JPS6252499B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reservation system, and more particularly to a reservation system that allows a plurality of earth stations to share a communication satellite, access each other, and communicate efficiently.

2. Description of the Related Art Conventionally, a satellite communication system in which a plurality of earth stations share a communication satellite for communication is shown in the schematic configuration diagram of FIG. In FIG. 1, reference numeral 1 indicates a communication satellite, and reference numerals 2a, 2b, and 2c indicate earth stations A, B, and C. Each earth station A2a, B2
b and C2c 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 over radio waves. The radio wave travels to the communication satellite 1 as a continuous burst of one packet, and the communication satellite receives this burst, converts the frequency, amplifies it, and sends it back to the ground. Each earth station A2a, B2b, C2c receives the burst,
Depending on the destination information, bursts addressed to the local station are captured, and bursts addressed to other stations are discarded. In this way, communication is carried out between each earth station via the communication satellite 1, but when multiple earth stations transmit bursts at arbitrary timings, collisions between bursts occur, and each earth station The station will not be able to receive signals correctly. Therefore, as one of the access methods for preventing such burst collisions, a reservation method described below has been conventionally used.

FIG. 2 is an explanatory diagram showing the operation mode of the conventional reservation system. In Fig. 2, 3 is the earth station transmitting time, 4 is the earth station receiving time, 5 is the cycle, 6 is the data area, 7 is the reserved area, 8 is the data slot, 9 is the reserved slot, 10 is the small slot, 11
is the round trip propagation delay time, 12, 13,
14 are respective earth stations A2a, B2b, C2c
The small slot 10 assigned to the slot 10 is shown.

The satellite line is used by dividing the time into units called slots, which are large enough to accommodate bursts, on the communication satellite 1 shown in Figure 1, and is used by each earth station A2a to C2c.
will send a burst into this slot. In this reservation method, a fixed number of consecutive slots are collected to form a cycle 5, and one cycle 5 is further divided into a data area 6 and a reserved area 7 for use. In the following explanation, the slot in the data area 6 will be referred to as a data slot 8, and the slot in the reserved area 7 will be referred to as a reserved slot 9. The reserved slot 9 is divided into shorter small slots 10 for use. Second
The figure shows a case where one reserved slot 9 is divided into two small slots 10 and used. In such a conventional reservation system, each small slot 10 in the reservation area 7 within one cycle 5 is fixedly assigned to all earth stations in the system, and each earth station A2a, B2b, Small slots 12, 13, and 14 are assigned to C2c, respectively. Communication is performed by transmitting a burst containing a packet using data slot 8 in cycle 5, but in this reservation system, data slot 8 cannot be used unless it is reserved. i shown in Figure 2
At the beginning of cycle 5, each earth station A2a-C2c
If each earth station has 4 packets to transmit, then in the reserved area 7 of the i-th cycle 5, these earth stations each have 4 slots each with fixedly assigned small slots 12, 13, and 14. Submit your reservation. Reservations are made via communication satellite 1, round trip propagation delay time 11
It arrives at each earth station only after a delay and is received. Here, all reservations sent in the i-th cycle 5 are received before the (i+1)-th cycle 5 starts. The data slot 8 in the (i+1)th cycle 5 is allocated to each earth station and used according to the reservation received in the i-th cycle 5. This slot allocation is performed independently by each earth station, but if all earth stations receive the same reservation and allocate according to the same algorithm, burst collisions and slot allocations due to mismatched allocations between earth stations will be avoided. Nothing goes to waste. This slot allocation algorithm must be able to allocate equally to each earth station, but its details are not directly related to the present invention, and therefore will not be discussed in detail. In the (i+1)th cycle 5, each earth station A2a, B2b is assigned three data slots 8, and receives packets a1, a, respectively.
2, a3 and b1, b2, b3 are being transmitted.
The earth station C2c has been assigned two data slots 8 and is transmitting packets c1 and c2. Here, all earth stations cannot transmit all packets in the (i+1)th cycle 5. This fact is known at the time of slot allocation processing performed at the start of the (i+1)th cycle 5. Therefore,
Each of the earth stations A2a to C2c fills the slots for the packets that cannot be sent in the (i+1)th cycle 5.
Make a reservation at Due to this reservation, the remaining packets b4, c3, a
4, c4 is transmitted.

