JPH06120859A - Satellite packet communication system - Google Patents

Abstract

PURPOSE:To make the communication of data possible with high quality and with an retransmission request despite the low quality of a satellite circuit by taking out the packet that is normally received based on a prescribed packet selection system at the receiver side. CONSTITUTION:The communication is carried out between a center station C and the compact ground stations T1-Tn and between the station C and the compact reception-only stations R1-Rn via a satellite S. When the information is transmitted from a transmitter side, a packet number, a continuous transmission number, and a frame check sequence are added to the packet to be transmitted. Then the same packet is continuously transmitted through a satellite circuit in plural times shown by the maximum value of the continuous transmission number. Meanwhile at the receiver side, each frame check sequence of plural packets received continuously is calculated. Then one of those packets having the frame check sequences coincident with the calculated one is selected as a packet for normal reception.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite packet communication system for transmitting information in a packet format from a transmitting station to a receiving station through a satellite line, and more particularly to a packet selecting system on the receiving side.

[0002]

2. Description of the Related Art Conventionally, in a satellite communication system capable of two-way communication, when information from the transmission side cannot be normally received by the reception side due to deterioration of the line state, a retransmission request such as ARQ is made and transmission is performed. The delivery confirmation of the ground station communication between the receiving side and the receiving side is being performed.

On the other hand, in a one-way satellite communication system, since it is not possible to make a retransmission request from the receiving side through the satellite line, a retransmission request may be made using the terrestrial line,
Information for error correction is added to correct the error on the receiving side.

[0004]

By the way, the reliability of transmission information in satellite communication is easily affected by rainfall and interference between transmission / reception channels, and especially in an antenna having a small diameter, the reception line is greatly deteriorated. For this reason, a large margin is usually taken in anticipation of deterioration.

However, in the case of a satellite line, an unexpected situation may occur in which the line state is deteriorated beyond the margin. Therefore, when such an unexpected state occurs, it is difficult to accurately reproduce the information from the transmitting side even if the error correction method is used, and there is a problem that the reliability of the system deteriorates. It was

Further, in a one-way satellite communication system, it is economically difficult to secure a return line for making a retransmission request, and therefore it is unexpected that the line state deteriorates beyond the margin. If such a situation occurs, there is a problem that the reliability of the system further deteriorates.

An object of the present invention is to provide a satellite packet communication system capable of communicating information with a constant quality without making a retransmission request even when the line condition deteriorates beyond the margin. Is.

[0008]

In order to achieve the above object, the satellite packet communication system of the present invention adds a packet number, a continuous transmission number and a frame check sequence for error checking to a packet to be transmitted, The same packet is continuously transmitted through the satellite line a number of times indicated by the maximum value of the serial number, and the receiving side calculates each frame check sequence of multiple packets that are continuously received, and matches the calculated frame check sequence. One of the packets having the frame check sequence is selected as a normally received packet.

[0009]

According to the above means, when the information is transmitted from the transmitting side, the packet number, the continuous transmission number and the frame check sequence are added to the packet to be transmitted, and the packet is transmitted only a plurality of times indicated by the maximum value of the continuous transmission number. The same packet is continuously transmitted through the satellite line.

On the other hand, on the receiving side, each frame check sequence of a plurality of continuously received packets is calculated, and one of the packets having a frame check sequence that matches the calculated frame check sequence is selected as a normally received packet. .

Therefore, even if the line condition deteriorates beyond the margin, it is possible to communicate information with a constant quality without making a retransmission request.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In the figure, C is a central station to which a host terminal (not shown) is connected. T1 to Tn are small ground stations and are capable of bidirectional communication. R1 to Rn are small reception dedicated stations and cannot transmit radio waves. User terminals are connected to T1 to Tn and R1 to Rn. S is a satellite. The central station C and the small ground stations T1 to Tn and the central station C and the small reception dedicated stations R1 to Rn communicate with each other via a satellite S. Reference numeral 101 is an outbound line from the central station C to the small ground stations T1 to Tn or the small reception dedicated stations R1 to Rn. 102 is an inbound line from the small ground stations T1 to Tn to the central station C.

