JPS5932020B2 - PSK demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a PSK demodulator that demodulates PSK modulated (phase shift key ink modulated) data signals and the like.

FIG. 1 is a block diagram showing an example of a conventional PSK demodulator.

In the figure, 1 is a received PSK modulation signal input terminal, 2 is a carrier wave regeneration circuit that regenerates a carrier wave from the received PSK modulation signal, 3 is a timing regeneration circuit that regenerates a timing signal from the received PSK modulation signal 1, and 4 is the carrier wave regeneration circuit. a detector for detecting the carrier wave regenerated by the circuit 2;
is a discriminator that identifies and reproduces the detected output of this detector using the timing signal from the timing reproducing circuit 3 and outputs it to the output terminal 6. The conventional PSK demodulator is configured as described above, and a received PSK signal inputted from the input terminal 1 is demodulated and outputted from the output terminal 6.

However, in the above-mentioned PSK demodulator, when it comes to measuring the bit error rate (BER), the first thing to do is to measure the BER.
To measure BER, a specific bit sequence must be transmitted and received, which reduces transmission efficiency.
There were disadvantages such as a long measurement time when the value was low.

Another disadvantage is that if a phase offset occurs in the carrier wave, it is impossible to easily measure and compensate for this. The present invention was made to eliminate these drawbacks, and an object of the present invention is to obtain a PSK demodulator that can estimate the BER from a relatively short-time received signal and at the same time compensate for the phase offset of the carrier wave. It is something.

FIG. 2 is a block diagram showing one embodiment of the present invention, and numerals 1 to 6 are completely the same as the conventional device shown in FIG. 1 above.

7 is a phase shifter that shifts the phase of the carrier wave regenerated by the carrier wave regeneration circuit 2, 8 is a second detector that detects the PSK signal from the input terminal 1 using the carrier wave whose phase has been shifted by this phase shifter, and 9 is this detector. A ternary discriminator 10 identifies the output using the timing signal from the timing regeneration circuit 3, and a ternary discriminator 10 determines the C/N ratio or BER of the received PSK signal and the carrier 11 is an output terminal of the C/N ratio or BER obtained by this processing circuit, 12 is the processing circuit 1 for calculating the phase offset angle of
This is a feedback circuit that feeds back the phase offset angle determined at 0 to the carrier wave regeneration circuit 2.

In the PSK demodulation circuit configured as described above, the signal appearing at the output terminal 6 is a signal demodulated by the same demodulation process as in the case of the PSK demodulator shown in FIG.

On the other hand, the signal input to the ternary discriminator 9 is a signal detected by the detection axis whose phase is shifted by the phase shifter 7. This relationship will be explained quantitatively. When the amplitude of the received PSK signal is normalized to 1 and shown in the signal space shown in FIG. 3, the received signal vector can generally be represented by a vector O center.

In the presence of a carrier phase offset θ, this signal becomes O
It becomes τ. When this received signal 0X is detected by the Q axis orthogonal to the original signal 0,{, a detection output corresponding to σ1 obtained by projecting the signal vector 6 onto the Q axis is obtained. This output is discriminated and reproduced by the ternary discriminator 9. The input/output characteristics of this three-value discriminator 9 are shown in FIG. In Figure 4, k
defines the discrimination level of the ternary classifier 9. O<. It is a constant of k≦1.

Assuming that the probability that the detected output is determined to be "H" by such a three-value discriminator is PH, and the probability that the detected output is determined to be "L" is PL, these quantities are expressed by the following equations. - Here, p is the CN ratio and Erfcx is the error function.

