JPH034647A - Phase jitter canceller - Google Patents

Abstract

PURPOSE:To quicken the tap coefficient convergence to an optimum state by estimating the frequency of a phase jitter with a frequency estimate device and setting a tap coefficient of an FIR adaptive filter to the frequency characteristic having the narrow band pass characteristic taking the said frequency as the pass band in response to a clear signal. CONSTITUTION:A phase difference between outputs of a phase rotating device 101 and a discriminator 102 is extracted by a 2nd phase detector 106 and it is given as a setting signal to an adaptive filter 104 and a frequency estimated by a frequency estimate device 105 is given to the filter 104 and the frequency characteristic in response to the output of the frequency estimate device 105 is set to the adaptive filter 105 according to a clear signal CLR given at the initial setting of a training period and the filter 105 sends a control output in response to each output of the phase detectors 103, 106 to control the phase rotating angle of the phase rotating device 101.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a phase jitter canceller used in a data modem using quadrature amplitude modulation.

[Conventional technology]

The phase jitter Φ Yanceler is used for the purpose of correcting the phase jitter of the quadrature amplitude modulation method, and generally the following configuration is adopted.

In other words, if the received signal 4 of orthogonal polarization modulation is subjected to two-axis synchronous detection and the 9 complex baseband signal is input signal R, then the jet formula% formula%) A section: Transmission symbol (transmission number 4) In θ: Jitter After applying phase rotation for jitter correction to the phase rotation means, the received symbol is judged by a judger), the phase rotation of the phase rotation means is is an FIR
It is designed to control the output of the type adaptive filter.

Therefore, if the output of the adaptive filter is the entire section and the input of the determiner is D, then D is the sum of equation (1) plus the phase rotation of r. Therefore,
If Di is determined to be incorrect (At) by the determiner, the phase difference between the output of the phase rotation means and the output of the determiner is extracted by the phase detector, and the phase error signal g,
=θ, -? The phase jitter is canceled by controlling the phase rotation means using a control system that predicts that the phase jitter will be 0.

On the other hand, if the control system includes a Hiro adaptive filter, its tap coefficients should be set to Or (1=1.2...N)・(N
is the number of taps), the inputs for this are R3 and A.

The output A of the adaptive filter is given by the following equation.

Therefore, ’ has the following formula.

In this case, by the maximum slope method! When finding the tap coefficient Ci (K) that minimizes 'cl, Lg,l is a function that protrudes downward for each tap coefficient ci, so find the slope of 15.1 in the N-dimensional space in C1,
When the tap coefficient is updated in the direction where the slope becomes zero, I'l
l converges to a minimum value.

That is, the slope is expressed by the following equation, and when calculated using l'xl instead of l'xl, the instantaneous slope is given by the following equation.

Substituting equation (4) into equation (6), the instantaneous slope ``-2'z' becomes -1...
......(7).

Therefore, by multiplying the instantaneous slope shown by equation (7) by the correction coefficient α and updating the tap coefficient many times, the result is equivalent to equation (5). 1511
converges to the minimum value.

Therefore, the tap coefficient can be corrected according to the following formula: CI (K+1) = CI (x) + αε 0 and 1
...song/song (8) (i=1.2.3...
・N) C1,0g-1 extracts the phase difference between the input signal and the output of the determiner by the first phase detector, and
The phase difference between the outputs of the phase rotation means and the determiner is obtained by extracting it with a second phase detector, and the adaptive filter is controlled by the extracted power.

Further, the tap coefficient C1 is initially set to zero by a clear signal during the training period of the data modem, and updates are performed using this as a reference.

[Problem to be solved by the invention]

However, in the past, the tap coefficients at the adaptive fin are rounded to zero due to the initial settings, and the phase jitter is not corrected until the tap coefficients converge to the optimal state, which takes a considerable amount of time. In particular, in data modems for multipoint lines that sequentially perform data communication with multiple parties, the data transmission time after training is relatively short, and the number of training cycles is large, resulting in tap coefficients not converging. However, the data transmission is performed in a timely manner, resulting in the drawback that phase jitter correction is incomplete.

[Means to solve the problem]

To solve the above-mentioned problems, the present invention is constructed by the following means.

That is, in the above-mentioned phase jitter canceller, the frequency characteristic is a narrowband bandpass characteristic whose passband is the frequency estimated by the frequency estimator based on the output of the first phase detector in response to the initial setting clear signal. The filter is provided with an FIR type adaptive filter in which tap coefficients are set.

[Effect]

Therefore, the tap coefficients of the adaptive filter do not become zero at the time of initial setting, but are set according to the estimated frequency, so that the time required to converge to the optimal tap coefficients is shortened.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to figures showing examples.

FIG. 2 is a block diagram of the entire configuration. A complex baseband signal obtained by two-axis synchronous detection of the received signal is given to the input terminal 100 as input signals R8 and L7, and this is sent to the phase rotator 101.
After undergoing phase rotation at
The determiner 102 determines which data point the output of 01 indicates, and sends out the determined data symbol AK.

On the other hand, the first phase detector 103 receives the input signal RK and the output AK of the determiner 102, and extracts the phase difference θ between the two, which is then applied to the FIR adaptive filter 104. is given as the tap coefficient of
4 is given to the frequency estimator 105.

The adaptive filter 104 updates the tap coefficient according to equation (8) based on the output of the phase detector 103, sends out a control output x + 1 to control the phase rotation angle of the phase rotator 101, and performs the following calculation. The phase jitter of the input signal RE is suppressed, and by repeating this, the υ phase jitter is corrected to the minimum value.

