JPS61117957A - Carrier recovery circuit - Google Patents

Abstract

PURPOSE:To recover a carrier whose phase is compensated in high speed automatically to minimize a demodulation output error rate by detecting a phase error caused by a circuit element such as a delay line and a frequency deviation between bursts from a demodulated output. CONSTITUTION:A 4-phase PSK signal (a) is distributed into an inverse modulator 1 and a 4-phase demodulator 2, the inverse modulator 1 is driven by demodulation outputs (b, c), inverse modulation is executed to the reception signal (a), noise is rejected from the extracted carrier component (d) by a tracking filter 3, and a recovered carrier (e) is obtained. A voltage controlled phase shifter 13 is controlled by using a phase error detection output of a phase error detection circuit 12 from the recovered carrier (e) and a recovered carrier e' whose phase error is compensated and the carrier e' is fed to the 4-phase demodulator 2. The 4-phase PSK wave (a) is demodulated by using the recovered carrier e', demodulates outputs (b, c) are fed to the phase error detection circuit 12, a Costas operation circuit applies base band operation to obtain a phase error detection output (f), by which the voltage controlled phase shifter 13 is controlled to decrease the phase error of the recovered carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a carrier recovery circuit using a narrowband filter used in a burst demodulator for TDMA.

(Prior art) In order to synchronously demodulate a modulated wave such as PSK, it is necessary to regenerate a reference carrier wave, and as a carrier wave regeneration circuit used in a burst demodulator for TDMA, there is no no-nguag and high-speed phase pull-in is possible. A carrier wave regeneration method using a narrow band filter is used, and an inverse modulation method, a transmission method, etc. are known as means for extracting carrier wave components. FIG. 8 shows an example of a conventional carrier wave recovery circuit using an inverse modulation method. When a 4-phase PSK wave is input, the received signal a is distributed to an inverse modulator 1 and a 4-phase phase demodulator 2, and the demodulated output is c enters the inverse modulator IK, performs an inverse modulation operation on the received signal a, and extracts the carrier wave component d. This carrier wave component d is added to a tracking filter 3 to remove noise and obtain a reproduced carrier wave e.

As shown in FIG. 9, the tracking filter 3 also includes mixers 4 and 5, a voltage controlled oscillator 6, a narrowband filter 7, a limiter 8, and a phase comparator 9, and compares the input and output phase difference of the narrowband filter 7. By controlling the output frequency of the voltage controlled oscillator 6 applied to the mixers 4 and 5 so that the output of the phase comparator 9 becomes zero, the output frequency of the mixer 4 is and the center frequency of the narrowband filter. Also, the 1st O
The figure shows an example of a conventional carrier wave regeneration circuit using a multiplication method in the case of a 4-phase PSK wave.
After being multiplied by 4 by υ and applied to the tracking filter 3, the frequency is divided by 1/4 by the 174 frequency divider 11. Using the recovered carrier wave e obtained from K, the demodulated outputs S and c are obtained in the 4-phase demodulator 2.

(Problems to be Solved by the Invention) In the conventional carrier wave recovery circuit as described above, the phase error in the narrowband filter is compensated by the tracking filter shown in FIG. In this case, a phase error occurs due to temperature fluctuations, etc., which causes a deterioration of the error rate. Also, the so-called AFC loop that controls the tracking filter is normally used in TDMA.
The loop is designed to have a sufficiently large time constant so as to reduce the loose noise bandwidth and the phase slip frequency of the recovered carrier wave. Therefore, the tracking filter only follows the average value of the frequency of each burst signal, but does not follow the frequency deviation between bursts.

For this reason, when low-slip characteristics are required, the bandwidth of the narrowband filter becomes extremely narrow, and the phase error of the recovered carrier wave due to the frequency deviation between bursts cannot be ignored, which causes deterioration of the error rate characteristics. Become.

The present invention therefore aims to solve these problems.

(Means for Solving the Problems) The present invention is characterized by controlling the phase of the regenerated carrier wave output from the narrow band filter using a phase control signal that maximizes the demodulated eye pattern, and controlling the temperature of each part. The purpose is to obtain a regenerated carrier wave that quickly compensates for phase errors due to changes in frequency and frequency deviations between bursts, and one of its embodiments includes an inverse modulator that extracts a carrier wave component from a received signal,
a narrowband filter connected to its output; a voltage-controlled phase shifter connected to the output of the filter; a phase demodulator that demodulates and outputs a received signal according to the output of the voltage-controlled phase shifter; and a phase error detection circuit that detects a phase error from the output, and the voltage controlled phase shifter is configured such that the phase error of the recovered carrier wave output from the narrowband filter is reduced by the phase error detection output of the phase error detection circuit. is in the carrier regeneration circuit that is controlled.

