JPH07115447A - Automatic frequency controller for m-phase psk receiver - Google Patents

Abstract

PURPOSE:To make detection frequency error characteristic to keep inclination almost constant in a pull-in frequency range. CONSTITUTION:An input 4-phase PSK signal is orthogonally detected, and the complex four multiplication of detection output is performed by a multiplier 17, and multiplication output is cross-product computed by a cross-product device 19, and it is discriminated whether or not the output of the device 19 is +1 or -1 by a code discriminator 33. The output of a two-multiplier part 17a at the initial stage of the four-multiplier 17 is cross-product computed. and an absolute value for it is generated, and it is multiplied by the output of the code discriminator 33 by a multiplier 34, and multiplication output is supplied setting as a detection frequency error to a local oscillator 13 as a control signal, and such control so as to derease the error is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applied to a receiver such as digital satellite communication or digital mobile communication, and has an input M.
Phase (M = 2 ⁿ : n is an integer of 1 or more) A digital phase modulation signal such as a PSK signal is multiplied with a local signal, a frequency error is detected from the multiplication output, and the frequency of the local signal is detected according to the detected error. The present invention relates to an automatic frequency control device adapted to control.

[0002]

2. Description of the Related Art FIG. 3A shows a conventional automatic frequency control device of this type. The 4-phase PSK signal is input from the input terminal 11, and is quadrature-detected by the quadrature detector 12 by the local signal from the local oscillator 13 to output the I signal and the Q signal. That is, in the quadrature detector 12, the local signal from the local oscillator 13 is multiplied by the input signal by the multiplier 14, and the local signal is shifted by π / 2 by the phase shifter 15 and is multiplied by the input signal by the multiplier 16. The multipliers 14 and 16 output the detection output I signal and Q signal of mutually orthogonal components of the input signal. The frequencies of the I signal and the Q signal are multiplied by 4 in the complex frequency multiplier 17, and the multiplied signals are subjected to cross product calculation in the cross product unit 19. That is, this operation is performed after being converted into a digital signal, and the two outputs I ^′ and Q ^′ from the multiplier 17 are delayed by the delay devices 21 and 22 for the conversion sampling period, and the output of the delay device 21 is obtained. The output Q ^′ of the multiplier 17 is multiplied by the multiplier 23, and the output of the delay device 22 and the output I of the multiplier 17 are multiplied by the multiplier 24, and the output of the multiplier 23 and the output of the multiplier 24 are The inverted ones are added by the adder 25 and output as the result of the cross product calculation. The output of the cross product unit 19 is passed through the low pass filter 20 and the local oscillator 13
Is supplied to. The output of the low-pass filter 20 is the carrier frequency of the PSK signal from the input terminal 11 and the local oscillator 13.
Error signal corresponding to the difference from the local signal frequency of
The error signal controls the oscillation frequency of the local oscillator 13 so that the error signal becomes smaller. It should be noted that the input terminal 11 converts the received radio wave from the ground station into the baseband signal of the I signal and the Q signal and inputs it, and the complex multiplication with the local signal (at the portion corresponding to the quadrature detector 12) is performed. There is also a system in which a deviation from the reference frequency of the baseband carrier frequency of, that is, a frequency error is detected from the cross product unit 19, and the local oscillator 13 is oscillated at a frequency corresponding to this deviation. In this case, if the deviation of the input signal carrier frequency from the reference frequency is zero, the local oscillator 1
The oscillation frequency of 3 becomes zero. When this error signal becomes zero, the local signal frequency for converting into the baseband signal becomes equal to the input carrier frequency. As a multiplier, for example, as shown in FIG.
The signal and the Q signal are squared by the squarers 31 and 32, respectively, and are multiplied by each other by the multiplier 33. Squarer 3
The outputs of 1 and 32 are added by the adder 34 and output as an I ′ signal. The output of the multiplier 33 is doubled by the multiplier 35 and output as a Q'signal, that is, complex-multiplied. This complex multiplication is 2 multiplication, and this is repeated once again in cascade to perform 4 multiplication.

[0003]

The detection output of the frequency error in the conventional automatic frequency control device shown in FIG. 3A, that is, the output of the cross product unit 19 can be pulled in by the difference between the input carrier frequency and the local signal frequency. Maximum frequency, that is, the maximum frequency offset that can be drawn is f
2A, as shown in FIG. 2A, the detection error signal changes sinusoidally as the frequency offset becomes larger than the point where the frequency offset is 0, and the period thereof is twice f.
m. As described above, in the conventional automatic frequency control device, the detection error becomes smaller as the detection error approaches the maximum value that can be pulled in, and therefore the input carrier frequency suddenly fluctuates due to Doppler shift, instability of equipment, etc. There is a problem that this frequency control does not catch up and goes out of the control range, a so-called hang-up phenomenon occurs, and it takes a long time to pull in the frequency.

An object of the present invention is to provide an automatic frequency control device for an M-phase PSK signal receiver which can rapidly follow the input signal frequency even if the frequency offset is relatively large.

