JPS5841013B2 - Initial path length equalization method in diversity for satellite communications - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to TDMA space diversity in a satellite communication system, and particularly to an initial channel length equalization method between a working channel and a standby channel.

In recent years, as the amount of international communication has increased, frequency bands above 10 GHz Ju are being used in addition to the 6 GHz and 4 GHz bands currently used for satellite communication lines.

However, in such high frequency bands, radio waves are attenuated by rain, and in areas with heavy rainfall, signal quality deteriorates and it becomes difficult to maintain communication lines.

The most effective means of countering this attenuation due to rain is to perform communication path switching space diversity by taking advantage of the regional characteristics of rainfall.

In such a diversity system, the distance between the two prepared antenna sites is more than 107m, so the difference in path length between the two from the signal switching point to the satellite via the antenna site is quite large, and is simply due to the rain condition. If the communication path is switched according to the difference in path length, signal loss or duplication will occur corresponding to the path length difference.

Particularly in TDMA communication, if the transmission burst from each earth station on the satellite is not transmitted at a predetermined time position (time slot), it will interfere with the burst from other earth stations, so this path length difference This not only causes loss or duplication of signals during diversity switching, but also causes serious problems in the operation of the TDMA system.

Therefore, in space diversity for TDMA communication, it is necessary to set the path lengths of both communication paths from the switching point to be equal by some means.

As a representative example of this path length equalization means, the patent application
There is No. 147602.

This method focuses on the fact that the path length difference consists of a fixed valve determined by the distance between antenna sites and a variable amount due to movement of the satellite position, and uses a fixed digital delay line and a variable digital delay line in the communication path. It is inserted to offset the difference in path length.

To perform path length equalization, it is first necessary to detect the difference in two path lengths.

When equalizing the path length of the receiving channel, the path length difference is detected by comparing the detection timing of the same signal from both antenna sites, for example, the detection timing of a unique word (synchronization signal) included in the beginning of the reception burst. is possible.

However, in spot beam operation, since the own station cannot receive the transmitted signal, it is not possible to directly detect the difference in path length of the transmission channel.

The solution to this problem is to send communication bursts from the working transmission path and also send very short bursts (
(hereinafter referred to as a preliminary burst) is transmitted within a time slot previously assigned to this preliminary burst.

The partner earth station receives these two signals via a satellite, detects the positional relationship between the two bursts, and sends this information back to the diversity earth station.

In this way, the diversity earth station knows the relative positions of the signal burst at the time of transmission and the preliminary burst, so if the relative position detected from the returned burst position information deviates from the relationship at the time of transmission, this deviation can be corrected. This is caused by the difference in the lengths of the two transmission channels, and by controlling the delay amount of the variable delay circuit, the lengths of the two transmission channels can be made equal.

The above explanation is a means of equalizing the path lengths during operation of the diversity system, but since the transmission path lengths have not been equalized yet at the time of starting the operation of the diversity system, it is necessary to predict the backup burst from the standby channel. A problem arises in that even if a preliminary burst is transmitted using a window (aperture), the destination earth station cannot receive the preliminary burst accurately.

In normal TDMA communication, in order to establish burst synchronization, a synchronization signal (unique word) at the beginning of a burst is detected to confirm the burst position.

However, the synchronization signal is +171 like the transmission signal.
, II Q', so if there is a combination of signals other than the synchronization signal that is the same as the synchronization signal, it will be mistakenly received as a synchronization signal, making it difficult to detect the exact burst position. become.

In normal TDMA communication, if the bursts are in a synchronous state,
It is possible to predict the time when the next synchronization signal will arrive based on the current synchronization signal detection timing.

Therefore, in TDMA communication, a window is set up to receive the synchronization signal only during the predicted time period when the next synchronization signal will arrive, thereby preventing erroneous synchronization signals from being detected in other parts. For this reason, in order to accurately know the preliminary burst position, it is desirable to provide a window and receive the preliminary burst synchronization signal, but it is clear that setting the window based on prediction is difficult when initially setting the path length. .

In order to solve the above-mentioned problems, the present invention provides an initial path length equalization method in diversity for satellite communication for setting both communication path lengths to be equal at the start of operation of the diversity system.

