JPS6367779B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a satellite communication system, and particularly to a data transmission system using satellite communication.

SCPC (Single Channel Per) is currently widely used as a data transmission method by satellite.
Carrier: There is a single channel per carrier) method. This divides the transmission band of a satellite transponder into multiple satellite channels with different frequencies, and allocates one satellite channel for data transmission from a station A to a station B in the system. The RF carrier at the satellite channel frequency is PSK modulated and transmitted, and the B station sets its demodulator to this frequency to receive and demodulate the data transmitted via the satellite. Of course, for other data transmissions from station C to station D in the system, a satellite channel with a different frequency is assigned and the same method as above is used to transmit data from C to D at the same time as the transmission from A to B. transmission can be carried out. In this way, using the SCPC method, data can be transmitted from any station in the system to any other station, but as mentioned above, data lines using these SCPC methods are used for pre-assignment operation (i.e., the transmission destination is (predetermined line operation). However, on the contrary, A
Even if a station suddenly wants to transmit data to station C, if the data line from station A to station C has not been prepared in advance, the disadvantage is that the data cannot be transmitted from station A to station C without permission. There is.

On the other hand, a packet data transmission method using satellite communication is a method that can be effectively utilized due to the characteristics of satellite communication. First, the data to be transmitted is divided into blocks of a certain length, a header containing information such as destination and source is added to the blocks, and the data is converted into information units called packets having a certain format. Each earth station uses this packet to perform PSK modulation on a burst-like carrier of the same frequency and approximately the same length as the packet, and transmits it to the same transmission band of the satellite. The satellite receives these PSK packets from each earth station and returns them to the downlink. Each earth station can obtain packets from all stations by receiving and demodulating this transmission band of the satellite, but from among these, it selects the packet containing the header addressed to its own station and sends it to the ground line. . By adopting this method, data can be freely transmitted from any earth station in the system to any other earth station, and the multiple access and broadcast characteristics of satellite communications are fully utilized. This enables a highly efficient data transmission method to be achieved.

However, this method also has the following difficult problems.

First, when the packets sent from each earth station pass through the same transmission band of the satellite, complex timing control is required for the timing of the packets sent from each station to prevent them from overlapping each other. . There is also the so-called Aloha method, which does not perform this timing control, but instead uses some method to detect when a packet overlaps with another packet and retransmits the same packet, but this method is not suitable for increasing line efficiency. Appropriate.

Second, these packets are of the same frequency.
The RF carrier is generally transmitted by PSK modulation, but in order to demodulate it, a carrier regeneration circuit for burst mode that extracts and generates a carrier for synchronous detection from each received packet signal within a short time,
Similarly, a demodulator for burst mode is required that has a bit timing recovery circuit for burst mode that extracts and generates a clock for sampling data from each received packet signal within a short time. Furthermore, in order to operate the burst mode demodulator correctly, it is necessary to add special preamble signals for carrier recovery and bit timing recovery to the beginning of each packet. These generally complicate the configuration of the modem and
It has the disadvantage of deteriorating the BER characteristics and increasing signal overhead (extra bits that must be added to transmit data).

SUMMARY OF THE INVENTION An object of the present invention is to provide a satellite data transmission system that eliminates the above-mentioned conventional drawbacks.

The method of the present invention is a satellite data transmission method in which data is transmitted between a plurality of first stations and at least one second station via a communication satellite, and the information from the first station is A carrier of a different frequency is PSK-modulated for each of the first stations and transmitted to the second station, the transmitted information is stored in the second station, and the stored information is read out. The continuous carrier of the second station is time-division PSK modulated and transmitted to the first station.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In this embodiment, a plurality (n) of relatively small-scale earth stations (hereinafter referred to as small stations) 1-1, 1-2, ..., 1-
This is a satellite communication system consisting of satellites k, .

