JPH04262631A - Satellite communication system - Google Patents

Abstract

PURPOSE:To attain information transmission while keeping a traffic in matching with a transmission capacity of a satellite line even when a traffic of a slave station is tentatively increased by generating a control signal to avoid collision of slave station burst signals in an incoming line. CONSTITUTION:A burst signal sent from each slave station for each time slot of an incoming line is sent to a burst detector 6 of a master station via a receiver 3 and a demodulator 4. A congestion control section 8 receiving each output signal of the burst detector 6 and a level detector 7 discriminates it that collision takes place in the time slot on the incoming line when no burst is detected from the output signal of the burst detector 6 and the presence of an incoming call is detected from the output signal of the level detector 7. Then the congestion control section 8 grasps a traffic in the incoming line based on the collision production to generate a control signal and it is fed to each slave station to avoid the collision in the prescribed time slots from each slave station to the master station.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention consists of one main station and a plurality of slave stations, and the uplink from the slave station to the master station is divided into fewer time slots than the number of slave stations, so that each slave station can access random access. This relates to satellite communication systems.

As shown in FIG. 5(a), in a satellite communication system consisting of one main station 1 and a plurality of slave stations 2,
b) As shown in Figure 2, there is a pre-assignment method in which the time slot TS for transmitting data through the uplink from the slave station 2 to the main station 1 via the communication satellite SAT is predetermined, or there is a transmission request from the slave station 2. TDMA communication methods such as the demand assignment method, in which transmission is sometimes permitted from the master station 1 side, are well known. ) As a communication method when there is a shortage of time slots, a random access method (a method in which each slave station randomly accesses the time slot) is more efficient in using time slots and easier to control than the demand assignment method described above. However, in this method, when the traffic of the slave station increases, multiple stations perform burst access to one time slot, resulting in collisions on the satellite and the situation where slave station information does not reach the main station. Therefore, it is necessary to avoid such situations as much as possible.

0003

[Prior Art] In conventional satellite communication systems, in order to confirm whether slave station information has reached the main station, the main station waits for a response signal to be sent back from the main station, and waits for a certain period of time to arrive. There has been a method in which retransmission is performed if there is no response even after the transmission has been received, but in this case, as shown in Figure 6, the problem is that the propagation delay time (approximately 250 ms x 2) is long and time is wasted for confirmation. be.

[0004] Accordingly, as a further method, each slave station receives a satellite return signal of its own station transmission signal (this is a signal in a different frequency band from the own station transmission signal, and the same as the transmission signal to the satellite). It has a function to receive signals in the same frequency band but with different frequencies, and if the signal transmitted from the own station can be received after the propagation delay time (approximately 250 ms) has elapsed through the satellite, it is determined that the signal has reached the main station. If the message cannot be received, it is assumed that a collision has occurred, and the message is retransmitted after waiting a certain period of time.

[0005]

[Problem to be Solved by the Invention] However, in order to receive the own station's transmitted signal, a larger diameter antenna is required compared to the case where only the main station signal is received and the own station's signal is transmitted. Since a burst signal demodulator is required to demodulate the satellite return signal, there is a problem in that the scale of the slave station increases and the cost increases.

Furthermore, in such a conventional example, even if the slave stations are provided with the retransmission function as described above, if the traffic of each slave station temporarily increases, the probability of collision increases, and in severe cases, In this case, the signals sent by each slave station become only retransmission signals, making it impossible to transmit information. Therefore, the number of slave stations accommodated in the system should be limited in advance to the same number of time slots of the satellite line, or the overall traffic volume should be reduced (approximately 10 to 2
0%) There was a problem in that it had to be limited.

Therefore, the present invention consists of one main station and a plurality of slave stations, and each slave station divides the uplink from each slave station to the master station into fewer time slots than the number of slave stations. To enable information transmission by maintaining traffic commensurate with the transmission capacity of a satellite line even when traffic at a slave station temporarily increases, without using a demodulator for burst signals, in a random access satellite communication system. With the goal.

[0008]

[Means for Solving the Problems] In order to solve the above problems, in the satellite communication system according to the present invention, the main station 1 (see FIG. 5), as shown in principle in FIG. A burst detector 6 inputs the burst signal sent from the receiver 3 and the demodulator 4 and detects the burst signal under the control of the reception controller 5.
and a level detector 7 which inputs the reception level of the burst signal via the receiver 3 and detects it under the control of the reception control unit 5, and outputs signals from both the burst detector 6 and the level detector 7. Based on this, by detecting collisions of slave station burst-like signals on the uplink from each slave station 2 to the main station 1, the uplink traffic is grasped, and a control signal for avoiding the collision is generated to control transmission. 9, a congestion control section 8 which transmits data to each slave station 2 via a modulator 10 and a transmitter 11.