To achieve this objective distantly, the present invention first determines the transmission timing of a backup burst by prediction when starting the operation of a diversity system, and then transmits a predicted time that is estimated to be sufficiently larger than the prediction error. Add it to the timing and send a preliminary burst at this timing.

For example, every time the signal burst transmission timing is corrected (approximately 0.6 seconds in spot beam operation), the delay amount of the variable delay line is reduced by one symbol, and the preliminary burst is received at the window of the partner earth station. The feature is that this operation is automatically repeated until the

The fact that the preliminary burst was received at the window of the destination earth station means that the side transmission path lengths have been equalized, and from this point on, as mentioned above, the signal bursts and preliminary bursts sent back from the destination earth station are Path length equalization is performed using position information.

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

FIG. 1 shows an example of a configuration of satellite communication space diversity.

Here, 1 is a communication satellite, 2 is an antenna site A, 3 is an antenna site B, 4 is a communication line, 5 is a switching control unit for performing diversity operation, 6 is a communication path B, and 7 is a communication path A
, 8 represents a changeover switch.

In this figure, communication is performed via communication path A on the active side at 7, and communication path B at 6 is a standby communication path.

A selector switch 8 in the diversity control section 5 is a switch for selecting a communication path depending on the state of rain on the communication path.

Further, d in the figure represents the distance between the first antenna site A and the second antenna site B.

FIG. 2 shows the TDMA signal on the satellite with time plotted on the horizontal axis.

11 is a reference burst, 12 is a signal burst transmitted from each earth station, and 13 is a preliminary burst.

These time slots are predetermined as a TDMA system and assigned to each earth station.

The area surrounded by diagonal lines is a synchronization signal for detecting the burst position and performing burst synchronization, a signal for creating the reference carrier wave and clock signal necessary for demodulating the burst signal, a communication signal, etc. This is the device signal part (preamble) configured.

FIG. 3 shows a configuration example of a path length equalization method in a TDMA space diversity earth station for satellite communication.

20, 20' are digital fixed delay circuits used to absorb the fixed path length difference caused by the antenna site A and the same distance d mentioned above.

Numerals 21 and 21' are digital variable delay circuits for absorbing variable path length differences due to satellite position fluctuations, etc. In particular, 21' is also used for equalizing the transmission path length of the present invention.

In the digital delay circuits 21 and 21', the minimum unit of delay is a symbol or a clock length unit, which is the minimum unit of a signal.

Further, the path length difference detection circuit 22 is a circuit for detecting the path length difference between both receiving communication paths using the detection timing of the synchronization signal.

24 SWR is a switch for switching the receiving communication path,
SWT 25 is a changeover switch for the transmission channel.

23 is a normal TDMA terminal device.

Here, we will explain the general flow of initial operations when starting the operation of the Diversity Earth Station.

First, using the detection timing of the reference burst 11 from both reception channels, the delay amount of the variable delay circuit 21 inserted in the reception channel of communication channel B is calculated so that the rain detection timing of the path length difference detection circuit 22 is equal. equalize both receiving path lengths.

Next, using the communication path A, the initial connection function of the TDMA terminal station 23 determines the approximate transmission timing of the signal burst, and based on this, only the prefix part of the signal burst is sent within the predetermined time slot of the signal. Sent.

The transmission timing is controlled by direct transmission information from the other station so that this burst is placed at a proper predetermined position, and then a message signal portion is added to it.

Next, the path lengths of both transmission channels according to the present invention are equalized, and from then on, the above-described operation will be performed.

Hereinafter, the means for equalizing the path lengths of both transmission paths will be explained in more detail.

In the conventional technology, since the transmitting and receiving channels in a satellite communication line are exactly the same, the length difference of both transmitting and receiving paths that occurs on the propagation path is assumed to be equal, and the delay amount of the variable delay circuit of the transmitting channel B is the same as that of the receiving channel B. It was set to .

However, in reality, perfect equalization of both transmission path lengths cannot be expected due to the difference in delay time in the transmitter/receiver system and the difference in transmission/reception path length in the communication line.

