JP2611318B2 - Digital satellite communication system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a digital satellite communication system in which a plurality of earth stations are interconnected via a communication satellite via a satellite link composed of digitally modulated waves having different carrier frequencies. ,
In particular, it relates to an improvement of a demand assignment multiple access system.

(Prior Art) A digital satellite communication system to which the present invention is directed is:
A plurality of earth stations use a satellite link composed of digitally modulated waves at different carrier frequencies via communication satellites and assigned a line by a demand assignment system, that is, an SCPC (Single Channel Per Carrier).
r) A communication system that performs two-way communication or one-way communication with at least one other earth station by a communication method.

The demand assignment multiple access system employed in this type of digital satellite communication system has two modes of line assignment control: a centralized control type in which one specific control station concentrates and a distributed control in which each earth station performs independent control. There is a shape. The centralized control type has a drawback that a failure of a specific earth station affects the entire system, but has advantages such as being economical, facilitating charging management, and facilitating operation and maintenance. Therefore, it is considered to be advantageous for satellite communication targeting a limited area such as one country. For example, STAR (Satellite Telecommunication Automa
tic Routing) method is known (Morita, Deep Sea, Yamato et al .: “STAR System,” NEC Research and Development,
No. 8, October, 1966).

On the other hand, the distributed control type has the advantage of the centralized control type. For example, SPADE (Single channel
per carrier PCM multiple Access Demand assignment
Equipment) system is known.

In the demand assignment method, a fixed number of satellite lines are pooled in common for each earth station, and each time a call is generated, a pair of transmission and reception carrier frequencies in the common pool is assigned to it. This is a line allocation method in which allocation is canceled and the satellite line is returned to a common pool. Also, it is well known that a satellite link has a transmission band of a fixed width (that is, a fixed communication capacity) and that a predetermined number of satellite links are arranged at fixed frequency intervals. .

(Problems to be Solved by the Invention) However, the digital satellite communication system employing the conventional SCPC demand assignment multiple access system has the following problems.

First, since each earth station communicates at a constant data rate within a fixedly set communication capacity of a satellite link, a plurality of terrestrial stations through which a plurality of types of information having different data rates are transmitted respectively. In the case of accommodating one terrestrial line in which a plurality of types of information having different lines or data rates are serially transmitted, a plurality of satellite lines corresponding to the number of data rates are required. That is, the earth station has a number of modems corresponding to the number of satellite lines even if there is only one communication partner earth station (modulator or demodulator in the case of one-way communication: hereinafter referred to as a modulator / demodulator).
Is necessary and uneconomical.

The difference in the data rate means that the occupied frequency bandwidth in one satellite link is different. However, when a plurality of pieces of information transmitted on the satellite link have different data rates as described above, the configuration of the conventional satellite link is different. In this method, the frequency bandwidth that can be relayed by the communication satellite, that is, the communication capacity resource of the system cannot be used to the maximum.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a digital satellite communication system capable of arbitrarily assigning a data rate and a carrier frequency of transmission information. .

(Means for Solving the Problems) In order to achieve the above object, a digital satellite communication system of the present invention has the following configuration.

In other words, the digital satellite communication system of the present invention uses a satellite line in which a plurality of earth stations are made of digitally modulated waves of different carrier frequencies via communication satellites, and which has been assigned a line by a demand assignment method. In a digital satellite communication system for two-way or one-way communication with at least one other earth station;
A multi-unit for each earth station or one earth station, which manages the frequency bandwidth and carrier frequency of the satellite link used by each earth station and specifies the data rate and carrier frequency in response to a line assignment request. Providing connection control means; and
A variable-rate modulator or demodulator or modulator / demodulator (hereinafter referred to as a "modem / demodulator") provided at each earth station for each communication partner earth station; detection means for detecting a data rate of a terrestrial line; Control means for receiving the detection output of the detection means, making the line allocation request, and controlling the corresponding one of the modems to operate in conformity with the designated data rate and carrier frequency. It is characterized by the following.

(Operation) Next, the operation of the digital satellite communication system of the present invention configured as described above will be described.

Each earth station includes one modem for each communication earth station, detects the data rate of information transmitted on one or more terrestrial lines accommodated by itself, and issues a line allocation request.

