JPH0653875A - Satellite channel access system - Google Patents

Abstract

PURPOSE:To reduce the number of time slots to be used for the transfer of the same data volume and to improve line efficiency in a time-divided multiconnection channel access system. CONSTITUTION:If lines are congested, the mutual collision of data slotted ALO HA system data is frequently generated and much data are stored in a peripheral station in the case of using both slotted ALOHA system and slot reservation system in the time-divided multiconnection channel access system, only one header is added to plural data and plural data are collectively sent to one reservation slot. Thereby the number of time slots to be used for the transfer of the same data volume can be reduced in comparison with a case for using one time slot in each data. Since long data over several time slots can be sent to one reservation slot without dividing them, the increment of overhead due to packet division can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite channel access system, and more particularly to a time division multiple access satellite channel access system for performing communication between a central station and a plurality of peripheral stations via a communication satellite.

[0002]

2. Description of the Related Art A first TDMA channel access method using a time division multiple access method in which one satellite line is shared by a plurality of stations (peripheral stations) in a time division manner to communicate with one central station.
As an example of, there is a slotted Aloha system. In this slotted Aloha system, all peripheral stations are allowed to randomly access a time slot, which is a terminal obtained by time-sharing a satellite line, and transmit packet data. The advantage of this scheme is that it allows low delay transmission when the message origination rate is low. However, in this method, when the line becomes congested as shown in the time chart of FIG. 13, collisions of data frequently occur, and the phenomenon of repeated collisions such as data 2 and data 5 in the figure may occur. It will cause the whole system to become unstable. The hatched portions at the beginning of the data 1 to 5 in the figure show the header.

A second example of the TDMA channel access system is a slot reservation system. In this method, data for a peripheral station to reserve a slot is first transmitted by random access, and the central station allocates a slot dedicated to the peripheral station to the data. The advantage of this method is that stable and flexible adaptation is possible when the message occurrence rate is relatively high or when the occurrence rate varies a lot. However, when the message occurrence rate is low, there is a drawback that the delay amount is large as compared with the random access method (slotted Aloha method).

As a third method, there is a random access / reservation combined method in which the first and second methods are combined. This is to selectively use the random access method and the slot reservation method depending on the situation of message occurrence. For example, it usually operates by a simple slotted Aloha method, but when the line is congested and collisions occur frequently and multiple retransmission data are retained in the peripheral stations, or when a large number of messages occur simultaneously in one peripheral station. The slot reservation method is used.

The time chart shown in FIG. 14 is an example of a random access / reservation combined system. When the lines are congested and the data frequently collide with each other and a plurality of retransmission data are generated in the peripheral stations, the slot reservation method is used for transmitting the retransmission data. In the example of this figure, not only the retransmitted data,
By the time the reservation request is added to the resending data 1 and sent, the slots for the data 4 and 5 newly generated from the terminal are reserved. As a result, it is possible to prevent the data from being transmitted by random access and prevent the system from becoming unstable.

The time chart shown in FIG. 15 is a second example of the random access / reservation combined system. In this example,
Since a message with a long data length occurred in the peripheral station, this message was divided into packets with the data length that can be sent in one time slot as a unit, and only the first packet was sent by random access for a reservation request. Packets are sent out using the assigned slots.

Further, as shown in FIGS. 13 to 15, each data is added with a header shown by hatching when it is transmitted to the satellite line. This header includes a carrier wave, a preamble part for clock reproduction, an address of a peripheral station, and redundant bits for detecting a transmission error. If the message generated from the terminal has a length that can be accommodated in one time slot of the satellite line, a header is added to each message and the packet is transmitted using one time slot as one packet data.

If the message has a length that cannot be accommodated in one time slot, it is divided into several packets, a header is added to each packet, and each packet is sent out using one time slot. It This is due to the random access method (slotted Aloha method),
It is common to both the slot reservation method and the random access / reservation combined method.

As shown in FIGS. 13 and 14, the length of the data generated from the terminal is different, and when the length of the data and the header is shorter than the length of the time slot, the extra portion is filled with dummy bits. Will be done. When transmitting the data 1, 2, 3 and 4 of FIG. 14, since the length of the slot is longer than the length of the actual data and the header, the last part of the slot is filled with dummy bits. When each piece of data is shorter than the length of the slot, the fact that each piece of data uses one slot lowers the line efficiency and, at the same time, worsens the line congestion due to the use of a large number of slots. Cause

Further, when a long message is divided into packets as shown in FIG. 15, a header must be added to each packet. Since the header part is large in satellite communication, the ratio of the header part to the length of the message itself generated from the terminal is large. Therefore, the line efficiency is low.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a satellite channel access system capable of improving line utilization efficiency by reducing the number of time slots used for data transfer as much as possible.

