JPH0253316A - Phase jitter canceller - Google Patents

Abstract

PURPOSE:To make a phase jitter canceller stable by varying the value of a correction coefficient of a tap of an FIR adaptive filter in response to a distance of a reception symbol from the origin. CONSTITUTION:The size of an input symbol is calculated by a square device 301, a threshold level given by a comparator 302 is compared with an output ¦AK¦<2> of the square device 301 and a signal representing two cases, the output ¦AK¦<2> is larger than the threshold level and smaller than the threshold level, is outputted. Then a selector 303 selects one of two kinds of correction coefficients by using the signal, and a correction coefficient alpha1 is outputted when the value ¦AK¦<2> is larger than a threshold level and a correction coefficient alpha2 is outputted when the value ¦AK¦<2> is smaller than the threshold level. Since much noise component is included in the output of a phase detector 103 when the value ¦AK¦<2> is smaller than a threshold level, the coefficient alpha1 is made small so as not to correct the tap gain of the FIR adaptive filter 105 largely, and when the value ¦AK¦<2> is larger than the threshold level conversely, the coefficient alpha2 is made large so as not to correct the tap gain of the FIR adaptive filter 105 largely. Thus, a stable phase jitter canceller is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a data modem using quadrature amplitude modulation, and more particularly to a phase jitter canceller.

[Conventional technology]

An example of a conventional phase jitter canceller is shown in FIG. 4 and will be described.

In the figure, 401 is a complex multiplier, 402 is a judger, 4
03.404 is a phase detector, 405 is a multiplier, 406 is an FIR (F1nit@Imputae Re5pons
e) Adaptive filter, 407 is a trigonometric function generator.

The received signal RK affected by the phase jitter is expressed as follows.

1t = A ejI'K ・・・・・・・・・・・・
... α)! ! (j,: transmitted symbol, θ, phase angle due to rainbow) On the other hand, if the output of the FIR adaptive filter 406 is θ, the input D1 to the determiner 402 is expressed as θ,
It is expressed by giving a phase rotation of , as shown in the following equation.

,)yo=A1j(θ,-〇π> ,,,,,,,,,,,
, , , , , , , , ■) Here, the phase error signal is h
= θ-Q, then by predicting the Q factor so that @8=O, the phase jitter θ error introduced by the line can be suppressed.

Next, t! However, conventionally, for the generation of 9 filters, the fifth method shown in the configuration diagram showing the details of the FIR type adaptive filter is used.
It is generated by an FIR type adaptive filter as shown in the figure.

In FIG. 5, 501 is a delay element, 502 is a multiplier, 503 is an adder, 504 is a complex conjugate multiplier, and 505 is a multiplier.
is an adder. Further, IN indicates an input, and ER indicates an error signal.

Now, the coefficient of the FIR type adaptive filter is 01(x)(1=
e1.2......,N), (N is the number of taps), the output of the filter can be expressed as follows.

1=1 Therefore, 6 ri is 3, -θ, -Σ C1(t) Work' x-1 song...0...
(4) i=x.

Here, the maximum slope method is used to find the tap gain that minimizes 1·,1.

Since 1$1 is a downward convex function for each tap gain CIK, it is 1 in the N-dimensional space for each tap gain cxK.
If the slope of 8.1 is found and the tap gain is updated so that the slope becomes zero (0), it converges to the minimum value.

θglex12 slope = ・・・・・・・・・・・・・・・
・・・・・・・・・・・・ 0) θel (hiro) Here, E ('II'') is converted to the above (5
) is expanded, it is expressed as . Furthermore, since al is expressed as in equation (4) above, instantaneous slope=-2"K 't-1...
・・・・・・・・・・・・・・・ (7)

Therefore, by multiplying the slope used by the equation σ) by the correction coefficient α and updating the tap gain many times, it becomes equivalent to the equation 0) above, and the tap gain is eventually updated modulo. As a result, E(reference-) converges to the minimum value.

CI (+t-H) = C1(+c)+α8xθto1
°−−−−−−−−−−°−°°−@) (1: 1.
2, 3.・・・・・・・・・・・・N) In addition, “1l
-1 at Ll' can be obtained by connecting the phase extraction means as shown in FIG. 4, as shown in FIG. 2, which is a diagram showing details of the phase detector.

