JPS62199129A - Satellite communication system - Google Patents

Abstract

PURPOSE:To attain stable communication even at the increase in a short data of <=1 slot by detecting a short data quantity to be sent at a peripheral station and switching the transmission system when the quantity of the said data is a prescribed value or over. CONSTITUTION:A peripheral station having a transmission request sends a data of one time slot stored in a random access data buffer 16 via a message length detection section 18 via a data selection section 19 or the like controlled by a transmission slot management section 15 according to the random access system. When the transmission collides with the transmission of other peripheral station and the reception is failed, an NAK broadcast from a central station is received by a reception section 13. Then a message of >=3 slots stored in the buffer 16 by a retransmission control section 21 is transferred to a reservation data buffer 17 via a reservation control section 23 or the like. The data of the buffer 17 is selected by a data selection section 19 controlled by a management section 15 in response to the broadcast section 19 controlled by a management section 15 in response to the broadcast reception, a prescribed quantity or over of data is sent by the reservation system and stable communication is applied even at the increase in a short data of one slot or below.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a multiple access satellite communication system in which communication between one station (central station) and many stations (peripheral stations) is performed via a common channel via a satellite. In particular, the present invention relates to improvements in access methods from peripheral stations to the central station.

(Prior art) In a multiple-access satellite communication system in which communication between a central station and peripheral stations via satellite is performed through a common channel, the peripheral stations transmit data at any time as a method for accessing the central station from the peripheral stations. A so-called random access method that transmits data in a reserved time slot and a reservation method that transmits data in a reserved time slot have been adopted.

In the random access method, scheduling is not performed between each peripheral station, and each peripheral station freely sends data to a line shared with other peripheral stations when data is generated, and some or all of the data may be lost due to collision. The original method is to retransmit the data if the data is lost, but since this increases the probability of data collision, the slotted Aloha method shown in FIG. 4 has been adopted as the random access method.

In FIG. 4, reference numeral S indicates a time slot, and the time slot S is obtained by dividing the time axis of the communication channel into fixed time units corresponding to -bucket length. In each peripheral station, for example, station 1. 2 and 3 receive data generation, synchronize so that the transmission packet falls into this time slot S, and then transmit it. However, since the surrounding stations independently decide which time slot S to enter, packets from other stations may collide and be lost if they enter the same time slot as other stations' packets, such as transmission baguettes A and B of stations 1 and 2. be. When this collision occurs, each peripheral station receives no reception response (ACK) from the central station, so the corresponding station 1. 2 learns that data has been lost due to the collision.

Stations 1 and 2 each transmit packet A' after an arbitrary period of time has elapsed.
The same B' is retransmitted. On the other hand, the reservation method is a method of scheduling between peripheral stations, and FIG. 5 shows an example of this reservation method.

In Figure 5, when a peripheral station finishes receiving data from a terminal connected to its own station or a landline line, it sends a reservation packet to the central station, and then sends a reservation packet to the central station to send out all the data to the line. Reserve the number of slots. The central station schedules reservations from each station and sends slot assignment transmissions to peripheral stations that have requested reservations, informing them of the allocated slots and at the same time instructing other peripheral stations not to transmit data to that slot. do.

As a result, the peripheral station that has reserved the slot can transmit data 1, data 2, and data 3 in the allocated slot.

(Problem to be solved by the invention) By the way, since the slotted Aloha method does not require time for scheduling, if there is no collision,
Data delay time can be reduced.

However, as the traffic increases, the number of data retransmissions due to collisions increases, which causes a further increase in traffic, and there is a risk of an unstable state in which only retransmitted data is left.

On the other hand, with the reservation method, before transmitting data, it is necessary to determine the slot length from the peripheral stations to the central station and allocate slots from the central station to the peripheral stations, resulting in a large data delay time. However, since the central station schedules each peripheral station, there is no data collision and the advantage is that lines can be used efficiently. Therefore, in order to improve data transmission efficiency and line utilization efficiency, it is conceivable to use both methods together. That is, when a peripheral station sends long data of one slot length or more to the line, the probability of collision with data from other peripheral stations increases, so the data is sent out using a reservation method.