FIG. 2 is a block diagram showing the configuration of the central station C. A timing signal generator 210 for generating a timing signal for transmitting the packet shown in FIG. 3 and a baseband signal 201 from a host terminal (not shown). Is formed of a packet generation control circuit 211, a transmission circuit 212, a reception circuit 213, a packet decomposition / combination circuit 214, a data buffer 215, and a high frequency unit 216.

The packet generation control circuit 211 uses, in the data DATA from the host terminal side, a flag sequence F indicating the beginning of the packet shown in FIG. 3, an address part ADR, a control part CTR, a packet number PN, a continuous transmission number RN, and a frame check. A sequence FCS and a flag sequence F indicating the end of the packet are added and transferred to the transmission circuit 212 in accordance with the packet timing generated by the timing signal generator 210. At this time, packet division is performed according to the length of the user data. Further, according to the frame timing shown in FIG. 3, a packet FTC for performing frame timing and control is transmitted to the head of the frame.

The transmission circuit 212 is a packet generation control circuit 2
The baseband signal from 11 is converted into the intermediate frequency band signal 20
3 and supplies to the high frequency part 216.

The high frequency section 216 is provided with the intermediate frequency band signal 203.
Is converted into a high frequency band signal and transmitted to the satellite S. Further, the high frequency unit 216 receives the signal from the satellite S, converts it into the intermediate frequency band signal 204, and supplies it to the receiving circuit 213.

The receiving circuit 213 converts the intermediate frequency band signal 204 from the high frequency section 216 into the base band signal 202 and transfers it to the packet disassembling / combining circuit 214.

The packet disassembling / combining circuit 214 removes the header part and the footer part from the received packet, combines the original user data, and transfers it to the data buffer 215.

The host terminal (not shown) is a data buffer 2
Data is received via 15.

FIG. 3 is a frame structure and packet structure diagram of information to be transmitted and received, and one frame is composed of n packets and FTC packets.

The FTC packet is a packet used for timing and control of the frame, and is placed at the head of the frame.

A packet is represented by a bit string surrounded by a flag sequence F. The structure of this packet is AD
It consists of R, CTR, PN, RN, DATA and FCS.
ADR is an address part. CTR is a packet number, and PN is constant while continuously transmitting DATA having the same content. RN indicates a serial transmission number when continuously transmitting DATA having the same content. DATA is user data.
FCS is a frame check sequence for error checking.

FIG. 4 is a diagram showing an array for storing a packet received from the partner station, which is PB (1) to PB (R).
NM) is the packet arrangement, RNM is the maximum number of consecutive transmissions,
FCSR uses received PN, RN, DATA to perform FC
This is the value after S processing, and the maximum number of received packets is R
NM pieces can be arranged.

FIG. 5 is a block diagram showing the configuration of the receiving devices of the small ground stations T1 to Tn and the small receiving stations R1 to Rn. A receiving circuit 510, a packet selecting circuit, which receives from the central station C, converts the intermediate frequency band signal 501 converted by a high frequency section (not shown) into a base band signal 502 and supplies it to a packet selecting circuit 511 and a packet disassembling / combining circuit 512. 511, a packet disassembling / combining circuit 512, and a data buffer 513.

The packet selection circuit 511 obtains the packet number PN and the number of continuous transmissions RN from the received packets, and the data normally received according to the packet selection method shown in the flowcharts of FIGS. 6 to 8. The signal 503 for selection is notified to the packet disassembling / combining circuit 512.

The packet disassembling / combining circuit 512 stores the received packet in the packet array shown in FIG. The storage method at this time follows the packet selection method. In addition, the data normally received according to the instruction of the packet selection circuit 511 is combined with the original user data and transferred to the data buffer 513.

The data buffer 513 is connected to a user terminal (not shown), and the user terminal uses the data buffer 5
Data is received via 13.

6 to 8 are flowcharts showing a packet selection method for selecting a packet received from the partner station.