[0012]

According to the satellite channel access system of the present invention, a plurality of peripheral stations access a central station through a communication satellite by using a common channel in a time division manner,
As a method to access the time slot, which is the unit in which all the peripheral stations time-divide the channel, a slotted Aloha method that randomly accesses and a slot reservation method that uses a dedicated time slot reserved in advance are used together. In the satellite channel access system for time division multiple access, the reserved time slots are in the form of a plurality of consecutive time slots, and when a plurality of transmission data are accumulated in one peripheral station, a plurality of such times are stored. Data is transmitted in a format in which only one header part is added on one reserved time slot.

In another satellite channel access system according to the present invention, when a plurality of peripheral stations access a central station by using a common channel in a time division manner via a communication satellite, all the peripheral stations use the channel. Time-division multiple access that uses a slotted Aloha method that randomly accesses and a slot reservation method that uses a dedicated time slot reserved in advance as the access method to the time slot that is the unit of time division Satellite channel access system, the reserved time slots are in the form of a plurality of consecutive time slots, and when one transmission data having a data length over the plurality of time slots occurs, the one transmission data is To send in a format with only one header part added on the one reserved time slot Characterized in that was.

In still another satellite channel access system according to the present invention, when a plurality of peripheral stations use a common channel in a time division manner via a communication satellite to access a central station, all the peripheral stations have the same channel. A time-division multiple access method that uses a slotted Aloha method that accesses a randomasem and a slot reservation method that uses a dedicated time slot reserved in advance In the connected satellite channel access system, the reserved time slots are in the form of a plurality of consecutive time slots, and each of the peripheral stations has the number of transmission data retained in its own station and the transmission data of each of these. Determine the length of the reserved time slot required for sending these transmission data according to the length and allocate it to the own station. The central station, the central station having means for determining how many pieces of the transmission data are to be collectively transmitted on the reserved time slot and means for converting the transmission data into a packet having one header according to the determination. Means for recognizing individual data of the transmission data transmitted on one of the reserved slots, detecting transmission error for each recognized individual data, and confirming reception of the individual data. And a means for generating a response signal for transmitting the response signal to the peripheral station that is the transmission source.

[0015]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of the configuration of a satellite communication network to which an embodiment of the present invention is applied. This satellite communication network has one central station C and a plurality of peripheral stations T1 and T.
2 ..., and the peripheral stations T1, T2, ..
Access to the central station C. A star network is realized by connecting a host terminal to the central station C and user data terminals to the peripheral stations T1, T2, ....

FIG. 2 shows the format of signals from the peripheral stations T1, T2, ... To the central station C. Peripheral stations T1, T
2. In transmitting signals from the central station C to the central station C, one channel is first divided into frames of a certain time length, and this frame is further divided into several time slots.
This time slot is a basic transmission unit. In the example of FIG. 2, one frame is divided into eight slots.
A sequence number is assigned to the frame, and the central station C and the peripheral stations T1, T2, ... Have the same consciousness about the number.

The packet data transmitted from the peripheral stations T1, T2, ... To the central station C basically has the format shown in FIG. All the packet data sent by the random access method (slot Aloha method) must take the format of FIG.

That is, a carrier wave, a preamble part for clock recovery, an overhead part (OH) consisting of a unique word part indicating the start of data, a field (ADRS) indicating the peripheral station address of the transmission source, and the length of the reserved slot requested. Field (REQ), the sequence number (SEQ) of the packet transmitted by each peripheral station, and the field (COUNT) indicating the number of data units included in the packet.
T), a frame check sequence field (FCS1) for detecting a transmission error from the ADRS section to the COUNT section, a data unit section (UNIT) accommodating one message generated from the terminal, and a packet length of one time slot. , A dummy bit for adjusting the length of the packet, a redundant bit (FEC) for error correction, and a guard time (GT) for ensuring an interval with a packet transmitted in the next slot.

Of these, the data unit (UNIT)
Is a message generated from a terminal (DATA), an information field (PC) for reassembling the packet into one message in the central station when the peripheral station divides one message into a plurality of packets, and the message. (PL) that indicates the length of the
Section, and a frame check sequence field (FCS2) for the DATA section.

When a packet using the format of FIG. 2 is sent by the random access method, "0" is set in the COUNT section. Also, when a packet that also uses the format of FIG. 2 is sent to the reserved slot,
"1" is set in the COUNT section.

The OH section, ADRS section, REQ section, S
Since the lengths of the EQ section, COUNT section, FCS1 section, FEC section, and GT section are all fixed, the maximum length of the data unit section that can be accommodated in one time slot is determined. Furthermore, since the lengths of the PL part and the PC part are also constant, the maximum length Lmax of a message that can be accommodated in one time slot is also determined.

