Communication device, transmitting method and receiving method

Communication device, sending method and receiving method

[0001] This application is a divisional application of an invention patent application filed on August 07, 2008, with an application number of No. 200810144920. 5, and an invention title of "communication device, transmission method, and receiving method".

Technical field

[0002] Aspects of the present invention relate to a communication device including a transmission device and a reception device, a transmission method and a reception method for transmitting/receiving a wireless signal.

Background technique

[0003] In a wireless communication system including a mobile communication system, a wireless signal is transmitted from a transmitting device to a receiving device. Packet data and the like are examples of wireless signals. There are various data stored in the data portion of the packet data. The data is not limited to text data and image data, but may include audio data and the like. If the wireless signal is continuously transmitted, the transmission of the wireless signal is generally performed at predetermined intervals. For example, transmission is performed every 20 ms.

[0004] However, although the transmitting device transmits a wireless signal, there is no guarantee that the receiving device can successfully receive the wireless signal. That is, because transmission and reception are performed in a wireless manner, the transmission signal is affected by a propagation channel (path) (for example, a fading channel). Therefore, the received signal obtained by the receiving device by receiving the transmitted signal may be incorrect. The transmission signal can be error correction coded, and it is possible to generate a correct received signal through error correction coding in the receiving device. However, depending on the degree of the error, the error may not be completely corrected, and the receiving device may not obtain the correct received signal.

[0005] In view of the above-mentioned problems, there is a technique for performing retransmission from the transmission device by determining the reception result of the transmission signal in the reception device and feeding back the reception result to the transmission device.

[0006] FIG. 1 shows a known method of data transmission/reception processing in which retransmission control is introduced.

[0007] As described in FIG. 1, the transmitting device sequentially transmits data (for example, audio packet data) every 20 ms. The receiving device attempts to receive the sent data. Then, the receiving device transmits an ACK signal when the data is successfully received. If the ACK signal is received, the transmitting device recognizes that the transmission has been successfully performed and then transmits another transmission signal (for example, the next transmission signal to be transmitted to the same receiving device) at the next transmission time. However, as described in FIG. 1, when the receiving device cannot successfully receive data due to an error in the third transmission due to the influence of the wireless channel, the receiving device transmits a NACK signal. If the NACK signal is received, the transmitting device recognizes that the transmission was not successfully performed and thus performs retransmission. Therefore, the receiving device further receives the retransmitted data. When the reception of the retransmission is successful, the ACK signal is transmitted from the receiving device and then the next data is transmitted from the transmitting device at the next transmission time. Therefore, even if the first transmission fails, one or more retransmissions may be successful by introducing retransmission control.

[0008] The above-mentioned retransmission control is described in 3GPP TS25.212, 3GPP TS25.321, and 3GPP TS36.212.

[0009] As previously described, the introduction of retransmission control increases the chance of successfully sending data from the sending device to the receiving device. However, because the retransmission control is (inserted), it is difficult to perform control to simply perform intermittent reception at predetermined intervals.

Summary of the invention

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[0010] The object of the present invention is to reduce waste in receiving operations and/or sending operations when retransmissions occur outside of a predetermined interval due to retransmission control.

[0011] According to one aspect of the present invention, there is provided a communication device for performing first reception processing on data sent at predetermined intervals, the communication device comprising: a sending unit configured to When the data sent at the Nth time of the predetermined interval is not successfully received, after sending a signal indicating that the data sent at the Nth time has not been successfully received, respond to the data sent at the Nth time Retransmission of data performs reception control until the next time according to the predetermined interval, that is, time N+1, and performs control to provide a period in which at least a period different from the first reception process is performed The second receiving process, or the receiving process is not performed, until the next moment according to the predetermined interval, that is, the N+1th moment appears.

