JPS632510B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an access method for efficiently communicating with a plurality of earth stations by sharing a communication satellite.

Figure 1 shows the configuration of the satellite communication system. In Figure 1, 1 is a communication satellite, 2a, 2b, 2c
indicates earth stations A, B, and C. Earth station A (2
A), B (2b), and C (2c) use the same satellite line to divide data into units called packets of a certain length or less, add destination information to them, and transmit them on radio waves.

The radio wave travels to the communication satellite 1 as a continuous burst of one packet, and the communication satellite 1 receives this burst, converts and amplifies the frequency, and sends it back to the ground. Earth stations A (2a), B (2b), and C (2c) receive the bursts, and according to the destination information, they take in the bursts addressed to themselves, and reject the bursts addressed to other stations. In this way, communication is performed between the earth stations via the communication satellite 1, but when multiple earth stations transmit bursts without permission, a collision occurs between the bursts, and the earth station receives the data correctly. become unable. Therefore, as one of the access methods to prevent such burst collisions, a reservation method, which will be described below, has conventionally been used.

Figure 2 shows the operation of the conventional reservation system.
3 is the time of transmission from the earth station, 4 is the time of reception from the earth station,
5 is the reception time of communication satellite 1, 6 is the cycle, 7 is the slot, 8 is the data area, 9 is the reserved area, 10
are small slots, 11a, 11b, 11c, 11d
are packets P1, P2, P3, P4, t1 to t7
indicates the time.

The satellite line is used by dividing the time into units called slots 7 on the communication satellite 1 that are large enough to accommodate one burst, and each earth station transmits a burst so that it fits into each slot 7. In the reservation method, a fixed number of consecutive slots 7 are collected to form a cycle 6, and one cycle 6 is a data area 8.
and a reserved area 9. In the following explanation, slot 7 in data area 8 will be referred to as a data slot, and slot 7 in reserved area 9 will be referred to as a reserved slot. The reserved slot is further divided into 10 smaller slots for use. FIG. 2 shows a case in which one reserved slot is divided into two small slots 10.
In the reservation system to be described from now on, it is assumed that one small slot 10 is fixedly allocated in advance to all earth stations.

Communication is performed by transmitting bursts containing packets using data slots in cycle 6, but in the reservation system, data slots cannot be used unless they are reserved. In Fig. 2, time t1
and sends packets P1 (11a) and P to earth station B (2b).
2 (11b), P3 (11c), and P4 (11d), earth station B (2b) is at time t2.
4 slots 7 using the small slot 10 fixedly assigned to the own station within the reserved area of the i-th cycle.
Submit your minute reservation. The reservation is received by the global station at time t3 after the round trip propagation delay time. In the reservation method explained here, the (i+1)th
The data slot assignment in the cycle is
It is assumed that the number of reservations is determined from the reservations of each earth station received in the cycle, and that the earth station transmits the reservation number O even if there are no packets to transmit. If earth station B (2b) is the only one that actually reserved a data slot among the reservations received from each earth station in the i-th cycle, then earth station B (2b) will have the data area 8 in the (i+1)th cycle. 4 from the beginning
Slot 7 is assigned, and earth station B (2b) receives packet P1 (11) at times t4, t5, t6, and t7.
a), P2 (11b), P3 (11c), P4 (1
1d). In such a conventional reservation method, even if the data slot of the i-th cycle remains unallocated because there are few reservations for the (i-1)th cycle, the data slot of the earth station B (2
In b), this unreserved data slot in the i-th cycle cannot be used, and this data slot is wasted, and the delay becomes large even when the traffic is small.

In order to solve the drawbacks of the conventional reservation method, the present invention is characterized in that unreserved data slots are also allocated to each earth station, and these data slots can be used even if they are not reserved in advance. The purpose is to effectively utilize the remaining unreserved data slots to reduce the delay of the reservation system when traffic is low.

