Communication system, communication device, and data frame retransmission control method

The present invention relates to a communication system, a communication device, and a data frame retransmission control method.

In an ARQ (Automatic Repeat Request) method which is one of error correction methods, when there is an error in a received data frame, the receiving side transmits a retransmission request of the data frame to the transmitting side. The transmitting side identifies the data frame to be retransmitted based on the received retransmission request, and retransmits the data frame to the receiving side. The retransmission request includes a sequence number (order number) for identifying the data frame to be retransmitted, and the transmitting side identifies the requested data frame based on the sequence number and retransmits the requested data frame (for example, refer to Patent Document 1).

For improving the error correction efficiency in the ARQ method, it is effective to reduce the number of retransmissions of the data frame, reduce the time period from reception of the retransmission request to retransmission of the data frame, etc. In this regard, Patent Document 2 discloses a wireless transmitting device to which a hybrid ARQ is applied wherein the number of retransmissions of the data frame is reduced so that the system throughput is improved.

However, in the ARQ method of the related art as described above, the data size of the retransmission request is enlarged corresponding to the number of bits of the sequence number. In particular, when communication data and other data are transmitted along with the retransmission request, it is desired that the number of bits assigned to the retransmission request be reduced so that more number of bits can be assigned to the communication data or the like.

In addition, because a certain processing time (hereinafter referred to as “reference required time”) is required from the reception of the retransmission request to the retransmission of the data frame, it may become difficult to retransmit the data frame using the transmission frame immediately following the frame in which the retransmission request is received, particularly in a communication according to a TDMA/TDD (Time Division Multiple Access/Time Division Duplex) system. Because of this, in the ARQ of the related art applied to the TDMA/TDD system, in order to secure a sufficient time for the retransmission process of the data frame, the data frame is uniformly retransmitted using the transmission frame of two or more frames later than the frame in which the retransmission request is received. As a result, there is a problem in that a retransmission delay of greater than or equal to 1 TDMA frame always occurs when there is an error in the data frame.

The present invention was conceived in view of the above-described problem of the related art, and a first object is to provide a communication system, a receiving device, a transmitting device, and a data frame retransmission control method which can achieve an automatic retransmission control of the data frame without including the sequence number of the data frame in the retransmission request.

A second object is to provide a communication device and a data frame retransmission method which can preferably shorten the time from the reception of the retransmission request to the retransmission of the data frame.

In order to achieve the first object, a communication system according to the present invention is a communication system having a transmitting device and a receiving device which employ an automatic repeat request method of a data frame, wherein the receiving device includes retransmission request transmission timing identifying means for identifying, based on a timing of reception of a data frame transmitted from the transmitting device, a timing of transmission of a retransmission request of the data frame to the transmitting device, the transmitting device includes retransmission data frame selecting means for selecting, based on a timing of reception of the retransmission request transmitted from the receiving device, a data frame to be retransmitted from among a plurality of data frames transmitted to the receiving device, and retransmits the data frame selected by the retransmission data frame selecting means to the receiving device.

According to the present invention, the receiving device identifies, based on a reception timing of a data frame (transmission timing for the transmitting device), a response timing (reception timing for the transmitting device) of the retransmission request for the data frame. On the other hand, the transmitting device identifies, based on the reception timing of the retransmission request, the timing when the data frame corresponding to the retransmission request was transmitted. In other words, in this communication system, the receiving device and the transmitting device share the timing difference (time interval) between the transmission (reception) timing of the data frame and the reception (transmission) timing of the retransmission request for the data frame. Because of this configuration, even if the sequence number of the data frame is omitted in the retransmission request, the transmitting device can identify to which data frame the received retransmission request corresponds.

The transmitting device may further include transmitted data frame storage means for storing at least some of the plurality of data frames transmitted to the receiving device in a manner to allow identification of a timing of transmission of each of the data frames, and the retransmission data frame selecting means may identify a timing of transmission of the data frame to be retransmitted based on the timing of reception of the retransmission request and select the data frame to be retransmitted from the transmitted data frame storage means based on the identified timing.

The communication system may further employ a time division multiplex communication system, and the timing may be identified by a time slot or a time frame according to time division multiplexing.

A receiving device according to the present invention is a receiving device which receives a data frame transmitted from a transmitting device and which transmits, upon detection of an error in the received data frame, a retransmission request of the data frame to the transmitting device, the receiving device including retransmission request transmission timing identifying means for identifying, based on a timing of reception of the data frame, a timing of transmission of the retransmission request of the data frame.

A transmitting device according to the present invention is a transmitting device which transmits a data frame to a receiving device and which retransmits, in response to a retransmission request from the receiving device, a data frame corresponding to the retransmission request, the transmitting device including retransmission data frame selecting means for selecting, based on a timing of reception of the retransmission request, a data frame to be retransmitted from among a plurality of data frames transmitted to the receiving device, and retransmits a data frame selected by the retransmission data frame selecting means to the receiving device.

A data frame retransmission control method according to the present invention is a data frame retransmission control method in a communication system having a transmitting device and a receiving device, the data frame retransmission control method including a retransmission request transmission timing identifying step of identifying, based on a timing at which the receiving device receives a data frame transmitted from the transmitting device, a timing of transmission of a retransmission request of the data frame to the transmitting device, and a retransmission data frame selecting step of selecting, based on a timing at which the transmitting device receives the retransmission request, a data frame to be retransmitted from among a plurality of data frames transmitted to the receiving device.

In order to achieve the second object, a communication device according to the present invention is a communication device which communicates with another communication device according to a time division duplex system and which retransmits, in response to a retransmission request transmitted from the other communication device, a data frame corresponding to the retransmission request to the other communication device, the communication device including data frame retransmission timing determining means for determining a retransmission timing of the data frame based on a reception timing of the retransmission request so that a timing difference between the reception timing of the retransmission request and the retransmission timing of the data frame corresponding to the retransmission request is close to a reference required time required from reception of a retransmission request to retransmission of a data frame.

According to the present invention, a retransmission timing of a data frame is determined based on a reception timing of the retransmission request so that the time from reception of the retransmission request to the retransmission of the data frame is close to a reference required time required for the retransmission process of the data frame. Because of this configuration, it is possible to preferably shorten the time from the reception of the retransmission request to the retransmission of the data frame.

The communication device may further include timing difference information storage means for storing, in correlation to information indicating a reception timing of a retransmission request, timing difference information indicating a timing difference which satisfies a condition related to the reference required time, wherein the data frame retransmission timing determining means may read timing difference information from the timing difference information storage means in correlation to the reception timing of the retransmission request and determine the retransmission timing of the data frame based on the reception timing of the retransmission request and the read timing difference information.

A communication device according to the present invention is a communication device which communicates with another communication device according to a time division duplex system and which retransmits, in response to a retransmission request transmitted from the other communication device, a data frame corresponding to the retransmission request to the other communication device, the communication device including data frame retransmission timing determining means for determining a retransmission timing of the data frame based on a processing capability of the communication device so that a timing difference between a reception timing of the retransmission request and the retransmission timing of the data frame corresponding to the retransmission request is close to a reference required time required from reception of a retransmission request to retransmission of a data frame.