[0012] According to one aspect of the present invention, there is provided a communication method of a communication device, wherein the communication device performs first reception processing on data sent at predetermined intervals, and the communication method includes: When the data sent at the Nth time at a predetermined interval is not successfully received, after sending a signal indicating that the data sent at the Nth time has not been successfully received, the data sent at the Nth time Retransmission performs reception control until the next time according to the predetermined interval, that is, time N+1; and performs control to provide a period in which at least a second reception process different from the first reception process is performed. Receiving processing, or not performing receiving processing, until the next time according to the predetermined interval, that is, the N+1th time appears.

[0013] According to an aspect of the present invention, a communication device for receiving and processing data sent at predetermined intervals or a method used in the communication device is provided, the communication device having a sending unit, and the sending The unit is configured to send a signal indicating that the data is successfully received when the data sent at the Mth time according to the predetermined interval is successfully received; and a control unit, the control unit is configured to After the transmission, control is performed to provide a period in which at least other receiving processing different from the receiving processing is performed, or receiving processing is not performed, until the next time according to the predetermined interval, that is, the M+ 1 moment comes.

[0014] According to an aspect of the present invention, a communication device that performs receiving processing on data transmitted at predetermined intervals or a method used in the communication device is provided, the communication device includes a transmission unit, the The sending unit is configured to send a signal indicating that the data has not been successfully received when the data is not successfully received at the Mth time according to the predetermined interval; and the control unit is configured to send a signal indicating that the data has not been successfully received After performing the retransmission control process after the transmission of the signal indicating that the data was not successfully received, perform control to provide a period during which at least another reception process different from the reception process is performed, or The receiving process is not executed until the next time according to the predetermined interval, that is, the M+1th time comes.

[0015] According to an aspect of the present invention, a communication device capable of performing retransmission or a method used in the communication device is utilized, the communication device having a retransmission control unit, and the retransmission control unit is configured to Retransmission is performed when a response to new data is not received and when a signal indicating that the data was not successfully received is received, wherein when a response to the Nth retransmission is not received, the retransmission is The control unit does not perform the Nth retransmission, and when receiving a response indicating that the Nth retransmission was not successfully received, the retransmission control unit performs the N+1th retransmission.

[0016] According to an aspect of the present invention, a communication device for receiving and processing data transmitted at predetermined intervals or a method used in the communication device is provided, the communication device has a transmission unit, and the transmission The unit is configured to send a signal indicating that the data is successfully received when the data sent at the Mth time according to the predetermined interval is successfully received; and the control unit is configured to determine when the sending instruction is Whether the retransmission control process is executed when the data is successfully received in the signal, wherein when the retransmission control process is executed, the control unit

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The meta sends a signal indicating that the data was successfully received.

[0017] Other objectives and advantages of the present invention will be explained in the following description, and will be apparent from the description, or can be learned through the practice of the present invention. The objectives and advantages of the present invention will be realized and obtained through the elements and combinations specifically pointed out in the appended claims.

[0018] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and not a limitation of the claimed invention.

Description of the drawings

[0019] FIG. 1 illustrates a known method of data transmission/reception processing.

[0020] FIG. 2 illustrates a first embodiment of transmission/reception processing.

[0021] FIG. 3 illustrates a second embodiment of transmission/reception processing.

[0022] FIG. 4 illustrates a first embodiment of the structure of the receiving apparatus.

[0023] FIG. 5 illustrates an embodiment of a control flow in the receiving device.

[0024] FIG. 6 illustrates another embodiment of the control flow in the receiving device.

[0025] FIG. 7 illustrates retransmission control in a case when the transmitting device does not receive an ACK signal.

[0026] FIG. 8 illustrates a first embodiment of the structure of the transmission device.

[0027] FIG. 9 illustrates a first embodiment of transmission processing.

[0028] FIG. 10 illustrates an embodiment of a control flow in the transmitting device.

[0029] FIG. 11 illustrates a second embodiment of the transmission process.

[0030] FIG. 12 illustrates an embodiment of a control flow in the receiving device.