As described above, in the conventional reservation method, the small slot 10 of the reserved area 7 is fixedly allocated to each earth station, so it is not possible to increase the number of earth stations, and when the number of earth stations is increased, the data area 6 was reduced, and the satellite line was not used efficiently. As a way to overcome this drawback,
A system has been considered in which the unused data slot 8 is used as a reserved slot 9, and the small slot 10 is not fixedly assigned to each earth station, but the reservation is transmitted in the slotted Aloha system in units of small slots 10. This Aloha system with slots is a system in which each earth station randomly selects a small slot 10 in the reservation area 7 and transmits a reservation. In this system, each earth station randomly selects a small slot 10 and transmits a reservation, so if two or more earth stations transmit reservations at the same time in the same small slot 10, a collision occurs and the reservation cannot be received. However, if reservations are transmitted infrequently, there is a high probability that reservations will be received without collision, and reservations can be sent using this method as well. By the way, in the conventional distributed reservation method, in order to perform distributed access control, the reservation is valid only for the next cycle 5, and as shown in Figure 2, it is not possible to make a reservation once and send it all in the next cycle 5. If there was not enough, the missing amount had to be reserved in the next cycle 5. In this way, the frequency of transmission of reservations for each earth station increases, but in the conventional distributed reservation system, this did not pose a particular problem because the small slots 10 were fixedly allocated to each earth station. On the other hand, if the reserved area 7 is made variable in order to increase the number of earth stations and the slotted Aloha method is used for transmission, as the frequency of transmission of reservations increases, many reservation conflicts will occur and reservations will not be received properly, resulting in data packets being There is a drawback that it becomes impossible to send. A centralized reservation method is a method that does not have such drawbacks. This is a method in which a control station accepts reservations, centrally allocates slots, and notifies all earth stations of the results.
In this method, when a control station receives a reservation, it accumulates it for each earth station, and subtracts the amount when slot allocation is performed. Once the reservation is accepted by the control station, the reservation will be stored until the slot is allocated, so even if the slot is not allocated in the next cycle 5 after sending the reservation, there is no need to send the reservation again. reservations will be sent less frequently. However, this method has the disadvantage that one round trip propagation delay time 11 is required at each stage of transmission of the reservation, transmission of slot allocation information, and transmission of data packets, resulting in a large delay overall. For these reasons, in the conventional reservation system, the distributed type reduces the delay but accommodates fewer earth stations, while the centralized type allows the accommodation of a larger number of earth stations but increases the delay. There were some shortcomings.

The present invention has been made in order to eliminate the above-mentioned drawbacks of the conventional system.A single communication line is time-divided into slots of a certain length of time, and a cycle is composed of a certain number of consecutive slots. The slots in the cycle are divided into reserved slots and data slots, the communication station sends a reservation requesting allocation of data slots in the reserved slots, data slots are allocated to the communication station from the received overall reservation,
In this reservation method in which information divided into packets is transmitted through data slots, one control station accumulates the reservations for each communication station that are not sent through the data slots within one cycle for each communication station. means for the control station to periodically broadcast the accumulated reservation information to all communication stations; all the communication stations allocate data slots in a distributed manner based on the received reservation information and the reservations of each communication station; It is an object of the present invention to provide a reservation system which has a configuration comprising means and which reduces delays in reservations and can accommodate a larger number of communication stations.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. FIG. 3 is an explanatory diagram showing the operation mode of a reservation system which is an embodiment of the present invention, and parts equivalent to those in FIG. 2 are indicated using the same reference numerals, and detailed explanation thereof will be omitted. In FIG. 3, 15 indicates the reservation status, and 16, 17, and 18 indicate the reservations of each earth station A2a, B2b, and C2c, respectively.