When the length of the message generated from the terminal is shorter than the maximum message length Lmax, the message is accommodated in a packet having a format as shown in FIG. 2, and the random access method (slotted Aloha method) is used. It is sent on one time slot.

FIG. 3 shows the central station to the peripheral stations T1, T2, ...
The format of the signal going to is shown. The central station C transmits packet data toward the peripheral stations T1, T2, ... And also transmits a frame timing signal indicating a frame delimiter of a fixed time length in a broadcast mode. This frame timing signal serves as a timing reference used by the peripheral stations T1, T2, ... When transmitting from its own station, and the interval at which this frame timing signal is transmitted is the peripheral station T1.
, T2, ..., Equal to the length of the frame that time-divides the channel. Further, the central station C has a fixed cycle (for example, once in 16 frames or once in 128 frames).
A frame timing signal having a special pattern for indicating the timing of the frame number 0 is transmitted, and is used as a reference for matching the awareness of the frame number between the central station C and each peripheral station.

Following the frame timing signal, the central station C transmits a reception response signal of data transmitted by the peripheral stations T1, T2, ... The reception response signal is obtained by arranging the source peripheral station addresses of the data correctly received by the central station C in the order of slots, and the slots in which no data is received, or the collision between data or the transmission error, All "0" s are written to the slots for which data could not be normally received. Reserved slots assigned to any of the peripheral stations are treated on this reception response signal in the same manner as slots in which no data is received, and all "0" s are written.

Further, the central station C transmits the slot allocation broadcast information in the broadcast mode following the reception response signal. The slot-assigned broadcast information is information indicating whether each time slot of a frame is a randomly accessible slot or a slot assigned to any of the peripheral stations. In the example of FIG. 3, slot 1 and slots 5-8 are randomly accessible slots, and slots 2-4
Is a slot assigned to one of the peripheral stations.

Both the reception response signal and the slot allocation broadcast information are transmitted in units of one frame. FIG. 16 illustrates the relationship between the reception response signal sent from the central station C, the slot allocation broadcast information, and the frame which is the reference of the transmission timing of the peripheral stations T1, T2, ....

In FIG. 16, the satellite delay is one time slot, and one frame is divided into eight time slots.
The peripheral station T1 uses the slots 2, 4, and 7 of frame 1 to transmit three packets. However, collision of data occurs in slot 4. It is also assumed that another peripheral station T2 transmits one packet using slot 6 of the same frame 1.

When the central station C finishes receiving the frame 1, it immediately creates and sends a reception response signal. The content of the reception response signal at this time is that the peripheral station T is located at the positions of slots 2 and 7.
The address of 1 and the address of the peripheral station T2 are written in the position of the slot 6, and all "0" are written in the other slots.

It is assumed that the reception response signal for the frame 1 always arrives at the peripheral station on the way with the frame 2. Also,
The slot allocation broadcast information transmitted together with this reception response signal is the slot allocation information for frame 3. According to this slot allocation information, slots 2 to 4 of frame 3 are reserved slots allocated to any peripheral station. Therefore, the peripheral station T1 refrains from random access in slots 2 to 4 of frame 3 and transmits data in the next slot 5.

FIG. 4 shows the format of the packet data transmitted on the reserved slot among the signals transmitted from the peripheral stations T1, T2, ... To the central station C. The reserved slot is allocated by connecting a plurality of time slots (there may be one).

The packet data sent to the reserved slot shows an overhead part (OH) consisting of a preamble part and a unique word part, a field (ADRS) indicating the source peripheral station address, and the length of the reserved slot requested. A field (REQ), a sequence number (SEQ) of a packet transmitted by each peripheral station, a field (COUNT) indicating the number of data units included in the packet,
A frame check sequence field (FCS1) for the ADRS part to the COUNT part, a data unit part (UNIT) for accommodating one message generated from the terminal, and a length of the entire packet to match the length of the reserved slot. It is composed of a dummy bit, a redundant bit for error correction (FEC), and a guard time (GT) for securing an interval with a packet transmitted in the next slot.

The difference between the packet data transmitted on the reserved slot and the packet data transmitted by the random access method shown in FIG. 2 is that the packet data transmitted on the reserved slot accommodates a plurality of data units. It is a point that can be done. In other words, a plurality of data units can be sent with only one header from the OH section to the FCS1 section added. The packet data transmitted on the reserved slot can contain up to 8 data units as long as the packet data is accommodated in the reserved slot.

Next, FIG. 5 similarly shows the peripheral stations T1, T2, ...
It shows the format of the packet data sent from the ... to the central station C on the reserved slot, which includes only one data unit (UNIT). As a result, it is possible to add a single header from the OH part to the FCS1 part and send it out as one packet without splitting a long message that spans several time slots. In this case, the format is exactly the same as the packet format shown in FIG. 2 except that the packet length corresponds to a plurality of time slots.