Detailed ways

[0031] Preferred embodiments of the present invention will be explained with reference to the drawings.

[0032] [a] The first embodiment

[0033] When the transmitting device transmits a wireless signal at a predetermined interval, the receiving device may receive the wireless signal by performing reception in response to the predetermined interval. It is possible to determine whether to perform transmission (retransmission) outside the interval based on the type of signal sent by the receiving device itself. That is, if the YACK signal (type 1) is sent from the receiving device, the transmission (retransmission) does not occur outside the interval, and if the NACK signal (type 2) is sent from the receiving device, the transmission (retransmission) occurs outside the interval .

[0034] Therefore, in the present embodiment, when a receiving device that performs intermittent reception control in response to a transmission interval transmits a NACK signal, the reception operation period must be set to be longer compared with the case when an ACK is transmitted. For example, the period may be a period in which a wireless signal is transmitted through retransmission (for example, a first retransmission) and then received. If another NACK signal is transmitted in response to a retransmission, the period may be a period in which a wireless signal is transmitted through another retransmission (second retransmission) and then received.

[0035] When the NACK signal is transmitted, the power of the receiving unit is turned on for the entire period corresponding to the transmission interval. When sending the ACK signal, the power of the receiving unit can be turned off when the reception is completed, which can reduce power consumption.

[0036] However, in a scenario assuming a bad reception environment, such as an environment in which a NACK signal is transmitted, the receiving unit may allocate a transmission interval greater than or equal to 1/2 to 2/3 to the period for receiving retransmissions, The remaining 1/3 to 1/2 transmission interval is allocated to a period for measuring (searching) the reception quality of signals from neighboring base stations. That is, the reception processing unit can be controlled to perform other reception processing.

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[0037] FIG. 2 shows a first embodiment of transmission/reception processing.

[0038] As described in FIG. 2, the transmitting device transmits data (for example, audio packet data) every 20 ms, for example. The receiving device performs intermittent reception in response to the interval. When the data is successfully received and the ACK signal is sent, a predetermined period (T1) is allocated to the receiving operation of the received data. When the NACK signal is sent, another predetermined period (T2 (T1<T2)) is allocated to the receiving operation of the received data. The period T2 is a period in which at least one retransmission can be received. When multiple retransmissions are performed, the period T2 can be set as the period TL, in which the last retransmission can be received.

[0039] The second embodiment is that although the receiving device transmits the NACK signal, the transmitting device fails to receive the NACK signal. In this case, no retransmission is performed. Therefore, another NACK signal can be sent in anticipation of another retransmission, but this requires a considerable amount of time.

[0040] Therefore, when the retransmission is not successfully received although the receiving device transmits the NACK signal (or when the transmitting device does not receive the advance notice of the retransmission), the receiving device may control the receiving unit not to perform the receiving operation of the received data until The arrival of the next periodic sending time. That is, for example, the power supply of the receiving unit may be turned off or the receiving unit may search for another transmitting unit as an out-of-reception waiting mode.

[0041] FIG. 3 shows a second embodiment of transmission/reception processing.

[0042] As described in FIG. 3, when the receiving device cannot receive the first transmission signal, the receiving device sends a NACK signal to try to receive the retransmission, but does not receive the retransmission (or does not receive the advance notice of the retransmission). Therefore, the receiving device then brings the receiving unit out of the waiting state for receiving the retransmitted data. On the other hand, because the third transmission signal was not successfully received, the receiving device transmits the NACK signal to the transmitting device. In this case, because the transmitting device can receive the NACK signal, retransmission is performed. Because the receiving device can receive the first retransmission, the receiving device sends an ACK signal and makes the receiving unit out of the waiting state for receiving the retransmitted data. The operation to leave the reception waiting state may be the same as the first embodiment.

[0043] The basic control flow according to the first and second embodiments of the first embodiment has been described above. The structure of the receiving device corresponding to the above-mentioned control will be described using FIG. 4.