(Function) The present invention detects phase errors caused by circuit elements such as delay lines and inter-burst frequency deviations from the demodulated output, so the carrier signal is automatically compensated for the phase at high speed so that the demodulated output error rate is minimized. can be played.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of the present invention, in which a carrier wave is regenerated from a four-phase PSK wave by an inverse modulation method. The 4-phase PSK signal a is distributed to the inverse modulator I and the 4-phase phase demodulator 2, and the demodulated outputs S and C are used to send the inverse modulator 1.
is driven, performs an inverse modulation operation on the received signal a, and extracts the carrier wave component d. This carrier wave component d is added to a tracking filter 3 to remove noise and obtain a reproduced carrier wave e.

This recovered carrier wave e is input to the voltage controlled phase shifter 13, which controls the phase error detection circuit 120 and the voltage controlled phase shifter 13 to obtain a recovered carrier wave e' whose phase error has been compensated. The recovered carrier wave e' is applied to a four-phase phase demodulator 2.

Here, in the 4-phase phase demodulator 2, 4
Demodulate the phase PSK wave a with the reproduced carrier wave e' and output the demodulated signal,
c is applied to the phase error detection circuit 12. The phase error detection circuit 12 has a known configuration such as a Costas arithmetic circuit, and performs baseband arithmetic on the demodulated output (CK) to obtain a phase error detection output f. f controls the voltage-controlled phase shifter 13 so that the phase error of the reproduced carrier wave becomes small. This eliminates the phase error in the delay line, etc., and the phase error of the reproduced carrier wave caused by the frequency deviation between bursts.
In other words, it is possible to compensate so that the error rate is minimized.

Fig. 2 is a block diagram showing an example of a phase error detection circuit in the case of 4-phase PSK. Carrier wave e′1. Phase detection is performed by e'2 (produced by a 90° phase shifter 14-3 from e'), and the demodulated outputs (c) are applied to the phase error detection circuit 12. The phase error detection circuit 12 includes a discriminator 15-1.15-2, a multiplier 16-1.16-2, and a subtracter 17.

The demodulated outputs (s) and (c) are identified by the discriminator 15-1. By subtracting , a phase error output f from which the modulation component has been removed can be obtained.

FIG. 3 shows the embodiment of the present invention shown in FIG. 1 using a transfer function. T(St is the transfer function of the tracking filter 3, 12 is a phase error detection circuit, and the difference between the input phase θ1n(81 and the output phase θout(81) is taken, and the phase error detection output is θ1n(S)−θou
Obtain t(S). 13 is a voltage controlled phase shifter, and the S/N of the phase error detection output θ1n(S)−θout(8)
is improved by a loop filter 18 having a transfer function of F(St, controlled by a phase error detection signal f multiplied by a DC amplifier 19, and expressed by a phase adder.

Assuming that the transfer function of this loop is H(8), θout(
S) = H(81θ1n(S) −・−
(1) H (Unit = Tsubo Nρ...(2).

Here, the transfer function T (8) of the tracking filter 3
Considering in the equivalent low-frequency system, WB T(81=8+wB-...-(31).WB
is the one-sided bandwidth of the tracking filter. On the other hand, considering a lag filter as the transfer function F(8) of the loop filter 18, WL F(S) = 7- (4)
becomes. However, WL is the one-sided bandwidth of the loop filter. Substituting this into equation (2) yields. This is the second-order PLL in the case of an incomplete lag-lead type loop filter.
It has the same form as the transfer function of . The transfer function of a second-order PLL with an incomplete lag-lead loop filter is expressed as H(S)
Then, H(S) is given by the following equation.

