JP2590128B2 - Satellite line access method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite communication method, and particularly to a slotted random access communication and a TDMA (time division multiple access) communication using a specific frequency band by time division. Related to satellite line access methods.

[Conventional technology]

One of the major obstacles to the development of satellite communications is the equipment price of earth stations. This price particularly depends on the price of the antenna and the transceiver, and in order to reduce the cost, the line speed is reduced and the frequency band used is narrowed. Since the absolute number of stations accommodated in a narrow-band system decreases, the apparent number of accommodated stations is increased by using a time division technique.

Conventional time-division access type satellite communication methods include slotted Aloha communication, R-Aloha communication, and pre-assigned TDMA.
Communication and demand-assigned TDMA communication are typical methods. Aloha communication with a slot is a method in which a time slot capable of transmitting a data packet signal is set on a satellite line, and an access station transmits its own packet to an arbitrary time slot. The R-Aloha communication has a TDMA frame, and the access station arbitrarily selects an empty time slot set in the frame, transmits its own burst toward it, and when the line connection succeeds without collision, the access station slot. This is a method that can be used exclusively. The pre-assign TDMA communication is a method in which a time slot is allocated to all stations accommodated in the system beforehand. The demand-assigned TDMA communication is a method for dynamically allocating a time slot on a TDMA frame in response to a request from an access station, and has a satellite circuit switching function. References regarding this type of access method include “Digital Satellite Communications-Practical Technologies and Latest Trends” (1981).
Year, JATEC, pages 252 to 262).

[Problems to be solved by the invention]

The slotted Aloha communication and the R-Aloha communication have the advantage that the line entry time is short and the line control device is inexpensive because the procedure for joining the system of the station where the call originated is extremely simple. However, since the bursts of simultaneous access stations collide with each other, there is a problem that the throughput is low and the system is not suitable for a system in which traffic is congested. In pre-assigned TDMA communication, collisions between bursts cannot normally occur, but there is a problem that the idle time of the time slot assigned to a station with a small number of calls becomes long, and the line utilization efficiency is low as a whole. In demand-assigned TDMA communication, collisions between bursts cannot normally occur, and lines can be used without waste. However, there is a problem that the time required for line connection is long, and the line controller becomes complicated and expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a satellite channel access method which realizes a packet (TDMA) communication having a low burst collision probability, a high line utilization efficiency and a short line connection time with a simple algorithm and an inexpensive line controller. is there.

[Means for solving the problem]

The above-mentioned object is to set a frame and a time slot obtained by time-dividing the frame in the same manner as in the TDMA communication, and to establish a communication mode in which stations in the system connect lines with burst (packet) signals on these slots. A specific station, which is the center of the line access control, is installed. The specific station constantly monitors the slot use status to grasp the empty slot position, the used slot position, the slot use station number, etc., and all the empty slots. In order to average the probability of burst collision in the system as small as possible, all stations in the system or stations determined to have access possibility may be unilaterally, for example, 1
Three stations are assigned to each slot, and the circuit plan once assigned in this way is connected for a long time, and accidentally enters an empty slot,
In order to prevent repeated collisions of a plurality of stations from repeating collisions for a long time, a new line is allocated at appropriate time intervals by changing the combination of the empty slot position and the assigned station number, and the empty slot thus allocated is assigned. This is achieved by notifying each station of the position as line allocation information and transmitting the burst to the empty slot allocated to the own station when the station that has received the information has issued a call.

[Action]

First, the specific station that performs line allocation control is the TD on the satellite line.
An empty slot is identified in the MA frame, and the empty slot is averagely allocated to all stations in the system or all the stations determined to have a possibility of access (eg, three stations are allocated to each empty slot). This is notified to each station as line allocation information, and each station transmits a burst toward the empty slot allocated to the own station when a call is generated in accordance with the received information, so that when a call in the system becomes congested, the conventional slot is added. In the Aloha system and the R-Aloha system, many stations transmit bursts toward the remaining empty slots and burst collisions frequently occur. On the other hand, in the present invention, burst collisions are always assigned to the same empty slot. Since only the collisions between the stations (only three stations in the above example) occur, a sufficiently low collision probability is realized as compared with the conventional access method.

Second, the specific station changes the combination of the empty slot position and the assigned station number at appropriate time intervals without maintaining the same line assignment plan for a long time, and notifies each station of new line assignment information. Each station transmits a burst to its own assigned slot in the same manner as described above. Therefore, even if access of stations assigned to the same slot happens to coincide with each other and burst collision occurs at the same time, continuation of the collision is avoided by changing the next line allocation plan. Since the algorithm of the line allocation procedure based on the first and second operations described above is simple, a line connection time equivalent to that of the conventional random access communication can be realized. The first and second operational characteristics of changing the pre-assigned line assignment according to a change in slot use status or a specific time interval are described in, for example, a system in which the total number of accommodated slots is 10 and the number of accommodated stations is 30. Assuming that
In the pre-assignment method, slots are assigned to only 10 stations, and when there are stations with very few calls among the 10 stations, the slots assigned to the stations have a long unused state and the overall line utilization efficiency is reduced. According to the present invention,
30 stations can be accessed, and the unused slot status is 10
The line utilization efficiency can be made sufficiently higher than the pre-assignment method, for example, as long as there is access beyond the station, which is negligibly short.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a configuration diagram of a satellite communication system to which an embodiment of the present invention is applied. A master station (RS) 8 provided with a line allocation controller 10 and a number of slave stations (TS) 9 are connected via a communication satellite 12. Reference numeral 11 denotes a user terminal device provided in each slave station 9.