Furthermore, when a peripheral station sends short data for one slot onto the line, it sends the data using the slotted Aloha method to slots that are not reserved for other stations. In this way, in a combination method that uses a random access method (Aloha method with slots) and a reservation method, it is determined whether to use the random access method or the reservation method depending on the data length, so all data is accessed using random access. Compared to the conventional method, long data can be transmitted continuously without data collision, improving transmission efficiency.

However, when the number of short data of one slot or less increases, there is a problem that data collisions increase, causing an increase in retransmitted data, and the communication system may become unstable.

The present invention has been made in view of the above problems, and its purpose is to provide a satellite communication system that allows stable communication even when the number of short data of one slot or less increases.

(Means for Solving the Problems) In order to achieve the above object, the satellite communication system of the present invention has the following configuration.

That is, the satellite communication system of the present invention is composed of a central station and a plurality of peripheral stations, and is a system in which the plurality of peripheral stations access the central station through a common channel via a satellite. A reservation method that determines whether the data length of the transmission data is short data within one time slot or long data that spans two or more time slots, and transmits long data based on the reservation of the transmission time slot. , a satellite communication system that uses a random access method in which short data is transmitted in unreserved time slots; the peripheral station detects the amount of short data to be transmitted, and the peripheral station detects the amount of short data to be transmitted, and The present invention is characterized in that it includes a switching control means for switching the short data transmission method from the random access method to the reservation method when the value is greater than or equal to the value.

(Function) Next, the function of the satellite communication system of the present invention having the above configuration will be explained.

When a peripheral station accesses the central station, the peripheral station determines the data length of its own transmission data, and transmits long data that spans two or more time slots using a reservation method that reserves the required number of transmission time slots. However, short data of one time slot or less is transmitted using a random access method that selects an arbitrary time slot from among the time slots that are not reserved.

In this case, when local station transmission data is generated, the transmission data, whether long data or short data, is stored once in the transmission buffer as data to be transmitted, and is sequentially transmitted from this transmission buffer.

At this time, long data is transmitted using a reservation method, so no problems such as transmission delays occur.However, since pheasant data is transmitted using a random access method, there is a possibility of collision with random access data transmitted by other peripheral stations. However, if there is a large amount of short data to be transmitted, the transmission delay will increase. In addition, when a collision occurs, each peripheral station retransmits, but if it is not successful, the short data is left in the retransmission buffer as data to be transmitted and retry is performed, so if the amount of data in the retransmission buffer is large, In addition to the problem of transmission delay, this creates the disadvantage of increasing the amount of traffic on the communication channel.

Therefore, in each peripheral station, the switching control means detects the amount of short data in the transmission buffer, the amount of short data in the retransmission buffer, or the sum of the short data in the transmission buffer and the short data in the retransmission buffer. When the amount is greater than a predetermined value, the short data transmission method is switched from the random access method to the reservation method.

As a result, even if the amount of short data is large, the number of retransmitted data can be reduced, the communication system can be prevented from becoming unstable, and a kind of congestion control can be performed.

(Example) Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 shows the overall configuration of a satellite communication system embodying the present invention. The satellite communication system according to the present invention consists of a central station C and a plurality of peripheral stations R (1, Il, II[,...). configured,
A system in which multiple peripheral stations R access the central station C through a common channel via a satellite S, which uses both a reservation system that reserves transmission time slots and a random access system that uses unreserved time slots. The central station C and the peripheral station R are configured as shown in FIGS. 2 and 3.

In FIG. 2, a central station C includes a transmitting/receiving device 1 that transmits and receives radio waves to and from a satellite S, and a timing signal generating unit that generates a timing signal indicating a frame break consisting of a predetermined number of time slots at a transmitting timing and a receiving timing. 2, a receiving section 3 which performs reception processing of the transmission data (including reservation packets) of the peripheral station R that is input via the transmitting/receiving device 1 and inserted into the time slot, and a receiving section 3 that receives the output of the receiving section 3 and receives it. Reception data buffer 4 that performs buffering for use as reception data
In response to the output of the receiving section 3, a reception response signal (ACK
or NAK), determines whether the data is a reservation packet, and requests the required number of time slots if it is a reservation packet.

