JPH08331032A - Slot assignment method in satellite communication system - Google Patents

Abstract

PURPOSE: To obtain the slot assignment method in a satellite communication system in which number of slots assigned to a peripheral station making transmission by the PA system is increased tentatively and the transmission system is changed in the unit of data. CONSTITUTION: A transmitter-receiver 1 of a center station applies time division to a slot via an artificial satellite from plural peripheral stations and shares channels in common and receives a signal sent by a permanent allocation(PA) system. A control signal generating section 6 uses a reservation table based on a PA table stored in a slot assignment storage device 5 to assign required number of slots with respect to a reservation request included in a reception signal from a reception section 2 and applies slot information to a multiplexer section 8. The multiplexer section 8 applies time division multiplexing to slot information and transmission data. The center station of this configuration manages all PA slot information and delivers the result of management for each frame to the peripheral station through broadcasting and adds slot assignment processing to the PA system on reservation request.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a slot allocation system in a satellite communication system, and more particularly, in a satellite communication system in which a central station and a plurality of peripheral stations are connected via a satellite, We communicate by broadcasting,
The present invention relates to a slot allocation method for allocating a slot to each peripheral station when a channel is shared by time-sharing a line for transmission from a peripheral station to a central station.

[0002]

2. Description of the Related Art In a satellite communication system in which a central station connected to a host computer and a plurality of peripheral stations each connected to a terminal are line-connected via a satellite, communication from the peripheral stations to the central station is common. To do on the channel
A time division multiple access method is used in which a channel is time-shared and shared in a short time called a slot.

In this time division multiple access system, a collection of a certain number (here, N) of slots called frames is used as a cycle of an outbound line from a central station to peripheral stations, and at the same time, the peripheral It is also used by the station for slot synchronization. Frames and slots are numbered, and frame numbers are cyclically numbered from 0 to M and slot numbers from 0 to N.

A method of allocating slots to be transmitted from a peripheral station to a central station is roughly classified into a fixed allocation method (PA method) in which slots are fixedly allocated to peripheral stations, and a reservation allocation method in which a slot is reserved according to a request from a peripheral station ( DA
System) and a random access system (RA system) that permits peripheral stations to transmit in arbitrary slots.

In the PA system, each time a peripheral station makes a transmission request to the central station, it transmits data to the central station via the satellite by an inbound line using a unique slot assigned to the local station. The PA method is an allocation method which has the highest transmission efficiency when there is always a transmission request to each peripheral station and is suitable when the number of peripheral stations is small due to high traffic. However, if the traffic of all peripheral stations is not high, this PA method is a wasteful method.

Further, in the DA method, each peripheral station transmits a reservation request for the number of slots to be used to the central station each time a transmission request is generated, and in response to this, the central station makes a reservation request. Reserved slot allocation information indicating allocation of reserved slots that can be used only by all the peripheral stations is transmitted.
This DA method can increase slot efficiency even when the traffic of all peripheral stations is not high,
This is an allocation method suitable for low traffic and a large number of peripheral stations.

In this DA system, the reservation request is usually transmitted to the central station by using the RA system described below. But,
Since it is indispensable to send a reservation request to the central station to make a reservation, and the central station accepts the request to notify the peripheral station of the allocation slot, the peripheral station receives the reservation slot allocation information. Data cannot be sent unless
The transmission delay time becomes longer than other methods.

In the RA system, when a request for transmission to the central station is issued by each peripheral station at an arbitrary time, the data to be transmitted is transmitted to the central station via a satellite by an inbound line using an arbitrary slot. , There is a possibility that transmissions from multiple peripheral stations may collide in the same slot. This RA system is less likely to cause collisions when the traffic of peripheral stations is low, and does not have the time to wait for an allocation slot or the time required to make a reservation like the DA system, so that it is better than other systems. The transmission delay time is the shortest.

