JPS6255337B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a technology for compensating for cross-polarization interference caused by the shared use of orthogonal polarizations in wireless transmission, and particularly to a cross-polarization compensation circuit.

Radio communications in the microwave band are rapidly developing, centering on terrestrial communications and satellite communications. The demand for wireless communications is expected to further increase in the future due to the expansion of mobile communication services, and along with the development of sub-millimeter wave and higher frequency bands, the idea of so-called frequency reuse of currently used frequency bands with high practical value is being developed. is increasing. CCIR (International Radiocommunication Consultative Committee)
Recommendations for 4-6 GHz FM radio frequency deployment specify the use of orthogonal polarization. Also, in satellite communications, INTELSAT (International Telecommunication Satellite Organization) is expected to put into practical use technology for sharing orthogonal polarization in the 4-6 GHz band, which has been used with single polarization on the V-series satellites.

In order to achieve this shared use of orthogonal polarization, it is important to improve the polarization characteristics of antennas and power supply equipment, as well as develop cross-polarization compensation circuits that compensate for deterioration of polarization characteristics during radio wave propagation due to rain, etc. This has become an issue.

Originally, free space is independent for two orthogonal polarized waves, and it is a transmission line that can transmit both polarized waves simultaneously, but in actual propagation paths, there is anisotropy in the medium such as rain, and it is necessary to use orthogonal polarized waves. If this method is adopted, the coupling between polarized waves due to the generation of cross-polarized waves will cause interference between different polarization channels.

Cross polarization compensation technology automatically compensates for such coupling between polarized waves by providing a compensation circuit within an antenna feeder or wireless device.

Conventionally, microwave band communication has centered on analog transmission centered on FM, so the cross-polarization compensation method described above also restores orthogonality by installing a variable phase shifter and attenuator around the antenna feeder. Methods that eliminate interference between different polarized waves by providing an interference wave compensation circuit at the intermediate frequency have been well studied and put into practical use.

In recent years, digital transmission has come into use in the microwave band as well, and there is a need to propose a more efficient cross-polarization compensation method that takes advantage of the characteristics of digital transmission.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cross-polarization compensation circuit that performs a cross-polarization compensation method in a baseband band based on demodulated baseband signal information in digital transmission.

According to the present invention, digital transmission for shared orthogonal polarization can be performed through a currently used antenna system for single polarization and intermediate frequency equipment.

Currently, the beam width of satellite antennas is considerably wider than that of terrestrial microcircuits, and
Global beam antennas use asymmetric beams to increase effective transmission power;
Furthermore, due to Faraday rotation in outer space, a high degree of orthogonal polarization discrimination cannot be expected.

In such a transmission system, the present invention is significantly superior to conventional systems, and is more economical in that it does not require any modification to the currently used transmission system. Even when signals from multiple stations are received in a time-division manner using the same antenna, as in TDMA, cross-polarization compensation can be performed for each transmitting station individually.

The circuit of this invention has a first polarized wave and a second polarized wave that are orthogonal to each other.
a pre-identification circuit that estimates and identifies the second data in a method of wirelessly transmitting first data and second data that are independent digital signals using polarized waves; a memory circuit that selects one memory element whose contents can be modified according to the output value of the subtracter; a subtracter that subtracts the output of the memory circuit from the first data; and a subtracter that subtracts the output of the memory circuit from the output of the subtracter; a final identification circuit that estimates and identifies;
a storage content modification circuit that corrects and outputs the output of the storage circuit according to the input/output difference of the final identification circuit; The first data that removes the interference of the second data with the data of
data, and changes the contents of the currently selected storage element of the storage circuit based on the output of the storage content modification circuit to respond to changes in the state of cross-polarization interference.

Next, the present invention will be explained in detail with reference to the drawings. First, the prior art will be explained with reference to FIGS. 1a, b to 5.

Reference numbers 4000,400 in Figures 1a and b
1,4002 and 4003 and reference numeral 410
0, 4101, 4102 and 4103 are four signal points of the four-phase phase modulation signal shown on the orthogonal IQ phase plane.

Figure 1a shows the first data desired to be received in the first polarization, and Figure 1b shows the second data, which is another digital signal transmitted in the orthogonal second polarization. . If cross-polarized interference occurs in the transmission path, the signal obtained by synchronously detecting the first polarized wave will be the four signal points shown in Figure 1a and the lower-level interference component shown in Figure 1B. The result is a signal in which four signal points are superimposed.

