JPH0466414B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to cross-polarization interference compensation technology that occurs when orthogonal polarizations are shared in wireless transmission.

Microwave band wireless communications are rapidly developing, centering on terrestrial communications and satellite communications. The demand for wireless communication is expected to further increase due to the expansion of mobile communication services, and along with the development of sub-millimeter wave and higher frequency bands, so-called frequency reuse of currently used frequency bands with high practical value is expected. Thoughts are growing. CCIR (Consultative Committee on International Radiocommunications)
The ~6GHz FM Radio Frequency Deployment Recommendation includes:
It is specified that orthogonal polarization is to be used. In addition, in satellite communications, INTELSAT (International Telecommunication Satellite Organization) is expected to commercialize orthogonal polarization sharing technology in the 4 to 6 GHz band, which has been used with single polarization on V-series satellites.

In order to achieve the 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 of two orthogonal polarized waves, and is a transmission line that can simultaneously transmit both polarized waves. However, in actual propagation paths, there is anisotropy in media such as rain, and orthogonal polarized waves If a shared system is adopted, 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 uses a variable transfer device and an attenuator around the antenna feeder to restore orthogonality. Methods of canceling interference between different polarized waves by providing an interference wave compensation circuit in the intermediate frequency band and intermediate frequency bands have been well studied and put into practical use.

In recent years, digital transmission has come into use even in the microwave band, and there is a demand for proposals for more efficient cross-polarization compensation methods that take 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, it is possible to perform digital transmission for shared orthogonal polarization at the same carrier frequency through a current 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 exhibits significant superiority over conventional systems.It is more economical in that it does not require any modification to the currently used transmission system, and moreover, it is compatible with TDMA. Cross-polarization compensation can be performed individually for each transmitting station even when signals from multiple stations are received in a time-division manner using the same antenna, as in the case of FIG.

The circuit of the present invention is capable of transmitting first and second digital data sequences of the same bit rate...ak
-2, ak-1, ak, ak+1, ak+2...and...bk-2, bk-1, bk, bk+1, bk+2...
In digital wireless transmission in which the signals are carried on first and second polarized waves that are orthogonal to each other, signals obtained from the first and second polarized waves on the receiving side in correspondence with the first and second sequences are obtained from the first and second polarized waves, respectively. 3rd and 4th
Series...Ak-2, Ak-1, Ak, Ak+1,
Ak+2...and...Bk-2, Bk-1, Bk,
Bk+1, Bk+2...and the fifth and sixth sequences which are estimated values on the receiving side of the third and fourth sequences...A^-2, A^k-1, A^k, A^k+1 , A^k+2
...and...B^k−2, B^−1, B^k, B^k+1,
From B^k+2..., let M, M', N, and N' be zero or positive integers C _K = _N 〓 ^i=-N α _i・A _K+i + _M 〓 ^i=-M β _i・B _{K +i} − _N ′ 〓 ⁱ⁼⁰ α′ _i・A^ _k+i − _M ′ 〓 ⁱ⁼⁰ β′ _i・B^ _k+i (However, αi, βi, αi′, βi′ are multiple constants) The fifth series...Ck-2, Ck-1, Ck, Ck
Equipped with a filter that outputs +1, Ck+2...
The present invention is characterized in that the first sequence from which cross-polarized interference from the second polarized wave is removed is obtained from the filter.

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

FIG. 1 shows a block diagram of a conventional linear automatic equalizer for digital transmission. The terminal 100 has a band-limited random pulse...ak-1,
ak, ak+1... are added one after another at intervals of T seconds.

In the figure, reference numerals 1, 2, 3 and 4 are T-second delay circuits, reference numerals 5, 6, 7, 8 and 9 are variable attenuators, reference numeral 10 is an adder, reference numeral 11 is a sampler, Reference numeral 12 is a signal identification circuit that obtains an estimated value A^k from the received signal Ak when the pulse ak is transmitted, and if no transmission error occurs, it is estimated that ak = A^k.