Further, in the present invention, the congestion control section 8 controls each slave station 2 for a predetermined time slot according to the control signal.
It is possible to prohibit the burst transmission of , and to sequentially collect information on the number of transmission bursts retained in each slave station 2 by polling, and to allocate the time slots to which the access is prohibited in the order of the slave stations with the highest number of retention.

Alternatively, in the present invention, the congestion control section 8
The control signal prohibits burst transmission of each slave station 2, and at this time, each slave station 2 can access the time slot to which access is prohibited in a predetermined priority order.

[0011]

[Operation] In FIG. 1, a burst signal sent from each slave station 2 for each uplink time slot is sent to the burst detector 6 at the main station 1 via the receiver 3 and demodulator 4. Here, it is determined based on the timing signal from the reception control unit 5 whether or not a burst signal has been detected.

[0012] Furthermore, the level detector 7 detects the level of the output signal of the receiver 3 in a time slot designated by the timing signal of the reception control unit 5, and determines whether or not there is an incoming signal in the time slot. do.

The congestion control unit 8 that receives the output signals of the burst detector 6 and the level detector 7 determines that the output signal of the burst detector 6 is not detecting a burst, and the output signal of the level detector 7 is When it is determined that there is an incoming call,
It is determined that a collision has occurred in the relevant time slot on the uplink.

Then, the congestion control unit 8 grasps the traffic on the uplink based on the occurrence of this collision, generates a control signal, and sends it to each slave station 2, thereby controlling the traffic from each slave station 2 to the main station 1. Collisions of predetermined time slots can be avoided.

[0015] There are various measures to avoid this collision of predetermined time slots, but for example, it is possible to prohibit burst transmission of each slave station 2 for a predetermined time slot using the control signal sent from the congestion control unit 8. can. At this time, the congestion control unit 8 polls each slave station 2 and sequentially collects information on the number of transmission bursts retained, allocates time slots in the order of the number of retained stations and releases the prohibition of access, thereby allowing the satellite Ensure throughput commensurate with line transmission capacity.

Alternatively, in the present invention, each slave station 2 accesses the time slot according to a predetermined priority order when the congestion control unit 8 prohibits burst transmission of each slave station 2 using the control signal. You can also.

[0017]

[Embodiment] FIG. 2 shows a configuration diagram of an embodiment of the main station used in the satellite communication system according to the present invention shown in FIG. It is composed of a buffer 81 that receives each output signal of the detector 7, and a congestion processing CPU 82 that receives the output signal of this buffer 81 and the retention number information from the reception control section 5. A buffer 91 that stores transmission data from the CPU 82, a buffer 92 that stores the control signal from the CPU 82, and these buffers 91, 9
A timing frame generation section 93 generates the output timing of No. 2 and a frame synchronization code, and the data from the buffers 91 and 92 and the frame synchronization code from the timing frame generation section 93 are multiplexed as shown in FIG. Frame synchronization code F, control signal C and data DA such as
The multiplexing section 94 outputs a frame composed of a TA and a multiplexing section 94.

The operation of the main station 1 shown in FIG. 2 will be explained below with reference to the processing algorithm of the congestion control section 8 shown in FIG.

First, as explained in FIG. 1, the burst detector 6 and the level detector 7 are supplied with a timing signal indicating the uplink time slot position from the reception control section 5. and level detector 7 determine burst detection/non-detection and the presence or absence of an incoming signal within this timing signal section, respectively, and control congestion control section 8.
Output to. In this case, the congestion control unit 8
The presence or absence of burst detection/non-detection signals and incoming calls is monitored over a frame (sections F to F of the downlink in FIG. 5(b) and FIG. 6). Incidentally, burst detection can be performed by detecting the unique word of each slave station 2.

There are combinations of signals obtained from the burst detector 6 and level detector 7 as shown in the table below.

[Table 1]

Therefore, among these combinations, the congestion control unit 8 monitors the above modes and determines the results during normal operation when no congestion occurs (step S1 in FIG. 3). (S2, S3), and determines whether this result has continued for a certain period of time (S4), but in step S5 it is determined whether or not to transition the state, and in step In S6, a control signal for transmitting to each slave station 2 via the downlink is outputted to the transmission control unit 9 as necessary, but if mode ■ or ■ continues, these steps S1 to S6 are repeated.

On the other hand, when it is determined in step S4 that the above-mentioned congestion reception mode is set, a decision is made in step S5 to transition the state control from normal operation to congestion control, and a control signal is output to the transmission control section 9 in step S6. do. Note that this congestion state occurs as the traffic of each slave station 2 increases, but when determining in step S3, for example, if the number of modes in one monitoring cycle exceeds a preset threshold (approximately 20%). In this case, it can be determined that there is congestion.

