JPS6217420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a data transmission receiver having a function of controlling carrier phase using phase information extracted from a received data signal in data transmission using partial response SSB transmission.

Conventionally, in data transmission using SSB or VSB, it has been common to extract carrier wave phase information from the pilot signal in order to avoid the influence of orthogonal components.

However, the pilot signal frequency usually needs to be selected at both ends of the signal band to avoid the influence of signal components, and since the transmission path characteristics at these band edges generally have strong delay distortion, it is difficult to extract information about fast phase fluctuations from the pilot signal. It was difficult to extract accurately. Furthermore, when the transmission line is subject to power limitations, sending out a pilot signal inevitably leads to a reduction in signal power, resulting in a loss of signal-to-noise ratio.

The purpose of the present invention is to estimate orthogonal components on the premise that most of the transmission path distortion is removed by an automatic equalizer, and to perform reception without relying on a pilot signal in a manner similar to phase control in DSB. An object of the present invention is to provide a data transmission receiver that extracts phase information including fast phase fluctuations from data and performs phase control.

The principle of the present invention will be explained in detail below with reference to the drawings. In the figure, the received signal is divided into two components, in-phase and quadrature, by a 90° phase difference waveform generator 1, and a fixed oscillator 2
The generated sine wave is demodulated by the product detector 26. The in-phase component of the demodulated baseband signal is equalized by an automatic equalizer 3, and the orthogonal component is equalized by an equalizer 4 having exactly the same characteristics as the automatic equalizer 3.
is input to obtain equalized orthogonal components. The in-phase and quadrature components of the equalized baseband signal are processed by a sampler 8 operating at data transmission intervals.
9, and the sample value is sent to the phase rotation circuit 5.
undergoes phase rotation. Now, assuming that the sample value at t=nT of the quadrature component of the baseband signal subjected to this phase rotation is X _o and that of the orthogonal component is y _o , x _o and y _o are respectively expressed as follows.

However, ak: Transmission symbol of t=kT ci: i-th tap gain of automatic equalizer hn: In-phase component of transmission path impulse response h: 〃 Orthogonal〃 θ _o = φ _o −φ _o φ _o = 2πonT+ _o φ _o : Estimated phase o at t=nT: Frequency offset _o : Value of phase fluctuation in the phase path at t=nT Here, the sample value at t=nT of the in-phase component of the impulse response including the automatic equalizer is p _o , let q _o be that of the orthogonal component. If equalization is complete, for example, in the case of class partial response SSB, (Positive sign: lower sideband, negative sign: upper sideband). Therefore, the above X _o and y _o are each Or x _o = Re [{(a _o −a _o −2)±jd _o }×e ^j 〓 ⁿ ] y _o =Im [{(a _o −a _o −2)±jd _o }×e ^j 〓 ⁿ 〕 however becomes. From formula (1), x _o +jy _o = (a _o −a _o-2 ±
jd _o )・e ^j 〓n, so if (a _o −a _o-2 ) and d
If _o can be known, sinθ _o = Im [(x _o + jy _o ) (a _o −a _o −2〓jd _o )] [(a _o −a _o-2 ) ² + d _o ² ] (2) Phase information can be extracted.

d _o in equation (1) is however Like {a _o −(2N−1)−a _o −(2N+1)}～
It is decomposed into a term including {a _o +(2M-1)-a _o +(2M-3)} and other terms r _o .

Now considering the time t=(n+2M)T, if the transmitted symbol is estimated correctly, a _o + (2M-1) - a _o + (2M-3) ~ a _o - (2N
Since +1) -a _o -(2N+3) is known on the receiving side, the value of the second term on the right side of equation (3) can be found using these.

Here, if M=N=2, the average power ratio of d _o and r _o is 0.1 or less, and the value of d _o can be estimated with some accuracy. The disturbance term r _o can be made as small as desired by increasing the values of M and N, but increasing the value of M introduces a delay into the control loop and deteriorates the tracking characteristics. , it is necessary to set an appropriate value based on the relationship between the data transmission rate and the phase fluctuation frequency.

