JPS61161838A - Cross polarized wave compensating circuit - Google Patents

Abstract

PURPOSE:To share a cross polarized wave by applying cross polarized wave compensation at a base band so as to avoid modification of a transmission/ reception signal for an in-use single polarized wave. CONSTITUTION:A demodulated base band signal transmitted in a horizontal polarized wave is inputted to an input terminal 400, it is retarded by delay circuits 40-43, added by variable attenuators 48-52 and synthesized. A tentative identification value is inputted by a tentative identification device 70 to an input terminal 401 in place of application of a vertical polarized wave side base band signal. Since a true identification value is obtained timewise for a signal given to delay circuits 46, 47, the true identification value is inputted from a terminal 403. Through the constitution above, only the cross transmission line characteristic from the interruption side to a desired wave side is simulated and the reduction of the cross polarized wave compensating capability due to generation of a deep fading dip at the main transmission line of the interruption side is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a technology for compensating for cross-polarization interference that occurs with orthogonal polarization sharing in wireless transmission.

(Prior art and its problems) Microwave band wireless communication is rapidly developing, centering on terrestrial communication and satellite communication. 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. My thoughts are growing. The use of orthogonal polarization is already specified in the CCIR (Consultative Committee on International Radiocommunications) recommendation regarding FM radio frequency allocation between 4 and 6 GHz.

In addition, in satellite communications, the IN-based SAT (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 in satellite satellites with single polarization.

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. It has become a challenge.

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 method is adopted, there will be cross bias.

Coupling between polarized waves caused by generation of waves causes interference between channels of different polarizations. 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 requires a variable phase shifter and an attenuator to be installed around the antenna feeder to restore orthogonality. Various methods have been well researched and put into practical use, such as methods that eliminate interference between different polarized waves, and methods that eliminate interference between different polarized waves by installing an interference wave compensation circuit in the intermediate frequency band.

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

(Objective of the Invention) An object of the present invention is to provide a cross-polarization compensation circuit for sharing cross-polarization and doubly utilizing a frequency band in digital transmission.

According to the present invention, it is possible to perform digital transmission for orthogonal polarization at the same carrier frequency through a current single-polarization antenna system and intermediate frequency equipment.

Currently, the beam width of satellite antennas is considerably wider than that of terrestrial micro-links, and global beam antennas use asymmetric beams to increase effective transmission power.・Due to rotation, etc., high orthogonal polarization discrimination cannot be expected.

In such a transmission system, the present invention has a marked advantage over the conventional system, and is more economical in that it does not require any modification to the existing 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.

(Structure of the Invention) According to the present invention, in digital wireless transmission in which first and second digital sequences (ak) and (bk) of the same bit rate are placed on first and second polarized waves that are orthogonal to each other, The signals received from the first and second polarized waves are each (Ak
), (Bk), identify the above (Bk) and calculate the value for each temporary line (
A cross-polarization compensation circuit is obtained, which is comprised of a temporary line separator that obtains Bk), and a filter that is supplied with the above (Ah) and the output of the temporary line separator and obtains an output.

(Detailed explanation of configuration) Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram of a conventional linear automatic equalizer for digital transmission. Terminal 100 has band-limited random pulses...ak-1, ak + ak
+ 1 ”... are added one after another at intervals of T seconds.

In the figure, reference numbers 1, 2, 3 and 4 are T seconds 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, and reference numeral 12 is a signal identification circuit, which detects the received signal when pulse ake is transmitted. The estimated value Ak& is obtained from A, and if no transmission error occurs, ak=Ak2- is estimated.

As is clear from the figure, the function of the equalizer in Figure 1 is
The purpose is to cancel the code amount interference from the transmitted code using variable attenuation B5.6.7.8 and 9. Attenuation of variable attenuators 5.6.7.8 and 9.

There are various algorithms for automatically and ideally changing i.
ical Journal; BSTJ) vol, 4
4. "Automatic equalization for digital communication" described on pp547-588
for digital communication
) The zero forcing method shown in J.

BSTJ vol. 46, published November 1967. p
“An Automatic Equalizer 7 Authentic Purpose Communication Channel” described on p. 2179-2208.
alizer for general purpos
The root mean square equalization method shown in the communication channel January is generally known.

Also, although the structure is slightly different, IEE Transactions on Information Theory (IEEE TRN5ACTIO) published in May 1970
NSON INFORMATION THEORY) magazine, vol, IT-16, pp270-276 [
Analysis Op-Decision Directed Receiver with Unknown Prior
f a Decision Directed Rec
There are also nonlinear automatic equalization methods such as the one shown in Unknown Prlor.

Furthermore, if the signal applied to the input terminal in Fig. 2 is a complex signal subjected to quadrature phase modulation or 16-value quadrature amplitude modulation,
E TRN5ACTIONS ON COMMUNI-
CATIONS), vol, cOM-23, pp 68
4-687, “Two Extensional Applications Op.
applications of the Zer.

Forcing Equation Method
d) There is an automatic equalization method shown in J.

The actual equalizer configuration using 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 shown in Figure 2. It is structured like this.

FIG. 3 shows a block diagram of a conventional nonlinear automatic equalizer,
Reference numerals 1', 2', 3' and 4' refer to elements 1, 2, . -corresponding to 3 and 4, reference numeral 5',
6', 7', 8' and 9' correspond to elements 5, 6, 7, 8 and 9 of FIG. 1, reference numeral 10' corresponds to element 10 of FIG. '' corresponds to component 11 in FIG. 1, reference numeral 12' corresponds to component 12 in FIG. 1, and reference numerals 13 and 14 are adders.

