JP2803430B2 - Satellite communication system and equipment used for it - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a central station: a peripheral station of 1: n.
Used for multiple access satellite communication. In particular, it relates to the access technology of the central station and peripheral stations.

[0002]

2. Description of the Related Art A conventional example will be described with reference to FIGS. FIG. 7 is an overall configuration diagram of the multiple access satellite communication. FIG. 8 is a diagram showing a data transmission situation of the conventional slotted Aloha system.

As shown in FIG. 7, a multiple access system in which a plurality of peripheral stations T1 to T4 share a communication line by one communication satellite S in a time-division manner and communicate with one central station C is used. TDMA (Time Division Multi)
As one of ple Access) channel access methods, there is a slotted Aloha method. In the slotted Aloha method, all the peripheral stations T1 to T4 are allowed to randomly access a time slot, which is a unit obtained by time-dividing a satellite channel, and transmit packet data. The advantage of this scheme is that it enables low delay transmission when the message occurrence rate is low. A host terminal is connected to the central station C, and user data terminals are connected to the peripheral stations T1 to T4 to form a star network.

FIG. 8 shows a data transmission situation of slotted Aloha.

When using the slotted Aloha scheme, the packet data to be transmitted must be equal in length to a time slot. If the generated data is longer than the length of the time slot, it is divided into packets having a length that can be accommodated in the time slot. If the generated data is shorter than the length of the time slot, the shortage must be filled with dummy data.

[0006]

As described above, the data generated in the peripheral station has a large variation in length. When this is transmitted using a slotted Aloha method using a time slot of a fixed length, when transmitting extremely short data such as data D2 shown in FIG. 8, most of the time slots used are transmitted. However, since the data is filled with dummy data, the efficiency is low.

When the length of a time slot is determined in accordance with the length of short data such as data D2, when a long data such as data D3 occurs, the number of divisions increases and the probability of collision increases. Get higher. Also, in satellite communication, since the header portion such as the preamble portion is large, an increase in the number of packets causes a reduction in data transmission efficiency.

The present invention has been made in such a background, and the data transmission efficiency is improved by using time slots having different lengths in accordance with the distribution of the data length of communication performed at that time. It is an object of the present invention to provide a satellite communication device using a slotted Aloha system with good performance.

[0009]

According to the present invention, there is provided a communication satellite connected to a host terminal and relaying a line from a central station,
In a satellite communication system provided with a plurality of peripheral station devices for transmitting and receiving data to and from the central station device via the communication satellite, the central station device and the peripheral station device use two types of long and short time slots in one frame. And means for receiving and transmitting data by arranging the data in the storage device.

The central station apparatus includes means for changing the composition ratio of the two long and short time slots according to the distribution of the data length currently in progress, and the peripheral station apparatus is changed by the variable means. It is desirable to include means for synchronizing the slot timing with the time slot composition ratio.

A second aspect of the present invention is a central station device of the satellite communication system which is connected to a host terminal and transmits / receives data to / from a communication satellite. Means for arranging the time slots in one frame to receive data, and means for varying the composition ratio of the two long and short time slots in accordance with the distribution of the data length currently in progress. .

A third aspect of the present invention is a peripheral station device, which is a satellite communication type peripheral station device that transmits and receives data to and from the central station device via a communication satellite. Means for arranging the time slots in one frame to transmit data, and means for synchronizing slot timing with the time slot composition ratio changed by the variable means.

[0013]

In the slotted Aloha system, two types of long and short slots are provided as time slots, and the central station monitors the amount of data received within a fixed time and the frequency of retransmission of those data, thereby obtaining long and short slots. Calculate the slot usage rate for each of them, determine the ratio of the number of long slots and short slots suitable for the variation in the length of data generated in the peripheral station, and provide the slot configuration information for notifying the peripheral station of this. create.

The peripheral station creates slot timings for the long slot and the short slot based on the slot configuration information notified from the central station.

The data generated from the user data terminal is divided into long packet data to be transmitted in a long slot and short packet data to be transmitted in a short slot. Further, for data that has failed to be transmitted due to data collision, etc., it is transmitted again with the number of retransmissions added.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a central station device of an embodiment of the present invention. FIG. 2 is a block diagram of a peripheral station device of the embodiment of the present invention.