Embodiments of the phase control portion of the present invention will be described below with reference to the drawings. The in-phase component x _o of the baseband signal whose phase has been rotated by the above-mentioned phase rotation circuit 5 is level-judged by the determiner 6, and a _o -a
_o The value corresponding to the estimated value of −2 is 2(N+M−
1) are sequentially input to the transversal filter 7 of the stage. The even-numbered tap gains of the transversal filter are set to 0, and the (2L-1)th tap gains are set to 1/(2L-2M-1). The output of the transversal filter 7 is multiplied by a constant corresponding to 2/π by an attenuator 10.

On the other hand, the in-phase component x _o and the quadrature component y _o of the phase-rotated baseband signal are delayed by 2MT by delay lines 11 and 12, respectively, and the output of the delay line 11 is combined with the output of the attenuator 10 and the multiplier 13. The output of the delay line 12 is counted from the output of the determiner 6 of the transversal filter 7.
It was taken out on the 2Mth tap (a _o −a _o −
2) is multiplied by the estimated value in the multiplier 14.
The outputs of the multipliers 13 and 14 are added by an adder 15. The output of this adder 15 corresponds to the numerator on the right side of equation (2). The value corresponding to the denominator on the right side of equation (2) is obtained by passing the inputs of the multipliers 13 and 14 through squaring elements 16 and 17, respectively, and then adding the outputs of the squaring elements with adder 18. . However, if this value is smaller than the value generated by the constant generator 23 in the level comparator 24, the selector 25
selects the output of the constant generator 23 instead of the output of the adder 18. The output of the adder 15 is divided by the output of the selector 25 in a divider 20. The division result is a phase error signal shnθ _o , which is filtered by a loop filter 21, and the filter output is integrated by an integrator 22. The output of the integrator corresponds to phase information _φo , and according to this value, the phase rotation circuit 5 rotates the phase of the equalized baseband signal to perform phase control. This phase control removes phase fluctuations occurring in the transmission path, and a determination result that is not affected by phase fluctuations is output to terminal 27. Although the embodiments of the present invention have been described with respect to partial response SSB, the same principle can be applied to partial response VSB and PAM/VSB with a narrow excess band.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention, in which 1 is a 90° phase difference waveform generator, 2 is a fixed oscillator, 3,
4 is an automatic equalizer, 5 is a phase rotator, 6 is a judger,
7 is a transversal filter, 8 and 9 are samplers, 10 is an attenuator, 11 and 12 are delay lines, 1
3 and 14 are multipliers, 15 and 18 are adders, 21 is a low frequency filter, 22 is an integrator, and 26 is a product detector.

Claims (1)

[Claims] 1. A data transmission receiver that performs partial response SSB transmission includes a fixed oscillator, means for demodulating the received signal using the output sine wave of the fixed oscillator, and means for equalizing the in-phase component of the demodulated baseband signal. and means for equalizing orthogonal components of the demodulated baseband signal; means for obtaining sample values of the in-phase and quadrature components of the equalized baseband signal; and the equalized in-phase component of the baseband signal. and the orthogonal component sample values of the equalized baseband signal,
a phase rotation means that rotates the phase according to the value of a signal output from an integrator to be described later; and a determiner that determines which of predetermined levels the in-phase component of the baseband signal subjected to the phase rotation is closest to. , a transversal filter that receives the determination result and has a predetermined tap gain, an attenuator that attenuates the output of the transversal filter by a fixed value, and sample values of the in-phase and quadrature components of the equalized baseband signal. means for multiplying the delayed in-phase component sample value by the output of the attenuator; and multiplying the delayed quadrature component sample value by the output of the attenuator; means for multiplying the result of the determination, an adder for adding the two multiplication results, means for calculating the sum of squares of the output of the attenuator and the result of determination on a fixed tap of the transversal filter; means for comparing the sum of squares with a constant value and selecting the larger one; means for dividing the output of the adder by the selected value; a reduction filter inputting the division result; and integrating the filter output. A data transmission receiver comprising an integrator and means for providing the integrator output to the phase control means as phase rotation angle information.