An arbitrary small station 1-k is composed of a packet transmitting terminal 11, an SCPC transmitting section 12, and an air section 13 in the transmission direction. packets in a predetermined format with
Via the SCPC transmitter 12 and the antenna section 13, the carrier of the satellite channel frequency for SCPC assigned to that station is PSK-modulated and transmitted toward the communication satellite 2. In the communication satellite 2, SCPC packets from each of these small stations are amplified in common by an SCPC transponder 21, and then returned to the downlink. These SCPC packets are transmitted on different satellite channels (different frequencies), so even if they overlap in time, collision interference between the packets will not occur.

Now, the downlink SCPC packet is
In the general scheme 3, SCPC receiving units 32-1, 32- receive each SCPC satellite channel inputted via the antenna unit 31 and assigned in advance.
2,..., 32-k,..., 32-n, and its output is sent to each output line 330-1 to 330.
-n to the packet accumulation processing unit 33.

At the same time, the data to be transmitted from the large station 3 to the small stations is converted at the packet transmitting terminal 34 into a packet in a predetermined format with a header containing information such as the destination source, in the same way as at the terminal 11, and sent to the terminal. 34 output lines 330-n+1 to the packet accumulation processing section 33.

FIG. 2 is a block diagram showing details of the packet accumulation processing section 33. Each of the output lines 330-1
The packets supplied from 330-n and 330-n+1 are respectively stored in input registers 331-1 to 331-n and 331-n+1 connected to their respective output lines. When the storage of a packet in a certain arbitrary input register 331-k is completed, the read control circuit 332 immediately reads and decodes the destination part of the header of the packet stored in this register 331-k. If the packet is for
It is transferred and stored in the TDM packet buffer 333. If the destination is for the general station (that is, for the local station), the entire packet is read out from this register 331-k and transferred and stored in the receiving terminal packet buffer 334. Thus TDM
The packet with the header destined for the small station stored next in the buffer 333 is sent to the TDM transmission clock 360 supplied from the TDM transmission section 36.
One bit at a time is read out to the output line 337, starting from the first bit of the previously stored packet, according to the first-in-first-out rule (FIFO).
The signal is supplied to the TDM transmitter 36. Similarly, a packet with a header for the global destination stored in the receiving terminal buffer 334 is sent to the packet receiving terminal 35.
The signal is read out to the output line 338 according to the FIFO using the clock 350 supplied from the packet receiving terminal 35. Packet receiving terminal 3
The packets supplied to No. 5 undergo necessary processing here and are sent out to the ground line.

On the other hand, packets whose header is destined for a small station are
via output line 337 as previously described.
The signal is supplied to the TDM transmitter 36, where the continuous mode is modulated by PSK.
The packet is transmitted as a TDM-PSK packet to the communication satellite 2 via the antenna section 31.

Continuous mode TDM-PSK sent out in this way
The packet is returned to the downlink via the TDM transponder 22 of the communication satellite 2.

The multiple small stations 1-1 to 1-n receive the TDM-PSK packets input via the antenna section 13 of each station.
The TDM-PSK receiving unit 14 receives and demodulates the packets, and the packet receiving terminal 15 selects only those packets having a header addressed to the local station, performs necessary processing, and sends them to the ground line.

In this way, in the system of this embodiment, a packet sent from a certain small station destined for another small station is
It is immediately transmitted to Broadcasting 3 via the SCPC channel. The packets sent out randomly from each of these small stations are temporarily stored in the packet storage processing unit 33 of the large station 3, and are sequentially read out in the order of arrival, so that TDM packets that do not overlap in time are stored.
The packets are again transmitted as packets to the small station via the satellite 2, and from among the TDM packets demodulated at the destination small station, the packets having this destination are selected by the terminal 15 and transmitted to the destination.

In this way, in the method of this embodiment, even when transmitting data from one small station to another,
It takes the form of passing through Itsutan Daichu 3. Although this seems complicated at first glance, it has various excellent features as described below.