FIG. 6 is an explanatory diagram comparing the influence of phase on noise depending on the distance of the reception point from the origin.

In this Fig. 6, A and B respectively indicate receiving points,
N indicates a noise vector.

[Problem to be solved by the invention]

In the conventional phase jitter canceller described above, when updating the tap gain of the FIR type adaptive filter, the error signal is rounded and the received signal close to the origin with many noise components generates a signal. In this case, there was a frequent problem that the update of the tap gain was disturbed by noise.

FIG. 6 shows an example in which the influence of noise on the phase angle is compared between a reception point close to the origin and a reception point far from the origin.

[Means to solve the problem]

The phase jitter canceller of the present invention includes at least a phase rotation means for applying phase rotation according to a control angle to a complex baseband signal obtained by two-axis synchronous detection of a received signal, and a received symbol using the output of the phase rotation means as an input. a determiner that determines and outputs the determined symbol; a first phase detection means that extracts a phase error between the output of the determiner and the received signal; and a first phase detector that extracts a phase error between the output of the determiner and the output of the phase rotation means. It is composed of a second phase detection means for extracting a phase error, and an FIR type adaptive filter that receives the output of the first phase detection means and outputs a control angle to the phase rotation means,
In a data modem having a predictive jitter canceller that controls tap coefficients of the FIR type adaptive filter so as to reduce the output of the second phase detection means by the output of the second phase detection means, the output of the determiner A controller is provided that receives a symbol as input and outputs a signal for controlling the magnitude of the output of the second phase detection means according to the absolute value of the input, and when the absolute value of the received symbol is small, the FIR type adaptive filter is activated. This is to control so that the correction coefficient becomes small.

[Effect]

In the present invention, by changing the magnitude of the correction coefficient of the tap of the FIR type adaptive filter according to the distance from the origin of the received symbol, it is possible to improve the phase extracted by the received symbol close to the origin with poor S/NO. The correction coefficient is made small for the error signal to suppress tap correction.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram showing an embodiment of a phase jitter canceler according to the present invention.

In the figure, 101 is a rounding complex multiplier that suppresses phase jitter components, and this complex multiplier 101 is a phase rotation means that applies nine phase rotations according to the control angle to a complex baseband signal obtained by two-wheel synchronous detection of a received signal. It consists of

102 is a determiner that receives the output of the phase rotation means as input, determines the received symbol, and outputs the determined symbol;
Reference numeral 3 designates a phase detector which receives the output of the determiner 102 and the output of the complex multiplier 101 as input, and this phase detector 103 is a phase detector that extracts the phase error between the output of the determiner 102 and the output of the phase rotation means. constitutes a means. 104 is a phase detector which receives the output of the determiner 102 and the received signal as input;
This phase detector f04 constitutes a phase detecting means for extracting a phase error between the output of the determiner 102 and the received signal.

Reference numeral 105 is an FIR type adaptive filter which inputs the output of the phase detection means made up of the phase detector 104 and outputs a control angle to the phase rotation means made up of the complex multiplier 101. Then, the output of the phase detection means consisting of the phase detector 103 is used to reduce the output of the phase detection means (FIR
The tap coefficients of the type adaptive filter 105 are controlled.

Reference numeral 106 denotes a controller which receives the output symbol of the determiner 102 and outputs a signal for controlling the magnitude of the output of the phase detection means consisting of the phase detector 103 according to the absolute value of the input. When the absolute value of the received symbol is small, the correction coefficient of the F'IR adaptive filter 105 is controlled to be small. 107 is FI
A trigonometric function generator 108 which receives the output of the R-type adaptive filter 105 as an input and sends the output to the complex multiplier 101 is a multiplier.

Next, the operation of the embodiment shown in FIG. 1 will be explained.

First, the determiner 102 determines which data point the output of the multiple multiplier 101 is sent as, and outputs the determined data symbol. The phase detector 104 extracts the phase angle component of the jitter from the received signal A, , ja, output from the determiner 102, the details of which are shown in Figure 2.

