JPS58218249A - Reservation system - Google Patents

Abstract

PURPOSE:To reduce the frequency of reserved transmission, and to decentralize slot allocation to all ground stations and increase the number of accomodated ground stations, by allowing a reserved station which performs reception once to perform accumulation and control. CONSTITUTION:A single communication circuit is divided into small slots 10 with specific constant time length and a cycle 5 is composed of successive slots 10; each slot 10 in one cycle 5 has a reservation area 7 and a data area 6. A communication station uses the area 7 to send reservation information on a request ti assign the area 6, the area 6 is assigned to the communication station from the received reservation information on the whole, and information is transmitted, packet by packet, by the area 6. The remaining pieces of reservation information on each communication which can not be sent by the area 6 in one cycle 5 are accumulated by the accumulating means of one control station by communication stations and the accumulated reservation information is transmitted to all the communication station periodically. Then, all the communication stations assign slots 10 descretely on the basis of the received reservation information and pieces of reservation information from the respective communication stations, increasing the number of acommodated communication stations.

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 Figure 1, 1 is a communication satellite, 2a
, 2b, 2c are each earth station (5).

(B) and (G7) are shown. Each earth station (A)
2 a, (B) 2 b.

(O12c uses the same satellite line, divides data into units called packets of a certain length or less, attaches destination information to these, and transmits them on radio waves as a continuous burst of one packet.) The communication satellite l receives this burst, converts the frequency, amplifies it, and sends it back to the ground.Each earth station (A) 2 a 't (B) 2
b, (Q2c receives the burst, and according to the destination information, it takes in the burst addressed to its own station and rejects the burst addressed to other stations.In this way, the communication satellite 1 is transmitted between each earth station.
However, if multiple earth stations transmit bursts at arbitrary timings, collisions between bursts will occur and each earth 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 transmission time of the earth station, 4 is the reception time of the earth station, 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 round) IJ tube propagation delay time, 12, 13, and 14 are each earth station (A) 2 a
, (13) 2 b , (0) 2 c are 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 each earth station (A) 2a to (C) 2c transmits bursts. Send to fit 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, data area 6
The slot in the reserved area 7 is called the data slot 8, and the slot in the reserved area 7 is called the reserved slot 9. The reserved slot 9 is divided into shorter small slots 10 for use. FIG. 2 ζ shows a case where one reserved slot 9 is divided into two small slots 10 and used. In this conventional reservation method, 1
Each small slot 10 in the reserved area 7 in cycle 5 is fixedly assigned to all earth stations in the system, and each earth station (A) 2 a , (B) 2 in FIG.
b, (Q2c has small slots 12,
13 and 14 are assigned. 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. At the start of the i-th cycle 5 shown in FIG.
(C) If 2c each has 4 packets to be transmitted, the reserved area 7 of the i-th cycle 5
, these earth stations each transmit a four-slot reservation in fixedly assigned small slots 12, 13, and 14, respectively. The reservation is received via the communication satellite 1, arriving at each earth station with a delay of round trip propagation delay time 11. 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 and used by each earth station according to the reservation received in the i-th cycle 5. This slot allocation is done independently by each earth station, but if all earth stations receive the same reservation and allocate according to the same algorithm, burst collisions and wasted slots due to allocation mismatch between each earth station will be avoided. Nothing will happen. This slot allocation algorithm must be able to allocate equally to each earth station, but the details thereof are not directly related to the present invention and will not be explained here.

In m(i+1) cycle 5, each earth station (~2a, (
B) 2b are each assigned 3 data slots 8, each bucket) at, a2 . a3 and bl, b2. b
3 is being sent. Earth station (0) 2c has been assigned two data slots 8 and is transmitting packets cl and c2. Here, all earth stations cannot transmit all packets in the (i+1)th cycle 5. This is known at the time of slot allocation processing performed at the start of the (i÷1)th cycle 5. Therefore, each earth station (5
)23 to (q2c each reserve slots for the packets that cannot be sent in the (i+x)th cycle 5. With this reservation, the remaining packets b4.c3.a4.c4 are transmitted in the (i+2)th cycle 5. .