H (81=Sad news 1-cho...(6))
a Comparing (5) and (6), 0=WB+KWL...
... (sword a =) sui acupuncture ... (8) e
= WL・・・・・・(
9). According to the configuration shown in FIG. 4, the phase-related transfer function is the same as that of the quadratic PLL, so the phase error θ1n(S)−θout(S) can be controlled to be zero. be understood. Therefore, phase errors caused by circuit elements such as delay lines are detected from the demodulated output,
Since the phase demodulator is controlled so that the phase error is zero, the phase of the recovered carrier wave is automatically compensated so that the error rate of the demodulated output is minimized. On the other hand, TDMA
In this method, the tracking filter 3 does not follow the frequency deviation of each burst, so in the conventional configuration shown in FIG. The phase error Δθ caused by the frequency deviation ΔW is Δ
If W is sufficiently small with respect to WB, Δθ = ts, W 1 (IG), and as the frequency deviation W increases, the phase error Δθ becomes too large to ignore, and becomes a major cause of deterioration of error rate characteristics. becomes.

According to the configuration shown in FIG. 2, the transfer function related to the phase has the form of a quadratic PLL, so the phase error Δθ' due to the frequency deviation ΔW is eΔW ΔW Δθ'=W -=4η ---゛(lυ), and the phase error Δr is compressed to t/(t+K). Therefore, according to the present invention, it is possible to follow the frequency deviation between bursts at high speed.

FIG. 4 shows another embodiment of the present invention, in which a carrier wave is regenerated from a four-phase PSK wave by a quadrupling method. The 4-phase PSK signal a is multiplied by 4 by a quadruple multiplier lυ, applied to a tracking filter 3, and then divided by 1/4 by a 1/4 frequency divider 11 to obtain a reproduced carrier wave e. This recovered carrier wave e is input to the voltage controlled phase shifter 13, and the recovered carrier wave e' whose phase error has been compensated is applied to the four-phase phase demodulator 2. The demodulated outputs (s), (c) of the four-phase phase demodulator 2 are applied to a phase error detection circuit 12, and the phase error detection output (f) controls a voltage-controlled phase shifter 13 to compensate for the phase error of the reproduced carrier wave. Therefore, also in the embodiment shown in FIG.
In the same manner as explained in the embodiment of FIG. 1, phase errors caused by circuit elements such as delay lines and phase errors caused by inter-burst frequency deviations are automatically compensated so that the error rate of the demodulated output is minimized. I can do it.

FIG. 5 shows an embodiment of a voltage-controlled phase shifter used in the carrier wave regeneration circuit according to the present invention as set forth in claim 3. Output g-1 is phase-shifted by π/2 by π/2 phase shifter 21, and distributed output g-2 is added to multiplier 6B. The demodulated outputs S and C are input to the phase error detection circuit 12.
The phase error detection output f obtained by is added to multiplication 6B as a control signal. The π/2 phase shifter output h-i and the multiplier output R12 are added to a composite mask to obtain a recovered carrier wave e' whose phase error has been compensated. Regenerated carrier wave e=as
Assuming Wt, the synthesizer inputs h-1 and h-2 are as follows h -1= 5LoWt -・-
a3h −2= A as Wt
-...Q3 However, A is the multiplication coefficient of the multiplier, which is determined by the phase error Δθ.

At this time, the composite output e' is e'2J';
A) −・−Cl3, if A(1, then e”: sia (Wt + A)
-...Qf, the amount of phase shift can be controlled by voltage by giving the multiplication coefficient A by voltage. By applying this voltage-controlled phase shifter to the carrier wave regeneration circuit shown in FIG. 4 or FIG. 7, the phase error of the recovered carrier wave can be automatically compensated for.

FIG. 6 is a block diagram showing another embodiment of the present invention according to claim 2, in which a carrier wave is regenerated from a 4-phase PSK wave by an inverse modulation method. 4 phase PSK
The signal a is distributed to an inverse modulator 1 and a four-phase phase demodulator 2, and the demodulated outputs S and C drive an inverse modulator l to perform an inverse modulation operation on the received signal a and extract a carrier wave component d. This carrier wave component d is input to the voltage-controlled phase shifter 13, and the voltage-controlled phase shifter 13 is controlled by the phase error detection output obtained in the phase error detection circuit 12, and the carrier wave component d' whose phase error has been compensated for is By adding this carrier wave component d' to the tracking filter 3, a reproduced carrier wave e' whose phase error is compensated and noise is removed is obtained.

