JPS61167229A - Adaptive equalizing system - Google Patents

Abstract

PURPOSE:To improve the information transmission speed by applying once equalizing processing to all quantized transmission characteristics in variance to reduce the adaptive equalizing processing time. CONSTITUTION:An input digital base band signal from an input terminal 11 at the transmission side is converted into a transmission line code from which a code error and block synchronization are detected by a transmission line code converting circuit 21. The converted base band signal is converted (12) into a carrier modulation signal and transmitted to a time constant change transmission line 13. The signal is converted into a base band signal subjected to waveform distortion by a demodulation circuit 14 at the reception side, fed to quantized transmission parameter equalizing circuits 11-1N in parallel, subjected respectively to equalizing processing and the waveform distortion is compensated.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention relates to an adaptive equalization method for digital signals transmitted through a time-varying transmission line in which channel characteristics change over time, such as in a mobile communication system. be.

"Prior art" Equalization is the inverse function 1/H(f) of the transfer function H(f) of the transmission line.
This is a waveform shaping technique used in waveform transmission that corrects the waveform distortion of the signal that occurs in the transmission line by using the equalization function as an equalization function.

FIG. 4 shows a typical conventional adaptive equalization method for a transmission line whose characteristics change over time. (*For example, Hiroshi Miyayo et al.: Digital Signal Processing, pp. 233. Journal of the Institute of Electronics and Communication Engineers, November 1950). On the transmitting side, the input digital paceband signal from the input terminal 11 is converted by the modulation circuit 12 into a carrier wave modulation signal suitable for the transmission medium, and sent to the time-varying transmission line 13. On the other hand, on the receiving side, the demodulation circuit 14 converts the carrier modulation signal into a paypant signal. The transmission path characteristic estimation control circuit 15 estimates the transmission path characteristics by correlation processing from the paypant signal received by the waveform distortion signal through the transmission path 13, and determines the equalization parameters of the equalization circuit 16. Equalization parameters are determined 72: the equalization circuit 16 compensates for the waveform distortion received by the transmission line 13 on the payspunt signal from the demodulation circuit 14, and sends it to the identification circuit 17. The identification circuit 14Fi identifies the output equalized waveform f from the equalization circuit, and sends the identification output to the output terminal 18 as a reproduced digital signal.

"Problems to be Solved by the Invention" This conventional method estimates transmission path parameters from correlation information of transmission path output signal sequences, so it requires many samples to extract transmission path parameters with good phase variation. It takes a long time to find all the optimal values. For this reason, the equalization characteristic of the equalization circuit 16 is rarely able to track fluctuations in the transmission path characteristics of the time-varying transmission path 13, where the transmission path characteristics change quickly over time, such as in a mobile communication system. t-Means for solving the problem J According to the present invention, on the transmitting side, the input digital signal is converted into a transmission line code that can detect code errors and sent out, and on the receiving side, N (N is an integer of 2 or more) are transmitted. A received code sequence is equalized by a quantized transmission line parameter equalization circuit, and these quantized transmission line parameter equalization circuits calculate the range of changeable transmission line parameters in the transmission line when the space is divided into jkN spaces. The deterioration due to the equalization residual for the received signal corresponding to is set to be less than a predetermined value, that is, a value that does not cause code errors, and is therefore to the extent that it can be correctly identified by any of the received code string FiN quantized transmission line parameter equalization circuits. is equalized to Each of the outputs of these N quantized transmission parameter equalization circuits is code-identified by a separate identification circuit, and the output code series of these N identification circuits is subjected to a code error rate detection circuit, respectively, by a separate code error detection circuit. The equalization sequence selection switch control unit determines the equalization sequence with the minimum code error rate based on the nine code error rates detected, and the switch circuit unit is controlled by the equalization sequence selection switch control unit. One of the code sequences with the smallest code error piecewise on the time axis is selected from among the output code sequences of the N identification circuits, and this selected code sequence is a transmission line code that can detect code errors on the transmitting side. Embodiment FIG. 1 is a block diagram of an adaptive equalization system according to an embodiment of the present invention. On the transmitting side, the input digital baseband signal from the input terminal 11 is converted by the transmission line code conversion circuit 21 into a transmission line code in which code errors can be detected and block synchronization can be detected. If this circuit 21 performs DC balanced mB-nB code conversion, this code becomes the word digital sum (
Since WordDigitalSum) is always zero, code errors in modes that violate this rule can be detected (Tenjo, Otake: “Analog-digital width multiplexing communication system using DC balanced mB-nB codes” Institute of Electronics and Communication Engineers) Journal (B) vol, J66-B, 412, pp
-1470 to 1477. December 1983).