Also, the second phase detector 106 extracts the phase difference between the output of the phase rotator 101 and the output of the determiner 102, and provides this as a setting signal to the adaptive filter 104.
The frequency estimated by the frequency estimator 105 is also given to the same filter 104, and the frequency characteristic corresponding to the output of the frequency estimator 105 is determined according to the clear signal CLR given at the time of initial setting of the training period. Adaptive filter 1
05, the same filter 105 sends out a control output according to each output of the phase detector 103, 106,
Phase rotator 10? The phase rotation angle is controlled.

3 is a block diagram of the phase detectors 103 and 106. Taking the phase detector 103 as an example, an input signal Rx=A1G" is given to the input terminal 201, and a determiner is provided to the input terminal 202. Given the output A = X + jyx of 102, the output A = x
11- j y is absent, and j #
, the product of the input signal RK=A weight O and AK=J冨−3j0□ jyx, IAKII! is obtained and given to the multiplier 206 via the imaginary part selector 205, where the phase difference component 6 is extracted by multiplying it by t/Dxl and sent from the output terminal 20F. .

Further, as the frequency estimator 105, the phase detector 103
A method is used that samples the output for a certain period of time and performs, for example, Fourier transform on this to obtain the estimated frequency.

FIG. 4 shows the frequency characteristics set by the clear signal CLR of the adaptive filter 104, (G) shows the amplitude characteristics,
ω) is the delay characteristic, (4) shows the change in gain G with respect to frequency f, and (3) shows the simplification of the absolute delay time T with respect to frequency f. This jitter frequency fj is obtained by estimating the output frequency of the phase detector 103 using the frequency estimator 106 described above.

Therefore, according to the clear signal CLH, the jitter frequency f
If the narrowband bandpass characteristic shown in FIG. 4 with j as the passband is set as the tap coefficient of the adaptive filter 104, the delay characteristic will be such that when an input signal of m(2fffjKT) is given, the output will be (x+1)T). Since this is the impulse response characteristic, the jitter frequency can be adjusted without updating the tap coefficient 12 times. The phase jitter of j can be suppressed.

In addition, f in Figure 4, ω) is the Templing frequency 1. In (7-ζ) of Figure 4), m is 1.2.3...
・One of the integer values such as ・is applied.

FIG. 1 is a block diagram of the adaptive filter 104, in which the output of the phase detector 103 is input to the input terminal 401, and
Heckler signal CLR, frequency estimator 10 to the same terminal 403
The output ω of 5 and the output of the phase detector 106 to the same terminal 404 are given to each 112i1, and a control output is sent from the output terminal 405, while the delay elements 411t to
411B, 4131~413!1% multiplier 412x
~412n14151~415! l, Adder 414 Otori ~
414n and 416 constitute a known FIR type adaptive filter, and selectors 4115 to 417 are provided between the tap coefficient control inputs of delay elements 413 to 413n and the outputs of adders 4141 to 414n, respectively. In addition, these respond to the clear signal CLR, select each input B, and output the trigonometric function generators 4181 to 418.
Each output of n is given to each delay element 4131 to 413n as a stamp coefficient, and each trigonometric function generator 4181 to 418n outputs th(ωτ+ψ), gln(2ωT+ψ) according to the output ω of the frequency estimator 105.
)...-(ωT and +ψ) are generated.

Therefore, if the tap order of the adaptive filter 104 is K, its tap coefficient is t as L for the clear signal CLR.
h(ωT yo+ψ), and the frequency characteristics shown in FIG. 4 are set. After that, the selectors 4111 to 417n select each input A as the clear signal CLH disappears, and the same effect as before is achieved. becomes.

〔Effect of the invention〕

As is clear from the above explanation, according to the present invention, the frequency estimator estimates the frequency of the multiphase chic, and the frequency characteristic that becomes the narrowband bandpass characteristic with this as the passband is set to F.
Since the tap coefficients of the IR type adaptive filter are set according to the clear signal, the tap coefficients converge to the optimal state quickly, and phase jitter can be corrected immediately and completely, especially for data modems on multipoint lines. Remarkable effects can be obtained.

[Brief explanation of drawings]

The figures show an embodiment of the present invention, in which Figure 1 is a block diagram of an FIR type adaptive filter, Figure 2 is a block diagram of the entire configuration, and Figure 3 is a block diagram of the entire configuration.
The figure is a block diagram of the phase detector, and FIG. 4 is a diagram showing the frequency characteristics of the FIR type adaptive filter. 101... Phase rotator, 102... φ... Determiner, 1
03.108...Salary/phase detector, 1040-...-FI
R-type adaptive filter, 105...frequency estimator, 41
11. 〜411+x−4131〜413n...-Delay element, 4121〜4121.4151〜415n Hisashi...
・Multiplier, 414t to 414n, 416 ""
' ``Adder, 4171 to 417n---Selector,
41L~418n...φ・Trigonometric function generator, CLR...
φ・Clear signal.

Claims (1)

[Claims] a phase rotation means for imparting phase rotation to a complex baseband signal obtained by two-axis synchronous detection of received signals; a determiner for determining a received symbol by inputting the output of the phase rotation means; a first phase detection means for extracting the phase difference with the baseband signal; a frequency estimator for estimating the output frequency of the phase detection means; and a first phase detection means for extracting the phase difference between the output of the phase rotation means and the output of the determiner. and an FIR type adaptive filter that controls the phase rotation of the phase rotation means according to each output of the first phase detection means, the frequency estimator, and the second phase detection means. In the phase jitter canceller, the FIR type adaptive filter is provided in which the tap coefficient is set to a frequency characteristic having a narrowband bandpass characteristic whose passband is the frequency estimated by the frequency estimator in response to the initial setting clear signal. Features a phase jitter canceller.