Here, as the data transmitted from the central station C, as shown in FIG. 9, 6 characters A, B, C, D and E are transmitted by 3 characters per packet, and in FIG. As shown, the case where each packet is transmitted three times will be described as an example.

First, the processing shown in this flow chart is started when the receiving side receives a packet.

First, in step 601, the number PN of the first packet PB (1) in the packet array of FIG. 4 is compared with the packet number PN of the received packet. When the packet number of the packet array 1 is large (PN of PB (1)>
PN) waits for the next packet timing. That is,
Packets are transmitted from the transmitting side in the order of packet numbers, and are stored in the receiving order in the array of FIG. Therefore, in the case of PN> PN of PB (1), the packet with the received packet number PN has already been received, so it is ignored and the process returns to the waiting for the next packet.

On the contrary, when PN <PN of PB (1),
Since the next packet has arrived without being normally received due to the reason that the packet before the received packet is lost in the line, the array of FIG. 4 is cleared in step 603, and the count variable CNT is set to The consecutive transmission number RN of the packet received this time is substituted, and in the next step 604, the packet array is updated to that of the packet received this time.

However, if PN = PN of PB (1), it means that the packets have been received in the normal continuous transmission order. Therefore, in step 602, PN and R of this received packet are received.
Substitute N, DATA, and FCS in the row of PB (RN) of the packet array.

Next, at step 605, the FCS processing of the packet newly received this time and stored in the packet array is performed. That is, the FCS of the PN, RN, and FCS is calculated, and this is stored as the FCSR in the FCSR column in the same row of the packet array.

Next, in step 606, the RN of the packet received this time is substituted into the count variable i. The processing of steps 606 to 609 compares the FCSR of the packet received this time among the packets received so far with the FCR of the packet already received, and FCSR = FC
When it is R, the packet received this time is recognized as a normal packet.

That is, as a form in which an error occurs in a packet, as shown in FIG. 11A, PN, RN, DA
A receiving state in which TA has a bit error and FCS has no bit error, as shown in (b), PN, RN, D
The reception state that ATA has no bit error and FCS has bit error, as shown in (c), PN, RN,
A reception state in which there is a bit error in DATA and FCS, and a reception state in which there is no bit error in both PN, RN, DATA and FCS as shown in (d).
There are two reception states.

The reception state of (d) is immediately processed as a normally received packet by the processing of step 601 unless there is an error in the arrival order.

Then, the count variable i is set to step 608.
Then, i = RN is decremented by one, and the FCR of the packet already received and the FCSR of the packet received this time are
And are sequentially compared. As a result, the FC of the packet received this time is added to one of the FCRs of the packets already received.
If there is a packet that matches SR, the packet received this time can be identified as having been received in the state of FIG. 11D, so it is extracted as a normal packet in step 610, and the packet decomposing / combining circuit 512 outputs the data buffer. The packet array of FIG. 4 is cleared in step 611, and the count variable CNT is returned to “0”. Further, in step 612, the next packet number is set to the packet array 1
Set to the second and wait for reception of the next packet number.

At step 613, the count variable CNT
And RNM are compared, and it is checked whether the received packet has reached the order indicated by the maximum value of the continuous transmission number. If the received packet is the maximum continuous transmission number, the processing from step 615 is performed. If the maximum number of consecutive transmissions has not been reached, “1” is added to the count variable CNT in step 614,
Wait for reception of the next packet.

On the other hand, the reception state of (a) is normal for FCS, but cannot be adopted because there is an error in PN, RN, and DATA. The same applies to the packet in the reception state of (c).

However, the packet in the reception state of (b) is P
Since there is no error in N, RN, and DATA but only in FCS, PN, RN, and DATA can be adopted.

In step 615 and thereafter, the packet in the reception state shown in FIG. 11B is detected from all the packets received so far, and the data portion thereof is adopted.

Therefore, in step 615, the count variable j is initialized to j = 1.

Then, in step 616, PB (j + 1) to PB (RNM) are searched from the packet array having the same packet number using DATA as a key.