However, in this RA system, when a collision occurs, the central station transmits a negative acknowledgment (NAK) signal to all the peripheral stations, which indicates that the packet in the slot cannot be normally received, and the received transmission is received. Since the peripheral station retransmits the same data again after a certain period of time, when the traffic of the peripheral station becomes high, collisions occur more frequently, resulting in more retransmissions of the collided packets, which deteriorates both transmission efficiency and transmission delay.

As described above, all of the above three methods have advantages and disadvantages, and it cannot be said that which method is superior. Therefore, a combination of these methods is used to make up for the shortcomings. Among them, the applicant has particularly disclosed a slot allocation method using the DA method and the PA method in combination (Japanese Patent Laid-Open No. 3-7).
No. 7434: Title of invention "satellite communication system").

According to the conventional slot allocation system by the applicant, the PA system is suitable for the peripheral stations which constantly generate a transmission request at a certain cycle.
The transmission is performed by adopting the method, and the DA method is used for transmission in the peripheral stations in which the frequency of generation of the transmission request is not constant.

[0012]

However, in the above-mentioned conventional slot allocation system, when a transmission request is generated in a period longer than the slot allocated to the peripheral station transmitting in the PA system, the other station will transmit the request. Even if the load is small and the line has a margin, there is a problem that the transmission delay of the peripheral station becomes large. This is because the peripheral stations that perform transmission by the PA method do not transmit the reservation request to the central station even if there is a sufficient slot as a whole.

The present invention has been made in view of the above points,
When a large number of transmission requests are temporarily generated in the peripheral stations transmitting by the PA method, it is possible to transmit a reservation request to the central station and temporarily increase the slots allocated to the peripheral stations. It is an object of the present invention to provide a slot allocation system in an obtained satellite communication system.

Another object of the present invention is to determine whether the slot to which the peripheral station is allocated is allocated for transmission of the PA system or the DA system, and the transmission system is changed in data units. It is to provide a slot allocation method in a satellite communication system capable of performing the same.

[0015]

In order to achieve the above object, the present invention performs broadcast communication from a central station to a plurality of peripheral stations via artificial satellites, and from a plurality of peripheral stations via artificial satellites. In the slot allocation method of a satellite communication system in which a channel is time-divided to a central station and channels are shared to communicate by a fixed allocation method, in the slot allocation method of a satellite communication system, the central station is the information about the slots fixedly allocated to each of a plurality of peripheral stations. A slot allocation storage device that stores the slot assignment information, a fixed allocation slot information read from the slot allocation storage device, and a control signal including slot allocation information allocated based on the received signal reservation request from the peripheral station. A control signal generation unit for generating, a multiplexing means for time-division multiplexing the control signal and the transmission data to generate an outbound signal,
A plurality of peripheral stations, each of which transmits a outbound signal to a plurality of peripheral stations; each of the plurality of peripheral stations receives the outbound signal; and a frame synchronization unit that generates a slot timing signal based on the received signal. From the control signal extracted from the generated signal, identify whether the slot allocated for transmission of the own station is the fixed allocation method or the reserved allocation method, and generate and output the transmission slot designation signal in synchronization with the slot timing signal Transmission A slot management unit, a first holding unit for holding first data buffered data for transmission by the fixed allocation method, and a second data buffered second data for transmission by the reserved allocation method. Second holding means and transmission slot designation extracted from the transmission slot management unit A data selecting unit for selecting one of the output data of the first and second holding units in accordance with the allocation method designated by the number, and a transmitting unit for transmitting the data selected by the data selecting unit to the central station. It is configured.

Further, according to the present invention, the information on the slots fixedly assigned to each of the plurality of peripheral stations stored by the slot assignment storage device is such that the addresses of the plurality of peripheral stations are the number of the slot having one frame length and the frame number. It is the information based on the PA table set corresponding to the set of numbers,
The control signal generation unit has a reservation table including an address unit that writes addresses to a plurality of peripheral stations and a flag unit that indicates whether the slot is a fixed allocation slot or a reserved allocation slot, and is about to transmit. It is characterized in that the control signals having the values respectively written in the address part and the flag part of the frame number reservation table are generated.

