JPS5853810B2 - Retraction phase identification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for identifying the pull-in phase of a recovered carrier wave using a code word in a time division multiplex system using a four-phase PSK modulated signal.

In the 4-phase PSK modulation power formula, two-channel binary signals are converted into four phase-modulated signals having a symmetry using two carrier wave vectors with a phase difference of 90 degrees as shown in Figure 1. The signal is transmitted and demodulated on the receiving side (here, by performing phase detection using the same demodulation carrier as on the transmitting side).

At this time, the carrier wave used for demodulation is recovered from the input phase modulation signal, but the recovered carrier wave in the carrier wave recovery in the 4-phase PSK modulation method has four phase states with respect to the transmitting side carrier vector. There is a phase uncertainty to be gained.

Figure 2 shows the four states "1", "2", "3°", and "4" that the receiving side carrier vector reproduced on the receiving side corresponds to the transmitting side vector shown in Fig. 1. This is what is shown.

By comparing FIG. 2 with FIG. 1, we can see that there are four pull-in phases "1:'"2", 13'" of the regenerated carrier wave on the receiving side.
', "4", the output in each channel is as shown in Table 1 with the transmitter side vector as the reference.

In order to remove the phase uncertainty of the recovered carrier wave,
It is necessary to identify which of the four states the regenerated carrier wave pull-in phase is in.

Conventionally, in order to perform such pull-in phase identification, a unique codeword is assigned to each of the two channels I and Q and transmitted for each frame, and the receiving side uses a correlator after demodulation to compare the transmitted codeword and A method was used to detect the correlation between

FIG. 3 shows an example of a conventional pull-in phase identification circuit.

The human-powered 4-phase PSK modulated signal is demodulated in a 4-phase PSK demodulator 1 to produce binary signals corresponding to two channels I and Q.

Correlators 2 and 5 having the codeword of channel I and correlators 3 and 4 having the codeword of channel Q respectively test the correlation of the signals of channels 2 and Q. Signal A2, which is the sum of the match number signal d in the correlator 3 and the sum circuit 6, and signal A2, which is the sum of the match number signal d in the correlator 4 and the mismatch number signal d in the correlator 5. The sum of the mismatch number signal a in the correlator 2 and the mismatch number signal S in the correlator 3 is calculated by the summation circuit 8, and the sum of the mismatch number signal C in the correlator 4 and the match number signal d in the correlator 5 is calculated. When the signals A4 obtained by the summation circuit 9 are obtained, the signals Al tt A2 r A3 and t A4 can be respectively associated with the states "1°", "2", "3" and "4" in Table 1. So signal A1+A2, A3
, Am respectively threshold circuit 10°11.12,
13 to terminal B□.

B2. B3. By extracting the signal having the highest correlation with any of B4, it is possible to know the attraction phase corresponding to that signal.

As described above, the conventional pull-in phase identification method has the drawback that it requires the use of four correlators, which complicates the circuit configuration.

The entrainment phase identification scheme of the present invention uses two channels I, Q
make the codewords identical or complementary to each other, and
Using correlators with one identical or mutually complementary codeword for each channel I, Q, the 4 4 of the regenerated carrier waves from one signal
Since only two correlators are required, the pull-in phase identification circuit is simplified, the transmitting side code word generation circuit is also simplified, and carrier wave recovery and clock extraction are facilitated. It has advantages.

Hereinafter, the present invention will be described in detail with reference to Examples.

First, a case will be described in which four outputs from two correlators are multiplied, assuming that the code length is n.

FIG. 4 is a block diagram showing the configuration of an embodiment of the retracting phase discrimination method of the present invention, FIG. 5 is a diagram showing an example of the configuration of a correlator in the retracting phase discriminating power method of the present invention, and FIG. 6 is described later. FIG. 7 is a diagram showing the theoretical optimum values of the functions E1(k), B2(lk), B3(k), and B4(k).

In Fig. 4, 1 is a 4-phase PSK demodulator, 6,7°8.9
is a sum circuit, 10, 11, 12.13 are threshold circuits, 1
4.15 is a correlator.

