JPS6158065B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sampling phase control device in a data transmission receiver using class 4 partial response.

Class 4 partial response is a class of correlated transmission characterized by the impulse response shown in Figure 1, and waveforms with such impulse responses are produced by conventional sampling methods used to explore the symmetry of waveforms. It has been difficult to apply phase control methods. The present invention provides means for controlling the sampling phase to a symmetric point of a waveform in the same sense as normal correlation transmission by once removing the correlation of class 4 partial responses by inverse transformation.

The principle of the present invention will be described in detail below.

The random transmission symbol sequence is {ai}, and the sample value of the impulse response is h _-k as shown in Figure 1.
Let h ₀ , h ₁ , h ₂ , ... h _k be the sample value y _o of the received baseband signal at t=nT, excluding noise. It is expressed as In class 4 partial response, h ₀ 〓1, h ₂ 〓-1, so Therefore, the estimated value b _o of (a _o −a _o-2 ) is obtained from _yo .

Now, if we apply inverse transformation to b _o to remove the correlation of the class 4 partial response, c _o = c _{o -2} + b _o = a _o + c and the estimated value of _{a o and} the indeterminate number c. You can get peace.

Here, if the correlation between c _o-1 and y _o is R _o , then R _o
The average value of Here, assuming that the data sequence {a _k } is a random sequence with an average value of 0 (this assumption holds true in normal data transmission using a scrambler), ² holds that the code average power _i = 0, so the first term on the right side of the above equation is the judgment result a _o-1
If is almost correct, it takes a non-zero value only when i=n-1, and the second term becomes zero.

Therefore, R _o = ² h _o-(o-1) = ² h ₁ Furthermore, since the average power ² is normally normalized to 1, _o = h ₁ , which corresponds to the impulse response sample value h ₁ in Figure 1. becomes.

As shown in Figure 1, the value of h ₁ takes a negative value when the sampling phase is slow, and takes a positive value when the sampling phase is fast, so the point where h ₁ crosses zero is the optimal sampling phase. I know what will happen.
Therefore, this _o can be used as sampling phase control information, and according to this method, control can be performed only with information for each data transmission interval T seconds. What does controlling the sampling phase with the value of _h1 in the impulse response of a class 4 partial response, that is, the response shown in Figure 1, correspond to in a normal transmission system that does not use a correlation code? Let's think about it. Class 4 partial responses are (1, 0, -
Either a filter with response 1) and a normal Nyquist filter are combined to create a correlated response as shown in Figure 1, or a correlation operation is applied to the code sequence, i.e., b _o
=a _o -a _o-2 , and this sequence of b _o is passed through a normal uncorrelated transmission system. Now, suppose that the sample value of the impulse response of the uncorrelated transmission system is {P _i }. (At the ideal sampling point with no transmission path distortion, P ₀ = 1, P _i = 0 (when i≠0)
Since h _i is expressed as the difference between P _i and P _{i -2} , h _i = P ₁ - P _-1 , and controlling the sampling phase to h ₁ → 0 as in the present invention has been commonly used in the past. It can be seen that this method has similar properties to the method of finding a point of symmetry by balancing the sample values on both sides of the impulse response peak.

Note that the above-mentioned inverse transformation has the property that when an error occurs, it propagates one after another, but this only means that the indeterminate number C increases or decreases by a constant value in response to the error, and unless the frequency of errors is extremely high, The correlation value _Ro is not biased.

Embodiments of the present invention will be described below with reference to FIG.

The baseband signal coming from terminal 1 is on line 2
The current flow is sampled every T seconds by a sampler 3 controlled by a sampling clock. A level determiner 4 determines the level of the sampled sequence corresponding to the estimated value of a _o -a _{o-2, and} outputs the determination result to a line 5. The determination result for the line 5 is branched into two parts, and one part is inversely transformed by a partial response inverse transformer 6 to obtain an estimated value of _ao . The estimated value of a _o is delayed by T seconds in a delay element 7, the delayed estimated value of a _o is multiplied by the output signal of the sampler in a multiplier 8, and the multiplication result is integrated in an integrator 9.
The integrator output corresponds to an estimate of the partial response impulse response _h1 , which controls the digital phase lock loop 10 to provide a phase controlled sampling clock on line 2. 2
The other of the branched judgment results is decoded by the decoder 11, and the transmission data estimated value is output to the terminal 12.

The inverse converter includes an adder 13 and a 2T second delay element 1.
4, the inverse transformer input is added to the output of the delay element 14 in the adder 13, and the addition result becomes the inverse transformer output and simultaneously fed back to the delay element 14 to perform integral type inverse transform.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an impulse response of a class 4 partial response, and Fig. 2 is a block diagram showing an embodiment of the present invention. 14 is a delay element, 8 is a multiplier, 9 is an integrator, 10 is a digital phase lock loop, and 13 is an adder.

Claims (1)

[Claims] 1. In a data transmission receiver using class 4 partial response, means for sampling a received baseband signal, means for determining the level of the sampled signal, and inverse transformation of the class 4 partial response for the level determination result. means for delaying the inverse transform result by a data transmission interval T; means for multiplying the delayed inverse transform result by the sampled signal; and means for integrating the multiplication result; A sampling phase control device comprising means for controlling the phase of a sampling clock supplied to the sampler based on the integration result.