FIG. 6 shows the central station C to the peripheral stations T1, T2, ...
It shows the format of packet data in the signal transmitted to. The packet data transmitted by the central station C is classified into three types: a user data packet, a reserved slot allocation individual information packet, and a reserved slot reception response packet. Each packet data conforms to the high-level data link control (HDLC) frame format, and is sandwiched between flag patterns (F) indicating the head and end of the packet.

The user data packet is a packet for transmitting the data generated from the host terminal of the user connected to the central station C to the peripheral station side. The user data packet includes a destination peripheral station address (ADRS), a code (ID) indicating that it is a user data packet, and a data unit (DAT) accommodating data generated from the host terminal.
A), a frame check sequence (FCS) for detecting a transmission error.

The reserved slot allocation individual information packet is a packet for allocating a reserved slot to each peripheral station. The reserved slot allocation individual information packet includes a peripheral station address (ADRS) for allocating the reserved slot, a code (ID) indicating that it is a reserved slot allocation individual information packet, and a frame number (FR) indicating the start time slot of the allocated reserved slot. ), A slot number (SL), a slot number (NS) indicating how many time slots are reserved slots from the start time slot, and a frame check sequence (FCS) for detecting a transmission error.

The reserved slot reception response packet is transmitted to the peripheral station T.
1, T2, ... Are packets for transmitting a reception response signal for the data transmitted on the reserved slot. The reservation slot reception response packet is a destination peripheral station address (ADRS), a code (ID) indicating that it is a reservation slot reception response packet, and the sequence number set in the packet confirming reception of this reception response packet. (S
EQ), a field (COUNT) indicating the number of units included in the packet confirming the reception of this reception response packet
T), a field (ACK) indicating information for confirming reception of each data unit, and a frame check sequence (FCS).

Of these, the reception confirmation information (ACK) is 1-byte information, and one bit indicates the reception confirmation of one data unit. In the example of FIG. 6, the reception of three data units is confirmed. At this time, the reception confirmation information (A
Only 3 bits of CK) are valid. In this example,
Indicates that the peripheral station successfully received the first two data units out of the three data units sent on one reserved slot, but the last one data unit was discarded because a transmission error was detected. Is.

FIG. 7 is a block diagram of the central station C. The transmission / reception device 1 performs transmission / reception with the satellite S and performs frequency conversion between a high frequency band / intermediate frequency band. The receiver 2 demodulates and corrects the signal received by the transmitter / receiver 1.

The channel monitoring section 3 refers to the frame check sequence section (FCS1) of the received packet,
A transmission error from the ADRS section to the COUNT section of the received packet is detected. If an error is detected, the packet is discarded. CO only for packets where no errors are detected
Is "0" set by referring to the UNT section?
Depending on whether any other value is set, it is discriminated whether the data is the data transmitted in the normal time slot or the data transmitted in the reserved slot, and the normal slot data processor 4 or the reserved slot data processor Hand over to 5.

First, the normal slot data processing unit 4 firstly receives the allocation request reservation slot length (REQ) of the received packet.
If this is not “0”, the reserved slot allocation management unit 9 sets the requested reserved slot length and the requesting peripheral station address.
To notify.

Second, the normal slot data processing unit 4 uses U
Frame check sequence part of NIT part (FCS2)
To detect a transmission error in the UNIT section. If an error is detected, the packet is discarded. If there is no error, the PL part, the PC part, and the DATA part of the UNIT part are delivered to the reception data buffer 6, and at the same time, the peripheral station address of the source of this packet is sent to the normal slot reception response signal generation part 7.
To notify.

First, the reservation slot data processing unit 5 firstly requests the allocation slot reservation request of the received packet (REQ).
If it is not “0”, the reserved slot allocation management unit 9 sets the requested reserved slot length and the request source peripheral station address.
To notify.

Secondly, the reserved slot data processing unit 5 uses the frame check sequence unit (FCS) of each unit.
The transmission error of the UNIT part is detected by referring to 2). If an error is detected, the UNIT part is discarded. If there is no error, the PL part, the PC part, and the DATA part of each UNIT are delivered to the reception data buffer 6, and at the same time, the peripheral station address of the sender of this packet, the sequence number, and the data reception information are generated as a reserved slot reception response. Notify Part 8. The data reception information indicates the number of UNITs included in the packet and which UNIT is normally received.

The reception data buffer 6 buffers the UNIT unit received from the normal slot data processing unit 4 and the reserved slot data processing unit 5, and refers to the packet effective length (PL) and the packet reassembly information (PC). Then, the data divided into packets at the peripheral station is reassembled into one data, and the data not divided into packets is delivered to the host terminal as it is.

The normal slot reception response signal generator 7 uses the source peripheral station address received from the normal slot data processor 4 to create a reception response signal. Then, when the transmission timing of the frame timing signal comes, this is output to the multiplexing unit 14.

