JPH03286629A - Communication system - Google Patents

Abstract

PURPOSE:To improve S/N by providing a transmission level adjustment circuit on an earth station so as to make the difference of subtracting the reception level of its own station loopback signal from a reception level of a pilot loopback signal equal to a predetermined difference. CONSTITUTION:This system is provided with a pilot station 14 always sending the pilot signal of a prescribed transmission level. Each of 1st and 2nd earth stations is provided with a transmission level adjustment circuit 10, which receives a pilot loopback signal resulting from the pilot signal looped back on a communication satellite 13 and its own station loopback signal resulting from a transmission signal sent from its own station and looped back on the communication satellite 13 and adjusts the transmission level of the transmission signal of its own station so that a difference obtained by subtracting the reception level of own station loopback signal from the reception level of the pilot loopback signal is equal to a predetermined difference.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a first and a second small earth station, and a communication satellite between the first and second small earth stations. The present invention relates to a communication method for mutually communicating through a communication network.

[Prior Art] In communications between small earth stations via communication satellites, reception levels vary depending on differences in weather conditions, geographic conditions, functional conditions, etc. between the local station and the communication partner. Therefore, in order to achieve optimal reception conditions at a small earth station, generally
The receiver of the small earth station uses an AGC (automatic gain control) circuit and a limiter circuit.

[Problem to be solved by the invention] However, these AGC and limiter processing on the receiver side only correct the reception level, and the reception f! It was not possible to improve the signal-to-noise power ratio at the machine input end.

An object of the present invention is to provide a communication system that can improve the signal-to-noise power ratio.

[Means for Solving the Problems] According to the present invention, there is provided a first and second earth station, and the first and second earth stations communicate with each other via one communication satellite. In the communication system, a pilot station is provided that always transmits a pilot signal at a constant transmission level, and each of the first and second earth stations transmits either the pilot signal or a pilot return signal returned by the communication satellite. and a local station return signal in which the transmission signal transmitted by the own station is looped back by the communication satellite, and is obtained by subtracting the reception level of the own station return signal from the reception level of the pilot return signal. A communication system is obtained that is characterized by having a transmission level adjustment circuit that adjusts the transmission level of the transmission signal of its own station so that the difference is equal to a predetermined difference.

[Operation] In the present invention, when there is a level fluctuation due to rain attenuation, for example, on the uplink from the earth station, the level fluctuation is compensated for by increasing the transmission power.

Therefore, the signal-to-noise power ratio in the uplink is kept constant, and reception characteristics can be improved compared to conventional level compensation on the receiver side.

[Example] Next, an example of the present invention will be described with reference to the drawings.

Referring to FIG. 1, the communication system according to one embodiment of the present invention has first and second small earth stations 11 and 12, and the first and second small earth stations 11 and 12 are connected to a communication satellite 13. communicate with each other via.

Of course, there may also be third and fourth small earth stations that can communicate with the first and second small earth stations 11 and 12 via the communication satellite 13.

One pilot station 14 is provided for each communication satellite 13, and always transmits a pilot signal at a constant transmission level.

Each of the first and second small earth stations 11 and 12 receives a pilot return signal in which the pilot signal is returned by the communication satellite 13, and a transmission signal transmitted by the own station or an own return signal obtained by returning the pilot signal by the communication satellite 13. receive the station return signal,
The transmission level of the transmission signal of the own station is set such that the difference obtained by subtracting the reception level of the own station return signal from the reception level of the pilot return signal is equal to a predetermined reference level difference 20. It has a transmission level adjustment circuit (10 in FIG. 2) which will be described later for adjustment.

In this embodiment, the TDMA method is assumed as the communication method, and the small earth stations 11 and 12 and the pilot station 14 transmit a unique word including a source code when transmitting a signal. The receiving station can identify the source of the received signal by detecting the unique word from the received signal.

Referring to FIG. 2, the transmission level adjustment circuit 10 in each of the small earth stations 11 and 12 includes a reception circuit 15, a reception level detection circuit 16, a level difference measurement circuit 17, a transmission level setting circuit 18, It has a transmitting circuit 19.

In each small earth station, a reception level detection circuit 16 detects the reception level of the pilot return signal and the own station return signal among the burst signals received by the reception circuit 15.

The level difference measurement circuit 17 subtracts the reception level of the local station return signal from the reception level of the pilot return signal and outputs the difference obtained as a measured level difference.

The transmission level setting circuit 18 compares the level difference obtained by the level difference measurement circuit 17 with a predetermined reference level difference 20, increases the own station's transmission level based on the comparison result, and sets the transmitting circuit. Defines one output level.

That is, when the measured level difference is smaller than the reference level difference 20, the transmitting circuit 19 increases the own station transmission level, and in the opposite case, decreases the one station transmission level. In other words, the transmission circuit 19 controls the transmission level of its own station so that the measured level difference becomes the reference level difference 20.

It is assumed that the pilot station 14 compensates in advance for level fluctuations due to transmission level fluctuations of its own station equipment, rain attenuation around the own station, and the like.

As a result, the reception level at the small earth station of the signal transmitted from the small earth station 11 or 12 and returned by the communication satellite 13 will have a certain level difference based on the pilot signal, no matter what earth station it is looking at. .

Referring again to FIG. 1, the operation of the communication system of this embodiment will be explained. The pilot station 14 always transmits pilot signals regardless of the presence or absence of communication. Assuming that the small earth stations 11 and 12 are currently communicating, the small earth station 11 adjusts its own transmission level using the above-mentioned transmission level adjustment circuit 10, so from the perspective of the small earth station 12, The received signal received by the small earth station 12 from the small earth station 11 via the communication satellite 13 is based on the pilot signal.
It is at a certain level.

At this time, if there is rain attenuation around the small earth station 11, the upstream signal of the small earth station 11 will be attenuated before reaching the communication satellite 13. Since the transmission power of the own station is increased, the return signal is maintained at a constant level with respect to the pilot signal.

Therefore, from the perspective of the small earth station 12, there is no effect of rain attenuation around the small earth station 11, and the signal-to-noise power ratio is also constant.

[Effects of the Invention] As explained above, according to the present invention, even if there is a level fluctuation on the uplink from the earth station, the signal-to-noise power ratio on the uplink is kept constant, and the conventional receiver The reception characteristics can be improved compared to level compensation on the side.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a communication system according to an embodiment of the present invention, and FIG. 2 is a block diagram of a transmission level adjustment circuit in each of the small earth stations of the communication system of FIG. 1. 11 and 12 are small earth stations, 13 is a communication satellite, 14 is a pilot station, 10 is a transmission level adjustment circuit, 15 is a reception circuit, 16 is a reception level detection circuit, 17 is a level difference measurement circuit, and 18 is a transmission level setting circuit. , 19 is a transmitting circuit, 20
is the reference level difference. jll Figure 1N2 Figure 1 8

Claims (1)

[Claims] A communication system comprising: 1, a first earth station, and a second earth station, wherein the first earth station and the second earth station communicate with each other via one communication satellite, comprising: a constant transmission level; A pilot station is provided that always transmits a pilot signal, and each of the first and second earth stations transmits a pilot return signal obtained by returning the pilot signal by the communication satellite, and a pilot return signal transmitted by the own station. A difference obtained by subtracting the reception level of the own station return signal from the reception level of the pilot return signal by receiving the transmission signal and the return signal of the own station returned by the communication satellite is determined in advance. A communication system comprising a transmission level adjustment circuit that adjusts the transmission level of the transmission signal of its own station so that the difference is equal to the difference.