[0017]

According to the present invention, a line is slot-divided from a plurality of peripheral stations to a central station via an artificial satellite, and channels are shared to perform communication by a fixed allocation (PA) method. When a reservation request is sent when a large amount of data needs to be transmitted temporarily, such as when data is accumulated, the central station sends information about fixedly assigned slots read from the slot assignment storage device and received signals from peripheral stations. The control signal including the slot allocation information is generated based on the reservation request and the outbound signal in which the control signal and the transmission data are time-division multiplexed is transmitted. Therefore, the slot allocation is performed to the peripheral station that requests the reservation. Can be increased.

Further, according to the present invention, the control signal transmitted from the central station includes an address portion indicating addresses of a plurality of peripheral stations and a flag portion indicating whether the slot is a fixed allocation slot or a reserved allocation slot. With this configuration, it is possible for one peripheral station to judge which system the assigned slot written in the slot information is for.

[0019]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment of a central station which constitutes a main part of the present invention system, FIG. 2 is a block diagram of an embodiment of a peripheral station which constitutes another main part of the present invention system, and FIG. 1 is a system configuration diagram of a satellite communication system to which the inventive method is applied.

First, a satellite communication system to which the method of the present invention is applied will be described with reference to FIG. As shown in the figure, in the satellite communication system, one central station C and a plurality of n peripheral stations X1 to Xn are installed on the ground, and the satellite S
Is used as a relay station for communication.

From the peripheral stations X1 to Xn to the central station C, communication is performed by time division multiple access by slot division using a common channel by an inbound line via an artificial satellite S. Also, from the central station C to the peripheral stations X1 to Xn,
Broadcast-type broadcast communication is performed by an outbound line via the artificial satellite S.

The central station C is constructed as shown in FIG. As shown in the figure, the central station C transmits / receives radio waves to / from the artificial satellite S, a receiver 2 to which a signal received by the transmitter / receiver 1 is input, and an output of the receiver 2. A reception data buffer 3 and a control signal generation unit 6 to which a reception signal is input, a terminal device 4 and a slot allocation storage device 5 to which an output signal of the terminal device 4 is input, a transmission data buffer 7 constituting a transmission system, and a multiplexing unit. It is composed of a unit 8, a timing signal generator 9, and a transmitter 10.

The peripheral stations X1 to Xn are each constructed as shown in FIG. As shown in the figure, the peripheral station transmits / receives radio waves between the peripheral station and the artificial satellite S, a frame synchronization unit 12 and a reception unit to which a signal received by the transmitter / receiver 11 is input. 13 and the receiving unit 1
3, the reception data buffer 14 and the transmission slot management unit 15 to which the output signal of 3 is input, the packet division unit 16, the transmission mode selection unit 17, the PA data buffer 18, the DA data buffer 19, and the data selection unit 20 which form the transmission system. And a transmitter 21.

Next, the operation of this embodiment will be described.
First, the operation of the central station will be described. In FIG.
A transmission signal (inbound signal) transmitted from a peripheral station via an artificial satellite is received by the transmission / reception device 1, supplied to the reception unit 2, and subjected to reception processing, and then the reception data buffer 3 and the control signal generation unit 6 Is supplied to each. The reception data buffer 8 performs buffering so that the reception signal from the reception unit 2 can be used as reception data.

On the other hand, the terminal device 4 is a device used when changing the slot allocation information, and outputs its output signal to the slot allocation storage device 5 which stores the slot allocation information and a PA table described later. Based on the PA table stored in the slot allocation storage device 5, the control signal generation unit 6
The necessary number of slots are allocated to the reservation request included in the received signal from the receiving unit 2 using a reservation table described later, and the slot information is supplied to the multiplexing unit 8.

Further, the transmission data is transmitted in the transmission data buffer 7.
And is buffered and then supplied to the multiplexer 8. The timing signal generation unit 9 generates a fixed number of slots at the transmission timing or the reception timing, that is, a timing signal indicating a frame delimiter. This timing signal is supplied to the multiplexer 8 where it is time-division multiplexed with the control signal (slot information etc.) from the control signal generator 6 and the transmission data from the transmission data buffer 7.