The configuration of FIG. 3 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. 2. Therefore, the configuration of the automatic equalizer for wireless digital transmission, which will be treated later, is as follows.
Consider the one in Figure 2.

However, in this case, the variable attenuator handles complex signals.

FIG. 4 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 3
When 1 is the receiving ground station and reference numeral 32 is the communication satellite, transmitting horizontal polarization 300 and vertical polarization 301, cross-polarization interference from vertical polarization to horizontal polarization will occur on the up link (intra-satellite transmission). The main ones are interference 302 that occurs, interference 303 that occurs in the down link (transmission within the ground station), and self-interference 304 of the horizontal polarization itself.

Now, assuming that both waves have the same carrier frequency, all these interferences are caused by the base frequency obtained by synchronous detection.
In a band signal, it is obtained as the sum of each interference.

Therefore, if the interference components are accurately determined, it can be seen that the interference components 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. 5 is a block diagram of a conventionally known cross-polarization compensation circuit using linear calculation. Block 4010 in the figure is a filter, reference numbers 40.41, 42.43, 44, 45.46 and 47 are the same as each delay circuit in FIG. 2, reference numbers 48.49.50.51 .5
2.53.54.55° 56 and 57 are the same as each variable attenuator in FIG. 2, reference numeral 58 is the same as adder 10 in FIG. It is the same as the signal discriminator 11 in FIG. 1, and the reference numeral 60 is the same as the signal discriminator 12 in FIG.

First, a demodulated baseband signal sent by horizontal polarization is applied to input terminal 400, and a demodulated penis band signal sent by vertical polarization is applied to 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 can remove the sum of the waveform distortion of the horizontally polarized component itself and the self-interference 304 shown in FIG.

The outputs from attenuators 53, 54, 55, 56 and 57 can then eliminate the sum of cross-polarization interference 302 and 303 of FIG. Iil is output terminal 40
2, only the horizontally polarized wave component from which all interference has been removed is output.

Here, attenuators 48.49.50.51.52.53.
The control algorithm for the attenuation 'it pt of 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 using the orthogonality principle that the difference can be minimized by selecting the amount of attenuation (tap gain) of each attenuator so that the difference between the received code and its estimated value is orthogonal to the input of the attenuator. Can be done. This is an extension of the root mean square equalization method described above.

FIG. 6 shows an attenuation amount control circuit 500 for the variable attenuator 49 of FIG. In the figure, reference numeral 41,
45.49.58.59. and 60 are the same as the components with corresponding reference numerals in FIG. Addition G6B is used for receiving. Also, multiplier 6
1 and the detector 62 are used to detect the orthogonality between the next reception code A, +1 and the previous (A, -Ak), and the attenuation amount of the variable attenuator is determined depending on the sign of the correlation. It operates to increase or decrease i.

Attenuation control of other variable attenuators can be performed using the same method, and if the line is stable and there is no line switching, the attenuation control circuit 500 is unnecessary. In this case, the amount of attenuation of each attenuator may be preset appropriately.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention. 1st
The difference between the figure and FIG. 4 is that instead of adding the vertical polarization side baseband signal to the input terminal 401,
The point is that the temporary line-specific value (referred to as the temporary line-specific value to distinguish it from the signal identification value after cross-polarization interference removal) is input. However, for the signals entering the delay circuits 46 and 47, the true discrimination value can be obtained in terms of time, so the true discrimination value can be input from the terminal 403. By adopting such a configuration, the tap coefficient on the conventional interference side can be reduced to 53.54.
．． 55, 56, and 57 also simulated the inverse characteristics of the main transmission path characteristics on the interfering side, but this is no longer necessary and it is sufficient to simulate only the cross transmission path characteristics from the interfering side to the desired wave side. This reduces the reduction in cross-polarization compensation ability due to the occurrence of deep fading dips in the main transmission path on the interfering side. In addition, the identification error due to different temporary lines is caused by the modulation signal being 64Q.
In the case of multi-level signals such as AM, this is not a big problem.

(Effects of the Invention) As described above, according to the present invention, cross-polarized wave compensation can be performed in the base band, so cross-polarized wave compensation can be performed without any modification to the currently used single-polarized transmitting and receiving signals. Sharing can be realized.

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 TDMAffl signals, and is particularly useful for conventional power feeding systems and intermediate frequency bands. These effects cannot be expected from the compensation law in Japan.

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 are the largest disturbance, but 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 drawings]

Figure 1 is a block diagram showing an embodiment of the present invention, Figures 2 and 3 are block diagrams of a conventional automatic equalizer, and Figure 4 is for explaining cross-polarization interference in satellite communications. , FIG. 5 is a block diagram of a conventional cross-polarization compensation circuit using linear calculation, and FIG. 6 is a diagram showing an attenuation amount control circuit. In the figure, 4010...Filter 40-47...
Delay circuits 48 to 57...Variable attenuator 58.
... Adder 59 ... Sampler 60.
...Signal discriminator 70...Interfering side signal discriminator O 1 Figure

Claims (1)

[Claims] First and second digital sequences of the same bit rate {a
_k}, {b_k} on first and second polarized waves that are orthogonal to each other, the first and second
The signals received from the polarized waves of {A_k} and {B_k
}, a temporary classifier that identifies the {B_k} and obtains a temporary identification value {■_k}, and the {A_k} and temporary classifier output are supplied, and Σ^N^′_i_=_−_Nα_i・A_k_
＋＿i＋Σ＾M^′＿i＿＝＿−＿Mβ＿i・■＿k＿
+_i (α_i, β_i complex numbers, M, M', N, N' positive integers).