As a result, if there is a packet having DATA that matches DATA as the key (step 6)
17) In the next step 621, it is checked whether or not the FCSRs of the matched packet arrays are the same, and if they are the same, it is recognized as a normally received packet (step 622), and the entire array of the same packet number and the count variable CNT are cleared. (Step 623), the next packet number is set to the first packet array (step 624), and the next packet timing is waited for.

However, if the FCSRs do not match, the search is repeated while updating the count variable j by 1 (step 620).

The count variable j is the maximum number of consecutive transmissions R.
If you can not search even if it becomes the same as NM (Step 6
18) All packets are identified as packets having a reception error (step 619), and the entire array of the same packet number and the count variable CNT are cleared (step 6).
23), set the next packet number to the first packet array (step 624), and wait for the next packet timing.

In the above embodiment, the communication mode between the communication station, the reception-only station and the small ground station has been described as an example, but the communication between the earth station capable of both transmission and reception is possible. The same can be applied to the communication in.

[0050]

As described above, according to the present invention, at the time of data transmission, the packet number, the number of consecutive transmissions, and the packet to which the frame check sequence is added are transmitted in accordance with the consecutive transmission number
Since the receiving side extracts the normally received packet according to the predetermined packet selection method, high quality data communication can be performed without requesting retransmission even if the quality of the satellite line is low. As a result, high reliability can be ensured even in a system having an antenna with a small diameter and a one-way communication system.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a central station C.

FIG. 3 is a diagram showing a frame structure and a packet structure of information.

FIG. 4 is an array diagram for storing received packets.

5 is a block diagram showing a configuration of a receiving device of a small ground station R and a small receiving dedicated station R. FIG.

FIG. 6 is a flowchart illustrating a packet selection method.

7 is a flowchart following on from FIG. 6;

FIG. 8 is a flowchart following on from FIG. 7;

FIG. 9 is an explanatory diagram showing an example of a packet to be transmitted.

FIG. 10 is an explanatory diagram showing a continuous transmission form of packets to be transmitted.

FIG. 11 is an explanatory diagram showing a form of bit error of a received packet.

[Explanation of Codes] C ... Central station, S ... Satellite, T1 to Tn ... Small ground station, R1
-Rn ... Small receiving station, 101 ... Outbound line, 102 ... Inbound line, 201, 202 ... Baseband signal, 203, 204 ... Intermediate frequency band signal, 2
10 ... Timing signal generator, 211 ... Packet generation control circuit, 212 ... Transmission circuit, 213 ... Reception circuit, 214
... Packet disassembly / combination circuit, 215 ... Data buffer,
216 ... High frequency section, FTC ... Frame timing and control section, F ... Flag sequence, ADR ... Address section, CT
R ... Control unit, PN ... Packet number, RN ... Continuous transmission count, DATA ... User data, FCS ... Frame check sequence, PB ... Packet array, RNM ... Maximum continuous transmission count, FCSR ... PB FCS calculated after reception, 5
01 ... intermediate frequency band signal, 502 ... baseband signal,
503 ... Packet selection notification signal, 510 ... Reception circuit, 5
11 ... Packet disassembling / combining circuit, 512 ... Packet disassembling / combining circuit, 513 ... Data buffer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinsaku Okamura 1-26-5 Toranomon, Minato-ku, Tokyo NTT Data Communications Corporation

Claims (2)

[Claims] 1. In a satellite packet communication system in which information is transmitted from a transmitting station to a receiving station in a packet format through a satellite line, a packet to be transmitted is provided with a packet number, a continuous transmission number, and a frame check sequence for error checking. The same packet is continuously transmitted over the satellite line a number of times indicated by the maximum value of the serial number, and the receiving side calculates each frame check sequence of multiple packets received continuously, and the calculated frame check sequence A satellite packet communication system characterized in that one of the packets having a frame check sequence matching with is selected as a packet for normal reception. 2. The satellite according to claim 1, wherein the receiving side monitors the arrival order of the received packets, and only when the arrival order matches the serial number of the received packet, the frame check sequence collation processing is started. Packet communication method.