FIG. 4A shows the signal format of the time division multiplexed signal (outbound signal) output from the multiplexer 8. As shown in the figure, one frame of the time division multiplexed signal (outbound signal) is a control signal portion I.
The control signal section I includes a frame pattern 22 and slot information 23 from the control signal generation section 6.
The data section II is composed of data 0 to data N from the transmission data buffer 7.

The slot information 23 is the address 24i of the peripheral station to which the number of slots included in one frame is assigned.
A pair of (i = 0, 1, ..., N) and the PA / DA flag 25i corresponding to the slot is written. Each peripheral station checks whether the address 24i has its own address, and if there is, the corresponding PA / DA flag indicates whether the slot is a slot allocated for transmission of the PA system or the DA system. It is determined and the slot position is calculated from the position in the slot information.

Here, the PA / DA flag 25i is PA
Since it suffices to indicate whether the slot is a slot, a DA slot, or two, one bit of information is sufficient. For example, if it is PA, "1", DA
If so, an easily distinguishable one such as "0" is sufficient.

Returning to FIG. 1 again, the time division multiplexed signal (outbound signal) of the above format output from the multiplexer 8 is supplied to the transmitter 10 and is amplified and subjected to other signal processing. Broadcast-type transmissions to all the peripheral stations are performed toward the artificial satellites via the transmission / reception device 1.

Next, the PA table held by the slot allocation storage device 25 of the central station shown in FIG. 1 is shown in FIG.
Will be explained together. This PA table stores all the PA slots assigned to the peripheral stations transmitting in the PA system as a table and is not changed unless the arrangement of the PA slots is changed by the terminal device 4. , Used exclusively for the initialization of the reservation table.
As shown in FIG. 5, this PA table indicates peripheral stations which are assigned in advance by the slot number and the frame number, and VSAT1 to VSAT5, VSAT
Each of a and VSATb indicates an address of a peripheral station.

Next, to explain the operation of the peripheral station,
In FIG. 2, the peripheral station receives the transmission data from the central station transmitted by the transmitter / receiver 11 through the artificial satellite, extracts the timing signal from the received signal by the frame synchronization unit 12, and further converts it into the timing signal. The slot timing is calculated synchronously and the slot timing signal is output, while the receiving section 13 separates the slot allocation information and the received data section from the received signal.

The reception data buffer 14 buffers the reception data separated and taken out by the receiving unit 13 and outputs it. Further, the transmission slot management unit 15 receives the slot timing signal output from the frame synchronization unit 12, and generates a transmission slot designation signal indicating a slot allocated based on the slot allocation information separated by the reception unit 13. . The transmission slot designation signal also includes information indicating whether the slot assigned by the PA / DA flag is a PA slot or a DA slot.

When a transmission request is generated in this peripheral station, the transmission data is supplied to the packet division unit 16 and divided into packets of a length that fits in one slot, and then supplied to the transmission mode selection unit 17. When the transmission data is transmitted using the PA method, it is input to the PA data buffer 18, and when transmission is performed using a method other than the PA method, it is input to the DA data buffer 19.

The PA data buffer 18 is for buffering data to be transmitted in PA slots, and the DA data buffer 19 is a circuit for buffering data to be transmitted in slots other than PA slots. The data selection unit 20 inserts the data from the PA data buffer 18 into the slot allocated to the own station at the slot timing of the PA slot based on the transmission slot designation signal generated by the transmission slot management unit 15, and at the slot timing of the DA slot. DA data buffer 19
Select the data from and insert it into the slot assigned to the local station.

Further, when the transmission data stays in the PA data buffer 18 or the DA data buffer 19, the data selecting unit 20 adds a reservation request for the staying number to the transmission data in order to request an increase in the allocation slot. The transmission data output from the data selection unit 20 is transmitted by the transmission unit 2
After being converted into a predetermined format by No. 1, it is transmitted from the transmitting / receiving apparatus 11 to the central station toward the artificial satellite.