As is clear from the figure, the function _of the equalizer in _FIG . . There are various algorithms for automatically and ideally changing the attenuation amounts αi of variable attenuators 5, 6, 7, 8, and 9. For example, BSTJ published in April 1965
(Bell System Technical Journal vol.44,
“Automatic equalization” described on pp547-588
zero shown in for digital communication
Forcing law, BSTJ vol.46, November 1967,
“An automatic equalizer” described on pp2179−2208
for general-purpose communication channel”
The root mean square equalization method shown in is generally known.

Also, although the composition is slightly different, there is a version published in May 1970.
IEEE TRANSACTIONS ON
INFORMATION THEORY, vol.IT−16,
“Analysis of a Decision” on pp270-276
There is also a nonlinear automatic equalization method shown in "Directed Receiver with Unknown Prior".

Also, the signal given to the input terminal in Figure 1 is 4
If the signal is a complex signal that has undergone phase modulation or 16-value quadrature amplitude modulation, the IEEE
TRANSACTIONS ON
COMMUNICATIONS, vol.COM−23, pp684
~687 “Two Extensional Applications”
of the Zero Forcing Equalization Method”
There is an automatic equalization method shown in

The actual equalizer configuration according to each of the above automatic equalization methods differs only in the circuit that estimates the attenuation amount (tap gain) of the variable attenuator, and the components other than the nonlinear automatic equalizer are as shown in Figure 1. It's structured well.

FIG. 2 shows a block diagram of a conventional nonlinear automatic equalizer, with reference numerals 1', 2', 3' and 4' corresponding to components 1, 2, 3 and 4 of FIG.
5', 6', 7', 8' and 9' are component 5,
6, 7, 8 and 9, reference numeral 10' corresponds to element 10 of FIG. 1, reference numeral 11' corresponds to element 11 of FIG. Corresponding to component 12 in the figure, reference numerals 13 and 14 are adders.

The configuration of FIG. 2 differs from that of FIG. 1 in that interference from the preceding code is canceled based on the identification result of the preceding code, and the operation is basically the same as that of the configuration of FIG. 1. Therefore, the configuration of the automatic equalizer for wireless digital transmission, which will be discussed later, will be as shown in FIG. However, in this case, the variable attenuator handles complex signals.

FIG. 3 is a diagram showing the state of coupling between orthogonal polarized waves in satellite communication. When reference numeral 30 is the transmitting ground station, reference numeral 31 is the receiving ground station, and reference numeral 32 is the communication satellite, when transmitting horizontal polarization 300 and vertical polarization 301, cross polarization from vertical polarization to horizontal polarization occurs. The main types of wave interference are interference 302 occurring in the up ring (transmission to the satellite), interference 303 occurring in the down link (transmission to the ground station), and self-interference 304 of the horizontal polarization itself. Now, assuming that both polarized waves have the same carrier frequency, all these interferences are obtained as the sum of each interference in the baseband signal obtained by synchronous detection. Therefore, it can be seen that if the interference components are accurately determined, they can be eliminated by subtracting them from the detected baseband signal.

First, since the self-interference 304 is considered to be normal multi-propagation path circuit line distortion, its influence is removed by the normal automatic equalizer shown in FIG.

Next, regarding the interferences 302 and 303, if the transmission code transmitted on the vertical polarization side is known, the interference from the vertical polarization can be completely removed based on this code.

FIG. 4 is a diagram showing a cross-polarization compensation circuit using the configuration of the automatic equalizer shown in FIG. 1. In the figure,
Block 4010 is the filter, reference numeral
40, 41, 42, 43, 44, 45, 46 and 47 are the same as each delay circuit in FIG.
49, 50, 51, 52, 53, 54, 55, 56 and 57 are the first
Identical to each variable attenuator in the diagram, reference numbers
58 is the same as the adder 10 in FIG. 1, the reference numeral 59 is the same as the sampler 11 in FIG. 1, and the reference numeral 60 is the same as the signal discriminator 12 in FIG. be.

First, a demodulated baseband signal sent by horizontal polarization is applied to the input terminal 400, and a demodulated baseband signal sent by vertical polarization is applied to the input terminal 401.