In addition, in FIG. 5, 21 is an n-digit shift register, 22
−□.

22-2. ..., 22-n is a coincidence detection circuit, 23 is a coincidence number counting circuit, and 24 is a mismatch number counting circuit.

Now, in the correlator 14 of FIG. 5, the received signal vector received, demodulated, and transferred to the shift register 21 is
(Sl, B2..., Sn), the codeword vector stored in the correlator is C=(C1, C2°...
, Cn), the coincidence detection circuits 22-1, 212 . ..., 22.

Detect each corresponding bit at .

The match signals detected by each minus number calculation circuit are added in a match number counting circuit 16 to obtain a match number output a, and the match signals are calculated by a mismatch number counting circuit 17 to obtain a mismatch number output a.

Here, since the sum of the match number output a and the mismatch number output a is equal to the code length n of the code word, one output can be immediately determined from the other output.

In exactly the same way, the correlator 15 outputs the number of matches and the number of mismatches.

Next, the following functions will be defined in the embodiment shown in FIG.

ζ Here, Ci and Cq are the code word vectors written in the correlators for channels ■ and Q, respectively, Si and Sq
are the received signal vectors of channels I and Q, respectively, received and in the shift register, (C2S) is the number of matches between vector C and vector S, n is the code length of the codeword, and k is the vector C and vector S. This is a parameter indicating the time point after the symbol, with the time point at which the peak of the correlation of S is obtained as =0.

In the case of k\O, Si and Sq include other bits in addition to the code word, but for the sake of convenience, we will ignore this and proceed with the discussion.

Now, if the codewords of channel ■ and channel Q are the same, Cq = Ci, and if there is no error in the received signal, 5q = Si, so <x), (2), (3)
.

Equations (4) are as follows.

Figure 6 shows channel ■ as an example of a code word.

20-bit pattern (111100010011
01011110) for k when using
It shows the value of (k).

A pattern (1010...) is placed before the code word.
...10) and the bits following the code word were assumed to be random.

As seen from Figure 6, at =0 E□(k) =
40=2n, and the maximum correlation is obtained.

The above four functions <5), (6), (7),
(8) can be brought closer to the theoretical optimum value by selecting codeword vectors Ci and Cq with excellent autocorrelation and cross-correlation characteristics.

FIG. 7 shows such theoretical optimum values.

Similarly, if the codewords of channel ■ and channel Q are complementary to each other, Cq2Ci, and if there is no error, 5q=Ci, so (S.

Using the relationships C) = (S, C), (S, C) - (S, C), formulas (5), (6), (7), (
The same relationship as in 8) can be derived.

In the embodiment shown in FIG. 4, an input 4-phase PSK modulated signal is demodulated by a 4-phase PSK demodulation circuit 1 to produce binary signals corresponding to two channels I and Q, respectively, and a correlator 14
．． 15.

The correlators 14 and 15 are identical or complementary, and output match number signals a, b and mismatch number signals a, b, respectively.

Matching number signals a, b and mismatching number signals a, b are calculated using equations (5) and (6) in sum circuits 6 and 7°8.9, respectively.
, (7) and (8) are added to output A1.
A2. A3. A4 respectively.

From the above relationship, the outputs A□, A2, A3, A4
It is derived that outputs as shown in Table 2 are produced corresponding to each phase state "'1", "2", "3", and "4".

Now, the threshold circuit 10, 11°12.1 in FIG.
3 assumes that the threshold value is (2n-1ε) and a pulse is generated when an input greater than the threshold value is applied.

If the number of errors that have occurred is within ε, the threshold circuit 10,
When B1 is placed in 11, 12, 13, terminal B,,B
2. B3. A pulse is generated in the corresponding one of B4.

Therefore, as is clear from Table 2, it can be determined that when a pulse is generated from terminal Bj, the pull-in phase is in state j.

