A to each of the terminals, or transmits the packet group #A to each of the terminals through the repeater.

According to an example shown inFIG. 31, a base station3100transmits the packet group #A (3400) to each of a terminal3300a, a terminal3300i, and a terminal3300j, a repeater3200a, a repeater3200band a repeater3200c. Then, the repeater3200a, the repeater3200band the repeater3200crespectively relay the received packet group #A (3400) to terminals3300bto3300e, terminals3300fto3300gand a terminal3300h.

Note that the base station and the terminal respectively correspond to the transmitter and the receiver described in the above embodiments. Also, the repeater is a device that includes the functions of both the transmitters and the receivers described in the above embodiments, and further includes functions unique to the repeater. This applies to the rest of after-mentioned embodiments.

FIG. 32shows a configuration example of the packet group #A in the base station when the base station transmits the packet group #A to the terminals through the repeater. Since the base station performs the transmission in the multicast communication mode, the base station performs coding at a layer at which signal processing is performed earlier than at the physical layer (i.e. coding at a packet level). Thus, there is a merit that coding at a packet level is suitable for the multicast transmission. However, when the base station transmits the packet group to the terminals through the repeaters, the repeaters make retransmission requests to the base station if transmission error occurs between the base station and the repeaters. However, when many repeaters exist, the number of retransmission requests increases. As a result, the data transmission efficiency dramatically decreases. Therefore, it is suitable that the base station performs the coding at a packet level between the base station and the repeaters.

As shown inFIG. 32, the base station (1) generates the parity packets #1to #m by coding the information packets #1to #n at a packet level, (2) inserts the error detection codes (e.g. CRC) into the information packets #1to #n and the generated parity packets #1to #m, and (3) generates the information packets #1to #n (coded at the physical layer after the CRC insertion) and the parity packets #1to #m (coded at the physical layer after the CRC insertion) by performing the coding at the physical layer. Then, the base station performs predetermined transmission processing on these packets and transmits the resultant packets.

The repeater can switch a method of communicating with the terminals in accordance with the number of terminals the repeaters communicate with and a data type, for example. However, the present embodiment especially describes a case where the multicast retransmission method is adopted in which the repeaters retransmits data to a plurality of terminals. Note that a fourteenth embodiment describes details of switching between communication methods.

FIG. 33shows an example of communication between the repeaters and the terminals in the present embodiment. Each of the repeaters receives the information packets and parity packets that are transmitted from the base station. Each of the repeaters performs decoding at a packet level to obtain the information packets, inserts the error detection codes (e.g. CRC) into each of the information packets, performs the coding at the physical layer, and transmits the information packets #1to #n (coded at the physical layer after the CRC insertion) to each of the terminals. Here, a packet group to be transmitted is a packet group G1.

Here, it is recited that the repeaters initially transmit only the information packets to each of the terminals. The following describes the reasons for this. It is possible to accurately perform transmission to the terminals that are positioned far from the base station. Also, it is unlikely that the coding at a packet level needs to be adopted because: a transmission distance is often shorter compared to a case where the base station directly communicates with the terminals; and a communication quality between the repeaters and the terminals is high.

Then, each of the repeaters determines the number of parity packets to be retransmitted and the transmission method, with use of a transmission request and the feedback information that are received from one of the terminals #A, #B and #C. Then, each of the repeaters transmits the parity packets (coded at the physical layer after the CRC insertion) (i.e. parity packets corresponding to the packet group G1) as packets for retransmission, as shown inFIG. 33. In this case, a method that is identical to any of the methods described in the first embodiment, the second embodiment and the sixth embodiment can be executed.

An exemplary structure of the base station in the present embodiment is as shown inFIG. 1. SinceFIG. 1is described in the other embodiments, the details of the structure of the base station is omitted.

The packet data coding unit102hshown inFIG. 34is different from the packet data coding unit102shown inFIG. 2in that the packet data coding unit102hhas a processing unit3401. The base station performs coding at a packet level in the multicast communication mode as described in the above. Examples of the communication are the multicast communication, the unicast communication and a mode in which the base station communicates with the terminal without passing through the repeater. Therefore, the processing unit3401outputs the packets that are suitable for each of the communication modes. Accordingly, there are cases; where the base station transmits only the information packets; where the base station transmits the information packets and the parity packets; and where the base station transmits the information packets and transmits the parity packets at the time of retransmission. The processing unit3401outputs the packets133that are suitable for each of the cases.

FIG. 35is different fromFIG. 34, and shows a structural example of the packet data coding unit102of the base station shown inFIG. 1. The same references are given to elements that operate in the same manner as the elements shown inFIG. 2. The packet data coding unit102ishown inFIG. 35may be adopted instead of the packet data coding unit102hshown inFIG. 34. The following describes how a packet coding unit102ishown inFIG. 35is different from the packet data coding unit102hshown inFIG. 34. The coding unit102iperforms the coding at a layer at which signal processing is performed earlier than at the physical layer (i.e. decoding at a packet level) without distinguishing between the information packets and the parity packets to generate the packets composed of both the information pieces and parities. The coding unit152shown inFIG. 35receives the interleaved information171as an input. The coding unit152codes the interleaved information171, and outputs the packets172. In the example shown inFIG. 35, the coding unit152outputs the packets #1to #h. Note that the coder may be a coder for systematic codes, or a coder for non-systematic codes. The base station performs the coding at a packet level in the multicast communication mode as described above. However, the base station actually does not perform the coding in the multicast communication mode in some cases. Therefore, when the coding at a packet level is necessary, a selection unit3501selects and outputs the packets #1to #h. When the coding at a packet level is not necessary, the selection unit3501selects and outputs the information packets #1to #n.

FIG. 36shows an example of communication between the base station, the repeaters and the terminals in the present embodiment. As shown inFIG. 36, the base station transmits the packet group #A including missing packets composed of the information packets and the parity packets for the multicast communication.

Each of the repeaters receives the packet group #A including missing packets. The repeater decodes the packet group #A at a packet level, extracts the information packets and transmits the information packets to a plurality of terminals.

A terminal #A receives the information packets transmitted by the repeater. When packet loss occurs, the terminal #A makes a retransmission request to the repeater, and transmits the feedback information such as the number of lost packets and the numbers of the lost information packets. A terminal #B receives the information packets transmitted by the repeaters. When packet loss occurs, the terminal #B makes retransmission requests to the repeaters, and transmits the feedback information such as the number of lost packets and the numbers of the lost information packets.

The repeater determines the retransmission in accordance with the feedback information of the terminals #A and #B, and transmits the parity packets of the packet group #A. Then, each of the terminals decodes the previously received information packets and the received parity packets at a packet level to obtain the information packets.

FIG. 37shows an example of the structure of a repeater3200A of the present embodiment. The repeater includes the substantially the same structure as the structure of the receiver shown in the above embodiments. Therefore, the same reference numerals are provided with elements that operate in the same manner as the elements shown inFIG. 4. When the base station3200A transmits the packet group #A, the reception unit302extracts the control information (corresponding to signal332) transmitted together with the packet group #A. The communication method identifying unit303receives the signal332as an input. The communication method identifying unit303identifies information on the communication method, and outputs communication method information334.

A packet separation unit3701receives, as inputs, the decoded packet341and the communication method information334. In the case ofFIG. 37, the packet separation unit3701judges that the base station transmits the packets that have been coded at a packet level, with use of the communication method information334. Then, the packet separation unit3701separates the packet group #A of the decoded packets341into the information packets and parity packets, and outputs information packets3702and parity packets3903. Note that error detection codes may be inserted into the information packets3702and parity packets3903at this time. Since the error detection code insertion has been performed in the base station, the repeater3200A can easily obtain the information packets and parity packets to which the error detection codes have been inserted.

A control information detection unit3705extracts, for example, the control information included in data transmitted by the terminals. The control information detection unit3705recognizes whether or not the retransmission request is made and a situation of the packet loss occurred in the terminals. Then, the control information detection unit3705outputs a control signal3706relating to the transmission method of retransmission and whether or not to perform the retransmission. Also, the control information detection unit3705extracts the control information included in data transmitted by the base station. When the extracted control information indicates that the data is data for the multicast communication, the control information detection unit3705outputs, as the control signal3706, an instruction showing that the repeater3200A should transmit the information packets.

The storage unit3704receives the parity packets3903and the control signal3706as inputs, and stores the parity packets3903in the storage unit3704. When the control signal3706is information regarding retransmission to the terminals, the storage unit3704determines the number of parity packets to be outputted from among the stored parity packets based on the information, and outputs the parity packets3907to be retransmitted.

The selection unit3708receives, as inputs, the information packets3702, the parity packets3907to be retransmitted and the control signal3706. When the control signal3706indicates transmission of the information packets, the selection unit3708selects the information packets3702and outputs the selected packets3702as the packets3709. Also, when the control signal3706indicates retransmission to the terminals, the selection unit3708selects the parity packets3707and outputs the selected packets3707as the packets3709.

The physical layer coding unit3710receives, as inputs, the packets3709selected by the selection unit3708. The physical layer coding unit3710outputs data3711that has been coded at the physical layer.

A control signal generation unit3712receives the control signal3706as an input. The control signal generation unit3712outputs the control information3713including control information that needs to be transmitted to a communication apparatus (e.g. terminal). Examples of information included in such control information are information on whether or not data is retransmission data, information on the number of retransmissions, information on a modulation method, information on the coding method at a packet level and information on a method of coding at the physical layer.

The modulation unit3714receives, as inputs, the data3711that has been coded at the physical layer and the control information3713. The modulation unit3714performs modulation (mapping) such as PSK and QAM, and outputs a base band signal3715.

A transmission unit3716receives the base band signal3715as an input. The transmission unit3716performs OFDM (Orthogonal Frequency Division Multiplexing) and/or processing such as spectral dispersion, frequency conversion and amplification, and outputs the resultant transmission signal3717to an antenna3718. The antenna3718outputs the transmission signal3717.

The structure of each of the terminals is the same as the structure shown inFIG. 4described in the first embodiment, the second embodiment and the sixth embodiment. Therefore, since the operations of each of the terminals are described in the above embodiments, the descriptions thereof are omitted.

FIG. 38is different fromFIG. 36, and shows an example of communication among the base station, the repeater and the terminals. Specifically,FIG. 38shows an example of communication in a case where the base station either “uses the systematic codes in performing coding at a packet level, and transmits the packets composed of both the information pieces and parities” or “transmits packets that are coded with use of non-systematic codes at a packet level” described with use ofFIG. 35. In this case, the base station does not clearly distinguish between the information packets and the parity packets. Therefore, it is difficult for the packet separation unit3701to separate the packets as shown inFIG. 37. That is, the packet separation unit3701is unable to separate the packets into the information packets and parity packets. Therefore, as shown inFIG. 39which is a structural diagram of the repeater in this case, the repeater3200B includes a packet level coding unit3901instead of the packet separation unit3701shown inFIG. 37.

As shown inFIG. 38, the repeater receives the packet group #A transmitted by the base station, and restores packets of the missing packet group #A by decoding the packet group #A at a packet level. Then, the repeater generates the information packets with use of the restored packets. Then, the repeater transmits the information packets to each of the plurality of terminals.

A terminal #A receives the information packets transmitted by the repeater. When packet loss occurs, the terminal #A makes a retransmission request to the repeater, and transmits the feedback information including the number of lost packets and the numbers of the lost information packets, for example. Similarly, a terminal #B receives the information packets transmitted by the repeater. When packet loss occurs, the terminal #B makes a retransmission request to the repeater, and transmits the feedback information including the number of lost packets and the numbers of the lost information packets, for example.

In this case, when the terminals make retransmission requests (e.g. when the plurality of terminals make retransmission requests), the repeater transmits the parity packets as the data to be retransmitted. Here, the retransmission with use of the parity packets has a merit regarding the retransmission method in the multicast communication mode. However, this case is different from the case shown inFIG. 36in that the repeater needs to code the information packets at a packet level, and to generate the parity packets.

Therefore, the repeater3200B is different, as shown inFIG. 39, from the repeater3200A shown inFIG. 37as follows. The repeater3200B receives, as inputs, information packets, and the repeater3200B includes a coding unit3901that performs the coding at a packet level to output the information packets3902and the parity packets3903. Note that although the error detection coding unit is not depicted inFIG. 37, the coding unit3901inserts the error detection codes into the packets. Since elements shown inFIG. 39are the same as the elements shown inFIG. 37except for the coding unit3901, the descriptions of these elements are omitted.

As described in the above, when the repeater3200B relay the packets for the multicast communication (transmitted from the base station), the repeater3200B generates the information packets and parity packets so as to enable the retransmission in the multicast communication mode. When the plurality of terminals make retransmission requests, the repeater3200B transmits the parity packets. In such a way, it is possible to improve the data transmission efficiency. Note that the present embodiment describes retransmission with use of the packets. However, when the repeater receives the retransmission requests from the terminals, the repeater may combine the retransmission with use of the packets and the retransmission at the physical layer, as shown inFIGS. 17 and 19.

Also, a description is given of the exemplary case where the base station transmits, to the repeater, the packets that have been coded at a packet level. However, the present invention is not limited to this case. There may be a case where the repeater transmits the packets that have not been coded at a packet level. In this case, when the packet loss occurs, the repeater makes a retransmission request to the base station, and the base station retransmits the packets in accordance with the retransmission request. Also, the repeater may have both of the structures shown inFIG. 37andFIG. 39.

Twelfth Embodiment

The following describes a twelfth embodiment of the present invention with reference to drawings. The twelfth embodiment describes a multicast relay/retransmission method used in the repeater. Here, this method is capable of shortening time of delay before the packets reach each of the terminals compared to the eleventh embodiment.

FIGS. 40A,40B,40C and40D show an example showing a structure of packets to be transmitted by the base station, the repeaters and the terminals in the present embodiment.FIG. 40Ashows packets to be transmitted from the base station to the repeater (also referred to as a direct terminal). The base station performs the coding at a layer at which signal processing is performed earlier than at the physical layer (i.e. coding at a packet level). The base station transmits, to the repeater (also referred to as the direct terminal) information packets #1to #100(coded at the physical layer after the CRC insertion) and parity packets #1to #25(coded at the physical layer after the CRC insertion).

Then, the repeater receives the packets transmitted by the base station. As shown inFIG. 40B, suppose that: 20 packets (information packets #1, #5, #6, #8, #21, #29, #33, #34, #45, #47, #53, #57, #68, #79, #83and #90, and parity packets #4, #8, #9and #24) cannot be obtained as a result of decoding at the physical layer; these 20 packets are missing before the decoding at a packet level; and 105 packets excluding these 20 packets are obtained, for example.

In this case, at first, the repeater transmits, to each of the terminals, 105 packets excluding 20 packets of4001shown inFIG. 40C. When the terminals make retransmission requests, the repeater obtains 20 packets (information packets #1, #5, #6, #8, #21, #29, #33, #34, #45, #47, #53, #57, #68, #79, #83and #90, and parity packets #4, #8, #9and #24that are missing before the decoding at a packet level) shown inFIG. 40Das a result of the decoding at a packet level, and transmits these 20 packets as packets for retransmission. However,FIG. 40A,FIG. 40B,FIG. 40CandFIG. 40Dshow the exemplary case where 20 packets (information packets #1, #5, #6, #8, #21, #29, #33, #34, #45, #47, #53, #57, #68, #79, #83and #90, and parity packets #4, #8, #9and #24) are retransmitted. However, the data transmission efficiency may be prioritized and, the repeater may select the number of packets that is less than 20 from among 20 packets and retransmits the selected packets.

The following is possible, for example. The repeater may select 15 packets from among the above 20 packets at the time of the first retransmission, and transmits the selected packets as the packets for retransmission. When the terminals make retransmission requests again, the repeater transmits five packets that have not been transmitted to each of the terminals from among the above 20 packets, at the time of the second retransmission. In this case, the repeater may notify each of the terminals of the number of packets to be transmitted each time the repeater performs retransmission. The repeater performs the notification by transmitting the number of packets as the control information, for example.

As described in the above, the case shown inFIGS. 40A,40B,40C and40D is characterized in that the repeater transmits, to each of the terminals, the packets obtained before the decoding at a packet level first; and when the terminals make retransmission requests, the repeater transmits restored packets obtained as a result of the decoding at a packet level. Note that a description is given later of an effect of the multicast relay/retransmission method used in the repeater as shown inFIGS. 40A,40B,40C and40D, with use ofFIG. 42andFIG. 43.

FIGS. 41A,41B,41C and41D are different fromFIGS. 40A,40B,40C and40D, and show an example showing a structure of packets to be transmitted by the base station, the repeaters and the terminals in the present embodiment. In an example shown below, the data size of one information packet and the data size of one parity packet (excluding control information and information on error detection codes) are identical.FIG. 41Ashows packets to be transmitted by the base station to the repeater (also referred to as the direct terminal). The base station performs the coding at a layer at which signal processing is performed earlier than at the physical layer (i.e. coding at a packet level). The base station transmits, to the repeater (also referred to as the direct terminal), information packets #1to #100(coded at the physical layer after the CRC insertion) and parity packets #1to #25(coded at the physical layer after the CRC insertion). This transmission is performed in the same manner as the transmission shown inFIG. 40A.

Then, the repeater receives the packets transmitted by the base station. As shown inFIG. 41B, suppose that: ten packets (information packets #1, #6, #21, #34, #68, #79and #90and parity packets #4and #24) are missing; and that 115 packets excluding the above ten packets are obtained, for example.

In this case, the number of packets to be initially transmitted is limited in order to improve the data transmission efficiency. In this example, the data size of one information packet and the data size of one parity packet (excluding control information and information on error detection codes) are identical. Therefore, if 101 or more packets (composed of information packets and parity packets) are initially transmitted, each of the terminals can restore the information packets by performing the decoding at a packet level. Therefore, the repeater initially transmits 110 packets in this case. Specifically, the repeater selects 110 packets from among 115 packets obtained by the decoding at the physical layer (e.g. 110 packets shown inFIG. 41C), and initially transmits, to each of the terminals, the selected 110 packets.

When the terminals make retransmission requests, the repeater transmits 15 packets (e.g. 15 packets shown inFIG. 41D) excluding the packets selected and initially transmitted, for example. Note that when the repeater retransmits the packets, the ten packets (information packets #1, #6, #21, #34, #68, #79and #90and parity packets #4and #24) that are missing before the decoding at a packet level are restored by the decoding at a packet level. Therefore, the repeater may also retransmit the packets that have been restored by the decoding at a packet level.

In the example shown inFIGS. 41A,41B,41C and41D, the repeater initially transmits 110 packets, and retransmits 15 packets that have not been initially transmitted. However, the data transmission speed may be prioritized, and the repeater may select, from among 15 packets, the number of packets that is smaller than 15 packets and retransmits the selected packets.

The following example is possible. The repeater selects ten packets from among 15 packets that have not been initially transmitted and transmits the selected packets at the time of the first retransmission. When the terminals make retransmission requests again, the repeater selects five packets that have not been transmitted to the terminals, and retransmits the selected five packets at the time of the second retransmission.

As described in the above, the example shown inFIGS. 41A,41B,41C and41D is characterized in that: the repeater transmits a predetermined number of packets to each of the terminals from among the packets obtained before the decoding at a packet level; and when terminals make retransmission requests, the repeater selects packets to be retransmitted from among the restored packets obtained as a result of the decoding at a packet level and the packets that have not been initially transmitted, and transmits the selected packets. Note that a description is given later of an effect of the multicast relay/retransmission method used in the repeater as shown inFIGS. 41A,41B,41C and41D, with use ofFIG. 42andFIG. 43.

It is natural that the number of packets to be initially transmitted is not limited to 110 packets inFIGS. 41A,41B,41C and41D. Therefore, the number of packets to be initially transmitted may be any number as long as the number is enough to restore the information packets by the decoding at a packet level in each of the terminals. Also, the repeater may change the number (the number of packets to be initially retransmitted) as time lapses. For example, the repeater may recognize a communication state with each of the terminals with use of the feedback information obtained from the terminal, and changes the number of packets to be initially transmitted in accordance with the state. Specifically, when the communication state is judged to be well, the number of packets to be initially transmitted is reduced. When the communication state is judged to be not well, the number of packets to be initially transmitted is increased. The state of the communication state is judged in accordance with reception strength and a packet error rate in each of the terminals, for example. Note that it is preferable that the repeater notifies the terminals of the numbers of packets to be transmitted each time the repeater performs transmission in this case. That is, the repeater preferably transmits the number of packets that have been transmitted, as control information.

Also, in the example described with use ofFIGS. 41A,41B,41C and41D, the data size of one information packet and the data size of one parity packet (excluding control information and information on the error detection codes, for example) are identical. However, it is possible to execute the above operations even if the data size of one information packet and the data size of one parity packet are different. However, it is necessary that the amount of information the repeater needs to initially transmit is set such that a total number of bits composing information packets and parity packets to be initially transmitted is larger than X bits. Here, X bits is the number of all information bits composing actual data that is obtained after each of the terminals receives and decodes the packets.

For example, when the number of bits composing one information packet (excluding information other than information such as control information) is 512 bits inFIGS. 41A,41B,41C and41D, the numbers of bits to be transmitted to the terminals are each 51200 bits (512 (the number of bits composing one packet)×100 (number of information packets)). Therefore, the repeater should initially transmit the number of information packets and parity packets so that the number of bits composing all the information packets and parity packets is larger than 51200 bits.

The following describes the effects of the relay method and the multicast relay method used in the repeater (described with use ofFIGS. 40A,40B,40C and40D andFIGS. 41A,41B,41C and41D), with use ofFIG. 42andFIG. 43.

FIG. 42is a conceptual diagram showing one brief example of signal processing timing in a time axis at the time of the relaying and the multicast retransmission described in the eleventh embodiment. As shown inFIG. 42, the repeater performs the decoding at the physical layer, error detection and the decoding at a packet level in the state order. Subsequently, the repeater performs the initial transmission to each of the terminals. Then, when the terminals make retransmission requests, the repeater performs the retransmission to the terminal.

FIG. 43is a conceptual diagram showing one brief example of signal processing timing in a time axis at the time of the relaying and the multicast retransmission described in the present embodiment.FIG. 43is different fromFIG. 42in that the repeater performs, inFIG. 43, the initial transmission to each of the terminals without the decoding at a packet level. That is, in the example shown inFIG. 43, the repeater starts the decoding at a packet level inFIG. 42with timing that the repeater starts the initial transmission. Then, the repeater can perform the decoding at a packet level and generate packets to be retransmitted while performing the initial transmission to each of the terminals.

Therefore, it is possible to shorten time of delay before the packets reach each of the terminals compared to the eleventh embodiment with the multicast relay/retransmission method used in the repeater of the present embodiment.

FIG. 44shows an exemplary operation in the repeater. The repeater receives the packets transmitted by the base station, and judges whether or not the number of missing packets before the decoding at a packet level is equal to or less than the threshold value. This is because since the number of bits (or the number of packets) necessary for restoring the packets by the decoding at a packet level is known as described in the above, it is possible to judge whether or not it is worthwhile to perform the decoding at a packet level. When the number of missing packets is not equal to or less than the threshold value, the repeater makes a retransmission request to the base station. When the number of missing packets is equal to or less than the threshold value, processing proceeds to a next step.

Subsequently, the repeater checks whether or not the time of delay before the packets reach each of the terminals should be prioritized. When the time of delay before the packets reach each of the terminals is not prioritized, the repeater selects the relay method or the retransmission method described in the eleventh embodiment, for example. When the time of delay before the packets reach each of the terminals is prioritized, the processing proceeds to a next step.

Next, the repeater checks whether or not data transfer speed is to be prioritized. When the data transfer speed is not prioritized, the repeater selects the relay method and the retransmission method shown inFIGS. 40A,40B,40C and40D. When the data transfer speed is prioritized, the repeater selects the relay method and the retransmission method shown inFIGS. 41A,41B,41C and41D.

Each of the relay methods and the retransmission methods may be a fixed method. However, it is possible to switch among the relay methods and the retransmission methods in accordance with the state as shown inFIG. 44.

The following describes the operations of each of the elements composing the repeater with use ofFIG. 45andFIG. 46.

FIG. 45shows an example of the structure of a repeater3200C that uses the relay and multicast retransmission method shown inFIGS. 40A,40B,40C and40D. Therefore, the same reference numerals are given to the elements that operate in the same manner as the elements shown inFIG. 37. The following describes differences in operations betweenFIG. 45andFIG. 37.

InFIG. 45, it is possible to recognize packets having no errors after the decoding at the physical layer with use of the error detection result and the packet data336. Also, the error detection unit305outputs a control signal4501relating to the numbers of the erroneous packets.

The storage unit3704receives, as inputs, the packets341obtained by the decoding at a packet level and a control signal4501. The storage unit3704extracts the packets that have been restored by the decoding at a packet level and stores the decoded packets therein. Also, the storage unit3704receives a control signal3706as an input. When the control signal3706is information relating to the retransmission to each of the terminals, the storage unit3704selects the number of packets to be outputted from among the stored packets based on such information, and outputs the packets3707to be retransmitted.

The selection unit3708receives, as inputs, the error detection result, the packet data336, the packets3707to be retransmitted and the control signal3706. When the control signal3706indicates the initial transmission to the terminal, the selection unit3708selects the error detection result and the packet data336, and outputs the selected packets3709. The packet data336is packets having no error after the decoding at the physical layer. Then, the selection unit3708outputs the packets3707to be retransmitted when the control signal3706indicates retransmission to each of the terminals.

FIG. 46shows an example of the structure of a repeater3200D that uses the relay and multicast retransmission method shown inFIGS. 41A,41B,41C and41D. Therefore, the same reference numerals are given to the elements that operate in the same manner as the elements shown inFIG. 37. The following describes differences betweenFIG. 46andFIG. 37.

InFIG. 46, it is possible to recognize packets having no errors by the decoding at the physical layer with use of the error detection result and the packet data336.

A distribution unit4601receives, as inputs, the result of the error detection and the packet data336. The distribution unit4601outputs the number of packets to be initially transmitted from among the packets having no error (after the decoding at the physical layer) as packets4602to be initially transmitted, and outputs the rest of the packets4603as packets for retransmission. Also, the distribution unit4601outputs the control signal4604relating to the information of the distributed packets.

The storage unit3704receives, as inputs, the packets341obtained by the decoding at a packet level, the packets3707to be retransmitted and the control signal4604. The storage unit3704extracts the packets that have been restored by the decoding at a packet level and stores therein the decoded packets together with the packets3707to be retransmitted. Also, the storage unit3704receives the control signal3706as an input. When the control signal3706is information relating to the retransmission to each of the terminals, the storage unit3704selects the number of packets to be outputted from among the stored packets based on such information, and outputs the packets3707to be retransmitted.

The selection unit3708receives, as inputs, initial transmission packets4602, the packets3707to be retransmitted and the control signals3706. When the control signal3706indicates the initial transmission to each of the terminals, the selection unit3708selects the packets3707to be retransmitted and outputs the selected packets3709. Then, the selection unit3708outputs the packet3707to be retransmitted when the control signal3706indicates retransmission to each of the terminals.

FIGS. 47A,47B,47C and47D and48A,48B,48C and48D are different fromFIGS. 40A,40B,40C and41D and41A,41B,41C and41D, and show an example showing a structure of packets to be transmitted by the base station, the repeaters and the terminals in the present embodiment. In an example shown below, the data size of one information packet and the data size of one packet (excluding control information and information on error detection codes) are identical. The following describes howFIGS. 47A,47B,47C and47D and48A,48B,48C and48D are greatly different fromFIGS. 40A,40B,40C and41D and41A,41B,41C and41D. InFIGS. 40A,40B,40C and41D and41A,41B,41C and41D, the information packets and the parity packets are distinguished. InFIGS. 47A,47B,47C and47D and48A,48B,48C and48D, on the other hand, the information packets and the parity packets are not distinguished. Therefore, when the systematic codes are used in the coding at a packet level inFIGS. 47A,47B,47C and47D and48A,48B,48C and48D, the packets are composed of information pieces and parities. Note that the codes used in the coding at a packet level may be non-systematic codes.

FIG. 47Ashows packets to be transmitted by the base station to the repeater (also referred to as the direct terminal). The base station performs the coding at a layer at which signal processing is performed earlier than at the physical layer (i.e. coding at a packet level). The base station codes information packets #1to #100(coded at the physical layer after the CRC insertion) to generate parity packets #101to #125. Then, the base station transmits the packets #1to #125to the repeater (also referred to as the direct terminal).

Then, the repeater receives the packets transmitted by the base station. As shown inFIG. 47B, suppose that: 20 packets (packets #1, #5, #6, #8, #21, #29, #33, #34, #45, #47, #53, #57, #68, #79, #83, #90, #104, #108, #109and #124) cannot be obtained as a result of the coding at the physical layer; these 20 packets are missing before the coding at a packet level; and 105 packets excluding the above 20 packets are obtained, for example.

The following is possible, for example. The repeater may select 15 packets from among the above 20 packets at the time of the first retransmission, and transmits the selected packets as the packets for retransmission. When the terminals make retransmission requests again, the repeater transmits five packets that have not been transmitted to each of the terminals from among the above 20 packets, at the time of the second retransmission. In this case, the repeater may notify each of the terminals of the number of packets to be transmitted each time the repeater performs retransmission. The repeater performs the notification by transmitting the number of packets as the control information, for example.

As described in the above, the case shown inFIGS. 47A,47B,47C and47D is characterized in that the repeater transmits, to each of the terminals, the packets obtained before the decoding at a packet level first; and when the terminals make retransmission requests, the repeater transmits restored packets obtained as a result of the decoding at a packet level.

FIGS. 48A,48B,48C and48D show an example showing a structure of packets to be transmitted by the base station, the repeaters and the terminals in the present embodiment. In an example shown below, the data size of one information packet and the data size of one packet (excluding control information and information on error detection codes) are identical.

FIG. 48Ashows packets to be transmitted by the base station to the repeater (also referred to as the direct terminal). The base station performs the coding at a layer at which signal processing is performed earlier than at the physical layer (i.e. coding at a packet level). The base station codes information packets #1to #100(coded at the physical layer after the CRC insertion) to generate packets #101to #125. Then, the base station transmits the packets #1to #125to the repeater (also referred to as the direct terminal).

Then, the repeater receives the packets transmitted by the base station. As shown inFIG. 48B, suppose that: 10 packets (packets #1, #6, #21, #29, #34, #68, #79, #90, #104and #124) cannot be obtained as a result of the coding at the physical layer; these 10 packets are missing before the coding at a packet level; and 115 packets excluding the above 10 packets are obtained, for example.

In this case, the number of packets to be initially transmitted is limited in order to improve the data transmission efficiency. In this example, the data size of one information packet and the data size of one packet (excluding control information and information on error detection codes) are identical. Therefore, if 101 or more packets are initially transmitted, each of the terminals receives 101 or more packets without losing any of the packets. Therefore, each of the terminals can restore the information packets by the decoding at a packet level. Therefore, the repeater initially transmits 110 packets and selects 110 packets from among 115 packets obtained as a result of the decoding at the physical layer. Then, the repeater initially transmits the selected 110 packets shown inFIG. 48Cto each of the terminals.

When the terminals make retransmission requests, the repeater transmits 15 packets excluding the initially-transmitted packets, for example. Note that 10 packets (packets #1, #6, #21, #29, #34, #68, #79, #90, #104and #124that are missing before the decoding at a packet level) are restored by the decoding at a packet level.

In the case shown inFIGS. 48A,48B,48C and48D, the repeater initially transmits 110 packets and retransmits 15 packets that have not been initially transmitted. However, the data transmission speed may be prioritized, and the repeater may select, from among 15 packets, the number of packets that is smaller than 15 packets, and retransmits the selected packets.

The following is possible, for example. The repeater may select 10 packets from among 15 packets that have not been initially transmitted, and transmits the selected packets as the packets at the time of the first retransmission. When the terminals make retransmission requests again, the repeater transmits five packets that have not been transmitted to each of the terminals, at the time of the second transmission.

As described in the above, the case shown in48A,48B,48C and48D is characterized in that: the repeater transmits, to each of the terminals, a predetermined number of packets from among packets obtained before the decoding at a packet level first; and when the terminals make retransmission requests, the repeater selects packets to be transmitted from among the restored packets obtained by the decoding at a packet level and packets that have not been initially transmitted, and transmits the selected packets.

Note that when the relay and multicast retransmission method as shown inFIGS. 47A,47B,47C and47D or48A,48B,48C and48D is used, operations of the repeaters can be performed with use of the repeaters shown inFIG. 45andFIG. 46.

When the repeater relays packets for the multicast communication that are transmitted by the base station, the repeater initially transmits the packets having no error at the physical layer as shown in the above. The repeater retransmits the packets that are obtained as a result of the decoding at a packet level. In this way, it is possible to improve the data transmission efficiency and to shorten time taken for the packets to reach each of the terminals. Note that the present embodiment describes retransmission with use of the packets. However, when the repeater receives the retransmission request from each of the terminals, the repeater may combine the retransmission with use of the packets and the retransmission at the physical layer, as shown inFIG. 17andFIG. 19.

Also, a description is given of the exemplary case where the base station transmits, to the repeater, the packets that have been coded at a packet level. However, the present invention is not limited to this case. There may be a case where the repeater transmits the packets that have not been coded at a packet level. In this case, when the packet loss occurs, the repeater makes a retransmission request to the base station, and the base station retransmits the packets in accordance with the retransmission request.

Also, it is described inFIGS. 41A,41B,41C and41D andFIGS. 48A,48B,48C and48D that 110 packets selected by the repeater as packets to be initially transmitted are first 110 packets from among packets having no error. However, the packets can be selected in accordance with any criteria. Therefore, the packets may be selected completely randomly or may be selected in order of the decoding at the physical layer, for example.

Thirteenth Embodiment

The following describes a thirteenth embodiment of the present invention with reference to drawings. The eleventh and twelfth embodiments describe the examples of the multicast retransmission in the repeater. However, the present embodiment describes how the repeater switches the transmission method including the retransmission method as shown inFIG. 32. The repeater switches the transmission method based communication environment such as the type of data and the number of terminals to which the repeater relay the packets (i.e. terminals to which the packets are simultaneously transmitted).

FIGS. 49A and 49Beach show an example of the frame structure of a signal transmitted by the base station.FIG. 49Ashows an example of the frame structure of the signal transmitted by the base station when the repeater determines the transmission method, andFIG. 49Bshows an example of the frame structure of the signal transmitted by the base station when the base station determines, for the repeater, the transmission method.

InFIG. 49A, information4901is information relating to the type of data, and including information showing whether the packets to be transmitted are for packets for the multicast communication.

Information4902is information relating to need for real-time processing, and is used for indicating whether or not the packets to be transmitted to each of the terminals need to be processed in real time.

Information4903is relay number information that shows the number of times the repeater transmits the received packets.

Information4904is information relating to a relay/transmission interval and is for setting the number of times the repeater transmits the same packets. Note that the fourteenth embodiment describes how to use the information4903and the information4904.

The information4904onwards each show the packets (coded at the physical layer after the CRC insertion) that are transmitted by the base station. The base station transmits the packets #1to #n. Note that the information packets and the parity packets may be distinguished or not distinguished.

InFIG. 49B, information4905is indication information of the relay method in the repeater, and is used by the base station for indicating, to the repeater, the relay method. The information4905onwards each show the packets (coded at the physical layer after the CRC insertion) that are transmitted by the base station, as withFIG. 49A.

FIG. 50shows how the repeater that receives the signal transmitted by the base station selects the transmission (relay) method. InFIG. 50, the repeater receives the signal transmitted by the base station shown inFIGS. 49A and 49B, and selects the transmission (relay) method. As shown inFIG. 49B, when the base station indicates the transmission (relay) method, the repeater transmits the packets in accordance with the indicated transmission method. As shown inFIG. 49A, when the base station transmits the signal from the base station, the terminal, for example, obtains the information pieces4901to4904transmitted by the base station, and selects the transmission (relay) method based on these information pieces. Then, the terminal transmits the packets in accordance with an appropriate transmission method.

InFIG. 50,5001shows a case where the repeater receives the packets transmitted by the base station under condition that no retransmission is performed, and transmits the packets. Specifically, the base station transmits the packets that have been coded at a packet level, and the repeater receives the packets. Then, the repeater completes decoding of the packets at a packet level, and then transmits the information on the packets transmitted by the base station. That is, the repeater transmits the packets that have been coded at a packet level. The case5001shown inFIG. 50shows an exemplary case where the packets transmitted by the base station and the packets to be transmitted by the repeater have the same structure. The present invention is not limited to this case. Therefore, the packets transmitted by the base station and the packets to be transmitted by the repeater may have a difference packet size. Also, some details of the case5001shown inFIG. 50are omitted. Specifically, control information etc. is transmitted together with the packets shown in the case5001.

5002shows a case where the repeater receives the packets transmitted by the base station under condition that retransmission is to be performed, and transmits the packets. Specifically, the base station transmits the packets that have been coded at a packet level, and the repeater receives the coded packets. The repeater initially transmits some of the received packets (instead of all of the received packets) as described in the first, second, sixth, eleventh and twelfth embodiments. The repeater receives, from each of the terminals, feedback information relating to the initial transmission. When the retransmission is necessary, the repeater transmits packets for retransmission.

5003shows a case where the repeater receives the packets transmitted by the base station under condition that retransmission is to be performed, and transmits the packets. Specifically, the base station transmits the packets that have been coded at a packet level, and the repeater receives the coded packets. The repeater performs the communication method of the frame structure shown inFIG. 17andFIG. 19as described in the fourth and fifth embodiments. In this case, the repeater receives the packets transmitted by the base station. The repeater initially transmits some of the received packets. Then, the repeater receives, from each of the terminals, the feedback information relating to the initial transmission. Subsequently, the repeater performs the retransmission shown inFIG. 17andFIG. 19.

Note that there may be a case where the base station does not perform the coding at a packet level. In that case, the repeater transmits a signal transmitted by the base station. The repeater transmits the packets shown by the received signal.

FIG. 51shows an example relating to how to select the relay (transmission) method in the repeater. First of all, when the repeater relays the packets transmitted by the base station, the repeater checks whether or not the packets are for the multicast communication. When the packets are not for the multicast communication, the repeater transmits the packets. Also, the repeater performs the retransmission at the physical layer (e.g. Chase Combining and Hybrid ARQ) when the terminals make retransmission requests.

When the packets are packets for the multicast communication, the repeater subsequently checks whether or not the packets need to be processed in real time (whether or not real-time processing is necessary). When the real-time processing is necessary, the repeater does not respond to retransmission of the terminals, and transmits the packets that have been coded at a packet level. Thus, the terminals can obtain the high reception quality as a result of the decoding at a packet level.

When the real-time processing is not necessary, the repeater checks whether or not to perform the relay a plurality of times (i.e. whether or not the packets are to be transmitted a plurality of times after receiving the packets transmitted by the base station). Then, when the packets need to be transmitted a plurality of times, the repeater adopts the transmission method described in the fourteenth embodiment. Note that since the transmission method is described in detail in the fourteenth embodiment, the descriptions thereof are omitted.

When the packets do not have to be transmitted a plurality of times, the repeater checks whether or not the data transfer speed is to be prioritized. When the data transfer speed is prioritized, the repeater receives the packets transmitted by the base station in the transmission/retransmission method shown inFIGS. 41A,41B,41C and41D. When the terminals make initial transmission/retransmission requests, the repeater adopts the transmission method as shown inFIGS. 41A,41B,41C and41D.

When the data transfer speed is not prioritized, the repeater receives the packets transmitted by the base station first, and transmits packets to be initially transmitted from among the received packets. Next, the repeater checks the number of terminals that have made the retransmission request. Then, when the number of retransmission requests is large, the repeater performs the retransmission shown inFIGS. 40A,40B,40C and40D. When the number of retransmission requests is small, the repeater performs the retransmission shown inFIGS. 17 and 19.

FIG. 52shows an example of the structure of part of the functions of a repeater E. InFIG. 52, the same reference numerals are given to elements that operate in the same manner as the elements shown inFIG. 4.

When receiving a signal transmitted by the base station, a control information detection unit5201extracts control information included in the signal transmitted by the base station, and outputs control information5202.

A relay method determination unit5203receives the control information5202as an input. The relay method determination unit5203determines the relay method (initial transmission method) and/or the retransmission method, and outputs a determining method signal5204.

When receiving a signal transmitted by each of the terminals, the control information detection unit5201extracts control information included in the signal transmitted by the terminal, and outputs control information5202. The relay method determination unit5203receives the control information5202as an input. The relay method determination unit5203detects whether or not the terminals have made the retransmission requests. When the terminal has made the retransmission request, the relay method determination unit5203determines the retransmission method, and outputs the determined method signal5204.

When receiving the signal transmitted by the base station, a packet generation unit5205receives, as inputs, the determined method signal5204and the decoded packets341in any of the cases: where the packet generation unit5205receives the signal transmitted by each of the base station; and where the packet generation unit5205receives the signal transmitted by each of the terminals. The packet generation unit5205generates the packets5206for the transmission/retransmission method in accordance with the determined method signal5204, and outputs the generated packets. Then, the repeater performs predetermined processing on the packets5206for the transmission/retransmission method, and transmits, to each of the terminals, the signal corresponding to the transmission/retransmission packets5206.

As described in the above, the repeater switches the transmission method including the retransmission method in accordance with the communication environment such as the type of data and the number of terminals to which the packets are simultaneously relayed. This makes it possible to improve both the data transfer speed and the packet reception quality in each of the terminals.

Here, a description is given of the exemplary case where the base station transmits, to the repeater, the packets that have been coded at a packet level. However, the present invention is not limited to this case. Therefore, there may be a case where the repeater transmits the packets that have not been coded at a packet level. In this case, when the packet loss occurs, the repeater makes a retransmission request to the base station, and the base station retransmits the packets in accordance with the retransmission request.

Fourteenth Embodiment

The following describes a fourteenth embodiment of the present invention with reference to drawings. The fourteenth embodiment describes the method of transmitting the same packets a plurality of times, as described in the thirteenth embodiment.

FIGS. 53A and 53Beach show an example of a change in the network. Suppose that the base station, the repeater and the terminals are in a state A at a certain time point. After time lapses, the base station, the repeaters and the terminals change to fall in a state B. In this state B, the terminal5300newly joins the network.

FIG. 54shows an example of a transmission state of the packets in the repeater on the time axis. Suppose that the base station indicates, to the repeater, to relay the packets for the multicast communication (that do not need to be transmitted to each of the terminals in real time), as shown inFIG. 49A. The packets are collectively referred to as a packet group #a.

As shown in changes from the state shown inFIG. 53Ato the state shown in the state53B, it is necessary to accurately transmit the packets to each of the terminals that joins the network partway through the retransmissions, in some cases. Normally, a communication mode is not discussed in which certain packets are transmitted to each of a plurality of terminals, and then retransmitted to each of the terminals. However, when apparatuses are controlled, for example, there is a possible case where the packets indicated by the control information are transmitted to the apparatuses. In this case, information on the control packets are not transmitted to each of the apparatuses, and these apparatuses are not controlled any more. It is necessary to introduce a transmission mode that is configured in view of such a case.

InFIG. 54, the base station, the repeaters and the terminals are in the state A shown inFIG. 53Aat a time T1. In this case, the base station transmits the packet group #a that needs to be transmitted (relayed) a plurality of times, and each of the repeaters transmits the packet group #a.

Then, the base station, the repeaters and the terminals change to fall in the state B shown inFIG. 53Bat a time T2. The repeater transmits the packet group #a for the second time at a time T3. In this case, the repeater does not transmit the packet group #a which is a new packet group received from the base station at the time T1. The repeater transmits the packet group #a according to setting that the packet group #a is to be transmitted a plurality of times. Thus, the packet group #a is transmitted to the terminal5003that newly joins the network shown in the state B inFIG. 53Bat the time T2.

Note thatFIG. 49Ashows a frame structure in which the base station sets the number of relays and the relay/transmission interval. When such a setting is not made, the repeater transmits the packet group #a indefinitely. This setting is necessary to prevent such a situation.

FIG. 55is an example showing a structure of the repeater of the present embodiment. The same reference numerals are given to elements that operate in the same manner as the elements shown inFIG. 46.

A storage unit5501receives, as inputs, the result of the error detection, the packet data336, the decoded packets341and the communication method information334. When the communication method information334shown by a signal transmitted by the base station to the repeater indicates the transmission method of performing transmission a plurality of times, the storage unit5501stores therein the error detection results, the data336and the decoded packets341. Then, the storage unit5501outputs packets5502a predetermined number of times, at the transmission interval, based on the information included in the communication (reception) method information334. Here, the information relates to a transmission interval and the number of transmissions

When the inputted packets5502need to be transmitted, the selection unit3708outputs the packets3709as the packets5502.

FIG. 56shows an example of transmission timing of the transmission packets in each of the base station and the repeater. This example is different from the example shown inFIG. 54. Suppose that, inFIG. 56, a packet group #a is a packet group that needs to be transmitted by the repeater a plurality of times and a packet group #b is a packet group needs to be processed in real time (i.e. time of delay before these packets reach each of the terminals needs to be shortened). Also, a packet group a is transmitted a plurality of times at a time interval a.

At this time, a transmission time T6(at which the packet group #a should be transmitted) is reached while the repeater is transmitting the packet group b (between time points T5to T7). In such a case, however, the repeater prioritizes transmission of the packet group that needs to be processed in real time. The repeater does not permit interrupt of transmission of the packet group that needs to be transmitted a plurality of times (i.e. the packet group that does not have to be processed in real time). Therefore, an important role of the repeater is to prioritize the transmission of the packets that need to be processed in real time.

As described in the above, the repeater can accurately transmit the packets to each of the terminals that join the network partway through the retransmissions by transmitting (relaying) the packets transmitted by the base station a plurality of times.

Here, a description is given of the exemplary case where the base station transmits, to the repeater, the packets that have been coded at a packet level. However, the present invention is not necessarily limited to this case. Therefore, there may be a case where the repeater transmits the packets that have not been coded at a packet level. In this case, when the packet loss occurs, the repeater makes a retransmission request to the base station, and the base station retransmits the packets in accordance with the retransmission request.