FIG. 3 is a diagram showing an embodiment of this invention,
t8 to t11 indicate times used in the explanation.
In the reservation system according to the present invention, data slots that remain unallocated are also allocated according to predetermined rules. In FIG. 3, if all the reservations of each earth station received in the reservation area 9 of the (i-1)th cycle are O, all the data slots of the i-th cycle remain unallocated, but this is Global stations A in the system from the data slot
For example, A between (2a), B(2b), and C(2c)
→B→C→A→B→C→A→B are assigned to each earth station in this order. This allocation is just an example, and whether or not to start allocation from the station may be determined in accordance with the slot allocation algorithm for reservation in the reservation system. When data slots are allocated in this way, packets P1 (11a) and P2 (11a) generated at earth station B (2b) at time t1 are
b), P3 (11c), and P4 (11d), earth station B (2b) can use three data slots in the i-th cycle, and sends packets P1 (11a), P2 (11b) at times t8, t9, and t10. ,P3(1
1c). However, packet P4 (11d) cannot be transmitted in the i-th cycle, and a reservation for 7 slots for one slot is transmitted in the small slot 10 of the local station in the reserved area 9 of the i-th cycle. With this reservation, a data slot for the next (i+1)th cycle is allocated, and a burst containing packet P4 (11d) is transmitted at time t11. The above is an explanation of the operation of the reservation system according to the present invention, and it can be seen that the delay from packet generation to transmission is reduced by using unreserved data slots. When allocating the data slots that remain unreserved, the target stations for allocation are all earth stations in the system, but if any earth station in the system is out of operation, the data slots will be wasted. There are drawbacks that can be assigned.

If this drawback is a problem, it is recommended that the allocation of unreserved data slots not be performed on all earth stations, but only on earth stations for which reservations have been received within a certain period of time. good. For example, the stations to which data slots that are not reserved in the i-th cycle are assigned are limited to only those stations for which reservations were received in the (i-1)-th cycle.

Although this makes the processing a little more complicated, data slots will not be wasted and allocated to earth stations that are out of operation, and the data slots will be used more effectively.

Although the above description has been made regarding communication using a communication satellite, the present invention is not limited to this, and may be used for wireless packet communication or for packet communication by connecting terminals to multiple points.

Furthermore, in the explanation, the small slot 10 in the reserved area 9
is fixedly assigned to each earth station, and the earth station transmits reservations with O reservations even if there are no packets to transmit, and data slot allocation is determined only from the reservations received in the previous cycle 6. Although we have described a reservation method for
A reservation method that competes for the small slot 10 in the reservation area 9, a reservation method that does not send a reservation if there is no packet to be sent, a reservation method that allocates data slots by accumulating reservations from the past, and a combination of these methods. It may also be used in a combined reservation scheme.

As described above, the reservation method according to the present invention makes effective use of the remaining data slots that have not been reserved, and has the effect of shortening the delay from when a packet is generated until it is sent.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a satellite communication system, FIG. 2 is a diagram showing the operation of a conventional reservation system, and FIG. 3 is a diagram showing an embodiment of the present invention. In the figure, 1 is a communication satellite, 2a, 2b, 2c are earth stations A, B, C, respectively, 3 is the transmission point of the earth station,
4 is the reception time of the earth station, 5 is the reception time of the communication satellite 1, 6 is the cycle, 7 is the slot, 8 is the data area, 9 is the reserved area, 10 is the small slot, 11a,
11b, 11c, 11d are packets P1, P2,
P3, P4, and t1 to t11 indicate times used in the explanation. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

Claims (1)

[Claims] 1. A single communication line is time-divided into slots of a fixed time length, a cycle is composed of a fixed number of continuous slots, the slots within one cycle are divided into reserved slots and data slots, and a communication station In a reservation system, a communication station transmits a reservation requesting the allocation of a data slot in a reservation slot, a data slot is allocated to a communication station based on the received overall reservation, and information divided into units called packets is transmitted using the data slot. A reservation method characterized by sequentially allocating unreserved data slots among all the earth stations within one cycle. 2. Claim 1, characterized in that data slots that remain unreserved within one cycle are sequentially allocated among earth stations for which reservations have been received in the past up to a certain period of time. Reservation method listed.