Then, the earth station having the multiple access control means specifies an appropriate data rate and carrier frequency in consideration of the communication traffic volume in the system.

As a result, at the earth station that issued the line allocation request, the corresponding one of the modems is controlled to operate at its specified data rate and carrier frequency.

In short, according to the digital satellite communication system of the present invention, the communication capacity and carrier frequency of each satellite line can be dynamically allocated according to changes in the demand for communication traffic. As a result, each earth station can respond to changes in various communication requests only by providing one modem for each communication partner earth station, thereby simplifying the apparatus and improving the economic efficiency. At the same time, there is an effect that the frequency bandwidth that can be relayed by the communication satellite can be effectively used to the maximum.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a digital satellite communication system and an example of channel assignment control according to an embodiment of the present invention. The digital satellite communication system according to the present embodiment includes:
As shown in FIG. 1, three earth stations via a communication satellite 1
2, 3 and 4 are systems for performing bidirectional communication with each other.

Accordingly, as shown in the figure, there are two satellite links between the earth stations 2 and 3, two links between the earth stations 2 and 4, and three earth stations 3 and 4.
Two lines are respectively set between them, and a common line for demand allocation (CSC: Common Signaling Channel) is provided. As described above, the demand assignment system includes a centralized control type and a distributed control type. In this embodiment, the centralized control type is adopted, and the earth station 3 performs the line allocation control as the central station. is there.

Next, FIG. 2 shows a configuration example of an earth station. FIG. 2 shows the configuration of the earth station 3 which is the central station, but the other earth stations are constituted by the respective elements excluding the parts surrounded by chain lines in FIG.

In FIG. 2, reference numeral 11 denotes an antenna for transmitting and receiving radio waves to and from the communication satellite 1, reference numeral 12 denotes a low-noise amplifier to which the reception output of the antenna 11 is input, and reference numeral 13 denotes a down-converter for converting the amplified output of the low-noise amplifier 12 to an intermediate frequency band. The converter 16 is an intermediate frequency connection circuit. 15 is an up-converter for converting the frequency of the input intermediate frequency band modulated wave into a microwave band, and 14 is an antenna 11
This is a large power amplifier that outputs to Reference numerals 17 and 18 denote traffic modulation, that is, variable speed modems provided for each communication partner earth station. FIG. 2 shows the configuration of the earth station 3, so that the modem 17 is for the earth station 2 and the modem 18 is for the earth station 4. Reference numeral 19 denotes a terrestrial line connection unit. The terrestrial line connection unit 19 has input / output ports for a ground line for the earth station 2 and a ground line for the earth station 4, respectively. And the detecting means according to the present invention. Reference numeral 20 denotes a modem for exchanging the signal of the common line for demand assignment with the earth station 3 as a central station, and reference numeral 21 denotes a demand assignment controller for controlling the rate-variable modulators 17 and 18 in response to a change in traffic. It is a control unit. 23 is a demand assignment multiple access control for assigning a data rate and a carrier frequency according to traffic to each station via a modem 22 for exchanging a signal of a common line for demand assignment with the earth stations 2, 3, and 4; Device.

In the above configuration, first, as shown in the upper part of FIG. 1, communication traffic of the earth station 2 is 1048 kbps with the earth station 3 and 2048 kbps with the earth station 4 at a certain time.
Suppose it was ps.

Similarly, the communication traffic of the earth station 3 is 1048 kbps and 256 kbps between the earth stations 2 and 4, respectively, and the communication traffic of the earth station 4 is 2048 kbps and 2048 kbps between the earth stations 2 and 3 respectively.
Suppose it was 256kbps.

Note that the communication traffic volume between the two earth stations does not necessarily need to match in both directions.