Figures 2a and 2b are diagrams showing these superimposed signals. Figure 2a is a signal in which the interference component is superimposed in the same phase as the first data, and Figure 2b is a signal in which the interference component is superimposed with a phase difference of 45 degrees. It shows. It can be seen from FIGS. 2a and 2b that the interference component contained in the first data is a constant value specific to the identification value of the second data.

Therefore, if the identification value of the second data is obtained, a constant value unique to this value is subtracted as an interference component from the detected signal of the first polarization that has received cross-polarization interference. It turns out that it is possible to remove.
This is the principle of interference cancellation.

FIG. 3 is a block diagram of an example of a cross-polarization interference compensation circuit. In the figure, all signals of each part are complex number signals. First and second polarized detection signals are applied to terminals 100 and 101, respectively. Therefore, second data as shown in FIG. 2 is superimposed on the terminal 100 as an interference component. The second polarized detection signal input from the terminal 101 is converted into a second data estimated identification value by the next pre-identification circuit 1. At this time, if the signal distortion of the second data is below a certain level, the error rate of estimated identification is considered to be sufficiently small. The obtained estimated identification value controls the signal line selector 34 in the next storage circuit 3, selects one unique to the estimated identification value from among the storage elements 30, 31, 32, and 33, and outputs it. Connect to terminal 104.

On the other hand, the first polarized detection signal is applied to the subtracted terminal of the subtracter 20, and the value at the output terminal 104 of the storage circuit connected to the subtraction terminal of the subtracter 20 is subtracted as an interference component. The output of the subtracter 20 is pure first data from which interference components have been removed. This output is then applied to the final identification circuit to obtain the correct estimated identification value of the first data desired to be received. Similarly, the second
The same type of cross-polarization compensation circuit for data of can be operated simultaneously.

FIG. 4 is a block diagram of another example of the cross-polarization interference compensation circuit. When non-regenerative relay is performed in a wireless transmission system, cross-polarized interference occurs multiple times, each with a different propagation path length. Not only that, but its own signal also changes its propagation path length and returns as an interference component.

In such a case, the interference component includes intersymbol interference, and the received signal sample values (symbols) corresponding to the first and second data points to be identified are
All values of the several symbols before and after will be affected. Here, if the transmission path is linear, the effect is additive. Therefore, the interference component is also N before and after the identification data.
The first and second data of the symbol (N is a positive integer) need to be recognized as unique values.

In the block diagram of FIG. 4, when N=1, the _{identification} value H ₍
H _{(-T) ,} H _(T
) , V ( _{-T )} , V _(
O) , the five symbols of V _(T) are made to correspond to unique values as interference components. Therefore, the memory circuit 3 has the input terminal 10 of the memory circuit 3 shown in FIG.
Reference numerals 1030, 1031, 10 are stored in the memory circuit 3' corresponding to the 5 symbols as those corresponding to 3.
Five input terminals 103' designated 32, 1033 and 1034 are provided.

In addition, in order to obtain the estimated identification values H^ _(T) and V^ _(T) of the data subsequent to the time to be identified, a pre-discriminator 1' for the first data and a one-symbol delay circuit 4 are used.
A subsequent data identification value supply circuit 4 including 00 and 402 is provided. The estimated identification values H^ _(-T) and V^ _(-T) of the data preceding the time to be identified are already determined values, and H^ _(-T) is the delay circuit 403 and V _(-T).
is also stored in the same type of cross-polarization compensation circuit for the second data, so it is supplied to the input terminal 105. As a result, the output terminal 104 of the memory circuit receives the identification values {H^ _(-T) , H^ _(T) , V^ _(-T
) , V^ _(O) , V^ _(T) }, the interference components specific to them are output. Since block 2 in FIG. 4 is exactly the same as block 2 in FIG. 3, a correct estimated identification value of the first data can be obtained at the output terminal.

FIG. 5 is a diagram showing a subsequent data identification value supply circuit for a general value of N, and shows input terminals 107 and 10.
9 and 110 output terminals 108 correspond to the input/output terminals of FIG. 4, respectively. Output terminal 200
0,2001,...,(2000+N-1) and output terminal 2100,2101,...,(2100+
N) has identification values H(N _T ), H((N-1) _T ), H _(T
) , V(N _T ), V((N-1) _T ), and V _(O) are obtained, respectively, and are added to the input terminal of the memory circuit 3 as an address.

