JP2698979B2 - Carrier recovery method in PSK demodulator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carrier recovery system in a PSK signal demodulator.

(Prior art) Conventionally, in a general PSK demodulation circuit, V
Since the frequency and phase of the CO are not fixed, the loop operation of the PLL for carrier wave reproduction was set to a wide value at the initial stage of pull-in, and the reproduction operation was started.

(Problems to be solved by the present invention) However, in such a system, the carrier wave is regenerated,
The time required for the tracking loop to reach the steady state required a considerable length when the C / N of the received wave was small.

(Means for Solving the Problems) In order to solve such a drawback, the present invention provides a phase control VCO for outputting a phase-controlled reproduced carrier, and an in-phase (I) for comparing the phase of the output wave with the phase of a received carrier. ), A quadrature (Q) channel phase comparison circuit, a low-pass filter for removing intersymbol interference between I and Q channels for removing noise and the like from the output of the phase comparison circuit, and a I / Q channel output from the filter. A PSK comprising a sampler for sampling a signal, a phase error detector for detecting a phase error of the reproduced carrier from the output of the sampler, and a loop filter for smoothing the phase error signal and supplying the same to the phase control VCO.
In the synchronous quadrature demodulator, an arctangent that derives an angle in a signal phase space from an output value of the sampler, a multiplier that multiplies the derived angle by the number of phases, and an angle corresponding to the angle multiplied by the number of phases. A sine-cosine component calculator for deriving an in-phase component and a quadrature component, a complex Fourier transformer for performing a complex Fourier transform based on the derived in-phase and quadrature data to calculate a frequency having the strongest intensity, and a calculated frequency A frequency divider that divides the number of phases by the number of phases to obtain a frequency difference between the received carrier and the recovered carrier, and a phase estimator that calculates a phase difference from the output of the frequency divider and the output of the arctangent, At the beginning of carrier recovery,
By controlling the phase control VCO with the output of the frequency divider and the output of the phase estimator, processing on the baseband that is advantageous for miniaturization and integration reduces the frequency of the modulated wave before dividing it. Thus, an effect equivalent to the multiplication method for extracting the frequency and phase of the carrier is obtained.

 Hereinafter, embodiments will be described in detail with reference to the drawings.

(Embodiment) FIG. 1 shows the present invention as 0 (offset) -QPSK (n = 2).
FIG. 3 shows a configuration diagram when applied to a demodulator. The principle and operation will be described. Note that the description of each part of the drawing is partially omitted except for those related to the present invention.

At the initial stage, the mode setting switch 22 is set to the position S. When a signal wave to which noise is not added is received from the PSK wave receiving terminal 1, signal waveforms such as curves I and Q in FIG. 2 are observed at the monitor terminals 9 and 10, respectively. However, the phase difference Δ between the carrier and the phase control VCO2
Depending on ψ, the appearance is different as in the examples of FIGS. 2 (a) and (b), so if Δψ changes successively, even if the transmission data pattern is the same, the data is displayed on the monitor terminals 9 and 10. The waveform that is displayed changes with Δψ. When noise, fading, and the like are added, the I and Q signal curves are distorted.

This signal wave is sampled at the midpoint of each data slot having information on the signal phase space by adjusting the timing of the sampling clock output from the clock regenerator 8. The outputs of the samplers 11 and 12 are input to the arctangent 13 each time, and the equation (1) is calculated.
Determining the angle [psi _K on the signal phase space. However, in this case, I,
In consideration of the data codes of the two sequences of Q, it is determined within the range of 0 ≦ ψ _K <2π. FIG. 3A shows this state.

ψ _K = tan ⁻¹ (Q _K / I _K ), 0 ≦ ψ _K <2π (1) However, in this state, as shown in FIG. since there is a phase ambiguity, the phase [psi _K multiplier (4 doubler) 14 4 multiplies, in the form except for the pattern dependence as FIG. 3 (b).

Then, in-phase component I _'K, quadrature component Q' on the time axis corresponding to the 4 times the phase 4Pusai _K phase of _K, quadrature component calculator
In step 15, the value is obtained by equation (2).

_{I 'K = cos (4ψ K} ), Q' since the rotational frequency of _{K = sin (4ψ K) ......} (2) 4 -fold phase determined by a complex Fourier transformation, the number to ensure frequency resolution requires (M
Equation (1),
By performing the processing of the equation (2), I ' _K and Q' _K are stored in the memory.