The present embodiment will now be described on the assumption that the preconditions of the satellite communication system are as follows. (1) Number of accommodation stations: 1 for master station RS
10 stations and slave stations (TS 1 to 10), (2) Number of accommodated lines: 6 slots (# 1 to # 6), (3) Transmission method of line allocation information from master station to slave station: master station transmission Reference burst RB (method using TDM channel in a different frequency band from TDMA channel is also possible), (4) Capacity of each earth station: 1 slot for slave stations TS 2 to 10 and 2 for slave station TS 1 (5) Restriction on the number of simultaneously assigned stations per slot: up to 3 stations (possibility of burst collision).

All slave stations 9 (TS 1 to 10) are synchronized with the TDMA frame in which the reference burst RB generated by the master station 8 is transmitted, acquire the channel assignment information, and generate a call of the own station user terminal equipment 11. Then, the own station burst K can be transmitted normally toward the assigned time slot on the TDMA line.

Next, the basic operation of line assignment will be described with reference to the flowchart of FIG. First, the master station 8 performs the first line assignment after the system starts. At this time, the number of slave stations allocated to each slot is averaged, and the allocation information is notified to all the slave stations 9 by the reference burst RB. At the same time, the same line plan holding timer (Tm) is started.
This is to prevent a problem that, when the same circuit plan is held for a long time, burst collision occurs in a slot that has caused a burst collision unless a slave station transmitting a burst to the slot stops transmitting. This is because the same line plan is allowed to continue for the time until the timer (Tm) times out, and a new line is allocated when the time is over.

Each of the slave stations 9 receives the line assignment information, identifies the slot number assigned to the own station, and waits for a call from the user terminal equipment 11. When a call is generated, a burst is transmitted to an empty slot allocated to the own station.

The master station always receives the slave station burst K and identifies the station address to keep track of the slot usage on the satellite line. When an access is made from a certain slave station, the empty slot is changed, so the line is allocated again and a new line plan is created. Even if access from all slave stations cannot be detected and there is no change in the empty slot, the line is reassigned when the timer (Tm) expires. At the time of line reassignment, a new line plan is created so that the combination of the empty slot number and the assigned station number differs from the previous line plan. The line allocation information based on the new line plan is notified to each station in a reference burst in the same manner as the previous allocation information.

Next, a specific example of satellite channel access in which channel allocation is performed by repeating the basic access operation of FIG. 3 will be described with reference to FIG. The states I to IV in FIG. 2 show the process of changing the slot use status and the channel allocation plan on the satellite channel over time. In state I, slots # 2 and # 3 are added to the slave stations TS 1,2 in addition to the reference burst RB.
Indicates that the line is in use, and the line is allocated as shown in line allocation A to the empty slots # 1, # 4, # 5, and # 6. Since the only station having a line capacity of 2 slots among the slave stations of TS 1 to 10 is TS 1 (according to the above prerequisites),
A circuit plan is created in consideration of the fact that up to two slots can be assigned to TS1. As a result of the access by each slave station according to the line assignment A, the state becomes the state II.
S2 uses # 3 without change. Here, the master station allocates a new line, and allocates empty slots # 4, # 5, and # 6 as shown in line allocation B. Next, in state III, # 1, # 2, # 3
Is unchanged, the slave station TS 9 uses # 6, and the slave station TS # 5
6,7 bursts collide (x). The master station identifies that # 6 is not an empty slot, creates a new line allocation plan C, and notifies each station, but the burst collision of TSs 6 and 7 in # 5 continues. In this state, when the line allocation holding time Te has passed (the timer Tm in FIG. 3 has timed out), a new line is allocated and a new line allocation plan D is notified to each station. As a result, the state becomes the state IV, the burst collision of the TSs 6 and 7 is resolved, and the empty slot is only # 3. To # 3, TSs 3, 4, and 5 are allocated as in line allocation E, and the others are notified of a busy state without allocation. At the time of line assignment, the assignment regulation of up to three stations in one slot is kept. This is in accordance with the above preconditions.

〔The invention's effect〕

According to the present invention, since the access control method in which the line control device of the master station unilaterally allocates the line without responding to the call of each station, the slave station does not need to detect an empty slot on the satellite line, and the demand assignment TDMA It requires much simpler access procedures than the method. Therefore, the control device that supports it is inexpensive, and the line connection time is reduced.

In addition, when allocating lines, the number of stations allocated to empty slots is averaged, and line allocation is periodically changed so that the same line plan is not maintained for a long time. Aloha method and R-
There is an effect that it can be made sufficiently smaller than the Aloha system, and a much higher line utilization efficiency can be realized than the pre-assign system.

[Brief description of the drawings]

FIG. 1 is a block diagram of a satellite communication system according to the present invention.
FIG. 3 is a diagram showing an access state change of the satellite communication access system according to one embodiment of the present invention, and FIG. 3 is a flow chart of a line assignment process. 8: master station, 9: slave station (TS) 10: circuit allocation control device 12: communication satellite, RB: reference burst K: slave station burst, x: burst collision

Claims (1)

(57) [Claims] 1. A slot-based random access packet communication in which a plurality of earth stations share a time slot obtained by dividing one satellite communication channel along a time axis and perform communication under the control of a specific station. TDMA
In the satellite line access method in communication, the specific station monitors the use status of the time slot, and determines the position of a vacant time slot among the time slots, the position of a used time slot, and the time slot. Know the number of the earth station you are using,
For all of the plurality of earth stations or an earth station determined to have a possibility of access based on the use state of the time slot, create line allocation information for allocating an unused time slot among the time slots. Setting an update time interval of the line allocation information based on the use state of the time slot, updating the line allocation information at the update time interval, transmitting the line allocation information to the plurality of earth stations, A satellite channel access method, wherein the plurality of earth stations transmit a signal to an assigned time slot according to the channel allocation information after acquiring the channel allocation information.