[0044] FIG. 4 shows a first embodiment of the structure of the receiving device.

[0045] The number 1 represents a receiving antenna. The number 2 represents the receiving processing unit. The number 3 represents the reception result determination unit. The number 4 represents the receiving unit. The number 5 represents the timer. The number 6 represents an ACK/NACK signal generating unit. The number 7 represents a transmission processing unit. The number 8 represents the transmitting antenna.

[0046] The receiving antenna 1 receives a transmission signal periodically transmitted from a transmission device and a transmission signal retransmitted from the transmission device. The reception processing unit 2 performs reception processing on the signal received by the receiving antenna according to the transmission form used for transmission to obtain reception data through demodulation and decoding (which may include error correction decoding). The transmission form may be included in the transmission advance notice transmitted from the transmission device, or may be assumed to be a form selected from a predetermined form. The reception data obtained by the reception processing unit 2 is given to the reception result determination unit 3. Then, it is determined whether the reception was successfully performed. For example, if the transmission device performs error detection encoding processing regarding transmission data (adding CRC calculation results, etc.), error detection is performed using the CRC calculation results and the error detection results are given to the ACK/NACK signal generating unit 6. If the data is successfully received, the received data is given to a received data processing unit not shown in the figure on the left, and then displayed on a display, output from a speaker as a sound, or output to an external unit as needed. Although the data can be discarded if the data is not successfully received, the data can also be stored in a memory unit inside the reception result determining unit 3 to be combined with the received data sent by the next retransmission. The reception processing unit 2 may perform decoding based on the combined data, and may give the result to the reception result determination unit 3 (so-called hybrid ARQ method).

[0047] If the reception result indicates that the data is successfully received, the ACK/NACK signal generating unit 6 uses the ACK signal as

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Response signal output. If the reception result indicates that the data was not successfully received, the ACK/NACK signal generating unit 6 outputs the NACK signal as a response signal. The transmission processing unit 7 performs transmission processing regarding the response signal (ACK signal/NACK signal) to convert it into a wireless signal and then transmits the wireless signal from the transmission antenna 8. The transmission time of the response signal may arrive after the transmission time of the packet has passed by a predetermined offset time.

[0048] The transmission antenna and the reception antenna may be a common antenna by using a duplexer or the like.

[0049] The reception control unit 4 controls each reception unit based on the time signal output from the timer 5 (time management unit). The control unit 9 controls other units.

[0050] FIG. 5 shows a first embodiment of a control flow in the receiving device. This control is mainly performed by receiving the control of the control unit 4.

[0051] The reception control unit 4 controls to start the reception operation and determines whether a packet is received (step S1).

[0052] If the packet is received in step S1, the reception result determining unit 3 determines whether the packet is successfully received (step S2).

[0053] If the packet is successfully received, the ACK/NACK signal generating unit 6 generates an ACK signal, and transmits the ACK signal from the transmission processing unit 7 and the transmission antenna 8 (step S3).

[0054] On the other hand, if the packet is not successfully received, the ACK/NACK signal generating unit 6 generates a NACK signal, and transmits the NACK signal from the transmission processing unit 7 and the transmission antenna 8 (step S5). The reception control unit 4 causes the reception processing unit 2 and the like to enter the reception waiting state without turning off its power to receive the retransmission packet. After that, the process returns to the determination of step S1.

[0055] If the ACK signal is received in step S3, the reception stop processing of packet data is executed (step S4). As the reception stop processing of the packet data, for example, the power supply of the reception processing unit 2 or the like is turned off, or the search operation of another transmission device may be performed.

[0056] Then, the reception control unit 4 controls the reception processing unit 2 and the like at the next transmission timing to receive the next packet.

The process returns to the determination of step S1.

[0057] If it is determined in the determination of step S1 that the packet is not received at the predetermined periodic transmission time, it is determined in step 1 whether the retransmission packet is received without turning off the power of the receiving processing unit 2, as in step The processing after the NACK signal is sent in 5 (step S1).