As mentioned above, in the conventional reservation method, the small slot 10 of the reserved area 7 is fixedly allocated to each earth station.
It is not possible to increase the number of earth stations, and when the number of earth stations is increased, the data area 6 decreases, and the satellite line is not used efficiently. As a way to overcome this drawback, the unused data slot 8 is used as a reservation slot 9, and instead of fixedly allocating the small slot IO to each earth station, the reservation is made in the Aloha method with slots in units of 10 (small slots). A transmission method is being considered. 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 method, each ball station randomly plays a small slot)
In order to select 10 and submit the reservation, the same - small slot 1-1
If two or more earth stations transmit reservations at the same time, a collision will occur and the reservations will not be received. However, if the transmission frequency of reservations is low, there is a high probability that reservations will not be received without conflict, 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 Fig. If there is not, 1. You must reserve the missing amount in the next cycle 5.1. , there wasn't. In this way, for each earth station φ,,,,″
Although the transmission frequency of F-time increases, in the conventional distributed reservation system, this did not pose a particular problem because a small slot 1o was fixedly allocated to each earth station. On the other hand, if the reservation 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 transmission frequency of reservations increases, many reservation collisions will occur and reservations will not be received properly, resulting in data The disadvantage is that packets cannot be sent. A centralized reservation method is a method that does not have such drawbacks.

This is a method in which a control station receives pre-embryos, centrally allocates slots, and notifies all global stations of the results.

In this method, when the control station receives a reservation, it accumulates it for each earth station, and subtracts the amount when slot allocation is performed. Once a reservation is accepted by the control station, it is stored in memory when slots are allocated from now on, so even if five slots are not allocated in the next cycle after sending the reservation, there is no need to send the reservation again. The frequency of sending reservations, □1, will decrease. However, this method requires one round-trip propagation delay time 11 at each stage of reservation, transmission of I, transmission of slot allocation information, and transmission of one data packet, which has the disadvantage of increasing the overall delay. Ta.

For this reason, in the conventional reservation method, using a distributed type reduces the delay, but it also reduces the number of earth stations that can be accommodated.
On the other hand, the centralized type allows for a larger number of earth stations to be accommodated, but it has various drawbacks such as increased delay.

- The present invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it divides a single communication line into slots of a fixed time length, and configures a cycle with a fixed number of consecutive slots. The slots in one cycle are divided into reservation slots and data slots, and the communication station sends a reservation to allocate data slots in the reservation slot, and data slots are allocated to the communication station from the received overall reservation, and this data In the reservation/reservation method in which information is transmitted in packets separated by slots, the remaining reservations for each communication station that cannot be sent in the data slots in one cycle are
means for one control station to accumulate information for each communication station; means for the control station to periodically broadcast the accumulated reservation information to all communication stations; and from the received reservation information and each communication station's reservation,
Provided is a reservation system that has a configuration in which all communication stations are provided with means for allocating data slots in a distributed manner, which reduces delays in reservations and can accommodate a larger number of communication stations. It is intended to.

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 the same parts as 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 each earth station (A) 2a.

(B) 2 b , (showing the reservation of Q 2 c.

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 (A) 28 to (0) 2 c. In this reservation method, all slots that remain unallocated in one cycle 5 are used as reserved slots 9. Also,
These reserved slots 9 are all divided into small slots 10 and used, and the small slots 10 are not fixedly assigned to each earth station, and the reservation is 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, the 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 reservations that remain unallocated for all earth stations, and periodically broadcasts this information as reservation status 15 to all earth stations. In Figure 3 - 1 cycle 5
The reservation status 15 is transmitted once every 15 days in the last slot of cycle 5. This control station is one in the system.
Each earth station (A) 2 a to (0) is required.
It can be any earth station in the system, including 2c.