The reserved slot reception response generation unit 8 creates a reserved slot reception response packet by using the source peripheral station address, the sequence number, and the data reception information received from the reserved slot data processing unit 5. Output to the multiplexing unit 14.

The reserved slot allocation management unit 9 uses the requested reserved slot length and the request source peripheral station address notified from the normal slot data processing unit 4 and the reserved slot data processing unit 5 to create a slot allocation table. Also,
The individual / broadcast slot allocation information generation unit 10 is requested to issue the reserved slot allocation individual information to each peripheral station, and the slot to be allocated and the peripheral station address of the allocation destination are notified.

Individual / broadcast slot allocation information generator 10
Is based on a request from the reserved slot allocation management unit 9,
A reserved slot allocation individual information packet is created, and the multiplexing unit 1
Output to 4. When the transmission timing of the frame timing signal arrives, the individual / broadcast slot allocation information generation unit 10 reads the slot allocation for one frame from the slot allocation table managed by the reserved slot allocation management unit 9 and uses this as the slot. The multiplexing unit 14 is used as the allocation broadcast information.
Output to.

The transmission data buffer 11 receives user data from the host terminal, buffers it, edits it into user data packets of a predetermined format, and then multiplex section 1
Output to 4.

The frame timing signal generator 12 receives the frame timing signal indicating a frame delimiter from the multiplexer 1
Output to 4. At the same time, the frame timing signal generation unit 12 notifies the reception slot timing generation unit 13 of the reception frame timing used by the central station C.

The reception slot timing generation unit 13 creates the reception slot timing used in the central station C based on the output of the frame timing signal generation unit 12, and uses this for the channel monitoring unit 3 and the normal slot reception response signal generation unit. 7 and output.

The multiplexing unit 14 includes a normal slot reception response signal generation unit 7, a reserved slot reception response generation unit 8, an individual / broadcast slot allocation information generation unit 10, a transmission data buffer 11,
The output from the frame timing signal generator 12 is time-division multiplexed, and this is output to the transmitter 15.

The transmission unit 15 adds redundant bits for transmission error detection by the CRC method to the packet data in the input from the multiplexing unit 14, encodes / modulates and outputs to the transmission / reception apparatus 1.

FIG. 8 is a block diagram of the peripheral stations T1, T2, .... The transmission / reception device 16 transmits / receives signals to / from the satellite S, and performs frequency conversion between a high frequency band and an intermediate frequency band. The reception unit 17 performs demodulation / error correction processing on the signal received by the transmission / reception device 16, and outputs the processed signal to the separation unit 18.

The separating section 18 receives the output of the receiving section 17,
The frame timing signal generated by the central station C is detected from among them, and the frame timing is determined by the frame synchronization unit 21.
Reserved slot allocation broadcast information to slot management section 2
8, the reception response signal is output to the delivery confirmation unit 29, and the packet data is output to the identification unit 19.

The identifying unit 19 performs error detection on the user data received from the separating unit 18, determines only the data addressed to the own station that has no transmission error, and discards the other packet data. . Furthermore, the identification unit 1
9 refers to the ID portion of the valid received data to recognize the type of packet data, the user data packet to the received data buffer 20, the reserved slot allocation individual information to the reserved slot allocation management unit 28, and the reserved slot reception response packet. Each is delivered to the delivery confirmation unit 29.

The reception data buffer 20 buffers the user data packet received from the identification section 19 and delivers only the DATA section to the user data terminal.

The frame synchronizer 21 determines the frame timing to be used when the local station transmits by considering the distance between the local station and the satellite with reference to the frame timing transmitted from the central station C. It is output to the slot timing generation unit 22.

The slot timing generator 22 divides the frame created by the frame synchronizer 21 into a predetermined number of slots to determine slot timing.

The packetizing unit 23 receives data from the user data terminal, and if the data has a data length which can be accommodated in the DATA portion of one time slot, the packet reassembly information portion (PC) and the data length (PL) are added to this. , A frame check sequence part (FCS2) is added to create one unit.

If the data received from the user data terminal has a data length that cannot be accommodated in the DATA portion of one time slot, the packetizing unit 23 has a length that allows the beginning portion of this data to be accommodated in the DATA portion of one time slot. Only the first packet and the subsequent two packets are separated. Then, the packet assembly information (PC), the data length (PL), and the frame check sequence part (FCS2) are added to the head packet and the subsequent packet, respectively, to create one UNIT part.

As the packet reassembly information (PC),
For example, whether the data is a part of the packet-divided data or not, and if the data is a part of the packet-divided data, information such as a leading packet or a subsequent packet can be considered.