[0058] FIG. 6 shows another embodiment of the control flow in the receiving device. This control is performed by receiving the control of the control unit 4 and the like.

[0059] The reception control unit 4 performs control to start the reception operation in response to the transmission timing, and determines whether a packet is received (step S11).

[0060] If the packet is received in step S11, the reception result determining unit 3 determines whether the received packet is successfully received (step S12).

[0061] If the packet is successfully received, the ACK signal is generated by the ACK/NACK signal generation unit 6 and transmitted from the transmission processing unit 7 and the transmission antenna 8 (step S13).

[0062] On the other hand, if the packet is not successfully received, the NACK signal is generated by the ACK/NACK signal generation unit 6 and transmitted from the transmission processing unit 7 and the transmission antenna 8 (step S15). The reception control unit 4 causes the reception processing unit 2 and the like to enter the reception waiting state without turning off its power to receive the retransmission packet. After that, the process returns to the determination of step S11.

[0063] If the packet is not received in step S11 or the ACK signal is received in step S13, the packet data reception processing is stopped (step S14). When the reception processing of packet data is stopped, for example, the power of the reception processing unit 2 etc.

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The source is closed, or a search for other sending devices is performed.

[0064] Then, the reception control unit 4 controls the reception processing unit 2 and the like at the next transmission timing to receive the next packet. The process returns to the determination of step S11.

[B] Second embodiment

[0066] The transmitting device may perform retransmission control not only when the ACK signal is not received, but also when the NACK signal is received.

[0067] FIG. 7 shows retransmission control when the transmitting device does not receive an ACK signal.

[0068] As in the first embodiment, the transmitting device transmits packets at predetermined intervals (20 ms). The first transmission is successful, and the receiving device transmits an ACK signal. However, the transmission device failed to successfully receive the ACK signal (or the transmission device erroneously determined the ACK signal as a NACK signal). Therefore, the sending device performs retransmission.

[0069] On the other hand, because the receiving device transmits the ACK signal, retransmission is not expected, and the receiving device does not receive the retransmission. Therefore, because the receiving device does not transmit any response signal (ACK signal/NACK signal) in response to the retransmission, the transmitting device performs another retransmission. After that, useless retransmissions are performed in vain to the maximum number of transmissions until the next transmission time comes.

[0070] In this embodiment, if the NACK signal is not received in response to the first retransmission, the transmitting device does not perform the next retransmission. That is, in response to the first retransmission, not only when the NACK signal is received but also when the ACK signal is not received, the retransmission is performed. However, after the first retransmission, if the NACK signal is received, the retransmission is performed, but if the ACK/NACK signal is not received (no response case), the retransmission is not performed.

[0071] Therefore, it is possible to reduce useless retransmissions performed when the transmission device cannot detect the ACK signal.

[0072] FIG. 8 shows a first embodiment of the structure of the transmitting apparatus.

[0073] Numeral 11 denotes a receiving antenna. The number 12 represents the receiving processing unit. The number 13 represents the retransmission control unit. The number 14 represents a packet generating unit. The number 15 represents a grouping information generating unit. The number 16 represents a transmission processing unit. The number 17 denotes a transmitting antenna.

[0074] The receiving antenna 11 receives various signals (for example, an ACK signal and a NACK signal) transmitted from the receiving device. The reception processing unit 12 performs reception processing on the signal received by the reception antenna according to the transmission form used for transmission to obtain reception data through demodulation and decoding (which may include error correction decoding). The reception data (for example, ACK signal and NACK signal) obtained by the reception processing unit 12 is given to the retransmission control unit 13.

[0075] After a new transmission (non-retransmission) (transmission performed at predetermined intervals), when neither ACK nor NACK signal is received at the time of receiving the response signal (ACK signal/NACK signal), retransmission The transmission control unit 13 performs retransmission control.

[0076] That is, the retransmission data is generated based on the transmission data stored in the packet generation unit 14, and the transmission processing unit

16 and the transmitting antenna 17 transmit the retransmitted data.

[0077] In the present embodiment, the information about the packet form sent from the packet generating unit 14 is given to the packet information generating unit 15. Then, the packet information generating unit 15 generates transmission parameters (information such as packet size, encoding method, modulation method, and MIMO (applied/not applied)). Before packet transmission, transmission parameters as pre-information (including notification of execution of transmission to a specific receiving device) are transmitted from the transmission processing unit 16 and the transmission antenna 17.

[0078] When the modulation method is changed by changing the transmission parameter, the modulation method is notified to the transmission processing unit 16, and the transmission processing unit 16 transmits the packet according to the notified modulation method.

[0079] The transmission antenna and the reception antenna may be a common antenna by using a duplexer or the like.

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[0080] In this case, when the ACK signal is not received (including the case when the NACK signal is received), the retransmission control unit 13 performs retransmission in response to the first transmission (new transmission). However, after the Nth transmission (including the Nth transmission), the retransmission control unit 13 does not perform retransmission unless a NACK signal is received. In this case, the number N may be a predetermined value of 2 or greater. However, the number N may be less than the maximum number of retransmissions (for example, the maximum number of retransmissions -1).

[0081] FIG. 9 shows a first embodiment of transmission/reception processing.

[0082] As shown in FIG. 9, although the first (new) transmission of packet data is successful and the receiving device transmits an ACK signal, when the transmitting device fails to detect the ACK signal (at a predetermined time when the response signal is received) ) Or when a NACK signal is erroneously detected, the retransmission control unit 13 performs retransmission control.

[0083] However, because the receiving device transmits the ACK signal, the receiving device does not perform the receiving operation of the retransmission packet (turning off the power of the receiving processing unit or searching for other transmitting devices) and does not transmit a response signal.

[0084] Therefore, the transmitting device does not receive the ACK signal or the NACK signal in response to the retransmission at the time of receiving the response signal. Then, if the transmission device does not receive the NACK signal, the retransmission control unit 13 of the transmission device controls the transmission device not to perform retransmission.

[0085] FIG. 10 shows a first embodiment of a control flow in the transmitting device. This control is mainly performed by the control of the retransmission control unit 13.

[0086] The transmission device (retransmission control unit 13) determines whether there is a transmission packet that should be transmitted (step S31). [0087] If it is negative in step S31, the process returns to step S31. If it is affirmative in step S31, the packet generation unit 14 gives the transmission packet to the transmission processing unit 16 to transmit a new packet (step S32) and transmits the packet from the transmission antenna 17. Before packet transmission, transmission parameter information is generated by the packet information generation unit 15 and transmitted from the transmission processing unit 16 and the transmission antenna 17 to the receiving device.

[0088] Then, the retransmission control unit 13 sets the value i of the transmission counter to 0 (step S33). This counter can be provided in the retransmission control unit 13.

[0089] Next, the retransmission control unit 13 determines whether a response signal is received. If the ACK signal is received, the process returns to step S31. Then it is determined whether there is a next transmission packet.

[0090] On the other hand, if the received NACK signal is a response signal, the retransmission control unit 13 controls the transmitting device to retransmit the packet (step S35) and increment the value i of the counter by 10. Then, the process returns to the determination of step S34.

[0091] In the determination of step S34, if an ACK signal or a NACK signal as a response signal is not detected, it is determined that DTX (no response) is indicated. Then, it is determined whether the value i of the counter is greater than a predetermined value k (step S36). The value k is a count of 2 or greater, and may be less than the maximum number of retransmissions.

[0092] If the set value of the counter is greater than the value k in step S36, the retransmission control unit 13 does not perform retransmission processing. The process returns to step S31, and the retransmission control unit 13 transmits the next new packet.

