JPH082059B2 - Phase modulation signal demodulator - Google Patents

Description

TECHNICAL FIELD The present invention relates to carrier demodulation of a phase modulation signal.

(Prior Art) Conventionally, there are many types of phase-modulated signal demodulators, but most of them are phase-locked loops (reference: Floyd,
"Phaselock techniques" by M. Gardner, Jhon Wiley & Son
s, Inc., Newyork, 1966).

(Problems to be Solved by the Invention) In the conventional phase modulation signal demodulation technology, noise (N) is added to the signal (S) to significantly reduce the S / N, or the characteristics deteriorate if the carrier frequency offset amount is large. Was. It is generally known that the cause of problems such as narrow capture range and long pull-in time is deterioration of characteristics due to the influence of carrier frequency offset. The conventional phase modulation signal demodulator has such problems to be solved, and an object of the present invention is to solve these problems.

(Means for Solving the Problem) A phase modulation signal demodulator according to the present invention includes a frequency multiplier that removes a modulation component from an M-phase phase modulation signal, and the frequency multiplier from the output signals of the frequency multiplier. An adaptive bright line enhancement filter that extracts only the multiplied carrier, a filter characteristic extraction circuit that obtains the filter characteristic of the adaptive bright line enhancement filter, and the frequency of the original carrier is estimated from the filter characteristic obtained by the filter characteristic extraction circuit. A frequency estimator for outputting a carrier wave of the frequency as a reproduced carrier wave, a product detector for detecting the product of the reproduced carrier wave and the M-phase modulation signal, and a fixed phase error of the output of the product detector. And a phase shifter.

(Operation) FIG. 1 is a block diagram showing the configuration of the present invention. Terminal
The phase modulation signal is input from 10. The multiplier 1 multiplies the phase modulation signal by M times to remove the modulation component from the multiplication phase modulation signal. Therefore, the output of the multiplier 1 is a carrier component having a frequency M times that of the phase modulation signal and noise. The output of the multiplier 1 is input to the adaptive bright line emphasizing filter 2 to suppress noise and extract only the carrier component of M times frequency. The adaptive bright line emphasis filter 2 is a narrow band filter with a very high Q that adaptively emphasizes the line spectrum contained in the input signal and suppresses white noise, and is a type of adaptive filter. The convergence characteristic of this adaptive narrow band filter does not change regardless of the frequency of the line spectrum in the Nyquist band. For example, the capture range f _cap can be expressed as f _cap = ± F _b / 2M (1) when the signal transmission rate is f _b, and it can be understood that the characteristics are not affected by the carrier frequency offset. The filter characteristic extraction circuit 3 extracts the frequency characteristic of the adaptive bright line emphasis filter 2. The frequency estimator 4 reproduces the frequency of the original carrier wave from the adaptive bandpass filter characteristic obtained by the filter characteristic extraction circuit 3. This reproduced original carrier signal is applied to the product detector 5. The product detector 5 detects the product of the phase modulation signal at the terminal 10 using the carrier signal. The output of the product detector 5 is the received signal with the carrier frequency removed. Finally, the phase shifter 6 removes the fixed phase error from the output of the product detector 5 to demodulate the phase modulation signal.