a control signal generation unit 5 that generates an allocation signal for allocating the slot, and also generates a reservation information signal indicating which time slot in one frame is the reservation material based on the determination result; A transmission data buffer 6 that performs buffering, a multiplexing section 7 that receives the outputs of the transmission data buffer 6, the timing signal generation section 2, and the control signal generation section 5 and time-division multiplexes them; It basically includes a transmitting section 8 which transmits the received data to each peripheral station via the transmitting/receiving device 1 in broadcast mode. In FIG. 3, a peripheral station R receives transmission data from a central station C input via a transmitting/receiving device 11 that exchanges radio waves with a satellite S, and the transmitting/receiving device 11, and extracts the timing signal from the transmitted data. a frame synchronization unit 12 that generates a slot timing signal indicating the position of each time slot within one frame in synchronization with the timing signal thus extracted;
a receiving unit 13 that receives the transmitted data from the central station C input via the transmitting/receiving device 11 and separates and outputs the reception response signal, the assignment signal, and the reservation information signal from the transmitted data; A reception data buffer 14 buffers received data to be separated and output; and a reception data buffer 14 that receives the output (slot timing signal) of the frame synchronization section 12 and the allocation signal and reservation information signal separated and outputted by the reception section 13 and performs allocation. Generating a time slot designation signal that designates the time slot, and
Transmission slot management that refers to the reservation information signal, extracts time slots that are not reserved by other peripheral stations, and generates a time slot selection signal that indicates one of the extracted time slots at a temporally earlier point in time. Part 15 and
A random access data buffer 16 for storing short data of one time slot or less, a reservation data buffer 17 for storing long data of two time slots or more, and receiving data transmitted from the local station and detecting the data length; When the transmission data is the short data, it is transferred to the random access data buffer 16, while when the transmission data is the long data, for example, a reservation is made with a reservation for the number of time slots necessary for transmitting all the data. A message length detector 18 that transfers packets to the random access data buffer 16 and all data to the reserved data buffer 17, and a message length detector 18 that transfers the packet to the random access data buffer 16, and a message length detector 18 that transfers the packet to the random access data buffer 16, and a message length detector 18 that transfers the packet to the random access data buffer 16, and a message length detector 18 that transfers the packet to the random access data buffer 16, and a message length detector 18 that transfers the packet to the random access data buffer 16 and transfers all data to the reservation data buffer 17. While reading required data from the random access data buffer and inserting the data into the time slot designated by the time slot selection signal, reading all the data from the reserved data buffer in response to the time slot designation signal, and inserting the data into the time slot designated by the time slot selection signal, a data selection unit 19 that inserts data into the required number of time slots specified by the time slot designation signal;
For example, the receiving section 13 serves as a transmitting section 2o that receives the output of the data selection section 19 and performs data transmission, and an abnormality processing section that performs abnormality processing on data transmitted to the central station.
The contents of the reception response signal separated and output at NAK(N
a retransmission control unit 21 that retransmits the short data or the reservation packet when the OTAC is -NOWLEDGE;
, a buffer amount detection section 22 that detects that the amount of data stored in the random access data buffer 16 (including the amount of retransmitted data) exceeds a predetermined value, and a buffer amount detection section 2
2, the data stored in the random access data buffer 16 (including retransmission data) is transferred to the reservation data buffer 17, and the reservation is made to reserve the number of slots necessary for transmitting the stored data thus transferred. It basically includes a reservation control unit 23 that forms a packet and stores the reservation packet in the random access data buffer 16.

Next, referring to FIG. 4, the operation of the satellite communication system of the present invention will be explained, focusing on the combined system adopted by peripheral stations. Note that since the combined method in this embodiment is a combination of the conventional reservation method and the random access method (Aloha method with slots), explanations of the individual methods will be omitted, and the explanation will focus on the parts related to the present invention.

Now, there is a transmission request from a certain peripheral station, and short data A and B with a data length within one time slot (hereinafter simply referred to as "slot") are sent to the random access data buffer 16 via the message length detection unit 18. Suppose it is stored.

The data selection unit 19 is a random access data buffer 1
First, data A is read from 6 and inserted into the slot designated by the time slot selection signal from the transmission slot management section 15.

This data A is sent to the central station using a random access method, but because it collides with data sent by other peripheral stations and the central station cannot receive data A normally, it sends NAK#1 as a reception response signal. Transmit in broadcast mode. On the other hand, the peripheral station transmits the next data B using the random access method at an appropriate time before receiving NAK #1 from the central station.
Since this data B also caused a collision with the transmission data of other peripheral stations, the central station will transmit NAK #2 in broadcast mode.

