JPH0465574B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a technology for compensating for cross-polarization interference 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 communications is expected to further increase in the future due to the expansion of mobile communication services, etc., and along with the development of sub-millimeter wave and higher frequency bands, so-called frequency reuse of current 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. Also, in satellite communications, INTELSAT (International Telecommunication Satellite Organization) is expected to commercialize technology for orthogonal polarization in the 4-6 GHz band, which has been used with single polarization on 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 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, antenna waveband 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. Various methods have been well researched and put into practical use, such as a method in which an interference wave compensation circuit is provided in the intermediate frequency band to eliminate interference between different polarized waves.

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.

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 transmitted on first and second polarized waves that are orthogonal to each other, a third sequence obtained from the first and second polarized waves on the receiving side corresponding to the first and second sequences is transmitted. and the fourth
Series of...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^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,
From B^k+2..., let M, M', N, and N' be zero or positive integers: C _K = _N ' 〓 ^i=-N αi・A _K+i + _M ′ 〓 ^i=-M βi・B _{K +i} − _N ′ 〓 ⁱ⁼⁰ αi′・A^ _K+i − _M ′ 〓 ⁱ⁼⁰ βi′・B^ _K+i (however, αi, βi, αi′, βi′ are multiple constants) Series of 7...Ck-2, Ck-1, Ck, Ck
A filter that outputs +1, Ck+2... and d _K = − _M ′ 〓 ^i=-M βi・A _K+i + _N ′ 〓 ^i=-N αi・B _K+i + _M ′ 〓 ⁱ⁼⁰ βi′・A^ _K+i − _N ′ 〓 ⁱ⁼⁰ αi′・B^ _K+i 8th series...dk−2, dk−1, dk, dk+
1, dk+2..., and by passing through the first filter, cross-polarized interference from the second polarized wave to the first polarized wave is removed, and the first sequence is and pass through the second filter to remove cross-polarization interference from the first polarized wave to the second polarized wave to obtain the second sequence.

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 receives band-limited random pulses...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. 1 is to cancel the intersymbol interference αi・a _K+i from the two preceding and succeeding transmission codes using variable attenuators 5, 6, 8, and 9. . 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 cmmunication 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
TRANSACTION ON COMMUNICATIONS,
“Two” described in vol.COM-23, pp684-687
Extensional Applications of the Zero
There is an automatic equalization method shown in "Forcing Equalization Method".

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' representing the first
The reference numerals 5', 6', 7', 8' and 9' correspond to elements 5, 6, 7, 8 and 9 of FIG. , reference numeral 10' corresponds to element 10 in FIG. 1, reference numeral 11' corresponds to element 11 in FIG. 1, reference numeral 12' corresponds to element 12 in FIG.
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. Reference number 30 is the transmitting ground station, reference number 31 is the receiving ground station, reference number 32
As a communication satellite, when transmitting horizontally polarized waves 300 and vertically polarized waves 301, cross-polarized interference from vertically polarized waves to horizontally polarized waves is up-linked (transmission towards the satellite).
The main interferences are interference 302 occurring in the down link (transmission to the ground station), interference 303 occurring in the down link (transmission to the ground station), and self-interference 304 of the horizontal polarization itself. Now, if both polarizations have the same carrier frequency,
All of these interferences are obtained as a 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 self-interference 304 is considered to be normal multi-propagation 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 block diagram of a cross-polarization compensation circuit using the automatic equalizer configuration shown in FIG. 1. In the figure, block 4010 is a filter, with reference numbers 40, 41, 42, 43, 44, 4.
5, 46 and 47 are the same as each delay circuit in FIG. 1, and reference numbers 48, 49, 50, 5
1, 52, 53, 54, 55, 56 and 57 are the same as each variable attenuator in FIG. 1, reference numeral 58 is the same as adder 10 in FIG. is the same as the sampler 11 of FIG. 1, and the reference numeral 60 is the same as the signal discriminator 12 of FIG.

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 αi·a _K+i of the self-interference 304 shown in the figure can be removed.

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

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 is used, which states that the difference can be minimized. can do. This is an extension of the root mean square equalization method described above.

FIG. 8 shows an embodiment of the present invention, and shows a cross-polarization compensation circuit using the configuration of the nonlinear automatic equalizer shown in FIG. 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 the demodulated baseband signal A _K sent by horizontal polarization, and the input terminal 121
is supplied with a demodulated baseband signal _BK sent by vertical polarization. First signal processing circuit 1
24 processes the baseband A _K and outputs A _K+i ·α _i as a first processed signal. Similarly,
The second signal processing circuit 125 receives the baseband signal.
Processes B _K and outputs a second processed signal 〓B _K+i ·β _i . 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 1.
32 is subtracted (negative addition). This adder 13
The output of 2 is then identified by a discriminator 134 to obtain an estimate A^ _K of the baseband signal _AK . This estimated value A^ _K is processed by the third signal processing circuit 126, and the aforementioned third processed signal 〓A^ _K+i ·α _i ' is obtained. On the other hand, the fourth processed signal is a baseband signal
The estimated value of BK is defined as B^ _K , and this estimated value B^ _K is obtained by 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 = _N ′ 〓 〓 A _K+i・α _i +〓B _K+i・β _i −〓A^ _K+i・α _i ′−〓B^・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 B _K ,
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
The output d _K can be expressed as follows.

