JPS6217419B2 - - 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 phase control in the same way as phase control in DSB, without depending on the pilot signal. An object of the present invention is to provide a data transmission receiver characterized in that it extracts phase information including fast phase fluctuations from received 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 in-phase orthogonal components by a 90° phase difference splitter 1, and a fixed oscillator 2.
The generated sine wave is demodulated in the product detector 16. 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.
The equalized orthogonal components are obtained.

The in-phase and quadrature components of the equalized baseband signal are sampled by samplers 8 and 9 operating at data transmission intervals, and the sampled values undergo phase rotation by a phase rotation circuit 5. Now, t=nT of the in-phase component of the baseband signal that has undergone this phase rotation
The sample value at is X _o and that of the orthogonal component is y _o
Then, X _o and y _o can be expressed as follows.

However, a _k : Transmission symbol of t=kT ci : i-th tap gain of automatic equalizer h _o : In-phase component of transmission line impulse response h _o : 〃 Orthogonal〃 Θ _o = φ _o −φ _o φ _o = 2πf _p nT + _o φ _o : Estimated phase at t=nT f _p : Frequency offset _o : Value of phase fluctuation in the phase path at t=nT Here, t=nT of the in-phase component of the impulse response including the automatic equalizer Let p _o be the sample value of , and 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 becomes. Here, consider the quantity b _o △ ₋ (a _o −a _o −2) y _o .

b _o = (a _o −a _o −2) ² sinΘ _o 〓1/π(a _o −a _o −2) cosΘ _o・d _o (1) d _o is a quantity that does not include n−k=even symbols a _k , and if the sequence {a _k } is random, the average value of d _o is zero. Utilizing this fact, if the time variation of Θ _o is very slow, phase control can be performed by integrating b _o as phase information using a narrow band loop filter. However, when the fluctuation of Θ _o is relatively fast, in order to perform control following this fluctuation, d _o becomes a disturbance, and therefore it is necessary to suppress it as much as possible.

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+1) - a _o -
Since (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.
Θ _o is a phase error and is constantly a small angle, so cos
If we approximate Θ _o 〓1, sinΘ _o 〓Θ _o , we get Here, if M=N=2, the average power ratio of d _o and r _o is less than 0.1, and b _o ' is better quality phase information with the disturbance term sufficiently suppressed than in equation (1) b _o . give. The disturbance term can be made as small as desired by increasing the value of MN, but increasing the value of M introduces a corresponding delay into the control loop and deteriorates the tracking characteristics, so the data transmission speed It is necessary to set it to an appropriate value based on the relationship between 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 a 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 quadratic component y _o of the phase-rotated baseband signal is delayed by 2MT by a delay line 11 , and the output of the attenuator 10 is subtracted from the output of the delay line 11 in a subtracter 12 . The subtraction result is taken out at the 2Mth tap counting from the output of the determiner 6 of the transversal filter 7 (a _o
It is multiplied by the estimated value of [-a _o ]-2) in the multiplier 13. The multiplication result corresponds to b _o '.

The multiplier output is filtered by a loop filter 14,
The filter output is integrated by an integrator 15. The output of the integrator corresponds to _φo , and according to this value, the phase rotation circuit 5 rotates the phase of the equalized baseband signal, thereby applying phase control.

In this example, it is assumed that a _o is binary, but if it is other than binary, b _o ' is set to a value other than 0 (a _o −a _o −
2) It is necessary to normalize with the value corresponding to ² .

This phase control makes it possible to almost eliminate phase fluctuations such as phase data and frequency offsets occurring in the transmission path, and a determination result that is not affected by phase fluctuations is output to the terminal 17.

Note that the embodiment of the present invention is based on partial response.
Although we have described SSB, the same principle can be applied to partial response VSB and PAM/VSB, which have a narrow excess band.

[Brief explanation of the drawing]

The figure is a block diagram showing an 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 is a delay line, 12 is a subtracter, 13 is a multiplier, 14 is a low frequency filter, 15 is an integrator, 16 is a product detector It is.

Claims (1)

[Claims] 1. A data transmission receiver that performs partial response SSB transmission includes a fixed oscillator, means for demodulating a received signal using an output sine wave of the fixed oscillator, and means for equalizing the in-phase component of the demodulated baseband signal. , means for equalizing orthogonal components of the demodulated baseband signal, means for obtaining sample values of the in-phase component and the orthogonal component of the equalized baseband signal, and the in-phase component of the equalized baseband signal. operating on sample values and 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 certain value; and a sample value of the equalized baseband signal orthogonal component that is delayed for a certain period of time. means for subtracting the output of the attenuator from the delayed orthogonal component sample value; means for multiplying the subtraction result by a determination result on a predetermined tap of the transversal filter; and inputting the multiplication result. 1. A data transmission receiver comprising: a low-pass filter that integrates a filter output; an integrator that integrates a filter output; and means for providing the integrator output to the phase rotation means as phase rotation angle information.