JPH0777371B2 - Co-channel signal transmission system - Google Patents

Description

The present invention relates to a co-channel signal transmission system in microwave communication.

[Conventional technology]

In recent years, due to the increase in traffic between large cities, it is required to increase the transmission channels of wireless communication lines.

The frequency arrangement in a normal microwave radio communication system is an interleaved frequency arrangement as shown in FIG. On the other hand, a system that transmits signals using V / H different polarization and the same frequency for the purpose of increasing the number of transmission channels is called a co-channel signal transmission system. FIG. 4 shows an example of the co-channel frequency array.

One feature of co-channel signal transmission is that the frequency intervals of adjacent channels of the same polarization are narrower than in interleaved signal transmission. Looking at the examples in Figs. 3 and 4, the frequency spacing between adjacent channels of the same polarization is 5
It is 9.3 MHz, whereas it is 29.65 MHz for co-channel. Therefore, in the case of co-channel signal transmission, it is very difficult to demultiplex adjacent channels of the same polarization by a demultiplexing filter.

Two examples of general station configurations of a co-channel signal transmission system are shown in FIGS. 5 and 6.

In both cases, it is difficult to demultiplex adjacent channels of the same polarization. In Figure 5
Reference numeral 30 denotes a receiving device and 40 denotes a transmitting device. Further, the numbers 1 to 8 of the interfaces of the receiving device 30 correspond to the channel numbers 1 to 8 in the frequency array shown in FIG. 4, respectively. Numbers corresponding to the channel numbers 1a to 8a in FIG. 4 should be added to the transmitter 40, but they are omitted in FIG. 5 for the sake of avoiding the complexity of the figure. 50 is a 3 dB hybrid and is used as a power distributor or power combiner.

In the station configuration shown in FIG. 5, for example, a channel is used on the receiving side.
1,3,5,7 are demultiplexed by the demultiplexer, and channels 2, 4, 6, 8
Is being demultiplexed by a demultiplexer. Since the co-polarized adjacent waves of the co-channel frequency array cannot be demultiplexed, they are demultiplexed every other wave. The transmitting side is also the same, and demultiplexes with a combination of a set of channels 1a, 3a, 5a, 7a and a set of channels 2a, 4a, 6a, 8a,
After that, the power combiner 50 combines them.

The drawback of the station configuration example of FIG. 5 is the power loss due to the 3 dB hybrid 50. As can be seen from the figure, one 3dB hybrid 50 is placed on each of the transmitting side and the receiving side, and each has a 3dB insertion loss, so the system gain is 6 in total.
The dB will drop.

An example of a station configuration for preventing this system gain reduction is as shown in FIG.

The main station configuration does not use the 3dB hybrid, but uses the two-sided antennas 60 and 70. With this station configuration, the system gain reduction of 6 dB in the station configuration shown in Fig. 5 does not occur.

[Problems to be Solved by the Invention]

However, the station configuration of FIG. 6 has a problem due to the difference in fading caused by the difference in the propagation paths. This will be described with reference to FIG.

FIG. 7 shows an example of an opposite 1-hop system configuration. Stations A and B are several tens of kilometers apart on real lines. Station A,
When B has a station configuration using the two-sided antenna shown in FIG. 6, the state of radio wave propagation is as shown by reference numerals 81 and 91 in FIG.

Considering the example of the V polarization, the signals of channels 1, 3, 5, and 7 transmitted from the antenna 80 of the station A in the V polarization are received by the antenna 60 of the station B through the spatial propagation path 81, Guided by the receiver 30, the signals of channels 1, 3, 5, and 7 are extracted. Further, the antenna 60 receives channels 2, 4, 6, and 8 of the same polarization transmitted from the antenna 90 of the station A through the space propagation path 91 as undesired waves at the same time by the antenna 60. Then, the state of the reception spectrum of the antenna 60 is modeled as shown in FIG. 8 at the point P _{4 of the} station B.

In the spectrum of FIG. 8 received by the antenna 60, unnecessary wave components are suppressed by the reception demultiplexing filter and the intermediate frequency filter of the receiver 30, and the state as shown in FIG. 9 is obtained at the output point P ₅ of the receiver 30. Become. In Fig. 9, the interference wave is the adjacent channel.
Numerals 2 and 4 are the residual components suppressed by the reception demultiplexing filter and the reception intermediate frequency filter.

In the design, the filter system is set so that this interference wave component does not cause a problem in the line quality. However, the actual line has the following problems.