In addition, in Fig. 3, at the start of the i-th cycle) and 5, 1, '
・Each earth station (A) 2 a~(3 for only 3 stations of Ci12C)
Suppose that a packet that should be sent packet by packet is released.
The three stations randomly select the small slot 10 in the reserved area 7 and reserve 16. for 3 packets. Send '17.18.

i-th cycle 5 reservation 16.17.18 and reservation status 1
5 are all received before the start of the (i+2)th cycle 5. Immediately before the start of the (i+2)th cycle 5, all earth stations independently perform slot allocation for the (i'+2)th cycle 5 from the reservation 16.17.18 of the i-th cycle 5 and the reservation status 15. Each earth station has the same reservation 16-18
If each earth station receives the information and reservation status 15 and makes the allocation using the same algorithm, no collision will occur in packet transmission even if each earth station performs the allocation 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. In the slot allocation of the (i+2)th cycle 5,
Each earth station adds up the received reservations 16 to 18 and the reservation status 15 for each earth station, and based on the result, performs slot allocation based on the result.

In this case, reservation → 1111111. -15 has a value of 0 for all earth stations, so the summed result is the i-th cycle 5.
in'~.

According to the transmitted reservations 16-18, each earth station (A) 2a
□ ~ (Q 2 c is 3 each, and the other earth stations are O. Therefore, slot allocation is performed for each earth station (5) 2 a ~ (0) 2 c. Fig. 3 Then, by slot assignment, each earth station (5)
It is assumed that two slots are assigned to each of the three stations 2a to (02C).As a result, the (i+2)th cycle 5
Earth station (A) 2 a is packet al, a2, earth station (I3) 2b is packet bl, b2, earth station (0) 2
c transmits packets cl and 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. Each earth station (A) 2 a -4Q 2 c is I
Although it was not possible to send all the packets in the K(i+2)th cycle 5, the remaining packets are not reserved 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 performs slot allocation for the shortage in the (i+4)th cycle 5 in a distributed manner. l(i+
3) Since no reservation is received in cycle 5, and 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 (
A) One slot is assigned to each of 2a to 2c, and packets a3, 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 sent in a slot-handed Aloha manner,
Since there is no need to fixedly allocate small slots 10 to each earth station, a large number of undecided earth stations can be accommodated. 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 method.

Although the above embodiment describes communication using the communication satellite 1, the present invention is not limited to this, and may be used for wireless packet communication or 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. This reduces the overhead of sending reservation status 15, but each earth station accumulates reservations for each earth station in cycles in which reservation status 15 is not sent, and for each earth station to which the slot is assigned. must be subtracted by that number to maintain information on reservations that remain unallocated.

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 the configuration is such that the reservation ζ can be transmitted using the slotted Aloha method, not only can the number of earth stations that can be accommodated be increased, but also 11 ] It has excellent effects such as further reducing delays:'.

It is something that　　　　　1.1 □

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a 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. It is. 1... Communication satellite, 2a, 2b, 2c...
...Earth station (5), (Bl, (0), 3...
...... Time of transmission, 4... Time of reception, 5... Cycle, 6...
...Data area, 7...4...Reserved area, 8...
...Data slot, 9...4...Reservation slot, 10...Small slot, ll...
...Round trip propagation delay time, 12, 13
．． 14......Each earth station (A) 2 a~(
Small slot assigned to Q2c, 15...
・・・・Reservation status, 16, 17, 18...Tap・Each earth station (A) 2 a ~ ((3) 2 c (71) Reservation. In addition, the same reference numerals in the diagram indicate the same or corresponding parts. Indicates. Agent Makoto Kazuno - ) - 1, l.

Claims (1)

[Claims] A single communication line is time-divided into slots of a certain time length, a cycle is made up of a certain number of consecutive slots, and the slots within one cycle are divided into reserved slots and data slots, and the communication station uses the reserved slots as data slots. In the reservation method, a data slot is assigned to a communication station from the entire received reservation, and information divided into packets is transmitted in this data slot. Means for one control station to accumulate reservations for each communication station remaining after being sent out in a slot, and for the control station to periodically broadcast this accumulated reservation information to all communication stations. and means for all communication stations to allocate data slots in a distributed manner based on the received reservation information and the reservations of each communication station.