JP3973536B2 - Error control method, communication apparatus, and communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a communication apparatus and a communication system that employ an ARQ (Automatic Repeat ReQuest) system as an error control technique, and in particular, SR (Selective-Repeat)-which retransmits only an erroneous packet. The present invention relates to an error control method applicable to the ARQ scheme.
[0002]
[Prior art]
Hereinafter, a conventional error control method will be described. Conventionally, GBN (Go-Back-N) -ARQ has been used as an error control technique from the viewpoint of simplicity. However, as the communication speed increases, it depends on propagation delay and processing in the physical layer and the Mac layer. The delay time cannot be relatively ignored, and the SR (Selective-Repeat) -ARQ method has been used.
[0003]
In the SR-ARQ, only an error packet to which NACK (Not Acknowledge) is returned is retransmitted. In addition, a reception buffer is required to store received packets waiting for sequence control by retransmission processing. That is, since it is necessary to guarantee the order of packets passed to the user (terminal connected to a communication network such as the Internet), other packets received correctly are stored until the retransmission packet can be received correctly. .
[0004]
Here, SR-ARQ will be described based on the drawings. FIG. 6 is a diagram illustrating conventional SR-ARQ processing (see, for example, Non-Patent Document 1). Here, for example, it is assumed that the communication device on the transmission side transmits packets in the transmission order of 0, 1, 2, 3, 4, and 5 shown in the figure.
[0005]
In FIG. 6, the receiving side communication apparatus returns an ACK (Acknowledge) because there is no error in the received 0th packet, and then returns a NACK because the received first packet has an error. Since there is no error in the second packet received in ACK, an ACK is returned. Next, the third packet received has an error, so a NACK is returned. Next, the fourth and fifth packets received are in error. ACK is returned because there is no.
[0006]
On the other hand, after receiving the NACK corresponding to the first packet, the communication device on the transmitting side retransmits the first packet (1 ′), and then retransmits the first packet until an ACK is returned. Repeatedly. Here, ACK is returned in the second retransmission. Similarly, when a NACK corresponding to the third packet is received, the third packet (3 ′) is retransmitted. Here, ACK is returned in the first retransmission.
[0007]
When retransmission control as described above is performed, the communication device on the receiving side first relays the 0th packet to the terminal or the like. Next, while retransmitting the first packet, the second, third (one retransmission), fourth, and fifth packets are correctly received. To guarantee the order of the packets, Since the fourth and fifth packets cannot be relayed to the terminal or the like, these packets are temporarily stored in the reception buffer. When the first packet has been correctly received, the reception buffer is released all at once.
[0008]
[Non-Patent Document 1]
IEICE Technical Report NS2002-81 RCS2002-109 (2002-07) "Evaluation of burstiness of output traffic by order control of Selective-Repeat ARQ protocol", Fig. 1
[0009]
[Problems to be solved by the invention]
However, in the above conventional error control method, it is necessary to guarantee the order of the packets. Therefore, when retransmission occurs as described above, the normally received packet is normally received after that. There is a problem that the delay time becomes large. In addition, for the same reason as described above, a reception buffer for storing other packets normally received before the retransmission packet is normally received is necessary. There was also a problem that it was necessary to prepare a large buffer. In particular, in a communication system having a large propagation delay (satellite communication system or the like), the time required for retransmission processing is inevitably increased, and the number of received packets waiting for sequence control increases, so a larger reception buffer is required.
[0010]
In addition, when the retransmitted packet is normally received, the packets held in the reception buffer are released all at once, so that traffic on a communication network such as the Internet increases rapidly, and the router etc. There was a problem of becoming. In particular, in a communication system having a large propagation delay (satellite communication system or the like), the reception buffer tends to be large, and thus burstiness appears remarkably.
[0011]
The present invention has been made in view of the above, and an object of the present invention is to provide an error control method, a communication apparatus, and a communication system that can reduce the propagation delay time and the number of reception buffers and reduce the output burst of a packet. To do.
[0012]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, the error control method according to the present invention is a method applicable to an error control method for retransmitting an erroneous packet, and is performed in an order by retransmission processing. When the number of received packets waiting for control is less than or equal to the specified amount, the order of the received packets is guaranteed. When the number of received packets waiting for sequence control due to retransmission processing exceeds the specified amount, the packet is ahead of the retransmission packet. And an order control step for outputting the received packets.
[0013]
According to the present invention, the number of received packets (corresponding to the specified number) for realizing packet sequence control is limited, and when a packet exceeding the prepared reception buffer is received, the packet is ordered before the retransmission packet. Output a packet waiting for control. For example, when a packet exceeding the number of prepared reception buffers is received, the packet with the earliest transmission order among the packets waiting for sequence control is transmitted to the destination terminal device. When the retransmission packet is normally received, the releasable packets in the reception buffer are released all at once.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an error control method, a communication apparatus, and a communication system according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
[0015]
Embodiment 1 FIG.