Fifteenth Embodiment

The following describes a fifteenth embodiment of the present invention with reference to drawings. The fifteenth embodiment describes another method (that is different from the method described in the fourteenth embodiment) as to how the repeater transmits the same packets a plurality of times.

FIG. 57shows the transmission (relay) method described in the fourteenth embodiment. Suppose that both the packet group #a and the packet group #b are transmitted by the base station, and both of these packet groups are packet groups to be transmitted by the repeater a plurality of times.FIG. 57shows the above-stated state. After the base station transmits the packet group #a (time T1), the repeater transmits the packet group #a a plurality of times (e.g. time T2and time T3). Similarly, after the base station transmits the packet group #b, the repeater transmits the packet group #b a plurality of times (e.g. time points T5and T7).

FIG. 58shows a transmission (relay) method that is different fromFIG. 57. Both the packet groups #a and #b are transmitted by the base station (at time T1and time T4), and both of these packet groups are packet groups to be transmitted by the repeater a plurality of times.FIG. 58is different fromFIG. 57in that the groups #a and #b are coded at a packet level and a packet group #a+b is transmitted, at a time point (time T5) at which both the packet groups #a and #b are to be transmitted, inFIG. 58. The following describes a method for manufacturing the packet group #a+b, with use ofFIG. 59.

FIG. 59shows a method of generating the packet group #a+b as described in the above. As described in the above, both the packet groups #a and #b need to be transmitted by the repeater a plurality of times.

The repeater receives the packet group #a that has been coded at a packet level and transmitted by the base station. At this time, the repeater has not received the packet group #b. Therefore, the repeater transmits the packet #a at first (at the time T2inFIG. 58). Then, the repeater receives the packet group #b that has been coded at a packet level and transmitted by the base station. In that case, the repeater extracts an information packet group (hereinafter, referred to as an information packet group of the packet group #a) from the packet group #a, as shown inFIG. 59. Here, the information packet group is included in the packet #a obtained by the decoding at a packet level. Similarly, the repeater extracts an information packet group (hereinafter, referred to as an information packet group of the packet group #b) from the packet group #b. Here, the information packet group is included in the packet group #b obtained by the decoding at a packet level.

Then, the repeater codes the information packet group of the packet #a and the information packet group of the group #b at a packet level to generate the packet group a+b. Note that it is natural that the codes used for the coding may be systematic codes or non-systematic codes as described in the above so far. In the subsequent processing, the repeater transmits the packet group #a+b to each of the terminals. Note that when the repeater receives another new packet group #c from the base station, the repeater generates a packet group #a+b+c obtained by coding an information packet group at a packet level. The information packet group is obtained by combining the information packet groups #a, #b and #c.

When the packet groups #a and #b are short packets, padding bits are inserted into each of the packet groups #a and #b or control information pieces (or packets for controlling) are provided to each of the packet groups #a and #b in addition to the information packets, so as to support short packets. When the packet groups #a and #b are combined such that #a+b, there is a merit that these additional information pieces can be reduced. Thus, the information transfer efficiency can be improved. Also, when the size of the block codes are increased with use of the block codes as the error correction codes for coding that are used for generating the packet group #a+b, the error correction performance is improved. Therefore, there is a merit that the data reception quality in each of the terminals is improved.

Here, a description is given of the exemplary case where the base station transmits, to the repeater, the packets that have been coded at a packet level. However, the present invention is not necessarily limited to this case. Therefore, there may be a case where the repeater transmits the packets that have not been coded, and then the repeater generates the packet group a+b. In this case, when the packet loss occurs, the repeater makes a retransmission request to the base station, and the base station retransmits the packets in accordance with the retransmission request.

As described in the above, the repeater can accurately transmit the packets to each of the terminals that join the network partway, by transmitting (relaying) the packets (transmitted by the base station) a plurality of times at a packet level. Also, the repeater codes altogether the packets (that need to be transmitted a plurality of times) a plurality of times. This makes it possible to obtain merits that the data transfer efficiency and the data reception quality can be improved.

It is natural that although the present embodiment is effective when used alone, the repeater may switch between the method described in the present embodiment and the other transmission (relay) methods. The other transmission (relay) methods are as described in the other embodiments except for the present embodiment.

SUPPLEMENTARY REMARKS

The present invention is not limited to the above embodiments, and may be implemented in any forms as long as the object/aims of the present invention, as well as other relevant and accompanying objects/aims, can be achieved. The following cases are also possible, for example.

(1) Although the above-described exemplary embodiments are mainly realized by the coding apparatus and the transmitter, the present invention is not limited to this. Therefore, the present invention may be applied to a power line communication apparatus, for example.

(2) The following is possible. Procedures of the operations in the transmitter described in each of the above embodiments are written in a program. This program is pre-stored in a ROM (Read Only Memory). A CPU (Central Processing Unit) reads and executes the program stored in the ROM. Also, the following is possible. The program in which the procedures of the operations of each of the transmitters are written is stored on a computer readable storage medium. The program stored on the computer readable storage medium is stored in a RAM (Random Access Memory). The CPU of the computer reads and executes the program stored in the RAM.

(3) The elements described in each of the above-described embodiments may be realized as an LSI (Large Scale Integration) which is typically an integrated circuit. These elements may be constituted as separate chips, or all or a portion thereof may be constituted as a single chip.

Note that an integrated circuit generated as described above may also be referred to as an IC (Integrated Circuit), a system LSI, a super LSI, or an ultra LSI, depending on the degree of integration.

The integration is also not limited to LSI implementation, but instead may be realized by a dedicated circuit or a general-purpose process. A FPGA (Field Programmable Gate Array) that can be reprogrammed after LSI manufacture, or a reconfigurable processor in which the connection and settings of circuit cells in the LSI can be restructured after LSI manufacture can also be used.

Furthermore, if integration technology is developed that replaces LSIs due to progressive or derivative semiconductor technology, integration of functional blocks using this technology is naturally possible. For example, the application of biotechnology is a possibility.

(4) It is needless to say that the present invention is not limited to a wireless communication, and is effective for PLC (Power Line Communication), visible light communication and optical communication.

(5) It is needless to say that the frame structures described in the above sixth to eighth embodiments can be applied to the first to fifth embodiments by making appropriate changes.

(6) The above embodiments are described with use of terms (physical layer and application layer). However, these terms are merely definitions and may be referred to as other names.

(7) The error correction codes at the physical layer are generally referred to as “FEC (Forward Error Correction) scheme”.

(8) In the above twelfth to fifteenth embodiments, the repeater relays, to each of the terminals, the packets received from the base station. However, the repeater may relay the packets to another repeater other than the terminals.

INDUSTRIAL APPLICABILITY

The present invention is effective in generating retransmission packets with use of LDPC Codes (Low Density Parity Check Codes), for example.

REFERENCE SIGNS LIST