The basis for the establishment of the above formula will be briefly explained. In Figs. 3 and 4, the amplitude of the PSK signal is normalized to 1, but the signal amplitude before normalization is set to a, and Figs.
Let's consider multiplying the scale of the figure by a. Let the noise accompanying a signal with amplitude a be Gaussian noise with variance N. When the output of the carrier wave recovery circuit 2 is advanced by 9' in the phase shifter 7, detection is performed in the second detector 8 along the Q axis in FIG. The signal vector is O8! If so, the signal detection output from the second detector 8 is zero, but if there is a phase offset of the carrier wave, the signal detection output from the second detector 8 corresponds to the pitch. Assuming that there is no noise, the ternary discriminator 9 determines that the output of the second detector is ``H1'' when 0B>Ka, and 6L'' when 0B<-Ka. However, since normally distributed noise exists, the probability PH that the output of the second detector 8 is determined to be 0H'' is as follows.

Here, by converting the variables, t=(x-0B)/1 is obtained.

Here, Erfcx is the above-mentioned error function. In equation (2), 0B-A sin θ, and CN Kanohi ρ is ρ = A2
Since it is 2N, we get.

Similarly, the probability PL that the output of the second detector 8 is determined to be "L" is obtained as follows.

As is clear from the above formula, the 2
By measuring the probabilities PH and PL, the CN ratio and the carrier phase offset θ can be determined. Furthermore, if the CN ratio is known, the BER of the system can be immediately estimated. By reducing k at the discrimination level of the ternary discriminator, it is possible to make PH (5PL) sufficiently larger than BER. In other words, equation (3) and equation (6) can be obtained, and equation (
7), determine θ from equation (8), and set the feedback circuit 12.
can be output to.

Also, by substituting equation (8) into equation (6) and finding Vwa', it is obtained.

Therefore it becomes.

Furthermore, the bit error rate (BER) of PSK communication system
is defined by the CN ratio of the received signal.

For example, the BER of a four-phase PSK system is given by.
In actual hardware, instead of calculating the above equation, ρ and θ can be calculated using PH and PL as addresses.
OM can be used, and RO can also be used to convert ρ and BER.
M can be used. Based on the reproduced signal at the output terminal 6, the processing circuit 10 calculates the CN ratio or BER from the output of the ternary discriminator 9 and outputs it to the output terminal 11, while feeding back the estimated value of the carrier phase offset to the carrier wave regeneration circuit 2. It returns through circuit 12. This feedback compensates for the carrier phase offset of the received signal. Incidentally, in the above description, the present invention has been described with respect to a communication system using PSK modulation, but it goes without saying that it can also be used in communication systems using other modulation methods.

As explained above, the present invention has the advantage that the BER can be estimated from some received signals without transmitting or receiving a specific bit sequence for BER measurement, and that the phase offset of the carrier wave can be automatically compensated.

[Brief explanation of the drawing]

Fig. 1 is a block wiring diagram showing an example of a conventional PSK demodulator, Fig. 2 is a block wiring diagram showing an embodiment of the present invention, Fig. 3 is a received signal vector diagram, and Fig. 4 is a block wiring diagram showing an example of a conventional PSK demodulator. 3 is a graph showing an example of input/output characteristics of the ternary discriminator 9 shown therein. In the figure, 2 is a carrier recovery circuit, 3 is a timing recovery circuit, 4 is a detector, 5 is a discriminator, 7 is a phase shifter, 8 is a second detector, 9 is a ternary discriminator, 10 is a processing circuit, 12 is a feedback circuit.

Claims (1)

[Claims] 1 In a PSK demodulator that demodulates a PSK modulated signal, a carrier wave regeneration circuit that regenerates a carrier wave from a received PSK modulated signal, a phase shift circuit that shifts the phase of the output carrier wave of this carrier wave recovery circuit, and an output carrier wave of this phase shift circuit. received by P
A detector that detects an SK modulated signal, a ternary discriminator that identifies the output of this detector into three values based on the amplitude, and a probability P_H that the output of this ternary discriminator indicates an "H" level and a "L" level. a processing circuit that measures probability P_L and calculates the CN ratio or bit error rate and carrier phase offset angle of the received PSK signal by assuming that the noise superimposed on the received PSK modulated signal is normally distributed noise from these probability values; A PSK demodulator comprising a feedback circuit that feeds back to a carrier wave regeneration circuit so as to compensate for this carrier phase offset angle.