The transmission data buffer 24 is the packetizing unit 2
The unit 3 receives the UNIT unit from 3 and buffers it, and outputs it to the transmission control unit 26. At this time, the transmission data buffer 24 has a UNIT portion to be transmitted by random access on one time slot and a U portion to be transmitted on a reserved slot.
NIT part and UN that should not be retransmitted after one transmission failure
Buffer the IT section separately.

Further, the transmission data buffer 24 holds the UNIT section output to the transmission control section 26 in a temporary holding buffer for confirmation of delivery. Then, in response to the retransmission / buffer release instruction signal from the delivery confirming unit 29, the UNIT unit instructed to release from the holding buffer is erased from the buffer, and the UNIT unit instructed to retransmit is used as a dedicated buffer for retransmission. Buffer again.

The reservation management unit 25 uses the transmission data buffer 24.
The number of UNIT units buffered as reserved slot use data and the length of each unit are managed to determine how many times should be reserved.

When the transmission control unit 26 receives the output from the slot timing generation unit 22 and knows that the slot timing has come, it first refers to the slot allocation table of the reserved slot allocation management unit 28 to determine whether the random access is possible. , The reserved slot timing allocated to the own station or the reserved slot timing allocated to other peripheral stations.

If the slot timing is such that random access is possible, the transmission control unit 26 reads from the transmission data buffer the first one of the UNITs that can be transmitted by random access, and reads the address of its own station (ADRS) and the requested reserved slot length. (REQ), sequence number (SEQ), CO
UNT part, frame check sequence part (FCS1)
Is added and output to the transmission unit 27. At this time, the requested reservation slot length (REQ) is set to a value instructed by the reservation management unit 25. Also, at the slot timing at which random access is possible, the COUNT section is always set to "0".

If the slot is a reserved slot assigned to itself, the transmission control unit 26 reads from the transmission data buffer 24 the UNIT buffered as reserved slot use data by the number that can be accommodated in the reserved slot. . At this time, the number of UNIT units read from the transmission data buffer 24 by the transmission control unit 26 is equal to that of the reservation management unit 2.
We will receive instructions from 5. The transmission control unit 26 sends the address (ADR) of its own station to the read unit units.
S), required reservation slot length (REQ), sequence number (SE
Q), a COUNT section, and a frame check sequence section (FCS1) are added and output to the transmission section 27. The requested reservation slot length (REQ) is set to a value instructed by the reservation management unit 25. Also, at this time, the transmission control unit 26 instructs the transmission unit 27 how many time slots to continuously transmit, and the output time of the carrier wave.

When the slot timing is a slot assigned to another station, the transmission control unit 26 suspends data transmission in that slot.

Finally, the transmission control unit 26 notifies the delivery confirmation unit 29 as a transmission history of which time slot data transmission was performed, whether it was random access or transmission to a reserved slot.

The transmission unit 27 adds dummy bits to the input from the transmission control unit 26, further performs encoding / modulation, adds error correction redundant bits (FEC), and outputs the addition to the transmission / reception device 16.

The reserved slot allocation management unit 28 creates a slot allocation table by referring to the slot allocation broadcast information transmitted from the central station C and the reserved slot allocation individual information.

The delivery confirmation unit 29 receives the output from the transmission control unit 26, and stores in which time slot the own station has transmitted, whether it is transmission by random access, or transmission to a reserved slot. .

First, regarding the packet data transmitted by random access, the storage of the delivery confirmation unit 29 and the separation unit 1
The received response signal output from 8 is compared, and the response to the time slot in which the local station tried to transmit data is positive acknowledgment ACK (ACKNOWLEDGEMENT) or negative acknowledgment NAK (NOT AC
KNOWLEDGEMENT). That is, if the reception response signal indicates the address of the own station, the positive response AC
If K, all 0 or the address of another peripheral station is indicated, it is determined to be a negative response NAK.

Next, regarding the packet data sent to the reservation slot, only the one for which normal reception has been confirmed by the reservation slot reception response transmitted as a kind of packet data from the central station C has the ACK confirmed. And Packet data for which a reservation slot reception response is not returned at all after waiting for a certain period of time is judged as a NAK response because it was discarded at the central station side. In addition, although the reservation slot reception response has been sent, N
It may be an AK response.

The delivery confirmation unit 29 gives a negative response NAK as a response.
Was retransmitted and the response was a positive response A
For the UNIT that was CK, the transmission data buffer 24 is instructed to release from the temporary holding buffer.

FIG. 9 shows a first embodiment of the access system in the satellite communication system according to the present invention. In the slot configuration in this example, there are five time slots per frame and the satellite delay is one time slot.

Here, since the peripheral station T1 has generated two retransmission data, it judges that the line is congested and uses the reservation mode. At this time, data 1 must be retransmitted by random access in order to request a reserved slot, but data 1 is transmitted after waiting for the number of randomly selected slots in order to avoid re-collision as much as possible. During this waiting, new data 4 and 5 are generated from the terminal. Normally, the data 4 and 5 are data that can be transmitted by random access, but it is assumed that both the data 4 and 5 are transmitted to the reserved slot because the line is currently busy.

Since two slots are required to transmit the retransmission data 2 and the new data 4 and 5, the peripheral station T1 adds the reservation request 2 to the data 1 and sends it by random access. Then, when the reserved slot is allocated, the data 2, 4 and 5 are transmitted.

The packet transmitted at this time has three UNIs.
Including T part. Where 1 UNIT is transmitted as 1 packet data, 3 frames are used, but since 3 UNIT is transmitted as 1 packet data, only 2 slots are used.

FIG. 10 shows a second embodiment of the access system in the satellite communication system according to the present invention. Here, since a long message has occurred in the peripheral station T1, it is divided into a head packet 1 and a subsequent packet 2 which can be accommodated in one time slot. Since 3 slots are required to transmit the subsequent packet 2, the peripheral station T1 adds the reservation request 3 to the data 1 and sends it by random access. And
When the reserved slot is assigned, the subsequent data 2 is transmitted. When this long message is equally divided by the data length that can be transmitted in one time slot and each is transmitted as one packet data, a total of 5 slots are used, but in this example, the required slots are 4 slots in total. Good.

FIG. 11 shows the transmission data buffer 24 of the peripheral station.
FIG. The transmission data buffer 24 of the peripheral station includes a buffer 1102 for buffering a UNIT to be transmitted by random access, a buffer 1103 for buffering retransmitted data that has failed to be transmitted once, and a buffer 1104 for buffering a data UNIT to be transmitted in a reserved slot. , Buffers 1105, 1106, and 1107 for temporarily holding the data unit transmitted from each buffer to wait for confirmation of reception.

Of the data input from the packetizer 23, the subsequent packet obtained by dividing a long message into two packets is buffered in the reserved data buffer 1104.

On the other hand, the short data that can be accommodated in one time slot and the first packet obtained by dividing a long message into two packets are normally buffered in the random access data buffer 1102. However, the SW unit 11
By switching 01, these data may be buffered in the reserved data buffer 1104. This is called a random access suppression mode.

Retransmission data buffer 1103 requests SW section 1101 to enter the random access control mode when two or more retransmission data are generated.

Three temporary holding buffers 1105, 110
6, 1107 erases the temporarily held data or transfers it to the retransmission data buffer according to the instruction from the delivery confirmation unit 29.

When all the data in the retransmission data temporary holding buffer 1106 has been erased, that is, all receptions at the central station C have been confirmed and the retransmission data buffer 11 has been confirmed.
If no data remains in 03, the SW unit 1101
Cancels the random access suppression mode and returns to normal operation.

The retransmission data buffer 1103 and the reservation data buffer 1104 notify the reservation management unit 25 of the total number of UNITs buffered in each buffer and the length of each UNIT.

FIG. 12 is a detailed diagram of the reservation management unit 25 of the peripheral station. The reservation management unit 25 includes a reservation data buffer 1104 and a retransmission data buffer 1 of the transmission data buffer 24.
For 103, the number of internal units and each unit
Management units 1201 and 1202 for managing the length of the reserved slot, and the number of UNITs and the unit length, the reserved slot length desired to be requested by the own station and the reserved slot length determination for determining how many UNITs are transmitted on one reserved slot. / Data edit control unit 1203.

Reserved slot length determination / data edit control unit 1
203 notifies the request reservation slot length when the transmission control unit 26 tries to send data. Also, at the time when the reserved slot is allocated, how many UNITs are reserved data buffer 1102 or retransmission data buffer 110.
The transmission control unit 26 is notified of whether or not the data should be read from No. 3.

When the reserved slot allocation management unit 28 receives the reserved slot allocation individual information packet from the peripheral station C, it notifies the reserved slot length determination / data edit control unit 1203 of the allocation. The reservation slot length determination / data edit control unit 1203 determines that the reservation request has not been accepted and requests the reservation again if the reservation slot has not been allocated within a certain time after the reservation request is made.

However, in this example, the next reservation request is not issued until a slot is assigned to the reservation request transmitted previously.

[0095]

As shown in FIG. 9, when multiple lines of data collide with each other due to congestion of lines and a plurality of data are accumulated in the peripheral stations, these can be transmitted as one packet by sharing the header part. As a result, the number of time slots used to transfer the same amount of data is reduced and efficiency is improved as compared with the conventional method in which each data uses one slot as one packet data.

Further, as shown in FIG. 10, when a message with a long data length occurs in a peripheral station, only one header part can be added and transmitted by continuously using several time slots, so that one message can be transmitted. The number of time slots to be used is reduced and the efficiency is improved as compared with the conventional method in which a long message is finely divided in units of time slots and each one is used as one packet.

[Brief description of drawings]

FIG. 1 is a diagram showing a satellite communication network which is an embodiment of the present invention.

FIG. 2 is a peripheral station T in the satellite communication network of FIG.
It is a figure which shows the signal format toward 1, the central station C from T2 ....

FIG. 3 is a diagram showing a signal format from a central station C to peripheral stations T1, T2, ....

FIG. 4 is a diagram showing a format of a packet transmitted from a peripheral station T1, T2, ... To a central station C on a reserved slot formed by connecting a plurality of time slots.

FIG. 5 is a diagram showing a format of a packet transmitted from a peripheral station T1, T2, ... To a central station C on a reserved slot formed by connecting a plurality of time slots.

FIG. 6 is a diagram showing a format of packet data in a signal from the central station C to peripheral stations T1, T2, ....

FIG. 7 is a configuration diagram of a central station C.

FIG. 8 is a configuration diagram of peripheral stations T1, T2, ....

FIG. 9 is a time chart showing an embodiment of an access method according to the present invention.

FIG. 10 is a time chart showing another embodiment of the access method according to the present invention.

FIG. 11 is a detailed diagram of a transmission data buffer which is one of the constituent elements of a peripheral station.

FIG. 12 is a detailed diagram of a reservation management unit which is one of the constituent elements of a peripheral station.

FIG. 13 is a time chart showing an example of an access method in the related art.

FIG. 14 is a time chart showing another example of the access method in the related art.

FIG. 15 is a time chart showing another example of an access method in the related art.

FIG. 16 is a diagram showing the relationship between the transmission frame timing on the peripheral station side, the transmission response signal transmitted by the central station, and the slot allocation broadcast signal in the present invention.

[Explanation of symbols]

 C Central station S Communication satellite T1, T2, T3 Peripheral station 1,16 Transmitter / receiver 2,17 Receiver 3 Channel monitor 4 Normal slot data processor 5 Reserved slot data processor 6,20 Received data buffer 7 Normal slot reception response Generation unit 8 Reserved slot reception response generation unit 9,28 Reserved slot allocation management unit 10 Individual / broadcast slot allocation information generation unit 11,24 Transmission data buffer 12 Frame timing signal generation unit 13 Reception slot timing generation unit 14 Multiplexing unit 15, 27 Transmission unit 18 Separation unit 19 Identification unit 21 Frame synchronization unit 22 Slot timing generation unit 23 Packetization unit 25 Reservation management unit 26 Transmission control unit 29 Delivery confirmation unit

Claims (3)

[Claims] 1. When a plurality of peripheral stations time-divisionally use a common channel via a communication satellite to access a central station, all the peripheral stations enter a time slot, which is a unit in which the channel is time-divided. A satellite channel access system of time division multiple access, which uses a slotted Aloha method that randomly accesses and a slot reservation method that uses a dedicated time slot reserved in advance as an access method of The reserved time slot is in the form of a plurality of continuous time slots, and when a plurality of transmission data are accumulated in one peripheral station, these plural data are stored in only one header part on one reserved time slot. A satellite channel access system characterized by transmitting in an added format. 2. When a plurality of peripheral stations time-divisionally use a common channel via a communication satellite to access a central station, all the peripheral stations enter a time slot which is a unit in which the channel is time-divided. A satellite channel access system of time division multiple access, which uses a slotted Aloha method that randomly accesses and a slot reservation method that uses a dedicated time slot reserved in advance as an access method of The reserved time slot is in the form of a plurality of continuous time slots, and when one transmission data having a data length over a plurality of time slots occurs, this one transmission data is converted into one on the one reserved time slot. Satellite channel access system characterized in that it is transmitted in a format in which only the header part is added . 3. When a plurality of peripheral stations time-divisionally use a common channel via a communication satellite to access a central station, all the peripheral stations enter a time slot which is a unit in which the channel is time-divided. A satellite channel access system for time division multiple access, which uses a slotted Aloha method to access Randomem and a slot reservation method that uses a dedicated time slot reserved in advance as an access method of The reserved time slot is in the form of a plurality of continuous time slots, and each of the peripheral stations stores the transmission data according to the number of transmission data staying in itself and the length of each transmission data. The length of the reserved time slot required for transmission is determined, and the number of the transmitted data on the reserved time slot assigned to the own station is determined. The central station has been transmitted on one of the reserved slots, having means for deciding whether to transmit the data collectively and means for converting the transmission data into a packet having one header according to the determination. A means for recognizing individual data of transmission data, detecting a transmission error for each recognized individual data, and a peripheral station of a transmission source by generating a response signal for confirming reception of the individual data. Satellite channel access system including means for transmitting to the satellite channel access system.