FIG. 4B shows the format of an inbound signal transmitted from the above peripheral station to the central station via an artificial satellite. As shown in the figure, the inbound signal of one frame length consists of slots 260 to 26N, and (N +
1) It is divided into slots.

Next, to explain the reservation table,
FIG. 6 shows an example of the reservation table. The reservation table is shown in Figure 1.
5 is a table of information on slots allocated to peripheral stations, which is held in the slot allocation storage device 5 of FIG. 5, and when it is created based on the PA table of FIG. 5, as shown in FIG. There is an address part for writing the address of the, and a flag part indicating whether the slot is a PA slot or a DA slot. In FIG. 6, the flag portion indicating the PA slot is "P", and the flag portion indicating the DA slot is "D".
, And corresponds to the PA / DA flag.

For example, slots 0 and 1 of frame 2 have P
It is a PA slot reserved by the A system, and it is slot 2 to
The slot N is a DA slot reserved by the DA method. The control signal generation unit 6 of the central station writes the slot allocation information of the corresponding frame in this reservation table to the address 25i (i = 0, 1, 2, ..., N) of the slot information.

In the procedure for writing the slot information 23 of the outbound signal using the reservation table, first, the address part of the slot written in the reservation table of the frame number to be transmitted is the address 2 of the slot information 23.
4i, the flag portion corresponds to the PA / DA flag 25i, and is thus written as read slot information one after another.

Next, the procedure for determining the value of the PA / DA flag and updating the reservation table when the reservation request is received by the central station will be described with reference to the flowchart of FIG. The central station looks at the corresponding part of the reservation table of the received slot (transmission slot of the peripheral station), and determines whether the slot is a PA slot or a DA slot by the flag part (step 71).

If the slot was a PA slot,
The value assigned to the flag portion of the reservation table in FIG. 6 is determined to be "P" (step 72). If it is a DA slot, the value assigned to the flag portion is determined to be "D" (step 73). Then, the central station searches the reservation table for the required number of empty slots (step 7
4) Substitute the address of the requested peripheral station into the address section of the empty slot and the value determined in step 72 or step 73 into the flag section (step 7).
5).

After that, the contents of the reception slot of the reservation table are initialized based on the PA table (step 7).
6). When an address is written in the PA table, substitute that address in the address section and set "" in the flag.
Substitute P ". When no address is written in the PA table (" 0 "is written in FIG. 5), initialization is performed to indicate an empty slot. Here," 0 "is written in the address part. Either "P" or "D" may be substituted in the flag part.

As described above, according to this embodiment, since the central station manages all PA slot information and broadcasts it to the peripheral stations frame by frame, the slot allocation can be added to the PA system by a reservation request. Therefore, it is possible to temporarily increase the PA slots assigned to the peripheral stations transmitting in the PA method.

Further, in the present embodiment, since the central station attaches the PA / DA flag to the slot allocation information and transmits it, the allocation slot written in the slot information for one peripheral station is for which method. Since it can be determined whether or not there is a large amount of communication in the DA system, there is no effect on the transmission capability of the PA system.

In the peripheral station, the transmission mode selection unit 17 can automatically distribute the data, for example, from the PA data buffer 18 to the PA data buffer 19 according to the data amount, but the PA data buffer 18 can be set by the user. It is also possible to input data only to the DA data buffer 19 or only to the DA data buffer 19.

[0047]

As described above, according to the present invention,
Since the central station manages all the PA slot information and broadcasts and transmits it to the peripheral stations every predetermined frame, slot allocation can be added to the PA system by a reservation request. Even if a large number of transmission requests are temporarily generated, the requests can be transmitted to the central station to temporarily increase the PA slots allocated to the peripheral stations.