In this way, by knowing which of the terminals B1-B2, Bs, or B4 the pulse is generated from, the pull-in phase of the reproduced carrier wave can be identified, so 4-phase PSK
By correcting the phase of the carrier wave for demodulation in the demodulation circuit 1, or by converting the code of the already obtained two-channel binary signal string according to the phase state, correct demodulated signals can be generated as outputs of channels I and Q. Obtainable.

Furthermore, with reference to FIG. 7, it is also clear that the output E3(k) can be used instead of the output E1VΦ to identify the pull-in phase.

In this case, the threshold value is set to ε, and the threshold circuit generates a pulse for inputs below this value.

Above, we have shown an example of a method for identifying the phase by adding the four outputs from two correlators, but next we will show that the same effect can be obtained by subtracting these four outputs. .

FIG. 8 is a block diagram showing the configuration of an embodiment in this case, and the symbols are sum circuits 6, 7, 8 in FIG.
．． 4 except that 9 has been changed to a difference circuit 25, 26, 27° 28.

Here, in the embodiment shown in FIG. 8, the following functions are defined.

Now, if S of the codewords of channel ■ and channel Q are the same, then Cq=Ci, and if there is no error, then Sq
2Si, so (Ci, Si) + (Ci, 5i) =
If we use the relationship n, we get (9) and (10).

Equations (11) and (12) are as follows, respectively.

Comparing equations (13), (14), (15), and (16) with equations (5), (6), (7), and (8), respectively, it can be seen that they are smaller by the number of codewords n. .

Therefore, the sum circuits 6, 7, 8, 9 in FIG.
26.27.28, it is clear that exactly the same effect can be obtained by reducing the threshold value by n.

Note that in order to associate the state of j'' with terminal Bj, a, a
It should be noted that the connections from , bb are different between FIG. 4 and FIG. 8.

Furthermore, even when a sum circuit and a difference circuit are used together, a similar effect can be expected if the threshold value is appropriately set.

Note that terminal B1. B2. B3. It goes without saying that a pulse generated from either B4 can be used as a frame synchronization pulse.

As explained above, according to the pull-in phase identification method of the present invention, it is possible to identify the pull-in phase of a recovered carrier wave in a 4-phase PSK demodulation circuit using two correlators having the same content, and the circuit configuration can be significantly reduced. Simplified.

Furthermore, the codeword generation circuit on the transmitting side can also be simplified.

Furthermore, since the code words are the same, carrier wave recovery and clock extraction on the receiving side are facilitated.

The pull-in phase identification method of the present invention can be universally used in a communication system using a four-phase PSK modulation method.

[Brief explanation of the drawings] Fig. 1 is a diagram showing the carrier wave vector in the 4-phase PSK modulation force formula, Fig. 2 is a diagram showing the phase state of the reproduced carrier wave, and Fig. 3 is a diagram showing the phase state of the reproduced carrier wave.
4 is a block diagram showing the structure of an embodiment of the drawing phase discrimination power formula of the present invention. FIG. 5 is a diagram showing an example of the structure of a correlator. The figure shows an example of the characteristics of the function E1(h), and Figure 7 shows the characteristic of the function E□(k).
, B2 roll), B3(k). FIG. 8, a diagram showing the theoretical optimum value of B4(k), is an example in which the sum circuits 6, 7, 8.9 in FIG. 4 are replaced with difference circuits. 1...4-phase PSK demodulator, 2, 3, 4.5...
... Correlator, 6, 7, 8, 9... Sum circuit,
10. lL12.13...Threshold circuit, 14
, 15...correlator, 21...shift register, 22-8.22-2°...22-n...
... Match detection circuit, 23... Match number counting circuit,
24... Mismatch number counting circuit, 25, 26゜27
．． 28...Difference circuit.

Claims (1)

[Claims] In a 14-phase PSK modulation communication system, 2
The signals of the two channels demodulated at the receiving end are guided to two correlators in which one of the code words is stored, and each bit is Which of the four signals obtained by detecting matches and mismatches and calculating the number of matches and mismatches by multiplying or subtracting each other has the maximum or minimum correlation? An attraction phase identification method characterized by identifying four attraction phases of a reproduced carrier wave by determining.