The present invention relates to a communication satellite S connected to a host terminal for relaying a line from the central station 24, and a plurality of peripheral stations 26 for transmitting and receiving data to and from the central station 24 via the communication satellite S. In a satellite communication system having
The central station device 24 and the peripheral station device 26 are
A center station channel monitoring unit 3, a center station separation unit 4, and a transmission control unit 21 of a peripheral station device 26 as means for arranging types of time slots in one frame to receive and transmit data. It is characterized by.

The central station unit 24 includes a slot configuration determining unit 6 as means for varying the ratio of the two types of long and short time slots in accordance with the distribution of the data length currently in progress. The configuration includes a slot timing generation unit 18 as a unit for synchronizing the slot timing with the time slot configuration ratio changed by the slot configuration determination unit 6 of the variable unit.

Next, the operation of the apparatus according to the embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a diagram showing a transmission frame configuration of the peripheral station device 26. FIG. 4 is a diagram showing a transmission frame configuration of the central station 24. FIG. 5 is a diagram showing the transmission / reception status of the central station C and the peripheral stations T1 to T4 and the slot configuration changing process. FIG. 6 is a diagram showing a packet division situation in the peripheral station device 26.

First, the operation of the central station 24 will be described.

The central office line interface 1 performs transmission and reception with the communication satellite S, and performs frequency conversion between a high frequency band and an intermediate frequency band. The central-station receiving unit 2 demodulates and corrects an error of the signal received by the central-station line interface 1.
The central station channel monitoring unit 3 transmits a CRC (Cyclic R) signal.
The transmission error of the received packet data is detected by using an edundancy check method. Furthermore, if there is no transmission error in the received packet data, the central station channel monitoring unit 3 determines that the data transmitted on the time slot has been correctly received, and in other cases, whether data collision has occurred. , Or that no data has been transmitted in that time slot. Then, the central station channel monitoring unit 3 sends the source peripheral station address of the correctly received data to the reception response signal generation unit 8 and sends the traffic information indicating the number of data correctly received in one frame to the slot. Configuration determining unit 6
To each output. Finally, the central station channel monitoring unit 3 outputs the RE unit and the PL shown in FIG.
, The PC section, the DATA section, and the dummy bit section are transferred to the central station separating section 4. The central station separating section 4 receives the output of the central station channel monitoring section 3 and sends the output to the host terminal connected to the central station apparatus 24 for user data (DATA), effective packet length (PL), and packet retransmission. The information (PC) for assembling is output to the central station reception data buffer 5, and the number of retransmissions (RE) is output to the slot configuration determining unit 6.

The central station receiving data buffer 5 buffers the user data (DATA) received from the central station separating section 4 and refers to the packet reassembly information (PC) and the effective length of the packet (PL). Peripheral stations T1 to T4
Is reassembled into one piece of data, and the data that has not been packetized is delivered to the host terminal as it is.

The slot configuration determining unit 6 transmits slot configuration information 25 for notifying the slot configuration at that time to the multiplexing unit 1.
Output to 0. Further, the slot configuration determining unit 6 knows the amount of data using the long slot and the short slot based on the traffic information received from the central station channel monitoring unit 3 and the number of retransmissions received from the central station separating unit 4, It is determined whether the current slot configuration is appropriate. If the current slot configuration is inappropriate, change the slot configuration. Then, the slot configuration determining unit 6
The new slot configuration is notified to the central station channel monitoring unit 3 and the reception response signal generation unit 8 and output to the multiplexing unit 10. The content of the slot configuration information 25 is also changed to a new slot configuration.

The central station transmission data buffer 7 receives and buffers user data from the host terminal, and outputs it to the multiplexing unit 10.

The reception response signal generation unit 8 creates a reception response signal using the source peripheral station address received from the central station channel monitoring unit 3 and outputs this to the multiplexing unit 10.

The frame timing signal generating section 9, the multiplexing unit 1 frame tie Mi in g signal indicating a break of the frame
Output to 0. At the same time, the frame tie Mi in g signal generator 9 outputs a center station channel monitor 3 a reception frame timing for use in the central station 24 to the receiving the response signal generation unit 8.

The multiplexing section 10 multiplexes the outputs from the slot configuration determining section 6, the central station transmission data buffer 7, the reception response signal generating section 8, and the frame timing signal generating section 9 and multiplexes them with the central station transmitting section 11. Output to

The central station transmitting section 11 adds, to the input from the multiplexing section 10, the user data with a redundant bit for detecting a transmission error by the CRC system, performs encoding and modulation, and applies the redundant bit to the central office line interface 1. Output.