In the system shown in FIG. 7, the fading amount may be different between the space propagation paths 81 and 91. For example, when the space propagation path 81 receives a large fading compared to the space propagation path 91, the spectrum at the output of the receiver 30 becomes as shown in FIG. In the state shown in Fig. 10, the level of the interfering wave becomes higher than the level of the required wave, which causes the line quality to deteriorate. This problem has never been solved.

[Means for Solving the Problems]

A co-channel signal transmission system of the present invention is a co-channel signal transmission system that transmits a signal using two polarized waves having the same frequency and orthogonal to each other, and a first band-pass filter for extracting only a necessary wave component from a received intermediate frequency signal. A second bandpass filter for extracting only the interference wave component, first and second level detectors for detecting respective output levels of the first and second bandpass filters, and these first and second level detectors.
And a control circuit for comparing the detection values of the second level detector and outputting the comparison result as a first reception level detection signal, a transfer means for transferring the first reception level detection signal to a counter station, and the counter circuit. Transmission output varying means for controlling the transmission output level by the second reception level detection signal transferred from the station.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 (a).
~ (C) is a diagram showing a spectrum of a signal at point P ₁ to P ₃ in FIG. 1.

The embodiment shown in FIG. 1 is used for the station configuration shown in FIG. In FIG. 1, 10 and 20 are receivers and transmitters for one channel each of the receiver 30 and the transmitter 40 in FIG. Reference numeral 11 denotes a frequency conversion unit which is a function in the receiver 10. Reference numeral 12 denotes an intermediate frequency band divider, which has a role of branching into an intermediate frequency signal and an intermediate frequency signal for level detection described later. Reference numeral 13 is a bandpass filter for the intermediate frequency band, which passes the necessary wave and removes the interference wave (see FIGS. 2 (a) and 2 (b)). Further, 14 is a band filter (see FIG. 2 (c)) that passes the interference wave and removes the necessary wave, and 15 and 16 are level detectors. The control circuit 17 compares the required wave level detected by the level detector 15 with the interference wave level detected by the level detector 16, and outputs a signal according to the level difference. This signal output is transferred to the opposite station using the service channel of the transmitter 20.

Information on the level difference between the required wave and the interference wave sent from the opposite station using the service channel is extracted by the demodulator 18 and processed by the control circuit 21. The output of the control circuit 21 is sent to the transmitter 22. The transmission unit 22 has a function of varying its transmission output under the control of the output signal of the control circuit 22.

〔The invention's effect〕

As described above, the present invention transfers the level-down signal detected by the reception system to the transmission system of the opposite station when the required wave is level-down due to the difference in the propagation path, and varies the transmission output of the opposite station. The state of FIG. 10 can be controlled to the state of FIG. In this way, there is an effect that the deterioration of the line quality caused by the difference in fading due to the difference in the propagation path can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 (a).
~ (C) is a diagram showing a signal spectrum at points P _{1 to} P ₃ in Fig. 1, Fig. 3 is a diagram showing an example of an interleaved frequency array, Fig. 4 is a diagram showing an example of a co-channel frequency array,
FIGS. 5 and 6 are block diagrams showing two examples of general station configurations of the co-channel signal transmission system, and FIG. 7 shows an opposite one-hop configuration using the station configuration shown in FIG. A block diagram, FIG. 8 is a diagram showing a signal spectrum at a point P ₄ in FIG. 7, and FIGS. 9 and 10 are diagrams showing a signal spectrum at a point P ₅ in FIG. 7. 10 …… Receiver, 11 …… Frequency converter, 12 …… Distributor, 1
3,14 …… Band filter, 15,16 …… Level detector, 17…
… Control circuit, 18 …… Demodulator, 20 …… Transmitter, 21 …… Control circuit, 22 …… Transmitter.

Claims (1)

[Claims] 1. A co-channel signal transmission system for transmitting a signal using two polarized waves having the same frequency and orthogonal to each other, a first band-pass filter for extracting only necessary wave components from a received intermediate frequency signal, and an interference wave. A second bandpass filter for extracting only the components, first and second level detectors for detecting respective output levels of the first and second bandpass filters, and the first and second level detectors. A control circuit that compares detection values and outputs the comparison result as a first reception level detection signal, a transfer unit that transfers the first reception level detection signal to an opposite station, and a second unit that has been transferred from the opposite station. And a transmission output varying means for controlling the transmission output level according to the reception level detection signal of the co-channel signal transmission system.