The payspant signal converted into a transmission line code capable of detecting code errors and detecting block synchronization is converted into a carrier modulation signal such as an AM modulation signal in a modulation circuit 12 and sent to a time-varying transmission line 13.

On the other hand, on the receiving side, the carrier modulated signal is converted by the demodulation circuit 14 into a paypant signal which has undergone waveform distortion through the transmission path. quantized transmission line parameter equalization circuit 11 for payspunt signals ViN that have undergone waveform distortion;
They are supplied in parallel to IN and are each subjected to equalization processing to compensate for waveform distortion.

Here, the equalization characteristics of the quantization transmission line parameter equalization circuit are determined as follows.

It is assumed that the transmission path characteristics can be expressed by M percentage parameters, and the transmission path parameter vector can be expressed by equation (1).

IK= (X", X", X(@, -, x(M))
(: K (1) At this time, the transfer function of this transmission path is expressed as H(oc, f).For example, the transfer function of selective fading caused by multipath is H(f)=l−Σ 1(1 ) e J 2 K f t
It is expressed as f+1i=1. In this case, the characteristic parameters X of the transmission path characteristics are two, the reflection coefficient r(i) and the delay time difference τ(i), and the transmission path parameter vector X is expressed by the following equation.

x== (r(1), ,y-(2), ,,,,
1ω y(1), 7C2), ,,,,
r(k) ) (1) The range that can be obtained depending on the transmission path of the transmission path parameter vector expressed by the equation (1) is called a transmission path parameter space S. As shown in Fig. 2, this transmission line parameter space S has N (N is an integer of 2 or more)
) is divided into subspaces $1r'PNH...IN, and the transmission line parameter vectors Q(K
) are expressed as the respective formulas to calculate the transmission line parameters γ.

111 + "' * YN, it can be expressed as the re-edge of the multiplexed transmission line parameter space Y from the transmission line parameter space X. In other words, the relationship of equation 9 (1) is created.

At this time, if the number of fractions N of the transmission path parameter space S is as small as possible, then the signal with the transmission path parameter that can be taken in each subspace $i is converted to its quantized transmission path parameter Y.
Signal deterioration d(DC・y
l ) is below a certain value C. In other words, the number of representative points N is N=min (N' l X -, U $ 1)
(3) 1=1, and the degradation due to equalization residual d(llK+v4) is (
d(IX, vH)≦ε(constant)lor($4(i=i,
2, 3. ......, N)) (4). This g is set to a value as large as possible so that the equalized output code can be identified without error.

In this way, by quantizing the transmission path parameter 't and providing an equalization circuit for its doji-ized point in parallel, an equalization sequence that reduces the deterioration to 8 or less for the signal at any point in the transmission path parameter space can be created. , at least one of the N equalization sequences exists.

The equalization function E(
yH, f) is 1/)((vi, f).

H(yl, f) is a transfer function corresponding to each subspace $i. In the identification circuits 21 to 2N, each output signal of the quantized transmission line parameter equalization circuits 11 to IN is identified and converted into a digital code. These identification circuits 21
The output digital code of ~2N is a sign error detection circuit 31~
At 3N, block synchronization of each digital code sequence is performed, and code errors in codes within blocks of each digital code sequence are detected and counted.

Here, since there is at least one deterioration of the output signal of the quantized transmission line parameter equalization circuits 11 to IN that is less than or equal to ε, the block length is set so that the change in the transmission line characteristics can be regarded as steady within one block. If you choose gold, there will be an equalized sequence without at least one code error in the observation of code errors in one block time.