The transmission frame from the central station 24 is as shown in FIG. Along with transmitting the user data, a frame timing signal indicating a frame break of a certain time length is transmitted in the broadcast mode. The frame timing signal serves as a reference for timing used when the peripheral stations T1 to T4 transmit from the own station. The interval at which the frame timing signal is transmitted depends on the channel when the peripheral stations T1 to T4 transmit. Equal to the length of the frame to be split. The central station device 24, following the frame timing signal, receives a response signal to the data transmitted by the peripheral stations T1 to T4,
In the broadcast mode, slot configuration information indicating how many short slots and long slots a frame used for transmission by the peripheral stations T1 to T4 is divided into is transmitted. The reception response signal is transmitted from the peripheral station T which is the source of
The addresses 1 to T4 are arranged in the order of the used slots, and the data could not be normally received due to a slot in which no data was received or a collision or transmission error between data. All "0" is written for the slot. The reception response signal and the slot configuration information are transmitted in units of one frame.

Next, the operation of the peripheral station device 26 will be described.

The peripheral station line interface 12 transmits and receives signals to and from the communication satellite S, and performs frequency conversion between a high frequency band and an intermediate frequency band.

The peripheral station receiving section 13 performs demodulation and error correction processing of the signal input from the peripheral station line interface 12, and outputs the processed signal to the peripheral station separating section 14.

The peripheral station separating section 14 receives the output of the peripheral station receiving section 13, detects the frame timing signal generated by the central station apparatus 24 from the output, and sends the frame timing to the frame synchronizing section 17. Signal confirmation part 2
3, the slot configuration information 25 to the slot timing generator 18 and the user data to the peripheral station channel monitor 15
To each output.

The peripheral station channel monitoring section 15 performs error detection on the user data received from the peripheral station separation section 14 and outputs normally received data to the peripheral station reception data buffer 16.

The peripheral station reception data buffer 16 buffers the user data received from the peripheral station channel monitoring unit 15 and delivers it to the user data terminal.

The frame synchronizer 17 determines the frame timing to be used when the own station performs transmission, taking into consideration the distance between the own station and the communication satellite S based on the frame timing transmitted from the central station C. Then, this is output to the slot timing generator 18.

The slot timing generation unit 18 converts the frame created by the frame synchronization unit 17 into slot configuration information 25
, A predetermined number of long slots and short slots are divided, and slot timing is determined.

The packetizing section 19 receives data from the user data terminal, divides the user data into packets in units of a data length that can be accommodated by the DATA section of one long slot, and outputs the packet to the peripheral station transmission data buffer 20. I do. The packetizing unit 19 also includes information (PC) necessary for reassembling packet-divided data into one piece of data for each piece of data to be delivered to the peripheral station transmission data buffer 20, and information in the packet. Is added to the data effective length (PL). As the packet reassembly information (PC), for example, information such as whether the data is a part of the packet-divided data or whether it is the last data of the packet-divided data is given. Can be

The peripheral station transmission data buffer 20 receives the data from the packetizing section 19 and stores the data in the retransmission number (R
E) is added and buffered, and the transmission control unit 21
Output this to At this time, the peripheral station transmission data buffer 20 buffers long packet data to be transmitted in the long slot and short packet data to be transmitted in the short slot in separate buffers. Further, the peripheral station transmission data buffer 20 holds the data output to the transmission control unit 21 in the primary holding buffer for confirmation of delivery. Then, upon receiving a retransmission or buffer release instruction signal from the delivery confirmation unit 23, data instructed to be released from the hold buffer is deleted from the buffer, and data instructed to be retransmitted is buffered in a dedicated buffer for retransmission data. Re-ring. However, the dedicated buffer for retransmission data also has long packet data to be transmitted in the long slot,
It is assumed that a short packet data to be transmitted in the short slot and a separate buffer are provided. In addition, the peripheral station transmission data buffer 20 sets “0” as the number of retransmissions to the data that has just been input from the packetizing unit 19, and every time the data is re-buffered to the dedicated buffer for retransmission,
This value is incremented by one.

When the transmission control unit 21 receives the output from the slot timing generation unit 18 and knows that the slot timing has come, it recognizes whether it is a long slot timing or a short slot timing, and transmits to the peripheral station. One packet data for a long slot or one packet data for a short slot is read from the data buffer 20 and output to the peripheral station transmitting unit 22. At this time, the transmission control unit 21
Adds the address of the own station (ADRS) to the data to be transferred to the peripheral station transmitting unit 22. Also, the transmission control unit 21
Notifies the delivery confirmation unit 23 of whether data transmission has been attempted in the time slot.