First, the lines from each small station 1-1, ..., 1-n to the large station use the SCPC method with different frequencies, so each small station can operate completely independently and freely without interfering with other stations. packets can be sent to In order to use the satellite's EIRP (effective radiated power) as effectively as possible, it is relatively easy to use a burst mode operation modulator on each transmitting side (small station), which transmits a carrier only when transmitting a packet. , it is not a huge financial burden. On the other hand, in the big picture 3 that receives this,
Antenna section 3 with a large antenna with a large G/T
1, each SCPC receiving section 32-1 to 32-n can receive SCPC packets from each station with a sufficiently higher C/N than that received by a small station.
Even when operating in burst mode, critical performance is not required compared to when used in small stations.

Next, as already described in detail, the packet storage processing unit 33 sequentially stores randomly supplied packets destined for the large station or for the small station into the receiving terminal buffer 334 or the TDM packet buffer 333 depending on the destination. For the latter, TDM packets are generated by sequentially reading out the stored packets on a first-come, first-served basis using a TDM transmission clock. Said TDM
As long as the overflow of the packet buffer 333 is taken care of, the TDM transmission clock can be selected independently of the packet transmission timing from each station, making it possible to extremely easily transmit TDM packets without using complicated time control. can occur. How simple this is compared to traditional methods becomes clear as follows.

In other words, conventionally, when the packets sent from each station pass through the satellite's transponder, it is necessary to control the timing of each station's packet sending so that they do not overlap with each other and there is as little time as possible between them. This is because (i) each station is far away from each other and there is no easy way to know whether the other station is currently trying to send data, and (ii) the distance from the satellite varies from station to station, and This is extremely complex and difficult for two reasons: the distance changes with the movement of the satellite. However, once these packets are collected in the same place as in this embodiment, it becomes difficult to pass them through the satellite transponder so that they do not overlap each other and leave no gaps between them, as described above. It becomes extremely easy.

Next, the TDM packets converted into serial data are transmitted again to each small station via satellite 2, except for packets for the large station, but this transmission is not in burst mode, but in continuous mode. Continuous mode can be used to PSK modulate the carrier. Therefore, each small station's TDM-PSK receiving section 1
Since the demodulator included in No. 4 may be a continuous mode demodulator, the above-mentioned carrier recovery circuit and bit timing recovery circuit can be operated easily and reliably, and the BER performance can be improved accordingly.
This allows a large number of small stations to use small antennas with a lower G/T, thus contributing to the economicalization of the entire system.

According to this embodiment, data transmission from one small station to another is a two-hop satellite transmission as described above, but since this is data transmission, the delay caused by this is not a big problem. In particular, data traffic between local areas (small stations) and the central government (large stations) is overwhelmingly greater than traffic between local areas (small stations) and local areas (small stations), such as in administrative data communication networks. In communication networks, most of the traffic is 1
Just a hop.

In the above embodiment, each station has a packet transmission terminal, and the data to be transmitted is first converted into packet format and then transmitted to the large station, but instead of doing this, each small station is sent raw. data along with necessary header information is sent to the large station via the SCPC line, and the large station demodulates the received information from this SCPC line, supplies it to the small station packet transmission terminal installed at the large station, and the terminal It is also possible to create packets based on the transmitted data and head information and supply them to the packet accumulation processing section 33 in the order of occurrence. In this way, each of the packet transmitting terminals 11
Instead of placing the information in small areas, it is possible to collect it in a large area and use the possible parts in common, making the system as a whole more economical.

In addition, in the above embodiment, the SCPC method was used as the packet line from the small station to the large station, but this is not limited to the SCPC method. For example, the PSK-MCPC method (a method of transmitting multiple channels using one PSK-modulated carrier) or other methods may be used as long as the line is capable of transmission.

