JPS632508B2 - - 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 over radio waves. The radio wave travels to the communication satellite 1 in a continuous burst of one packet, and the communication satellite 1 receives this burst, converts the frequency, and amplifies it.
Send it back to the ground. Earth stations A (2a), B (2b), C
(2c) receives bursts, and according to the destination information, bursts addressed to the own station are taken in, and bursts addressed to other stations are discarded. In this way, communication is performed between the earth stations via the communication satellite 1, but when multiple earth stations transmit bursts at arbitrary timings, collisions between bursts occur, and the earth stations are not correctly It becomes impossible to receive data. 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 a cycle, 6 is a data area, 7 is a reserved area,
8 is a data slot, 9 is a reserved slot, 10 is a small slot, 11 is a round trip propagation delay time, 12 and 13 are packets of earth station A (2a),
14, 15 are packets of earth station B (2b), 16,
17 is a packet of earth station C (2c), S1 to S7
is the small slot number.

The satellite line is used on the communication satellite 1 by dividing the time into units called slots that are large enough to accommodate bursts, and each earth station transmits bursts so that they fit into these slots. In the 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 further divided into shorter small slots 10 for use.
In Figure 2, 1 reserved slot 9 is divided into 4 small slots 10.
This shows the case where it is divided into two parts. Each small slot 10 of the reserved area 7 within one cycle 5 is fixedly assigned to every earth station in the system. In Figure 2, earth stations A (2a), B (2b), and C
(2c) have small slot numbers S2, S4,
A small slot of S5 is assigned. Communication is performed by transmitting bursts containing packets using data slot 8 in cycle 5, but in the reservation system, data slot 8 cannot be used unless it is reserved. In FIG. 2, if earth stations A (2a), B (2b), and C (2c) each have two packets to transmit at the start of the i-th cycle, then in the reserved area 7 of the i-th cycle, These earth stations transmit reservations for two slots in each fixed sub-slot 10, S2, S4, S5. 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 are received before the (i+1)-th cycle begins. Data slot 8 in the (i+1)th cycle is allocated and used by each earth station according to the overall reservation received in the i-th cycle. 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 mismatches between earth stations can be avoided. Nothing will happen. By the way, when each earth station performs allocation in a distributed manner in this slot allocation algorithm, the problem is how to make all the earth stations agree on which station to start allocation from. If a predetermined specific station is always used as the slot allocation starting station, this problem will not occur, but the specific allocation starting station will receive allocation more advantageously than other stations, resulting in inequality.
One way to solve this problem is to cyclically move the allocation starting station.

This is done by setting a 1-bit flag in the reservation, and in each cycle 5, the number of stations that can turn on this flag is basically one station, and the stations that turn on the flag are circulated in a predetermined order for each cycle, and the previous station is This is a system in which the station whose flag is ON among the reservations received in the cycle is the station from which slot allocation starts.
In this case, as the traffic of the system increases, slots are periodically allocated between each earth station, which has the advantage of reducing delays. However, this method does not work when there are discrepancies in slot assignments between earth stations due to a certain earth station not being able to receive some reservations, when a certain earth station starts up midway, or when some earth stations start up midway. It was thought that it would be difficult to properly cycle through the stations whose flags were ON in the event of an outage.

This invention uses a method of cycling the allocation starting stations, so that even if reception at some earth stations is poor, stopped, or rises during operation, it is difficult to determine which station to start allocation from and which station to start the allocation in the next cycle. flag
It provides a method to uniquely determine whether to turn on the reservation, and its purpose is to ensure smooth circulation of allocated start stations even when some earth stations in the system fail or when some earth stations start up or fall. The purpose of this method is to achieve equal communication with each earth station with low delay time.

FIG. 3 is a diagram showing an embodiment of this invention,
It shows the relationship between the overall received flags and the slot allocation order. The value of the flag received here is
ON is represented by 1 and OFF is represented by 0, and a blank space indicates that the reservation was not received. It is also assumed that the small slots with small slot numbers S2, S4, and S5 are assigned to earth stations A (2a), B (2b), and C (2c), respectively. In the present invention, if only one station among all received reservations has its flag set to ON, that station will be the starting station for allocation, but if the flag is set to OFF for all stations or if the flag is set for multiple stations, Even if it is turned ON, the allocation starting station can be uniquely determined. In Figure 3, if all the reservation flags are OFF, the station with the smallest small slot number among the stations that sent the reservation is set as the station to start allocation, and conversely, the flags are ON for multiple stations.
In this case, the station with the largest small slot number among those stations is determined as the allocation starting station. In this case, strictly speaking, the allocation starting stations will not move equally if an error occurs in reception of the reservation, but the probability that such an event will occur is small and does not pose a particular problem in practice. As for which station will turn on the reservation flag in the next cycle, it will be decided in a predetermined order from among the stations that have received a reservation in the current cycle, based on the allocation start station determined by the above rules. Therefore, the next station in turn should turn on the flag. In Figure 3, the order in which the flags are turned on is determined by the small slot number assigned to each station, S1→S2→S3→...→S7→
The order is S1..., and earth stations A (2a), B (2
b), in the state where C(2c) is active, A→B→
The allocation starting station moves in the order of C→A...