In the complex Fourier transformer 16, each Δ
Calculation is performed on f ′, and the frequency Δf ′ having the highest intensity A is selected.

Since the obtained Δf ′ is four times the frequency difference between the carrier and the phase control VCO 2, the operation shown in equation (4) is performed. That is, the desired beat frequency Δ
Get f.

Δf = 1/4 · Δf ′ (4) Further, the phase estimator 18 calculates the expression (5), and calculates the phase difference Δψ at the end of the sampling period by each phase information _{Ｋ K} during the sampling period. And the phase rotation speed Δf. However, the calculation is performed with madulo-2π.

Subtracting π / 4 in the above equation means that the phase of the signal point and the reference axis are π
Due to shifting by / 4.

As described above, after the initial frequency difference Δf and the initial phase difference Δψ are obtained and converted into the VCO initial setting control voltage by the voltage converter 19, the mode setting switch 22 is set to the position I for initialization. Thereafter, the switch 22 is switched to the T position to switch to the tracking mode, and sampling and sampling of both I and Q sequences are performed.
The phase error is directly detected from the data by the phase error detector 20 and the PLL operation for averaging by the loop filter 21 is started.

In the above description, offset-QPSK (n = 2)
Although the present invention is not limited to this, the present invention is not limited to this, and it is assumed that n = 1, 2, and 3 for 2-phase PSK, 4-phase PSK, 8-phase PSK, etc. Can be applied.

(Effects of the Invention) As described above, the angle indicated by the position in the phase space of the sampling signals of the orthogonal I and Q channels is multiplied by 2 ^{n in} order to remove the phase uncertainty due to the modulation data pattern. By calculating the rotation frequency and multiplying by 1/2 ⁿ , the frequency shift and phase shift between the carrier of the received signal and the local VCO can be reduced while maintaining the signal state with PSK modulation.
It is possible to accurately derive by baseband processing which is advantageous for integration, and it is possible to reduce the time required until a steady demodulation state by tracking is reached.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a PSK demodulator using a carrier recovery system according to the present invention, and FIG. 2 is a diagram showing monitor terminals 9, 10 in FIG.
(A) is a diagram when the phase difference Δψ between the carrier and the VCO is 0, (b) is a diagram when Δψ> 0, and FIG. 3 (a) is an output の of the arctangent calculator 13. _K explanatory diagram showing the uncertainty on the signal phase space, FIG. 3 (b) is 2 ⁿ multiplier (n =
Output 4Pusai _K 2) is an explanatory view showing an unambiguous. 1 ... PSK wave receiving terminal, 2 ... VCO for phase control, 3 ... π
1/2 phase shifter, 4,5 phase detector, 6,7 low-pass filter for removing intersymbol interference, 8 clock regenerator, 13 arctangent, 14 ²ⁿ multiplier, 15 ... In-phase, quadrature component calculator,
16: Complex Fourier transformer, 17: 1 / ²ⁿ multiplier, 18: Phase estimator, 22: Mode setting switch.

Claims (1)

(57) [Claims] A phase control VCO for outputting a phase-controlled reproduced carrier, a phase comparison circuit for an in-phase (I) channel and a quadrature (Q) channel for comparing the phases of the output wave and a received carrier, A low-pass filter for removing inter-symbol interference of I and Q channels for removing noise and the like from the output of the comparison circuit, a sampler for sampling signals of both I and Q channels output from both filters, and reproduction from outputs of both samplers A phase error detector for detecting a phase error of a carrier, and a phase control VCO for smoothing the phase error signal.
A PSK-synchronous quadrature demodulator composed of a loop filter and an inverse tangent device that derives an angle in a signal phase space from output values of the two samplers, and a multiplication that multiplies the derived angle by the number of phases. And a calculator of a sine cosine component for deriving an in-phase component and a quadrature component corresponding to the angle multiplied by the number of phases, and the derived in-phase,
A complex Fourier transformer that calculates the highest frequency by performing a complex Fourier transform based on both orthogonal data, and a frequency divider that divides the calculated frequency by the number of phases to obtain a frequency difference between a received carrier and a reproduced carrier. And a phase estimator for calculating a phase difference from the output of the frequency divider and the output of the arctangent, and the output of the frequency divider replaces the output from the loop filter at the beginning of carrier wave recovery. And the output of the phase estimator controls and initializes the phase control VCO.
Carrier recovery method in SK demodulator.