In the present embodiment, an error control method when a quasi-zenith satellite system is used as an example of a communication system according to the present invention will be described. This quasi-zenith satellite system is an area-limited type in which three satellites go around the earth in one day through a predetermined orbit and at least one of the three satellites is always near the sky (zenith) in Japan. It is a satellite system. In addition, if the satellite is switched every 8 hours, an elevation angle of 60 degrees or more is always secured, and the user always has a good mobile communication service (car phone service, mobile phone, etc.) with little interruption of the communication line by a building or the like. Service, a simple positioning system other than GPS, etc.). Specifically, when viewed from the main areas of Japan, satellites always exist within 20 degrees from the zenith. For example, simply moving the car antenna toward the zenith will change the direction of travel of the car. However, good communication is always possible, and further satellite tracking becomes unnecessary, so that the communication device can be simplified.
[0016]
FIG. 1 is a diagram showing a configuration of a communication system and a communication apparatus according to the present invention. In the present embodiment, for convenience of explanation, for example, the terminal device 1 that is the data transmission source is connected to the terminal device 5 via the communication device 2 on the transmission side, the satellite (SAT) 3 and the communication device 4 on the reception side. Assuming that data is transmitted. In the communication devices 2 and 4, the ARQ control units 11 and 12 each include an interface unit 21, a transmission buffer 22, a transmission ARQ processing unit 23, a reception ARQ processing unit 24, a reception buffer control unit 25, and a reception buffer 26. The error control of this embodiment to be described later is realized.
[0017]
Here, the error control method of the present embodiment will be described in detail with reference to the drawings. 2 and 3 are diagrams showing an error control method according to the present embodiment. Here, for convenience of explanation, the transmission ARQ processing unit 23 in the ARQ control unit 11 of the communication device 2 reads out the packets from the transmission buffer 22 in the transmission order of 0, 1, 2, 3, 4, and 5 and transmits them. In addition, it is assumed that the reception buffer 26 in the ARQ control unit 12 of the communication device 4 can store two packets having a specified amount. The prescribed amount means the number of buffers that the reception buffer 26 can store at one time. That is, the specified amount in this case is two packets, which is the storage capacity of the reception buffer.
[0018]
In FIG. 2, in the ARQ control unit 12 of the communication device 4, the reception ARQ processing unit 24 notifies the transmission ARQ processing unit 23 of ACK because there is no error in the 0th packet received via the satellite 3. The transmission ARQ processing unit 23 returns the ACK to the communication device 2 via the satellite 3. Next, the reception ARQ processing unit 24 of the ARQ control unit 12 that has received the first packet through the satellite 3 discards the packet because there is an error, and returns NACK through the same route as the ACK. is doing. Thereafter, the reception ARQ processing unit 24 of the ARQ control unit 12 returns the ACK because there is no error in the next received second packet in the same process as described above, and the next received third packet contains an error. Therefore, the packet is discarded and NACK is returned, and the next received fourth and fifth packets have no error, and therefore ACK is returned.
[0019]
On the other hand, in the ARQ control unit 11 of the communication device 2, the transmission ARQ processing unit 23 receives the NACK corresponding to the first packet via the reception ARQ processing unit 24, and then again receives the first packet (not shown). 1 ') is read from the transmission buffer 22 and retransmitted. Thereafter, the retransmission processing of the first packet is repeatedly executed until ACK is returned. In FIG. 2, ACK is returned in the second retransmission. Similarly, when a NACK corresponding to the third packet is received, the third packet (corresponding to 3 ′ in the figure) is retransmitted. In FIG. 2, ACK is returned by the first retransmission.
[0020]
When the retransmission control as described above is performed, in the communication device 2 on the reception side, first, the reception buffer control unit 25 stores the 0th packet received from the reception ARQ processing unit 24 in the reception buffer 26. Without being transmitted to the terminal device 5 via the interface unit 21. Next, since the reception buffer control unit 25 that has received the second packet has not received the first packet, the second packet is stored in the reception buffer 26 as an order control waiting packet (FIG. 3A). reference).
[0021]
Next, since the reception buffer control unit 25 that has received the fourth packet has not received the first and third packets, the fourth packet is stored in the reception buffer 26 as an order control waiting packet (FIG. 3 ( b)).
[0022]
Next, in the reception buffer control unit 25 that has received the fifth packet, the second packet (the packet with the earliest transmission order) stored in advance is read from the reception buffer 26, and the terminal device is transmitted via the interface unit 21. 5 is transmitted. Then, the fifth packet is stored in the empty area of the reception buffer 26 as an order control waiting packet (see FIG. 3C).