Therefore, in the present invention, the delay amount of the variable delay circuit 21' of the transmission channel B is further set by adding α, and the preliminary burst for equalizing the transmission path length is delayed by a predetermined time difference To from the signal burst. and transmit from communication path B.

The setting amount of α at this time is the transmission/reception system and communication line 4 mentioned above.
This is made larger than the difference in path length that occurs.

For example, about 10 symbols are usually sufficient.

By doing so, the position of the preliminary burst 13 on the satellite 1 is always delayed from the predetermined time slot 13/, as shown in FIG.

To indicates a predetermined time difference between the signal burst 12' transmitted from the communication path A and the preliminary burst 13.

, JT is caused by the time difference caused by the above-mentioned added delay amount α and the path length difference between the transmitting/receiving system and the transmitting/receiving system of the contact line, and if the latter is expressed by Aα, the relationship is JT=α+lα.

Now, since the partner earth station is waiting to receive the preliminary burst 13 in the window 13' shown in FIG. 4a, the preliminary burst 13 cannot be received in this state.

In normal TDMA communication, the timing of the transmitted signal burst 12' is controlled so that the position of the transmitted signal burst 12' is always located in the time slot assigned to the local station with reference to the position of the reference burst 11.

In spot beam operation, this control is performed based on the position information of the transmission burst 12' of the local station sent back from the partner earth station, so it is normally performed every 0.6 seconds.

Therefore, in synchronization with the burst correction period (0.6 seconds), the delay amount of the variable delay circuit 21' of the transmission channel B is decreased by 1 step (usually the delay amount corresponding to 1 symbol) in units of the minimum delay amount. do.

As a result, the position of the spare burst 13 moves to the left as shown in FIG. 4b, and finally reaches a predetermined position 13', where it is received by the partner earth station.

This is the time difference T between transmissions from the same TDMA terminal station.

A signal burst 12' having T and a preliminary burst 13 are respectively transmitted on different communication channels, and T at the other earth station.

This means that the two transmission path lengths have been equalized.

As explained above, the present invention is a TDM system used for satellite communication.
A,' is related to the equalization of the transmitting channel in base diversity. First, the same delay amount as that inserted for equalizing the path length of the receiving channel is inserted into the transmitting channel, and then the delay on the transmitting side is The path length of both transmission channels is increased by setting the variable delay amount by α and decreasing the variable delay amount on the transmitting side in synchronization with the transmission burst correction cycle until the destination earth station can receive the preliminary burst at a predetermined position. It performs equalization.

In explaining this embodiment, an example has been described in which the delay amount of the variable delay circuit 21' of the transmission channel B is set by adding α, but by subtracting α, the variable delay is set in synchronization with the burst correction cycle. It will be readily understood that the desired purpose can be achieved even if the delay amount of circuit 21' is increased by one step.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing an example of a satellite communication diversity system to which the present invention is applied, and FIG. 2 is a diagram showing one example of a TDMA signal on a communication satellite.
FIG. 3 is a block diagram showing one embodiment of the present invention, and FIG. 4 atb is a time chart for explaining the operation of the embodiment of FIG. 3. 1...Communication satellite, 2...Antenna site A, 3
...Antenna size) B, 4...Connection line, 5...Switching control unit, 6...Communication path B, ? ...Communication path A,
8... Selector switch, 11... Reference burst, 12
...Signal burst, 12'...Diversity earth station signal burst, 13...Preliminary burst.

Claims (1)

[Claims] 1. In the space diversity method applied to PCM-TDMA communication using communication satellites, when equalizing the path lengths of two transmission communication paths, the variable delay circuit inserted on one side of the two transmission communication paths is With the amount of delay set to be shorter or longer than the amount predicted to be necessary to equalize the path lengths of the two transmission channels,
transmitting a preliminary burst for path length equalization from the standby side of the two transmission communication channels with a predetermined time difference from the signal burst being transmitted from the active communication channel;
The preliminary burst is received within the time slot of the preliminary burst in the TDMA frame by correcting the delay amount of the variable delay circuit in a direction closer to the predicted amount with reference to the return information from the partner earth station. An initial path length equalization method in diversity for satellite communications configured to equalize the path lengths of the two transmission communication paths of the diversity earth station by controlling the transmission path lengths to be equal to each other.