(Embodiment) FIG. 2 shows an embodiment of the present invention. The phase modulation signal is input to the multiplier 1, and its output is output to the adaptive bright line emphasis filter 2
Is input to The adaptive bright line enhancement filter 2 is described in the literature (B.Widr
ow, et al, “Adaptive Noise Cancelling: Principles
and Applications ", Proc.IEEE, VOL.63, No.12, Dec., 1975
It is composed of a correlation separator 20, which is composed of delay operators, an adaptive filter 21, and an adder 22, as described in the annual publication. This adaptive filter 21 is the optimum solution of the discrete Wiener filter, and the value of the adder 22 is used to correct the filter characteristics so that the average output of the adder 22 becomes zero. In addition, the transfer function H (ω) of the filter
Is the output signal r ₁ of the multiplier ₁ and the output signal x _{1 of the} correlation separator 20
If the cross-correlation spectrum S _{rx with} and the auto-correlation spectrum of x ₁ is S _xx , then H (ω) = S _rx / S _xx (2). The spectrum S _vw is the signal v (i) and w
It represents a cross-correlation spectrum with (i). Here, the signals r ₁ and x ₁ are defined as r ₁ = a ₁ + n ₁ (3) x ₁ = a ′ ₁ + n ′ _1, where a is a carrier component and n is a noise component. These (3) the transfer function of Substituting expression (2) below the filter _{H (ω) S = aa /} S aa + S nn) LT b (4) (L: integer) where LTb (= L / f _b) Is the delay amount of the correlation separator 20. (4) is a filter that inputs the multiplier output signal x ₁ with the delayed transfer function H (ω) and extracts only the carrier component a ₁ from the signal x _1. It means that The signal obtained here is an M-multiplied carrier signal in which noise is suppressed.
In order to demodulate the phase-modulated signal, the frequency estimator 4 obtains the frequency of the original carrier from the filter characteristics of the adaptive filter 21 and outputs the reproduced carrier signal. Regenerated carrier signal z ₁ = exp (jω _org i) obtained by the frequency estimator 4 (5) where j indicates a reciprocal operator. In the product detector 5, the conjugate circuit 51 uses the phase / frequency The complex conjugate of the estimated signal is taken and complex-multiplied by the input phase modulation signal in the multiplier 52. Since a fixed phase error remains in the output signal of the multiplier 52, this error is removed by the phase shifter 6. The phaser 6 includes a multiplier 60, a phase detector 61, an integrator 62, a complex signal converter 63, and a complex conjugate circuit 64,
A demodulation phase modulation signal is output from the multiplier 60.

FIG. 3 shows a specific example of a circuit for extracting the filter characteristic from the adaptive filter 21 by the filter characteristic extracting circuit 3 and obtaining the original carrier phase / frequency by the frequency estimator 4. There are various methods for this, but in this specific example, it is assumed that the adaptive filter 21 is a transversal filter. The adaptive filter 21 includes N delay elements 210, a complex multiplier 211, a coefficient multiplier 212, an adder 213, and a coefficient updater 214. Since the adaptive filter 21 is a bandpass filter, the contents of the N coefficient multipliers 212 show the characteristics of the filter.
Letting the value of the k-th coefficient unit 212 be C _k , the filter characteristic extraction circuit 3 is composed of N−1 dividers 31, phase detectors 32, and one adder 33, and performs the following operation. .

This ω _est is the characteristic of the filter (indicating the angular frequency component of the bandpass filter). In the frequency estimator 4 composed of the constant circuit 41, the divider 42 and the complex signal converter 43,
The original carrier frequency ω _org is obtained from the value of the expression (6) by the following expression, and the signal shown in the expression (5) is output from the complex signal converter 43.

ω _org = ω _est / NM (Effect of the invention) As described above in detail with reference to the embodiments, the present invention has an effect that characteristics such as a capture range are improved.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing the configuration of the present invention, FIG. 2 is a block circuit diagram showing an embodiment of the present invention, and FIG. 3 is a block circuit diagram illustrating a carrier frequency estimation method in the present invention. . 1 ... Multiplier, 2 ... Adaptive bright line enhancement filter, 3 ... Filter characteristic extraction circuit, 4 ... Frequency estimator, 5 ... Multiplier detector, 6 ... Phaser.

Claims (1)

[Claims] 1. A demodulator for receiving an M phase modulation signal and demodulating a modulation component contained in the M phase modulation signal, and a frequency multiplier for removing the modulation component from the M phase modulation signal,
An adaptive bright line enhancement filter that extracts only the carrier wave multiplied by the frequency multiplier from the output signal of the frequency multiplier, a filter characteristic extraction circuit that obtains the filter characteristic of the adaptive bright line enhancement filter, and the filter characteristic extraction circuit A frequency estimator that estimates the frequency of the original carrier wave from the filter characteristics obtained by outputting the carrier wave of that frequency as a reproduced carrier wave, and a product detection that multiplies the reproduced carrier wave and the M-phase modulation signal And a phase modulator for removing a fixed phase error of the output of the product detector.