In this circuit, interference from vertical polarization to horizontal polarization is removed and only the original horizontal polarization component is extracted.

The outputs from the attenuators 48, 49, 50, 51 and 52 reduce the waveform distortion of the horizontally polarized component itself and the third
The sum ₂ 〓 ^i=-2 α _i・a _K+i of the self-interference 304 shown in the figure can be removed.

Next, attenuators 53, 54, 55, 56 and 5
^{The sum of} the cross-polarized interferences 302 and 303 in FIG. ₃ can be removed by the output from 7. Therefore, only the horizontally polarized wave component Ck= ₂ 〓 ^i=-2 αi·Ak+i+ ₂ 〓 ^i=-2 βi+Bk+1ak from which all interference has been removed is output to the output terminal 402 .

Here, attenuators 48, 49, 50, 51, 5
The control algorithm for the attenuations αi, βi of 2, 53, 54, 55, 56 and 57 can be considered as an extension of that of the automatic equalizer of FIG.
That is, horizontally polarized waves and vertically polarized waves carry completely uncorrelated data, and each data series is uncorrelated in time series. Therefore, by selecting the amount of attenuation (tap gain) of each attenuator so that the output of the attenuator is orthogonal to the difference between the received code and its estimated value, the orthogonality principle can be used to reduce the difference. can do. This is an extension of the root mean square equalization method described above.

FIG. 7 shows an embodiment of the present invention, and shows a cross-polarization compensation circuit using the nonlinear automatic equalizer configuration of FIG. 2. In the figure, the cross-polarization compensation circuit consists of 8
signal processing circuits 124 to 131 and an addition circuit 1
32 and 133 and identification circuits 134 and 13
5. Each signal processing circuit is composed of a delay circuit, a variable attenuator, and an adder. The input terminal 120 is supplied with a demodulated baseband signal A _K sent by a horizontal wave, and the input terminal 121 is supplied with a demodulated baseband signal B _K sent by a vertically polarized wave. First signal processing circuit 12
4 processes the baseband A _K and outputs ΣA _K+i ·α _i as the first processed signal. Similarly, the second
The signal processing circuit 125 of the baseband signal _BK
is processed and a second processed signal ΣB _K+i ·βi is output.
These first and second processed signals are combined with third and fourth processed signals provided from third and fourth signal processing circuits 126 and 127 and adder 132.
is subtracted (negative addition). The output of this adder 132 is then identified by a discriminator 134 to obtain an estimate A^ _K of the baseband signal _AK . This estimate
A^ _K is processed by the third signal processing circuit 126,
The aforementioned third processed signal ΣA^ _K+i ·α _i ' is obtained. On the other hand, the fourth processed signal is obtained by using the estimated value of the baseband signal _BK as B^ _K and processing this estimated value B^ _K in the fourth signal processing circuit 127.

Therefore, the output C _K of the adder 132 mentioned above is expressed as follows.

C _K =ΣA _K+i・α _i +ΣB _K+i・β _i −ΣA^ _K+i・α _i ′−ΣB _K
+i・β _i ′ Note that the fifth to eighth signal processing circuits 128 to 13
1 adder 133 and discriminator 135 are used to obtain an estimate B^ _K of the baseband signal _BK ,
The operation is the same as the process of calculating the estimated value A^ _K of the baseband signal A _K , and the adder 133 at that time
The output d _K can be expressed as follows.

d _K =Σβ _i・A _K+i +Σα _i・B _K+i +Σβ _i ′・A^ _K+i −Σα
' _i ·B^ _K+i FIG. 5 shows an attenuation control circuit 500 for the variable attenuator 49 of FIG. In the figure,
Reference numerals 41, 45, 49, 58, 59 and 60 are the same as the correspondingly referenced components in FIG.
The adder 63 is used to detect the difference (Ak - A^k) between the received code Ak and its estimated value A^k. Furthermore, the multiplier 61 and the integrator 62 are used to detect the orthogonality between the next reception code Ak+1 and the previous (Ak−A^k), and the variable attenuator is used depending on the sign of the correlation. operates to increase or decrease the amount of attenuation.