In this @2 diagram, 201 is the first input, 202 is the second input, 203 is the complex conjugator, 204 is the multiplier, 20
5 is an imaginary part selector, 206 is a multiplier, and 207 is an output.

In this FIG. 2, an input 201 receives an input A, and an input 202 receives an input AA. This human power is 20
2K input AzB complex conjugator 203
is output, and the multiplier 204 outputs A of the input 201,
, j#, and then the output l A of the multiplier 204
t l""' is input to the imaginary part selector 205, and the multiplier 206 outputs /1□IC'! ” The phase difference component θ is extracted by multiplying by .

In this way, θ extracted by the phase detector 104 is input to the tap of the FIR adaptive filter 05.

Next, the tap gain of the F'IR type adaptive filter 105 is determined.

First, A1 is output to the phase detector whose details are shown in FIG. After this phase error component is multiplied by a correction coefficient α which is the output of the controller 108, it is input to the FIR adaptive filter 105 which is corrected as shown in the following equation.

C> (t + t) = c1 (0+ (1e t
a t ++ i +++ ++++++++ (9)
(i: 1, 2. . . . , N) In this way, the tap gain converges to 1 so that 1 is minimized.

The operation of the controller 10G at this time will be explained with reference to FIG. 3, which shows an embodiment of the controller.

In FIG. 3, 301 is a squarer, and 302i is a comparator 30 that compares the output of this squarer 301 with a threshold.
3 is a selector.

The output A1 of the determiner 102 is input to the input of the controller 106. Therefore, first, the magnitude of the input symbol is calculated by the squarer 301, and then the magnitude of the input symbol is calculated by the comparator 302 and the output InK1 of the squarer 301 is calculated.
The selector 303 selects one of the two types of correction coefficients based on this signal, and selects one of the two types of correction coefficients when lA31 is a certain threshold. α if greater than ! .

If a certain threshold is also smaller, α2 is output as the correction coefficient α.

At this time, if υ is smaller than the threshold at which I'l[+ is, the output of the phase detector 103 will contain many noise components, so the correction coefficient α is set so that the tap gain of the FIR adaptive filter 105 is not modified too much. Make it smaller and α! , conversely, α is assumed to be large.

〔Effect of the invention〕

As explained above, the present invention changes the magnitude of the correction coefficient of the tap of the FIR adaptive filter according to the distance from the origin of the received symbol, thereby making it possible to improve the accuracy of the received symbol near the origin with poor S/N. By reducing the correction coefficient for the output phase error signal and suppressing the tap correction, a more stable phase jitter canceller can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the phase jitter canceller 2 according to the present invention, FIG. M2 is a block diagram showing an embodiment of the phase detector in FIG. 1, and FIG. 3 is an embodiment of the controller in FIG. 1. 4 is a block diagram showing an example of a conventional phase jitter canceller, and FIG. 5 is a block diagram showing an example of a conventional phase jitter canceller.
A configuration diagram showing details of the FIR type adaptive filter in the figure,
FIG. 6 is an explanatory diagram comparing the influence of phase on noise depending on the distance of the receiving point from the origin. 101...Complex multiplier, 102-...Determiner, 1
G3,104 ・No.・・Phase detector, 105−・・φ
FIR type adaptive filter, 106...controller.

Claims (1)

[Claims] At least a phase rotation means for applying phase rotation according to a control angle to a complex baseband signal obtained by two-axis synchronous detection of a received signal, and a received symbol is determined using the output of this phase rotation means as input, and the determined symbol is output. a first phase detection means for extracting a phase error between the output of the determiner and the received signal; and a second phase detecting means for extracting a phase error between the output of the determiner and the output of the phase rotation means. It is composed of a phase detection means and an FIR type adaptive filter which receives the output of the first phase detection means and outputs a control angle to the phase rotation means, and the second phase is determined by the output of the second phase detection means. In a data modem having a predictive jitter canceller that controls the tap coefficients of the FIR type adaptive filter in order to reduce the output of the detection means, the second It is characterized by comprising a controller that outputs a signal for controlling the magnitude of the output of the phase detection means, and controlling the correction coefficient of the FIR type adaptive filter to become small when the absolute value of the received symbol is small. phase jitter canceller.