d _K = −〓β _i・A _K+i +〓α _i・B _K+i +〓K _i ′・A^ _K+i −
〓α _i '·B^ _K+i FIG. 5 shows an attenuation control circuit 500 for the variable attenuator 49 of FIG. 4. In the figure,
Reference numbers 41, 45, 49, 58, 59 and 6
0 is the same as the corresponding reference numeral component 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 a block diagram of an embodiment of the present invention, showing the configuration of a cross-polarization interference equalizer for two series of data transmitted by horizontally polarized waves and vertically polarized waves. In the diagram, blocks 4000 and 400
0' are the first and second filters, and the fourth
This is the same as block 4000 in the figure. Baseband signals transmitted with both horizontal and vertical polarization are applied to input terminals 600 and 601, respectively, and block 4000 receives horizontally polarized components from which interference from vertical polarization has been removed.
0' outputs vertically polarized wave components from which interference from horizontally polarized waves has been removed to output terminals 402 and 402', respectively.

In addition, block 4000 and block 4000'
The attenuation amounts (tap gains) of the variable attenuators 48-52 and 53-57 are interchanged.

Generally, from polarization 1 to polarization 2 due to cross polarization generation
The state of interference from polarization 2 to polarization 1 can be considered to be symmetrical, and if the filter tap gain that eliminates the interference can be found from the state of interference of the former, it will be possible to eliminate the interference of the latter. There is no need to obtain a new filter tap gain for erasure. That is, by changing the tap gain of the attenuator for self-interference cancellation and the tap gain of the attenuator for cross-polarization interference without changing the order and changing the polarity, the polarization to be canceled becomes 1. It will change from 2 to 2.

Due to this fact, the filter 4000 in FIG.
When performing so-called automatic equalization that automatically controls the filters 4000 and 400',
Instead of controlling the tap gain separately for 0', it is possible to automatically control the tap gain for only one of the filters, and simply supply the obtained tap gain to the other filter by replacing it as described above. As a result, the number of control units in the device configuration can be reduced to 1/2.

FIG. 7 is a block diagram of another embodiment of the present invention, which has the same functions as FIG. 6. Input terminals 700 and 701 have horizontal and
The baseband signals transmitted by both vertically polarized waves are added, and both baseband signals from which polarization interference has been removed go out to output terminals 702 and 703.

In the figure, reference numerals 76-77, 78-97 and 98-99 are the same as the delay circuit, variable attenuator and adder of FIG. 4, respectively. This embodiment differs from FIG. 6 in that the delay circuits 40 to 47 included in filter blocks 4000 and 4000' of FIG. 6 are shared.

With this configuration, the number of expensive delay circuits can be halved.

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, and it These effects cannot be expected from the Obi-based compensation method at all.

[Brief explanation of drawings]

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. FIG. 5 is a diagram showing an attenuation amount control circuit of the variable attenuator of the filter shown in FIG. 4, and FIGS. 1 is a diagram showing a block diagram of a first and second embodiment of the invention; FIG. FIG. 8 is a circuit diagram showing one embodiment of the present invention. In the figure, 4010 is a filter, 40 to 4
7 is a delay circuit, 48 to 57 are variable attenuators, 58 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 the first and second polarized waves, which are orthogonal to each other, on the receiving side in response to the first and second sequences. 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-1, 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 αi・A _K+i + _M ′ 〓 ^i=-M βi・B _K+i − _N ′ 〓 ⁱ⁼⁰ αi′・A^ _K+i − _M ′ 〓 ⁱ⁼⁰ βi′・B^ _K+i (however , αi, βi, αi', βi' are multiple constants)...Ck-2, Ck-1, Ck, Ck
A filter that outputs +1, Ck+2... and d _K = − _M ′ 〓 ^i=-M βi・A _K+i + _N ′ 〓 ^i=-N αi・B _K+i + _M ′ 〓 ⁱ⁼⁰ βi′・A^ _K+i − _N ′ 〓 ⁱ⁼⁰ αi′・B^ _K+i 8th series...dk−2, dk−1, dk, dk+
1, dk+2..., and by passing through the first filter, cross-polarized interference from the second polarized wave to the first polarized wave is removed, and the first sequence is cross-polarization compensation, characterized in that cross-polarization interference is removed from the first polarization to the second polarization by passing the wave through the second filter, and the second sequence is obtained. circuit.