Although the reservation system according to the present invention can accommodate an unspecified number of earth stations, the maximum number is determined. The explanation here assumes that there are many earth stations in addition to the earth stations A2a to C2c. In this reservation method, all slots that remain unallocated in one cycle 5 are used as reserved slots 9. Also, this reservation slot 9
The small slots 10 are all divided into small slots 10 and used, and the small slots 10 are not fixedly assigned to each earth station, and reservations are transmitted using the slotted Aloha method.
In addition, reservations received without collisions are received by the control station and accumulated for each earth station, and when allocating slots, this control station allocates the cumulative number of reservations for the earth stations to which slots are allocated. decrease by the number given. In this way, the control station stores the remaining unallocated reservations for all earth stations and periodically broadcasts this information as reservation status 15 to all earth stations. In Figure 3, once every cycle 5, the reservation status 1 is displayed at the last slot of cycle 5.
I am trying to send 5. Only one control station is required in the system, and each earth station A2a~
Any earth station in the system, including the C2c, can be used. Furthermore, in FIG. 3, at the start of the i-th cycle 5, if there are three packets to be transmitted to only three earth stations A2a to C2c, then the three stations use the small slot 10 in the reserved area 7. Randomly selected reservations for 3 packets 16, 17, 18
Send. i-th cycle 5 reservation 16, 17,
18 and the reservation status 15 are all received before the start of the (i+2)th cycle 5. th (i+
2) Immediately before the start of cycle 5, all earth stations independently make slot assignments for the (i+2)th cycle 5 based on the reservations 16, 17, 18 of the i-th cycle 5 and the reservation status 15. Each earth station has the same reservation16~
18 and the reservation status 15 and allocate them using the same algorithm, no collision will occur in packet transmission even if each earth station performs the assignment independently. In FIG. 3, assuming that all reservations 16 to 18 before the i-th cycle 5 have been allocated, the reservation status 15 sent in the i-th cycle 5 is 0 for all earth stations. th (i+
2) In slot allocation in cycle 5, each earth station adds up the received reservations 16 to 18 and the reservation status 15 for each earth station, and performs slot allocation based on the result. In this case, since the reservation status 15 is 0 for all earth stations, the summed result is the reservation status 16 to 18 transmitted in the i-th cycle 5.
Therefore, each of the earth stations A2a to C2c has a value of 3, and the other earth stations have a value of 0. Therefore, slot assignment is made to each of the three earth stations A2a to C2c. In Figure 3, due to slot assignment, each of the three earth stations A2a to C2c has two
It is assumed that a slot has been allocated. As a result, in the (i+2)th cycle 5, earth station A2a sends packets a1 and a2, and earth station B2b sends packet b.
1, 2b, earth station C2c transmits packets c1, c2. However, only one packet remains that cannot be transmitted to each earth station. Of the reserved number of slots, the remaining unallocated slots are stored by the control station and broadcast as reservation status 15 to all earth stations. Although each of the earth stations A2a to C2c was unable to transmit all the packets in the (i+2)th cycle 5, it does not reserve the shortfall in the (i+3)th cycle 5. This shortfall is the (i+
2) All earth stations are notified of the reservation status 15 of cycle 5, and as a result, each earth station allocates slots for the shortage in the (i+4)th cycle 5 in a distributed manner. Since no reservation is received in the (i+3)th cycle 5, only the reservation status 15 is received, the slot allocation for the (i+4)th cycle 5 is determined only from the latter. For this reason, each earth station A2a
~C2c is allotted one slot each, and a
Packets 3, b3, and c3 are transmitted.

As described above, in the reservation system of the present invention, reservations are centrally accepted and managed by the control station, so that reservations are transmitted less frequently than in conventional distributed reservation systems. As a result, reservations can be transmitted using the slotted Aloha method, and there is no need to permanently allocate small slots 10 to each earth station.
It can accommodate an unspecified number of earth stations. On the other hand, since slot allocation is done in a distributed manner at each earth station, the delay is shorter than in the centralized reservation system.

Although the above embodiment describes the case of communication using the communication satellite 1, 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. good.

Further, in the above embodiment, the reservation status 15 is transmitted every cycle 5, but it may be transmitted at longer intervals. In this way, the overhead caused by transmitting the reservation status 15 is reduced, but each earth station accumulates reservations for each earth station in cycles in which the reservation status 15 is not sent.
For earth stations to which slots have been assigned, the number must be subtracted by that number to maintain information on reservations that remain unassigned.

As described above, according to the reservation method according to the present invention, the control station accumulates and manages reservations once received, thereby reducing the frequency of transmission of reservations, and all earth stations decentrally allocating slots. Since it was configured so that it would be done,
It is now possible to transmit reservations using the slotted Aloha method, which not only increases the number of earth stations that can be accommodated, but also has excellent effects such as reducing delays even more than the conventional centralized reservation method. It is something.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram showing the satellite communication system.
FIG. 2 is an explanatory diagram showing the operation mode of a conventional reservation system, and FIG. 3 is an explanatory diagram showing the operation mode of the reservation system according to an embodiment of the present invention. 1...Communication satellite, 2a, 2b, 2c...Earth station A,
B, C, 3... Time of transmission, 4... Time of reception, 5... Cycle, 6... Data area, 7... Reserved area, 8... Data slot, 9... Reserved slot, 10... Small slot, 11... Round trip propagation delay time. ,1
2,13,14...Small slots assigned to each earth station A2a to C2c, 15...Reservation status, 16,1
7, 18... Reservations for each earth station A2a to C2c. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1 A single communication line is time-divided into slots of a certain length of time, a cycle is made up of a certain number of consecutive slots, the slots within one cycle are divided into reserved slots and data slots, and the communication station uses the reserved slots to control the data slots. In a reservation method in which a reservation requesting allocation is transmitted, a data slot is assigned to a communication station based on the total reservation received, and information divided into packets is transmitted using this data slot. means for one control station to accumulate the reservations of each communication station remaining for each communication station; means for the control station to periodically broadcast the accumulated reservation information to all communication stations; 1. A reservation system comprising: a means for all communication stations to allocate data slots in a distributed manner based on the reservation information obtained and the reservations of each communication station.