[0023]
Next, the reception buffer control unit 25 that has received the third packet (new sequence control waiting packet) by re-transmission does not store the third packet (packet with the earliest transmission order) in the reception buffer 26. It transmits to the terminal device 5 via the unit 21.
[0024]
Finally, the reception buffer control unit 25 that has received the first packet by retransmission (second time) transmits the first packet to the terminal device 5 via the interface unit 21 without storing the first packet in the reception buffer 26. . At the same time, the releasable 4th and 5th packets in the reception buffer 26 (the 4th and 5th packets can be released because the 3rd packet has already been transmitted) are released all at once, and the terminal via the interface unit 21 It transmits with respect to the apparatus 5 (refer FIG.3 (d)).
[0025]
That is, in this embodiment, a large reception buffer is not prepared and the order of packets is not completely guaranteed as in the prior art, but the number of reception buffers is limited as compared with the prior art, and the order control exceeding the number of reception buffers is performed. When a waiting packet is received, an order control waiting packet with the earliest transmission order is output prior to a retransmission packet (order reversal).
[0026]
As described above, in this embodiment, the number of received packets for realizing the packet order control is limited, and when a packet waiting for order control exceeding the prepared reception buffer is received by the retransmission process, the retransmission packet The sequence control waiting packet is output earlier than that. Specifically, when an order control waiting packet exceeding the number of prepared reception buffers is received, the packet having the earliest transmission order is selected from the order control waiting packets, and the selected packet is sent to the destination terminal device. Send to. When the retransmission packet is normally received, the releasable packets in the reception buffer are released all at once. As a result, while reducing the propagation delay time and the number of reception buffers, the output burst of packets can be greatly reduced by reducing the number of reception buffers.
[0027]
In the present embodiment, for convenience of explanation, it is assumed that the communication apparatus 2 transmits packets in the order of 0, 1, 2, 3, 4, and 5 shown in the figure, but there is no regulation on the number of packets to be transmitted. . For convenience of explanation, it is assumed that the reception buffer 26 can hold two packets. However, the number of packets that can be received by the reception buffer 26 depends on the communication speed and the order of packets. It is determined appropriately according to the allowable amount.
[0028]
In addition, the error control method according to the present invention is not limited to the quasi-zenith satellite system, as long as the communication system adopts the ARQ method as an error control method, other satellite communication systems, communication systems that do not relay satellites, etc. (mobile It can be applied to any communication system.
[0029]
In this embodiment, when an order control waiting packet exceeding the number of reception buffers prepared by the retransmission process is received, the earliest transmission order packet is selected from the order control waiting packets and the destination terminal However, the present invention is not limited to this. For example, as shown in FIGS. 4 and 5, it is possible to select the packet with the latest transmission order and transmit it to the destination terminal device. .
[0030]
For example, when the selection criterion of FIG. 4 is applied to the retransmission control of FIG. 2, in the communication device 2 on the reception side, first, the reception buffer control unit 25 receives the 0th packet received from the reception ARQ processing unit 24 as an interface. It transmits to the terminal device 5 via the unit 21. Next, since the reception buffer control unit 25 that has received the second packet has not received the first packet, the second packet is stored in the reception buffer 26 as an order control waiting packet (FIG. 5A). reference). Next, since the reception buffer control unit 25 that has received the fourth packet has not received the first and third packets, the fourth packet is stored in the reception buffer 26 as an order control waiting packet (FIG. 5 ( b)). Next, in the reception buffer control unit 25 that has received the fifth packet (new sequence control waiting packet), the interface unit 21 does not store the fifth packet (packet with the latest transmission order) in the reception buffer 26. And transmitted to the terminal device 5. Next, in the reception buffer control unit 25 that has received the third packet by retransmission, the fourth packet (packet with the slowest transmission order) stored first is read from the reception buffer 26 and passed through the interface unit 21. It transmits to the terminal device 5. Then, the third packet is stored in the empty area of the reception buffer 26 as an order control waiting packet (see FIG. 5C). Finally, the reception buffer control unit 25 that has received the first packet by retransmission (second time) transmits the received packet to the terminal device 5 via the interface unit 21 without storing it in the reception buffer 26. At the same time, the releasable second and third packets in the reception buffer 26 are simultaneously released and transmitted to the terminal device 5 via the interface unit 21 (see FIG. 5D).
[0031]
【The invention's effect】
As described above, according to the present invention, the number of received packets for realizing the packet order control is limited, and when a packet waiting for order control exceeding the prepared reception buffer is received by the retransmission process, the retransmission is performed. Output a sequence control waiting packet before the packet. Specifically, when an order control waiting packet exceeding the number of prepared reception buffers is received, the packet having the earliest transmission order is selected from the order control waiting packets, and the selected packet is sent to the destination terminal device. Send to. When the retransmission packet is normally received, the releasable packets in the reception buffer are released all at once. As a result, while reducing the propagation delay time and the number of reception buffers, the output burst of the packet can be greatly reduced by reducing the number of reception buffers.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a communication system and a communication apparatus according to the present invention.
FIG. 2 is a diagram illustrating an example of an error control method according to the present embodiment.
FIG. 3 is a diagram showing an example of a reception buffer control procedure in the error control method of the present embodiment.
FIG. 4 is a diagram illustrating an example of an error control method according to the present embodiment.
FIG. 5 is a diagram illustrating an example of a reception buffer control procedure in the error control method according to the present embodiment;
FIG. 6 is a diagram illustrating conventional SR-ARQ processing.
[Explanation of symbols]
1, 5 terminal device, 2, 4 communication device, 3 satellite, 11, 12 ARQ control unit, 21 interface unit, 22 transmission buffer, 23 transmission ARQ processing unit, 24 reception ARQ processing unit, 25 reception buffer control unit, 26 reception buffer.

Claims (8)

In an error control method applicable to an error control method for retransmitting an erroneous packet,
When the number of received packets waiting for sequence control due to retransmission processing is less than or equal to the prescribed amount, the order of the received packets is guaranteed, and when the number of received packets waiting for order control due to retransmission processing exceeds the prescribed amount, retransmission is performed. An order control step of outputting the received packet before the packet;
An error control method comprising: In the order control step,
The reception packet having the earliest transmission order is selected from the reception packets waiting for the sequence control when the specified amount is exceeded, and the selection packet is output before the retransmission packet. 2. The error control method according to 1. In the order control step,
The reception packet having the latest transmission order is selected from the reception packets waiting for the sequence control when the specified amount is exceeded, and the selection packet is output before the retransmission packet. 2. The error control method according to 1. In a communication device adopting an error control method for retransmitting an erroneous packet,
When the number of received packets waiting for sequence control due to retransmission processing is less than or equal to the prescribed amount, the order of the received packets is guaranteed, and when the number of received packets waiting for order control due to retransmission processing exceeds the prescribed amount, retransmission is performed. Retransmission control means for outputting the received packet before the packet;
A communication apparatus comprising: The retransmission control means includes
Receiving buffer means capable of storing the prescribed amount of received packets waiting for sequence control due to retransmission processing;
If the received packet waiting for sequence control exceeds the specified amount due to the new received packet and the received packet with the earliest transmission order is the new received packet, the new received packet is output before the retransmission packet, On the other hand, when the number of received packets waiting for sequence control exceeds a specified amount due to a new received packet, and the received packet with the earliest transmission order is the received packet stored in the reception buffer, the transmission packet has the earliest transmission order. A reception buffer control means for reading out the received packet and outputting it before the retransmission packet, and storing the new received packet in an empty area of the reception buffer;
The communication apparatus according to claim 4, further comprising: The retransmission control means includes
Receiving buffer means capable of storing the prescribed amount of received packets waiting for sequence control due to retransmission processing;
When the received packet waiting for sequence control exceeds a specified amount due to a new received packet and the latest received packet in the transmission order is the new received packet, the new received packet is output before the retransmission packet, On the other hand, when the number of received packets waiting for sequence control exceeds the specified amount due to a new received packet, and the received packet with the latest transmission order is the received packet stored in the reception buffer, the latest transmission order from the reception buffer. A reception buffer control means for reading out the received packet and outputting it before the retransmission packet, and storing the new received packet in an empty area of the reception buffer;
The communication apparatus according to claim 4, further comprising: In a communication system that realizes error control using a method of retransmitting an erroneous packet,
The receiving communication device
When the number of received packets waiting for sequence control due to retransmission processing is less than or equal to the prescribed amount, the order of the received packets is guaranteed, and when the number of received packets waiting for order control due to retransmission processing exceeds the prescribed amount, retransmission is performed. Retransmission control means for outputting the received packet before the packet;
A communication system comprising: A communication system that relays a packet transmitted from a transmission side communication device to a reception side communication device by relaying it at a satellite station, and implements error control using a method of retransmitting a packet having an error during transmission In the system,
The receiving communication device is
When the number of received packets waiting for sequence control due to retransmission processing is less than or equal to the prescribed amount, the order of the received packets is guaranteed, and when the number of received packets waiting for order control due to retransmission processing exceeds the prescribed amount, retransmission is performed. Retransmission control means for outputting the received packet before the packet;
A communication system comprising:

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