Now, consider a case where the state of cross-polarization interference changes. At this time, it is necessary to successively change each unique constant in the memory circuit.

FIG. 6 is a diagram showing a block diagram of an embodiment of the present invention, in which a function for successively changing this unique constant is added to the block diagram of FIG. 3. In the figure,
Blocks 1 and 2 have the same construction as 1 and 2 in FIG. 3'' is a memory circuit, and the difference from FIG. 3 is that the content of the memory element selected by the input terminal 103 can be changed to the value of the input terminal 111 through the signal line selector 35, and is a normal random access memory. (RAM), and in that sense, the memory circuit 3 in Figure 3 is converted from a read-only memory (ROM) to a RAM (RAM).
= Random Access Memory).

Here, block 5 is a memory content modification circuit. First, the input and output of the final discriminator are applied to input terminals 102 and 112, respectively, and both terminals are connected to the subtracter 5.
Added to 1. The output of the subtracter 51 is an error component if input noise is ignored. This is a value specific to the identification value obtained by the pre-discriminator 1. Attenuator 52 multiplies the previous error component by a constant α such that |α|<<1.

On the other hand, the value of the output terminal 104 of the memory circuit is read into another memory circuit 50 until the new memory content is determined, and this value and the output of the previous attenuator 52 are added to the adder 53 and sent to the output terminal 111. to go out.
The value at the output terminal 111 is read into the currently selected storage element in the next instantaneous storage circuit 3''.
That is, the signal to the terminal 103 that is applied as an address to this series of operating memory elements 3'' does not change, and the unique value selected by the signal is the output of the subtracter 51, that is, the direction of the compensation residual. It will be corrected.

FIG. 7 is a diagram showing a block diagram of another embodiment of the present invention, in which the memory content modification circuit 5 of FIG. 6 is added to the block diagram of FIG. It's the same thing. As you can see in this example,
The configuration of the memory content modification circuit 5 is a general configuration and is the same as that shown in FIG.

As described above, according to the present invention, cross-polarization interference compensation for digital signals can be performed in a perfect manner, and the circuit configuration is suitable for digital circuit configurations, so the present invention is suitable for device implementation. I can say it.

Furthermore, as mentioned above, since the present invention performs compensation in the baseband, there is no need to modify circuits such as intermediate frequency circuits, and the present invention is also effective for time-division signals from multiple stations. The feature is that it works.

[Brief explanation of the drawing]

Figure 1 a and b show the signal points of four-phase phase modulation.
Figures 2a and 2b are diagrams explaining a synchronous detection signal subjected to cross-polarization interference, Figure 3 is a block diagram showing an example of a cross-polarization interference compensation circuit, and Figure 4 is a diagram illustrating an IQ phase plane. Figure 5 shows another block diagram of the cross-polarization interference compensation circuit, Figure 5 shows an example of the subsequent data identification value supply circuit, and Figures 6 and 7 show block diagrams of two embodiments of the present invention. It is a diagram. In the figure, 1 is a prediscriminator, 20 is a subtracter, 3,
3', 3'' are storage circuits, 21 is a final identification circuit, and 4 is a subsequent data identification value supply circuit.

Claims (1)

[Claims] 1. In a method of wirelessly transmitting first data and second data that are independent digital signals using first and second polarized waves that are orthogonal to each other, the second data is estimated and identified. a pre-discrimination circuit that selects one storage element whose content can be modified according to the output value of the pre-discrimination circuit; a subtracter that subtracts the output of the memory circuit from the first data. and; a final identification circuit that estimates and identifies the first data from the output of the subtracter; and a storage content correction circuit that corrects and outputs the output of the storage circuit according to the input/output difference of the final identification circuit. ; from the output of the final identification circuit, obtain first data from which interference of the second data with the first data due to cross-polarization interference occurring in the wireless transmission path is removed; and from the output of the storage content modification circuit, obtain the first data A cross-polarization compensation circuit that changes the contents of a currently selected storage element of a storage circuit to respond to changes in the state of cross-polarization interference.