Further, according to the present invention, since the central station adds the PA / DA flag to the slot allocation information and transmits it,
Since it is possible for one peripheral station to determine which method the assigned slot written in the slot information is for, the transmission method can be changed in data units, and one method affects the other method. The effect can be reduced (for example, even when the DA system is congested with a large amount of communication, it does not affect the basic transmission capability of the PA system).

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a central station of a main part of the system of the present invention.

FIG. 2 is a block diagram of an embodiment of a peripheral station of another main part of the system of the present invention.

FIG. 3 is a configuration diagram of a satellite communication system to which the method of the present invention is applied.

FIG. 4 is an example of a format of outbound and inbound signals.

FIG. 5 is a diagram showing an example of a PA table.

FIG. 6 is a diagram showing an example of a reservation table.

FIG. 7 is a flowchart showing a procedure for updating a reservation table.

[Explanation of symbols]

 1, 11 Transmitter / receiver 2, 13 Receiver 3, 14 Received data buffer 4 Terminal device 5 Slot allocation storage device 6 Control signal generator 7 Transmitted data buffer 8 Multiplexer 9 Timing signal generator 10, 21 Transmitter 12 Frame synchronizer 15 transmission slot management unit 16 packet division unit 17 transmission mode selection unit 18 PA data buffer 19 DA data buffer 20 data selection unit C central station X1 to Xn peripheral stations S satellite

Claims (4)

[Claims] 1. A central station carries out broadcast-type communication to a plurality of peripheral stations via an artificial satellite, and a channel is slot-time-divided from the plurality of peripheral stations to the central station via the artificial satellite. In a slot allocation method of a satellite communication system in which communication is performed by a fixed allocation method by sharing the same, the central station stores a slot allocation storage device that stores information about slots fixedly allocated to each of the plurality of peripheral stations, And a control signal generation unit that generates a control signal including slot allocation information allocated based on the information about the fixed allocation slot read from the slot allocation storage device and the received reservation request for the signal from the peripheral station. Multiplexing means for time-division multiplexing the control signal and transmission data to generate an outbound signal; A transmission unit that transmits to each of the plurality of peripheral stations, each of the plurality of peripheral stations receives a frame synchronization unit that generates a slot timing signal based on a signal that has received the outbound signal, and receives the outbound signal. The control signal extracted from the generated signal is used to identify whether the slot allocated for transmission of the local station is the fixed allocation method or the reserved allocation method, and the transmission slot designation signal is generated and output in synchronization with the slot timing signal. A transmission slot management unit, first holding means for holding the data buffered first data for transmission by the fixed allocation method, and second data buffered data for transmission by the reserved allocation method. Second holding means for holding data, and the data taken out from the transmission slot management section A data selection unit that selects one of the output data of the first and second holding units according to the allocation method designated by the transmission slot designation signal, and the data selected by the data selection unit is addressed to the central station. A slot allocation system in a satellite communication system, comprising: a transmitting means for transmitting. 2. The slot allocation method in a satellite communication system according to claim 1, wherein the control signal generation unit outputs the control signal including the slot allocation information on a frame-by-frame basis. 3. The information on the slots fixedly assigned to each of the plurality of peripheral stations stored by the slot assignment storage device includes the slot number and the frame number in which the addresses of the plurality of peripheral stations are one frame length. Information based on the PA table set in correspondence with the set of the above, the control signal generation unit includes an address unit for writing addresses to the plurality of peripheral stations, and a slot of the fixed allocation system or the reservation allocation system. It has a reservation table composed of a flag portion indicating whether or not, and generates a control signal having a value respectively written in the address portion and the flag portion of the reservation table of the frame number to be transmitted. The slot allocation method in the satellite communication system according to claim 1. 4. The value setting means for determining whether the reception slot is a fixed allocation method or a reserved allocation method and substituting a value according to the determination method into a flag portion of the control signal. A means for retrieving an empty slot in the reservation table read from the slot allocation storage device, a means for substituting the address of the peripheral station that made the reservation request into the retrieved empty slot, and a receiving slot of the reservation table 4. A slot allocation system in a satellite communication system according to claim 3, further comprising means for initializing the contents of