FIG. 7 shows the embodiment shown in FIG. 6 using a transfer function. T(S) is the transfer function of the tracking filter 3, 12 is a phase error detection circuit, and the input phase θ+n(
The difference between Sl and the output phase θout (S) is taken, and a phase error detection output θ1n (81-θout(S)) is obtained. 13 is a voltage-controlled phase shifter, and the phase error detection output θ1n (Sl-θout The S/N of (S) is improved by a loop filter 8 having a transfer function of F (S), and the DC
It is controlled by the phase error detection signal f multiplied by the amplifier 19. This is represented by an adder in phase.

If the transfer function of this loop is H(81), θout(
S) = H(S)θ1n(S)...
−・−*”; becomes 1.

Here, from equations (3) and (4), 'Its)・F(81 is (
16) Substituting into the equation yields. This has the same form as the transfer function of a two-domain PLL in the case of an incomplete lag-lead type loop filter.

Here, when compared with equation (6), delivery = WB a = (1 + K) WL e = WL. Therefore, even with the configuration shown in FIG. 6, with the configuration shown in FIG. 1, the transfer function regarding the phase is the same as that of the quadratic PLL, so the phase error θin (S) - θ
out(81) is controlled to be zero, and the phase of the reproduced carrier wave is automatically compensated so that the error rate of the demodulated output is minimized.

(Effects of the Invention) As explained above, the present invention detects the phase error of a reproduced carrier wave from the demodulated output of a PSK signal using a phase error detection circuit, and reproduces the detected output as a control signal for a voltage-controlled phase shifter. It is characterized by compensating for carrier wave phase errors, and detects phase errors caused by circuit elements such as delay lines and phase errors caused by inter-burst frequency differences from the demodulated output.
This has the advantage of being able to reproduce a carrier wave whose phase is automatically compensated at high speed so that the demodulated output error rate is minimized.

Note that the present invention is not limited to the 4-phase PSK system, but also applies to a multi-phase PSK system such as 8-phase PSK that can detect phase errors from demodulated output, or a carrier wave regeneration circuit using a narrow band filter such as OQPSK or MSK. It is clear that it is generally applicable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a 4-phase PSK carrier recovery circuit using an inverse modulation method, which is an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a phase error detection circuit, and FIG. FIG. 4 is a block diagram showing the transfer function of the carrier wave regeneration circuit, and FIG.
A block diagram of a phase PSK carrier wave regeneration circuit, FIG. 5 is a block diagram showing an embodiment of a voltage controlled phase shifter applied to the present invention, and FIG.
7 is a block diagram showing the transfer function of the carrier wave recovery circuit according to the present invention, and FIG. 8 is an example of a conventional 4-phase PSK carrier wave recovery circuit using an inverse modulation method. FIG. 9 is a block diagram showing an embodiment of a tracking filter, and FIG. 1... Inverse modulator 2... Phase demodulator 3...
・Tracking filter 4.5...Mixer 6...Voltage controlled oscillator 7...Narrow band filter 8...Limiter (amplitude limiter) 9...Phase comparator lυ...4 multiplier 11. ... 1/4 frequency divider 12 ... Phase error detection circuit 13 ... Voltage control phase shifter 14 ... Phase detector 15 ... Discriminator 16 ... Multiplier 17
...Reduction 35 18...Loop filter 1
9...DC amplifier Beauty...Distributor 21...
π/2 phase shifter n...multiplier...synthesizer

Claims (2)

[Claims] (1) an inverse modulator that extracts a carrier component from a received signal;
a narrowband filter connected to its output; a voltage-controlled phase shifter connected to the output of the filter; a phase demodulator that demodulates and outputs a received signal according to the output of the voltage-controlled phase shifter; and a phase error detection circuit that detects a phase error from the output, and the voltage controlled phase shifter is configured such that the phase error of the recovered carrier wave output from the narrowband filter is reduced by the phase error detection output of the phase error detection circuit. A carrier wave regeneration circuit characterized in that the carrier wave regeneration circuit is controlled. (2) an inverse modulator that extracts a carrier component from a received signal;
a voltage-controlled phase shifter connected to the output of the voltage-controlled phase shifter; a narrowband filter connected to the output of the voltage-controlled phase shifter; a phase demodulator that demodulates and outputs a received signal according to the output of the filter; and a phase error detection circuit that detects a phase error from the output, and the voltage controlled phase shifter is configured such that the phase error of the recovered carrier wave output from the narrowband filter is reduced by the phase error detection output of the phase error detection circuit. A carrier wave regeneration circuit characterized in that the carrier wave regeneration circuit is controlled.