The peripheral station that sent data A and B is NAK#1゜NAK
Upon reception of #2, the peripheral station learns of the transmission failure, and the retransmission control unit 21 attempts to retransmit data A and B after an appropriate period of time (the procedure for transmitting retransmitted data is not shown). At an appropriate time after data B is transmitted, data C1n, C2, C,
Suppose that the message length detector 18 inputs the message length. As a result, five pieces of short data exist in the random access data buffer 16.

In the buffer amount detection unit 22, the detection predetermined value is, for example, “
If "3" is set, the amount of data in the random access data buffer 16 is 3 or more, so a detection signal is output to the reservation control section 23. Upon receiving the detection signal, the reservation control unit 23 transfers the data stored in the random access data buffer 16 to the reservation data buffer 17, and also forms a reservation packet with the number of reservation slots "5" and transfers it to the random access data buffer 16. Store.

Then, the reserved slot is transmitted to the central station in a random access manner by the operations of the transmission slot management section 15 and the data selection section 19 as described above. When the central station successfully receives the reserved slot, the control signal generator 5 generates an allocation signal (slot allocation) and a reception response signal (ACK).
generate.

It is then transmitted in broadcast mode to surrounding stations.

In the peripheral station, the transmission slot management unit 15 outputs a time slot designation signal to the data selection unit 19, so the data selection unit 19 selects the five data A, B, CI+C2 stored in the reserved data buffer 17. , C, respectively, and insert them into the designated slots. In other words, the five pieces of short data are transmitted in a reserved manner. As a result, the buffer amount detection section 22 and the reservation control section 23 collectively constitute a switching control means.

Note that in the above embodiment, a method of transmitting a reservation packet was adopted as the reservation method, but as another reservation method, the message length detection section can insert the long data to be transmitted into one slot with the leading data and the remaining data. If the method is such that the first data is transferred to the random access data buffer with a reservation for the number of slots required for transmitting the remaining data, and the remaining data is transferred to the reserved data buffer, Of course, the reservation control section will also operate in the same manner.

(Effects of the Invention) As detailed above, according to the satellite communication system of the present invention,
This is a method that uses both a random access method and a reservation method as a method for peripheral stations to access the central station, and when the amount of random access data exceeds a predetermined value, random access data is also transmitted using the reservation method. As a result, it is possible to provide a satellite communication system that can improve line usage efficiency, prevent synergistic increase in data collisions, and perform stable communication.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a satellite communication system implementing the present invention;
FIG. 2 is a block diagram of the configuration of a central station according to an embodiment of the present invention, FIG. 3 is a block diagram of a configuration of a peripheral station according to an embodiment of the present invention, and FIG. 4 shows a data transmission procedure of a peripheral station. FIG. 5 is a time chart showing data collision and retransmission in the conventional slotted Aloha method, and FIG. 6 is a time chart showing the data transmission procedure in the conventional reservation method. DESCRIPTION OF SYMBOLS 1... Transmitter/receiver device, 2... Timing signal generation section, 3... Receiving section, 5...
- Control signal generation section, 8... Transmission section, 11...
...Transmission/reception device, 12...Frame synchronization unit, 13...Reception unit, 15...Transmission slot management unit, 16...Random access data Buffer, 17... Reserved data buffer, 18... Message length detection section, 19...
...Data selection section, 20...Transmission section, 21
. . . Retransmission control section, 22 . . . Buffer amount detection section, 23 . . . Reservation control section. Agent Patent Attorney Yoshi Yahata Hiromi Takumei is absent from the 14th satellite Meng ship provision 7 figure c and bureau's Δ1 Daihan 2 figure 3 figure tm intestinal rope, kusugar throat figure 4 Slot size Aloha Hoten's theme - Genki Ikari and retransmission 1st r
Figure 5

Claims (1)

[Claims] Consisting of a central station and a plurality of peripheral stations, the peripheral stations access the central station through a common channel via a satellite.
Is it short data less than the time slot, or is it 2?
This method combines a reservation method that determines whether long data is repeated over a time slot and transmits long data based on the reservation of a transmission time slot, and a random access method that transmits short data in a time slot that is not reserved. The peripheral station detects the amount of short data to be transmitted, and when the amount of short data exceeds a predetermined value, switches the short data transmission method from a random access method to a reservation method. A satellite communication system characterized by comprising a control means.