In FIG. 3, in the first cycle, station A 2a wakes up and starts transmitting a reservation. Here, it is specified that the flag must be turned OFF when sending a reservation for the first time. In the entire reservations received in the first cycle, only station A 2a has transmitted reservations, so slot assignment is performed only to station A 2a regardless of the value of the flag. In this case, the next slot allocation starting station is A station 2a, and in the second cycle, A station 2a
turns on the flag and sends the reservation. In the third cycle, station B 2b rises, turns off the flag, and transmits the reservation. Therefore, the A station 2a becomes the allocation starting station, and slot allocation is performed in the order of A→B. In the fourth cycle, in order to move the slot allocation starting station, B station 2b turns on the flag and transmits a reservation, and the slot allocation order changes from B to A.
becomes. In the 5th cycle, the C station 2c rises, and the 7th
Reservations for each station are normally received until the cycle, and the allocation initiating station successfully moves in the order of A→B→C every cycle. In the eighth cycle, station A 2a turned on the flag and transmitted a reservation, but this was not received by each station.

In this case, there is no station with the flag turned ON in the received reservation, but the order of slot assignment is B due to the rule that the station with the smallest small slot number among the stations from which the reservation was received is the station that starts the assignment. → Determined as C. Also, the flag will be turned on in the next cycle.
The station that changes is C station 2c, and in the 9th cycle it becomes C station 2c.
Station 2c turns on the flag and transmits the reservation. No.
In the 10th and 11th cycles, reservations from each station are normally received, and the slot allocation starting station moves in the order of A→B. In the 12th cycle, C station 2c sends a flag.
A reservation was sent as ON, but this reservation was sent to station A2.
It is assumed that the signal was received by stations a and C 2c, but not received by station B 2b. In this case, A station 2a, C
Station 2c assigns slots in the order of C→A→B with station C 2c as the slot assignment starting station, but
Station 2b allocates slots in the order of A→B with station A 2a as the slot allocation starting station. For this reason,
In 12 cycles, the slot assignments do not match among the stations, and some of the transmitted bursts will collide.

Furthermore, in the next 13th cycle, A station 2a, B station 2
In both cases, the own station turns on the flag as the allocation starting station. In this case, according to the rules according to the present invention, station B 2b becomes the slot allocation starting station, and the same slot allocation from B to C to A is performed at each earth station, eliminating burst collision. In the next 14th cycle, C
Station 2c becomes the allocation starting station, turns on the flag, and transmits the reservation. The above is an example of the operation of the reservation system according to the present invention. Even if the earth station rises or falls, slot assignment is uniquely determined, and even if some earth stations fail to receive reservations, the slot allocation is fixed. It can be seen that although a burst collision occurs in one cycle, there is no effect on subsequent cycles, and the slot allocation starting station is smoothly moved.

In addition, although the case of communication using the communication satellite 1 has been described above, the present invention is not limited to this.
It may be used for wireless packet communication or when connecting terminals to multiple points to perform packet communication.

As described above, in the reservation method according to the present invention, even if poor reception, stoppage, or start-up occurs at some earth stations during operation, the allocation starting station is smoothly moved cyclically, and each earth station is On the other hand, it has the advantage of achieving equal communication with less delay time.

[Brief explanation of the drawing]

FIG. 1 is a block diagram 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 the relationship between reception flags and slot allocation order according to an embodiment of the present invention. In the figure, 1 is a communication satellite; 2a, 2b, and 2c are earth stations A, B, and C, respectively; 3 is a transmission time point; 4 is a reception time point; 5 is a cycle; 6 is a data area; 7 is a reserved area; and 8 is a data slot. , 9 is the reservation slot,
10 is the small slot, 11 is the round trip propagation delay time, S1 to S7 are the small slot numbers, PA1,
PA2 is a packet from earth station A, PB1 and PB2 are packets from earth station B, and PC1 and PC2 are packets from earth station C. Note that the same reference numerals in the figures 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. A reservation system 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 units called packets is transmitted in this data slot, and a flag is attached to the reservation. means and 1 among the total reservations received in a given cycle.
If only one station has the flag set to ON, that communication station is used as the starting station for slot allocation, and if the flag is set to ON for multiple communication stations or there is no communication station with the flag set to ON, the information from the previous cycle is used. A reservation method characterized in that an allocation start station is uniquely determined from the allocation start station, and communication stations whose flags are to be turned ON in the next cycle are determined in a predetermined order starting from the communication station that became the allocation start station.