That is, in the earth station 3 shown in FIG. 2, the variable rate modem 17 used for the earth station 2 has a data rate of 1048 kb by the control signal from the demand assignment control section 21.
Set to ps, input / output intermediate frequency is carrier radio frequency
An intermediate frequency corresponding to f ₁ and f ₂ is set. or,
Variable speed modem used for the opposite earth station 4
In No. 18, the data rate is set to 256 kbps, and the input / output intermediate frequency is set to an intermediate frequency corresponding to the carrier radio frequencies f ₅ and f ₆ . From this state, the traffic changes with the earth station 2 and the earth station 4, and the data rate becomes 2048, respectively.
Suppose you changed to kbps and 768kbps. Then, in the terrestrial line connection unit 19, the detecting means automatically detects the change in the data rate and notifies the demand assignment control unit 21 of the change. The demand assignment control unit 21 transmits the new data rate information to the central office using the demand assignment common line via the modem 20. That is, a line assignment request is issued.

Although the earth station 3 is a central station, it is assumed that the earth station 3 passes through the communication satellite 1 in the same manner as other earth stations in consideration of simplification of the apparatus and economic efficiency.

The central office converts the common line signal for demand assignment into a modem 22
Demodulated by the demand assignment multiple access controller (DA
MA CONT) 23 to obtain new traffic (ie, data rate) information at each station. In the DAMA CONT23, the data rate to be used by each earth station and the carrier radio frequency are reassigned according to the traffic change. In this case, the DAMA CONT 23 reallocates the data rate and the carrier radio frequency within a range in which the total sum of the new traffic does not exceed the maximum traffic volume that can be accommodated by the communication satellite 1 and a range of the power. The new data rate and carrier radio frequency information assigned is
The data is encoded by the ONT 23, modulated by the modulator / demodulator 22, and notified to each earth station through the common line for demand assignment.

The earth station 3 demodulates the signal of the common line for demand assignment by the modem 20 and decodes the signal by the demand assignment control unit 21 to know the new data rate and carrier wave radio frequency reassigned to the own station. According to the control signal from the demand assignment control unit 21, the corresponding rate variable type modems 17 and 18 change the input / output intermediate frequency corresponding to the new data rate and the new carrier radio frequency.

Similarly, in the earth stations 2 and 4, the change of the data rate of the line connected to the earth station 3 and the change of the carrier radio frequency are recognized through the common line for demand assignment, and the data rate of the corresponding variable speed type modulator / demodulator is recognized. The input / output intermediate frequency will be changed.

By the above operation, the communication traffic shown in the upper part of FIG. 1 can be automatically changed to the communication traffic shown in the lower part of FIG. 1 in accordance with a change in the demand for the communication capacity.

(Effects of the Invention) As described above, according to the digital satellite communication system of the present invention, the data rate and the carrier radio frequency of the digital modulation wave transmitted or received by each earth station are dynamically allocated according to the communication traffic volume. Therefore, each earth station can respond to changes in various communication requests only by providing one modem for each earth station to communicate with, thereby simplifying the apparatus and improving the economic efficiency. At the same time, there is an effect that the frequency bandwidth that can be relayed by the communication satellite can be effectively used to the maximum.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a digital satellite communication system according to one embodiment of the present invention and an explanatory diagram of channel assignment control.
The figure is a configuration block diagram of the earth station. 1 ... Communication satellite, 2-4 ... Earth station, 11 ... Antenna,
12 ... Low noise amplifier, 13 ... Down converter, 14 ...
High power amplifier, 15… Up converter, 16… Intermediate frequency connection circuit, 17,18… Variable speed modulator / demodulator, 19 ……
Terrestrial line connection unit, 20,22 ... modem, 21 ... demand allocation control unit, 23 ... demand assignment multiple access control device (DAMA CONT).

Claims (1)

(57) [Claims] At least one other earth station is provided by using a plurality of earth stations via a communication satellite, each of which is a satellite link composed of digitally modulated waves having different carrier frequencies and which has been assigned a line by a demand assignment method. In a digital satellite communication system for two-way communication or one-way communication with a station, each earth station or one earth station manages the used frequency bandwidth and carrier frequency of the satellite link used by each earth station. Multiple access control means for designating a data rate and a carrier frequency in response to a line allocation request; and a variable rate modulator or demodulator or modem provided for each earth station at each earth station. (Hereinafter, collectively referred to as “modem”); detecting means for detecting the data rate of the terrestrial line; Digital satellite communication system characterized in that a; that the allocation request corresponding said modem and a control means for controlling to operate to conform to the specified data rate and carrier frequency.