The above control signal is temporarily stored in a buffer 92 in the transmission control section 9, and is then transferred from the data interface section 12 together with the data stored in the buffer 91 by the multiplexing section 94 at the timing of the timing/frame generation section 93. The modulator 10 has a frame configuration as shown in FIG.
It is then transmitted to each slave station 2 via the transmitter 11, and enters congestion control (step S7) in FIG. In this congestion control, the following process shown in step S8 is performed between the main station 1 and the slave station 2. (1) Instruct all slave stations to prohibit burst transmission (access) to the specified time slot using a control signal. This instruction is given through a control channel C (see FIG. 6) that occupies a part of the data section of the downlink, and the number of time slots for which access is prohibited is any predetermined number from 1 to all numbers. An example of each slave station 2 in this case is shown in FIG. 4, in which the control signal in the received signal from the antenna 21 is separated by the separation section 22 and data processing thereof is performed. (2) According to a predetermined priority order, one or more of the access-prohibited time slots is used to collect the status of the number of transmissions retained by each slave station 2 using a polling method. In this case, in each slave station 2, when transmitting data from the multiplexing unit 24 via the buffer unit 23, in accordance with the well-known configuration shown in FIG. The multiplexer 24 multiplexes the data and sends it to the main station 1. (3) Based on the retention number information obtained from each slave station 2 in this manner, time slots are assigned in order from the slave station with the largest retention number, and the retention is resolved through steps S5 and S6.

The congestion control unit 8 continues to monitor even after the exclusive assignment is performed (steps S9 to S12), and when the number of mode (2) exceeds a preset threshold in the level detection and burst detection of the exclusive assigned slot, Steps S5 and S
The exclusive use shall be canceled by 6.

In addition to the above embodiments, the following modifications can also be made. (a) After issuing an access prohibition command for a predetermined time slot to each slave station 2, the priority order at the time of congestion is determined in advance between each slave station 2 without downloading the retention number information from each slave station 2 each time. By determining this in advance, it is also possible to shorten the processing time regarding exclusive allocation. (b) Main station 1 monitors the traffic of each slave station by polling only at the beginning of congestion, but it is unable to monitor the traffic after that, so a function to monitor the traffic amount is provided to each slave station to reduce the traffic. It is also possible to reduce the load on the main station 1 by requesting the main station 1 to release the exclusive use and canceling the exclusive allocation. (c) Regarding the number of access-prohibited time slots, if all time slots are prohibited and allocated exclusively, the stuck situation can be resolved in a short time, but the number of time slots is finite and is smaller than the total number of slave stations. Since there are slave stations with low traffic, some time slots may be left for random access.

[0026]

As explained above, according to the satellite communication system of the present invention, the main station performs burst detection and incoming call level detection to detect slave station burst patterns in the uplink from each slave station to the main station. The system is configured to detect uplink traffic by detecting signal collisions, generate control signals to avoid collisions, and send them to each slave station, resulting in a temporary increase in traffic at slave stations. Even in such a case, it is possible to avoid a decrease in throughput due to collision of slave station transmission bursts, and it is possible to construct a satellite communication system that accommodates a large number of small earth stations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of a main station used in a satellite communication system according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a main station used in the satellite communication system according to the present invention.

FIG. 3 is a flowchart showing the processing of a congestion control unit in the main station used in the present invention.

FIG. 4 is a block diagram showing an example of a slave station.

FIG. 5 is a diagram for explaining a general satellite communication system.

FIG. 6 is a communication time chart between a master station and a slave station.

[Explanation of symbols]

1 Main station 2.Slave station 3 Receiver 4 Demodulator 5 Reception control section 6 Burst detector 7 Level detector 8 Congestion control unit 9 Transmission control section 10 Modulator 11 Transmitter In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] [Claim 1] One main station (1) and multiple slave stations (2
), in which the uplink from each slave station (2) to the main station (1) is divided into time slots smaller than the number of slave stations, and each slave station makes random access. (1) is a burst detector which inputs burst signals sent from each slave station (2) via a receiver (3) and a demodulator (4) and detects them under the control of a reception control unit (5). (6), a level detector (7) that inputs the reception level of the burst signal via the receiver (3) and detects it under the control of the reception control section (5), and the burst detector (6). ) and the level detector (7), the uplink traffic can be determined by detecting collisions of slave station burst-like signals on the uplink from each slave station (2) to the main station (1). A transmission control unit (9) generates a control signal for avoiding the collision, and a modulator (
10) and a congestion control unit (8) that transmits data to each slave station (2) via a transmitter (11). 2. The congestion control unit (8) prohibits burst transmission of each slave station (2) for a predetermined time slot using the control signal, and
2. The satellite communication system according to claim 1, wherein information on the number of transmission bursts retained in the transmission burst is sequentially collected by polling, and the time slots in which the access is prohibited are assigned to the slave stations in order of the number of retained stations. [Claim 3] The congestion control unit (8) prohibits each slave station (2) from burst transmission using the control signal, and at this time, each slave station (2) prohibits the access in a predetermined priority order. 3. The satellite communication system according to claim 2, wherein time slots are accessed.