The peripheral station transmitting section 22 adds a dummy bit and a frame sequence check field (FCS) to the input from the transmission control section 21 and further performs encoding and modulation to perform error correction redundant bits (FEC).
And outputs the result to the peripheral station line interface 12.

Receiving confirmation section 23 receives the output from transmission control section 21 and stores in which time slot the own station has attempted transmission, and the reception response output from peripheral station separating section 14. The response to the time slot in which the local station has attempted data transmission is an acknowledgment ACK (A
acknowledgment) or negative acknowledgment NAK (N
ot Acknowledgement). That is, if the reception response signal indicates the address of the own station, it is determined that the response is an acknowledgment ACK. Then, the transmission confirmation unit 23 instructs the peripheral station transmission data buffer 20 to retransmit the data for which the response was a negative response NAK and release the data for which the response is an acknowledgment ACK from the temporary holding buffer.

Next, with reference to FIG. 5, a description will be given of a change in the slot configuration in the apparatus according to the present invention.

Slot configuration determining section 6 of central station apparatus 24
However, the rules for determining whether the slot configuration is appropriate or inappropriate are as follows: (1) The slot configuration determining unit 6 manages two variables: the number of used long slots and the number of used short slots.

(2) When the data using the long slot is 1
The number of long slots used is "1"
Is added. Similarly, when one piece of data using a short slot is correctly received, the number of used short slots is also increased by “1”.

(3) If the number of retransmissions of the received data is not "0", the number of retransmissions is added to the number of used slots.

(4) The slot configuration determining unit 6 determines the slot configuration with reference to the slot usage rate during three frames. The formula for calculating the slot usage rate is as follows: long or short slot usage rate = number of long or short slots used between three frames /
It is assumed that the total number of slots is three frames.

(5) If one of the long slot usage rate and the short slot usage rate is twice or more of the other, the slot configuration determining section 6 changes the slot configuration. (6) The minimum number of each of the number of long slots and the number of short slots in one frame is defined. Even when the usage rate of one slot is extremely high, the other slot is set to “0”. It will not be.

In FIG. 5 , the number of used long slots and the number of used short slots are shown above.

First, the first slot configuration has four short slots and three long slots per frame. Then, the four peripheral stations T1 to T4 transmit data to the central station C by the slotted Aloha method. The central station C transmits the reception response signal for one frame and the slot configuration information 25 to all the peripheral stations T1 to T4 in the broadcast mode during the next frame. In the frame 1, since the short slot data D1 from the peripheral station T4 and the long slot data C1 from the peripheral station T3 are normally received, the number of used slots at the end of the frame 1 is the number of used long slots =
1, the number of used short slots = 1. In the first long slot of the frame 1, the data A1 transmitted by the peripheral station T1 and the data B1 transmitted by the peripheral station T2 collide with each other, so that the central station C can receive the data normally. No, NA for peripheral stations T1 and T2
A K response is returned. Each of the peripheral stations T1 and T2 generates a random number at the time of receiving the NAK response, and retransmits the data A1 and B1 with a slot interval corresponding to the random number. At this time, the number of retransmissions “1” is set in the data A1 and B1.

In frame 3, retransmitted data A
1 and B1 are output to the central station C. When the data A1 is received in the first long slot of the frame 3, the number of used long slots is increased by “1” by receiving one data,
Further, the number of retransmissions “1” is added, and a total of 2 is added. In the second long slot, data B1
Is received, the number of used long slots is also “2”.
Is added.

According to the above rules, the slot configuration determining unit 6 of the central station 24 updates the number of used slots every time one data is received. The number of used slots is “7”, and the number of used short slots is “3”. Here, the slot configuration determining unit 6 calculates the slot usage rate of each of the long slot and the short slot during three frames from frame 1 to frame 3.

The total number of long slots is 9 for three frames.
And the number of short slots is twelve. For this reason, the slot usage rate from frame 1 to frame 3 is 0.78 for the long slot usage rate and 0.25 for the short slot usage rate. At this time, since the long slot usage rate is twice or more the short slot usage rate, the slot configuration determining unit 6 determines to reduce two short slots and increase one long slot. Then, the new slot configuration is changed to all the peripheral stations T1 to T1.
Notify T4 in broadcast mode.

Therefore, after frame 5, the slot configuration per frame is such that two short slots and four long slots are provided.