[0093] On the other hand, if the set value of the counter is smaller than the value k in step S36, the retransmission control unit 13 transmits a retransmission packet (step S35), and increments the value i of the counter by 1. Then, the process returns to step S34.

[0094] This makes it possible to reduce useless retransmissions even if there is an identification difference in the reception result between the sending device and the receiving device.

[0095] Next, FIG. 11 shows a second embodiment of transmission/reception processing.

[0096] As described in FIG. 11, although the first (new) transmission of packet data is successful and the receiving device transmits an ACK signal, when the transmitting device fails to detect the ACK signal (at the moment of receiving the predetermined response signal) Or when the NACK signal is detected by mistake, the retransmission control unit 13 performs retransmission control.

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[0097] Consider an unexpected situation in which although the receiving device transmits a YACK signal, the transmitting device fails to detect the ACK signal. Therefore, it is determined whether a retransmission packet is sent. At this time, this determination operation can be performed by checking the advance notice of retransmission sent from the packet information generating unit 15 or by actually trying to receive the retransmitted packet.

[0098] If it is detected that the retransmission is not performed, the receiving device turns off the power of the receiving unit, or performs a search for other sending devices.

[0099] On the other hand, if it is detected that the retransmission is performed despite the transmission device transmitting the ACK signal, the receiving device transmits the ACK signal regardless of whether the retransmission packet is successfully received. This is because the receiving operation has been successfully completed for this packet, so another retransmission is unnecessary.

[0100] Therefore, since the transmission device receives the ACK signal, the retransmission control unit 13 that controls the transmission device does not perform another retransmission.

[0101] FIG. 12 shows a first embodiment of a control flow in the receiving device. This control is mainly performed by receiving the control of the control unit 4. That is, the receiving device having the structure shown in FIG. 4 is applicable.

[0102] The transmission/reception device (reception control unit 4) controls to start a reception operation at the transmission timing for transmitting a new packet in response to a predetermined interval, and determines whether a packet is received (step S41).

[0103] If the packet is received in step S41, the reception result determining unit 3 determines whether the packet is successfully received (step S42).

[0104] If the packet is successfully received, the ACK/NACK signal generating unit 6 generates an ACK signal, and transmits the ACK signal from the transmission processing unit 7 and the transmission antenna 8 (step S43).

[0105] On the other hand, if the packet is not successfully received, the ACK/NACK signal generating unit 6 generates a NACK signal, and transmits the NACK signal from the transmission processing unit 7 and the transmission antenna 8 (step S46). The reception control unit 4 causes the reception processing unit 2 and the like to enter a reception waiting state without turning off the power supply of them to receive the retransmission packet. After that, the process returns to the determination in step S41.

[0106] If the ACK signal is transmitted in step S43, the reception control unit 4 determines whether a retransmission packet is received (step S44). In this step, if the transmission processing of the retransmission packet is not performed (if the advance notice of transmission is not received or if the transmission packet is not actually received), the reception processing of the packet data is stopped (step S45). When the reception processing of packet data is stopped, for example, the power supply of the reception processing unit 2 or the like is turned off or a search for other transmission devices is performed.

[0107] Then, the reception control unit 4 controls the reception processing unit 2 and the like at the next transmission timing to receive the next packet.

Then, the process returns to the determination of step S41.

[0108] In step S44, if the transmission process of the transmission packet is detected despite the transmission of the ACK signal, the process returns to step S43. Then, an ACK signal is sent to control the sending device not to perform another retransmission.

[0109] The operation from step S44 back to step S43 may be limited to only one time. And, it is allowed to follow this routine to return to step S43 from step S44 until the predetermined value N is reached. In this case, the predetermined value N may be less than the maximum number of retransmissions -1.

[0110] According to the present embodiment, due to such retransmission control, when retransmission occurs outside a predetermined interval, it is possible to reduce waste in receiving operations and transmitting operations.

[0111] Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations can be made to it without departing from the spirit and scope of the present invention.

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