Attenuation control of other variable attenuators can be performed using the same method.If the line is stable and there is no line switching, attenuation control circuit 5
00 is no longer needed. In this case, the amount of attenuation of each attenuator may be preset appropriately.

FIG. 6 shows the configuration of a cross-polarization interference equalizer for two series of data transmitted by horizontally polarized waves and vertically polarized waves. In the figure, blocks 4000,
4000' is the same as block 4000 in FIG. Baseband signals transmitted with both horizontal and vertical polarization are applied to input terminals 600 and 601, respectively, and block 4000 receives the horizontal polarization component from which interference from vertical polarization has been removed.
The block 4000' outputs the vertically polarized wave components from which interference from the horizontally polarized wave has been removed to output terminals 402 and 40, respectively.
Output to 2'.

As described above, according to the present invention, cross-polarization compensation can be performed in the base band, so cross-polarization sharing can be achieved without any modification to the current single-polarization transmission/reception system. can be done.

In addition, it is particularly effective as a cross-polarization compensation method for satellite communications, especially when signals from multiple stations are received one after another using the same receiving antenna, such as TDMA communications. These effects cannot be expected from the Obi-based compensation method at all.

The main cause of the deterioration of the orthogonal polarization discrimination degree due to fading is the attenuation of the positive polarization component. In this state, the different polarization components cause a large disturbance,
Since the information transmitted by the different polarization components is obtained by the demodulator, the different polarization components can be canceled on the receiving side. Therefore, whereas conventionally, the attenuation of the positive polarization component due to rain etc. and the orthogonal polarization discrimination degree decreased in a nearly linear manner, by using the present invention, the same degree of discrimination can be reduced by a certain degree of positive polarization attenuation. can be maintained to a level sufficient for practical use.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams showing a block diagram of a conventional automatic equalizer, Figure 3 is a diagram for explaining cross-polarization interference in satellite communications, and Figure 4 is the same as in Figure 1. 5 is a diagram showing an example of a polarization compensation circuit using the configuration of a polarization converter, FIG. 5 is a diagram showing an attenuation amount control circuit of the variable attenuator of the filter shown in FIG. 4, and FIG. FIG. 3 is a diagram showing a block diagram of a cross-polarization interference equalizer for two series data. FIG. 7 is a circuit diagram showing one embodiment of the present invention. In FIG. 4, 4010 is a filter;
~47 is a delay circuit, 48~57 is a variable attenuator, 5
8 is an adder, 59 is a sampler, and 60 is a signal discriminator.

Claims (1)

[Claims] 1. First and second digital data series of the same bit rate...ak-2, ak-1,
ak, ak+1, ak+2...and...bk-2, bk
-1, bk, bk+1, bk+2... on first and second polarized waves that are orthogonal to each other. The third and fourth sequences obtained from the two polarized waves respectively...Ak
-2, Ak-1, Ak, Ak+1, Ak+2... and Bk-2, Bk-2, Bk, Bk+1, Bk+2...
and the fifth and sixth sequences which are estimated values of the third and fourth sequences on the receiving side...A^k-2, A^k-
1, A^k, A^k+1, A^k+2...and...B^k−
2, B^k−1, B^k, B^k+1, B^k+2..., where M, M', N, and N' are zero or positive integers, C _K = _N ' 〓 ^i=-N α _i・A _K+i + _M ′ 〓 ^i=-M β _i・B _K+i − _N ′ 〓 ⁱ⁼⁰ α′ _i・A^ _k+i − _M ′ 〓 ⁱ⁼⁰ β′ _i・B^ _{k +i} (however, αi, βi, αi', βi' are multiple constants)...Ck-2, Ck-1, Ck, Ck
Equipped with a filter that outputs +1, Ck+2...
A cross-polarization compensating circuit, characterized in that the first sequence from which cross-polarization interference from the second polarization is removed is obtained from the filter.