However, regarding the data received in the frame 4, the slot configuration is being changed, so the number of used slots is not updated.

The packet division in the packetizing section 19 of the peripheral station device 26 will be described with reference to FIG.

Data such as the data D1 and D2, which is shorter than the length of the DATA portion of the long slot, is passed to the peripheral station transmission data buffer 20 as one packet data without being divided into packets. Data D3 and D
As shown in FIG. 4, data longer than the length of the DATA portion of the long slot is divided into two or more pieces of packet data, and is then passed to the peripheral station transmission data buffer 20. Among them, for the packet data shorter than the length of the DATA portion of the short slot, such as the latter half b of the data D1 and D3, the peripheral station transmission data buffer 20 judges this to be the data for the short slot, Buffer in the buffer for

On the other hand, for data longer than the data portion of the short slot, such as the first half a of the data D2 and data D3 and c and d obtained by dividing the data D4, the peripheral station transmission data buffer 20 stores the data. Is determined to be data for a long slot, and is buffered in a buffer for long slot data.

[0059]

By using time slots of different lengths in accordance with the distribution of the data length of the communication being performed at that time, satellite communication can be performed by the slotted Aloha method with high data transmission efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram of a central station device of an embodiment of the present invention.

FIG. 2 is a block diagram of a peripheral station device of the embodiment device of the present invention.

FIG. 3 is a diagram showing a transmission frame configuration of a peripheral station device.

FIG. 4 is a diagram showing a transmission frame configuration of a central station device.

FIG. 5 is a diagram showing a transmission / reception state of a central station device and a peripheral station device and a slot configuration changing process.

FIG. 6 is a diagram illustrating a packet division situation in a peripheral station device.

FIG. 7 is an overall configuration diagram of multiple access satellite communication.

FIG. 8 is a diagram showing a data transmission situation of a slotted Aloha system according to a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 central station line interface 2 central station receiving section 3 central station channel monitoring section 4 central station separating section 5 central station receiving data buffer 6 slot configuration determining section 7 central station transmitting data buffer 8 receiving response signal generating section 9 frame timing signal generating section Reference Signs List 10 multiplexing unit 11 central station transmitting unit 12 peripheral station line interface 13 peripheral station receiving unit 14 peripheral station separating unit 15 peripheral station channel monitoring unit 16 peripheral station receiving data buffer 17 frame synchronizing unit 18 slot timing generating unit 19 packetizing unit 20 peripheral Station transmission data buffer 21 Transmission control unit 22 Peripheral station transmission unit 23 Delivery confirmation unit 24 Central station device 25 Slot configuration information 26 Peripheral station device C Central station S Communication satellite T1-T4 Peripheral station A1-A3 data B1-B4 data C1- C4 data D1 to D4 data

Claims (3)

(57) [Claims] With a 1. A communication satellite for relaying the line from the connected central station apparatus to the host terminal, and a plurality of peripheral stations transmitting and receiving the central station and the data via the communication satellite, this The central station device and the peripheral station device are in a satellite communication system provided with means for receiving and transmitting data by arranging two types of long and short time slots in one frame.
In addition, the central station apparatus can use the two types of time slots, the long and short.
A tie that varies the composition ratio according to the distribution of data length currently in progress
The peripheral station device is changed by the variable unit.
Synchronize slot timing with time slot composition ratio
Means for determining the time slot configuration ratio,
The number of long time slot data used and the short time
Number of lot usage data and retransmission times added to each data
Counts over multiple frames and time slots
Determine the composition ratio of long and short time slots for efficient usage.
A satellite communication system comprising means for determining 2. A frame transmitted by the central station device ,
From the beginning, the frame timing signal section and peripheral station equipment
Indicates the ratio of received response signals and long and short time slots
Including time slot configuration information section and user data section
The satellite communication system according to claim 1, which is configured . 3. A central station device of a satellite communication system connected to a host terminal and transmitting / receiving data to / from a communication satellite, wherein the central station device arranges two types of time slots, long and short, in one frame to transmit data. comprising means for performing reception of the two long and short timeslot configuration ratio determined for varying the distribution of the data length of the time slot configuration ratio ongoing
And the determined time slot composition ratio information.
Means for notifying the peripheral station apparatus, wherein the time slot configuration ratio determining means
The number of long time slot data used and the short time
Retransmission of times that the number of the lot used data Ru is added to each data
Counts over multiple frames and time slots
Change the composition ratio of long and short time slots for efficient utilization.
A satellite communication system center station device comprising means for determining .