The equalization sequence selection switch control circuit 22 determines the digital code sequence having the minimum code error rate for each block based on the code error information of each digital code sequence detected by the code error υ detection circuit units 31 to 3N. . The switch circuit 23 is controlled by the determination signal from the equalization sequence selection switch control circuit 22, and one equalization sequence that minimizes the bit error rate is selected for each block from among the N equalization sequences.

Since the entire time of one block length is required to detect a code error in a block, the identification circuits 21 to 2N are used to select the block whose code errors have been counted in the integer circuit 23. switch circuit 23
A delay circuit 41 having a delay time of one block length between
~4N' respectively.

The digital code of the equalized sequence having the minimum code error rate selected from the N equalized sequences by the switch circuit 23 is converted into a transmission line in which code errors can be detected and block synchronization can be detected in the transmission line code inverse conversion circuit 24. The code is converted into an original digital signal and output to the output terminal 18.

FIG. 3 shows a partial configuration of an example in which the present invention is applied to a time-varying transmission line 13 having selectivity fading characteristics caused by multipath. This example is a case of two-wave interference, and the transfer function of the transmission line 13 due to the two paths HH(f)=1-r-
The transmission path parameter space ■ in the e-edition 2″fr table is given by X [O≦r<1.0≦τ], and the can equalization circuits 11 and 12 are delayed by the equalization output tτei in the delay circuit 25. At the same time, the reflection coefficient rei is multiplied by the multiplier circuit 26 and the resultant signal is added to the input signal by the AD calculation circuit 27.

``Effects of the Invention'' As explained above, the adaptive equalization method of the present invention can perform equalization processing for all fluctuating quantized transmission path characteristics at once, which eliminates the need for transmission that requires a lot of processing time. Since there is no need to perform processing for estimating transmission channel characteristics using correlation information of channel output signals, it is possible to significantly shorten the adaptive equalization processing time for a time-varying transmission channel whose transmission channel characteristics change over time. Therefore, by applying the method of the present invention to a digital communication system, such as a mobile communication system, in which transmission path characteristics change extremely quickly, the information transmission speed can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of the configuration of an adaptive equalization system according to the present invention. FIG. 2 is a diagram showing the relationship between the transmission path parameter space and the quantized transmission path parameter space.
FIG. 4 is a block diagram showing a configuration of a conventional adaptive equalization system. 11-IN... Equalization circuit, 21-2N... Identification circuit, 31-3N... Code error detection circuit, 41-4N...
・Delay circuit, 11... Signal input terminal, 12... Modulation circuit, 13... Time-varying transmission line, 14... Demodulation circuit, 1
8... Signal output terminal, 21... Transmission line code conversion circuit, 22... Equalization sequence selection switch control circuit, 23...
- Switch circuit, 24... Transmission line code inverse conversion circuit. Patent issued by Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] (1) In an adaptive equalization method that extracts and equalizes transmission path parameters that vary over time, the transmitting device is equipped with a transmission path code conversion circuit that converts the input digital signal into a transmission path code that can detect code errors. N (N is an integer of 2 or more) quantized transmission line parameter equalization circuits installed in the receiving device and installed in parallel, and these quantized transmission line parameter equalization circuits The fluctuation range is divided into N spaces, and the deterioration due to the equalization residual for the corresponding input code is set to be below a certain value, and each equalized output signal of these quantized transmission line parameter equalization circuits N identification circuits that identify the code, N code error detection circuits that respectively detect the code error rates of the output code sequences of these identification circuits, and a minimum equalization sequence of these detected N code error rates. and an equalization sequence selection switch control unit that determines one of the output code sequences of the N discrimination circuits on the time axis based on the equalization sequence selection signal of the equalization sequence selection switch control unit. It is characterized by being provided with a switch circuit that selects the minimum code error code sequence, and a transmission line code inverse conversion circuit that converts the transmission line code that can detect code errors, which is the output signal of the switch circuit, into the original digital signal. Adaptive equalization method.