Furthermore, in this embodiment, the transponder 21 of the communication satellite 2 that transmits signals of the SCPC method and the transponder 21 of the communication satellite 2 that transmits signals of the TDM method
Although the transponders 22 are different from each other, it is of course possible to use the same transponder with different transmission bands.

Further, in this embodiment, the packet accumulation processing section 33 temporarily stores the supplied packets, and reads them out in the order of the supplied time.
We have created TDM signals, but instead of arranging them in order of arrival time, we read them out according to a predetermined algorithm (for example, collect and read data for the same small station as much as possible), and transmit it to the local station at the small station. It is also possible to reduce the burden of selecting the target packet.

Furthermore, in the above embodiments, a satellite communication system that is composed of a plurality of small stations and one large station has been described, but it may also be possible to have a large number of small stations and a decimal number of large stations. The invention can be applied in much the same way. In other words, the entire system is divided into multiple subgroups each containing one global view, data is transmitted within each subgroup using the same method as described above, and data is transmitted between each subgroup using the same method as described above. is SCPC or
Data exchange may be performed using TDM transmission. That is, when a small station A1 in subgroup A sends data to a small station B1 in subgroup B, station B1 is designated as the destination of the header of the packet from A1. This packet reaches the packet storage processing unit of the large station A0 in subgroup A as described above, but when it is decoded from the header destination that it is addressed to the small station in subgroup B, this packet is Packets are transferred from the A0 station to the B0 station (the main station of subgroup B) via the data line (this is based on the SCPC method depending on the required traffic capacity).
(TDM method or other methods can be selected) to the B0 station. (In other words, the function of the packet storage processing unit in this case is to connect the header destination of each supplied packet, and if it belongs to the subgroup of the own station, process it in the same way as described above. (In addition to this, if this destination belongs to another subgroup, an additional switching function is included to output to the data line connecting the own station and the main station of that subgroup.)B0 In the station, the packet accumulation processing section of the B0 station handles the packets supplied from the data line between the A0 and B0 stations in the same way as packets transmitted from the small stations in subgroup B. That is, the packet with the header addressed to the B1 station mentioned above is processed by the packet storage processing unit of the B0 station into a TDM-directed packet destined for subgroup B.
The PSK signal is sent to the line, selected by the packet receiving terminal of the B1 station, and reaches the destination.

As described above, by using the present invention, in a satellite communication system including a small number of large stations and a large number of small stations,
It is possible to provide a satellite data transmission system that performs highly efficient data transmission using packets without requiring each station to perform complicated transmission timing control.

This makes it possible to make the satellite communication system highly reliable and economical.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the satellite data transmission system of the present invention, and FIG. 2 is a block diagram showing details of a packet accumulation processing section in the embodiment. In the figure, 1-1, 1-2,..., 1-k,
..., 1-n...Small station, 2...Communication satellite, 3...Big station, 11...Packet transmitting terminal, 12...SCPC
Transmitting section, 13...Antenna section, 14...TDM-
PSK receiving section, 15...Packet receiving terminal, 21
...Transponder for SCPC, 22...Transponder for TDM, 31...Antenna section, 32-1,
~32-n...SCPC receiving unit, 33...Packet storage processing unit, 34...Packet transmitting terminal, 35...
...Packet receiving terminal, 36...TDM transmitter, 3
30-1 to 330-n+1...Output line, 33
1-1 to 331-n+1...Input register, 33
2... Readout control circuit, 333... TDM packet buffer, 334... Receiving terminal packet buffer, 337, 338... Output line, 35
0...Clock input line, 360...Clock input line for TDM transmission.

Claims (1)

[Claims] 1. In a satellite data transmission system in which data is transmitted between a plurality of first stations and at least one second station via a communication satellite, information from the first station is different for each first station. A frequency carrier is PSK modulated and transmitted to the second station, the transmitted information is stored and stored in the second station, and the stored information is read out and the continuous carrier of the second station is transmitted. A satellite data transmission system characterized in that the data is time-division PSK modulated and transmitted to the first station.