[0005]

According to the present invention, the input M
The frequency of the phase PSK signal is multiplied by M / 2 by the first multiplying means, the cross product calculation is performed by the first cross product means on the M / 2 multiplied output, and the input M phase P
The frequency of the SK signal is multiplied by M by the second multiplying means,
The sign of the M-multiplied output and the absolute value of the M / 2-multiplied output are multiplied by the multiplying means to obtain a frequency error detection output. That is, the local signal frequency is controlled by this detection output.

[0006]

1 shows a case where the present invention is applied to a receiver for 4-phase PSK (M = 4) signals, and parts corresponding to those in FIG. 3A are designated by the same reference numerals. Also in the present invention, the I signal and Q signal from the quadrature detector 12 are quadrupler 17
In (4), the complex product is multiplied by 4 and the multiplied output is subjected to cross product calculation. In the present invention, the output from the quadrature detector 12 is multiplied by M / 2, that is, 4 / in this example.
It is multiplied by 2 = 2, and the output is subjected to a cross product operation in the cross product unit 31. In this example, the output of the first-stage doubler unit 17a in the fourth multiplier 17 is branched and supplied to the cross product unit 31. The cross product device 31 is configured similarly to the cross product device 19. An absolute value calculator 32 calculates the absolute value of the output of the cross product device 31. On the other hand, the sign of the output of the cross product device 19, that is, the sign of the conventional frequency error detection output is judged by the sign judging device 33, that is, it is judged whether it is positive or negative, and +1 or -1 is output. The judgment output of the sign judgment unit 33 and the absolute value calculator 32
And the operation output of are multiplied by each other in the multiplier 34. The output of the multiplier 34 is supplied to the local oscillator 13 as a detection error signal, and the local oscillation frequency is controlled so that the error signal becomes small.

As described above, the cross product device 19
2A changes sinusoidally as the frequency offset increases as shown in FIG. 2A. Therefore, as shown in FIG. 2B, the sign discriminator 33 outputs a +1 output on the positively displaced side. , -1 is output when it is shifted to the negative side. On the other hand, the output obtained by taking the absolute value of the output of the cross product unit 31 by the absolute value calculator 32 becomes large regardless of whether the frequency offset shifts to the positive side or the negative side as shown in FIG. The value changes to have a maximum value fm and a minimum value twice fm. That is, the negative side of the sine wave in FIG. 2A is inverted to the positive side, and the frequency axis is doubled. The output of the absolute value of such an error (FIG. 2C) and the sign determination output (FIG. 2B) are multiplied by the multiplier 34, and the output of the multiplier 34 is shown in FIG. 2D.
The output becomes 0 when there is no frequency shift (frequency offset 0), and if a frequency offset occurs on the positive side, the detection error output increases accordingly, and at the maximum pull-in frequency fm. The level of detection error is maximum. Conversely, when a frequency offset occurs in the negative direction, a negative detection error occurs, and when the offset frequency becomes fm, the detection error level becomes maximum in the negative direction. Therefore, the frequency is changed in the input signal, and the closer the frequency offset is to the pull-in frequency fm, the stronger the control. Therefore, the frequency pull-in is performed at high speed. Therefore, the frequency offset is large with respect to the frequency fluctuation due to the Doppler shift or the frequency fluctuation due to the instability of the oscillation frequency of the local oscillator, and even if it occurs relatively quickly, it sufficiently follows the fluctuation and correct demodulation is performed. It becomes possible to do.

Although the present invention has been applied to the reception of a 4-phase PSK signal in the above description, it can be generally applied to the reception of an M-phase PQS signal. In that case, the M multiplier used as the quadrupler 17 is used, and the doubling unit 17a is used. For this, an M / 2 multiplication unit may be used. The present invention can also be applied to the case where the deviation of the complex baseband signal input from the zero frequency is corrected as described above.

[0009]

As described above, according to the present invention, this phase detection error has an offset frequency of -fm to + fm.
The characteristic is that it has a substantially constant slope between, the detection level becomes maximum near the maximum value of the pull-in frequency, the larger the frequency offset, the greater the control over the local oscillator, and the quick pull-in is performed. It can follow fast frequency fluctuations.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing output waveform characteristics of each part for explaining the operation of FIG.

FIG. 3A is a block diagram showing a conventional automatic frequency control device, and B is a block diagram showing complex doubling.

Claims (1)

[Claims] 1. An input M-phase (M = 2 ⁿ : n is an integer of 1 or more) PSK signal is multiplied by a local signal of a local oscillator, a frequency error is detected from the multiplication output, and the local signal is detected according to the error. An automatic frequency control device for an M-phase PSK signal receiver which controls an oscillator to eliminate the above error, and a first multiplication means for multiplying the input M-phase PSK signal by a frequency M / 2, and its M / 2 multiplication output. A first cross product means for performing a cross product operation, a second multiplication means for multiplying the M-phase PSK signal by frequency M, a sign of the M multiplication output and an absolute value of the M / 2 multiplication output. An automatic frequency control device for an M-phase PSK receiver, comprising: