JPS60218942A - Data communication system - Google Patents

Abstract

PURPOSE:To reduce considerably the time needed to decide a retransmission position by using a cyclic counter which works asynchronously at each transmission/reception station in place of a conventional random number generaor and deciding the retransmission position of the collided data according to the count value of said counter in case the collision of data occurs. CONSTITUTION:A cyclic counter 14 has a satisfactory count-up speed compared with the slot length and performs counting repetitively like 0-4, 0-4,... up to the prescribed value. These counters 14 of each station work asynchronously with each other, and each station has a different time position to know the collision of packets according to the difference between the transmission delay time and the time needed for detection. Therefore the present count values are different from each other among counters 14 of each transmission/reception station when these count values are read by the transmission/reception station that detected the collision of packets. Thus the count value of the counter 14 is defined as the retransmission position of the packet of each station. This reduces the time needed to decide the retransmission position.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a data communication system, and particularly relates to a data communication system that uses blocks of data (hereinafter referred to as packets) in random access wireless data communication typified by the Aloha method and the Aloha method with slots. ) is related to determining the retransmission timing in the event of a collision.

This will be explained using an example. In the slotted Aloha method, as shown in FIG. The transmitting/receiving station receives these packets and captures the packets destined for itself.
This is a method of packet communication. The method of generating slot 2 on time axis 1 is not directly related to the present invention, and will therefore be omitted.

In addition, in the slotted Aloha method, as shown in Figure 1,
A plurality of stations 4b and 4c send packets 3b and 3b to the same slot.
If 3c is sent, packets will collide with each other and communication will not be possible. Therefore, the packet transmitting/receiving stations 4b and 4c that detected the collision between the sending buckets) 3b and 3c retransmit the colliding buckets) 3'b and 3c, but when they send the packet to the next slot immediately after the collision is detected, the packet collides again. occurs. To avoid this, the packet transmitting/receiving station 4b+
4c generates a random number up to a certain size and retransmits the packet with a delay of the number of slots indicated by the random number, thereby stochastically avoiding re-collision. Note that the packet collision detection method is not directly related to the present invention and will therefore be omitted.

FIG. 2 shows an example of a packet transmitting/receiving station that implements the slotted Aloha system. When a collision of transmission packets is detected, the control processor 1o instructs the random number generator 12 to generate a random number, reads the value after the generation of the random number is completed, and instructs the transmission timing control device 9 to use this value as the slot position to be retransmitted, Conventionally, a method has been used in which a retransmission packet set in the transmission data buffer 6 is retransmitted from the transmitter 5. Note that 7 is a receiver, 8 is a reception data buffer, and 11 is a receiver.
is memory.

However, in this conventional method, a random number is generated every time a packet collides, which takes time to calculate, making it impossible to quickly determine the retransmission slot position of the collided packet. .

[Summary of the invention]

This invention was made to eliminate the drawbacks of the conventional ones as described above. Instead of the conventional random number generator, a cyclic counter that operates asynchronously at each transmitting and receiving station is used to prevent data collisions. The object of the present invention is to provide a data communication system that can significantly shorten the time required to determine the retransmission position by determining the retransmission position of collision data according to the count value of the cyclic counter when a collision occurs. .

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 3 shows an example of the configuration of a packet transmitting/receiving station in a data communication system according to an embodiment of the present invention. In the figure, 5 is a transmitter, and 6 is a transmission data buffer for passing the packet to the transmitter 5. , 7 is a receiver, 8 is a reception data buffer for passing received packets to a control processor 10 (to be described later), 9 is a transmission timing control device that determines the transmission position of the packet, 11 is a memory, and 14 is a memory that is sufficient compared to the data length. It is a cyclic counter having a short count-up time, and operates asynchronously at each packet transmitting/receiving station 4a to 4n. Further, the maximum count value of this cyclic counter 14 is the maximum retransmission position of collision data,
That is, it is set equal to the total number of retransmission positions. lo controls the transmission and reception operations, and when a data collision occurs, reads the count value of the cyclic counter 14 and instructs the transmission timing 1lJfall device 9 to use the count value as the slot position to be retransmitted.
/e1m Prosensor. 13 are a transmission data buffer 6, a reception data buffer 8. Transmission timing control device 9
゜Memory 11. and a bus that connects the cyclic counter 14 and the control processor lo.

Next, the effects will be explained.

All operations other than those corresponding to conventional random number generation are the same as conventional ones (
Since they are similar, the explanation will be omitted, and the operation of the cyclic counter 14, ie, the operation related to determining the retransmission position, will be explained here.

As described above, the cyclic counter 14 has a sufficient count-up speed compared to the slot length, and can count up to a preset value, for example, 0.1°, 2.3°, 4.0.1°.
．． 2. Repeatedly count like... However, in this case, "0" indicates the next slot from the time position at which the packet collision was detected, "1" indicates the next slot, and so on.

The counters 14 in each station operate completely asynchronously, and the time position at which each station learns of a packet collision differs depending on the propagation delay time and the time required for detection. If the station reads the current count value of the counter 14 of the transmitting/receiving station, the count values should be different from each other. Therefore, by using that value as the retransmission position of the packet at each station, the retransmission position can be determined with the same randomness as the conventional method of using random numbers. The time required for this can be reduced.

In addition, although the above embodiment describes the case of the slotted Aloha method, the present invention is not limited to this, and may be used in the case of the pure Aloha method (the same effect as the above embodiment is achieved. There is no restriction on the radio frequency, and ground radio communication or satellite communication may be used.Furthermore, the cyclic counter may be configured by either hardware or software.

〔Effect of the invention〕

As described above, according to the present invention, a cyclic counter that operates asynchronously at each transmitting and receiving station is used, and when a data collision occurs, the retransmission position of the collision data is determined according to this count value. Therefore, there is an effect that the time required to determine the retransmission position can be significantly shortened.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of the slotted Aloha method, Fig. 2 is a diagram showing an example of the configuration of a conventional slotted Aloha method packet transmitting/receiving station, and Fig. 3 is applied to a data communication system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of the configuration of a packet transmitting/receiving station. 4a to 4n: transmitting/receiving station, 14: cyclic counter. In the drawings, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 2 Figure 3

Claims (1)

[Claims] +11 In a data communication system that performs random access wireless data communication between a plurality of data transmitting and receiving stations, each data transmitting and receiving station has a short count-up time compared to the data length and operates asynchronously with that of other data transmitting and receiving stations. 1. A data communication system comprising a cyclic counter, and when a collision of transmission data occurs, the collision data is retransmitted according to a counter value of the cyclic counter.