JPS6013630B2 - Digital frequency modulation communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention is based on MSK (MinimmmShiftKe〆n
g) with a modulation index of 0.5 (Fre
(quemyShiftKeying) communication method.

As a method of demodulating digital frequency modulated signals, a method in which a received signal and a signal delayed by a certain period of time are demodulated by comparing the phases using a sine phase comparator is known as a delay detection method, and the method is known as a delay detection method, and the method is known as a delay detection method. It is widely used because of its simplicity. By the way, in wireless communication of the SCPC format, that is, a format in which one channel is assigned to one carrier wave, narrowing the occupied bandwidth and suppressing out-of-band radiation are absolute requirements from the viewpoint of effective frequency utilization. In order to satisfy the above requirements, it is necessary to limit the base band or carrier band on the transmitting side. However, if such a strong band restriction is applied on the transmitting side, if the receiving side tries to use delayed detection that performs a secondary sine phase comparison, the phase transition will be insufficient and the reception characteristics will deteriorate significantly. there were. Also, the column number 116271
As shown in Hakamagao Sho 53-100-2, there have been improvement measures based on error correction using code constraints in sine phase comparison and cosine phase comparison, but these methods also solve the above-mentioned strong band-limiting condition. This had the disadvantage that the improvement effect was lost.

The purpose of this invention is to enable correct signal processing even when the transmitting and receiving sides are subject to strong band limitations and generate large intersymbol interference that cannot be identified by demodulation using secondary sine and phase ratios. An object of the present invention is to provide a digital frequency modulation communication system.

According to this invention, on the transmitting side, the digital information signal is subjected to summation logic conversion, and the carrier wave is frequency-modulated with a modulation index of 0.5 using the summation logic conversion output, and transmitted.
On the receiving side, the received signal is branched into signals with delay times T and (T is the repetition period of the digital information signal), respectively, and these delayed signals and the pre-delayed signal are subjected to cosine phase comparison delay detection, These detection outputs are combined in phase with the detected output, and the point in time when the combined signal has the maximum eye aperture is detected and decoded.

Next, the communication method of the present invention will be explained in detail. To simplify the explanation, we will use a digital frequency signal with a modulation index of 0.5, namely MSK (Minimum Shift Keyin).
g) Use signals as an example. Generally, in the phase continuous FSK method, that is, the digital frequency modulation method, the transmitted wave S(t) can be expressed as follows. S(t) = i os {2mfct+m
(t)} State (t) = Gakuha's z an・g (t-medium) d
t, an: variable that corresponds to each data 0 and 1 of the data code string and takes 11 and 11, g(t): input/output of the basic filter placed at the modulator input terminal Response, m: modulation index (=2△fd・T), △fd: frequency deviation, T: repetition period of data code, wide: center frequency, m(t): instantaneous phase peak A: peak of signal value.

For an MSK signal with modulation index m=0.5, g(t)
Since g(t)=1(0≦t≦T), 0, t>T, the phase of the modulated output signal is linear with respect to the phase of the center frequency fc when the data is 1 for T seconds. When the data is 0, there is a relative linear delay of m/2.

The output v(t) obtained by comparing the cosine phase of the received signal and a signal obtained by delaying the received signal by 7 seconds is expressed by the following equation.
v(t) = cos {m(t)-m(t-7)} In normal delayed detection, v(
t) Sin{m(t)-m(t-7)} is selected as the repetition period T of the data code.

Next, changes in phase m(t) will be explained. FIG. 1 shows how the relative phase of a phase-continuous FSK signal changes, where the axis is time and the vertical axis is the relative phase. In the figure, m=0.5 corresponds to MSK. Bending point of phase change,
That is, at time T, phantom, rainbow, etc., intersymbol interference occurs due to band limit. In FIG. 1, the dashed line indicates a phase transition when severe band limitation is applied. Under such severe band limitations, good demodulation characteristics can be obtained by delay detection that performs string phase comparison as shown in Hakamaiso Akihiroichi No. 81067. In the case where there is no band limit, the phase difference m(
t) the value of m(t-d) and v(t)=cos[m
FIG. 5 shows the relationship between the value of m(t-↑)] of (t)- and the transmitted data.

In the same figure, A is transmission data, B is relative phase transition, C is phase difference,
D indicates the output of the differential phase comparison differential detection. T,=
T,72=2r=27. As shown in this figure, the peaks of the two cosine phase comparison differential detection outputs appear at times shifted by T,/2. In the present invention, two cosine phase comparison differential detection outputs with delay times T and are made in phase with the information signal and are added and synthesized.

This corresponds to aligning the peak positions of the two detected outputs shown in FIG. 5 and adding and synthesizing them. That is, the detection output on the 7=T side is delayed by 7,/2=T/2 and then added and synthesized. Figures A, B, and C show sine phase comparison, cosine phase comparison, and delay time 7=T (T is the repetition period of the data code string) for a digital frequency modulation signal with a modulation index of 0.5.
and 7i2r cosine phase comparison showing the eye patterns of the detection outputs of each delayed detection.
The value of 0.2 is the standard for the reception band limit, and the phantom B band width is 1.
．． This is the case where it is set to 25.

The eye pattern of the sinusoidal phase comparison deteriorates as shown in Figure 2A due to intersymbol interference based on the strong band limit, and the eye may close considerably at the time rudder T. Even if set, it may be necessary to determine which side the signal is on with respect to the threshold value. The eye patterns of cosine phase comparison are shown in Figure 2B and C, respectively, at time (n 10 seasons) T,
It is shown that it is fully open at nT. The deviation at the time when this eye opens is T/2, and this value is 7/2 = fort. It matches exactly.

FIG. 2D shows an eye pattern obtained by combining the signal shown in FIG. 2B delayed by T/2 with the signal shown in FIG. 2C.

This synthesis increases the eye opening, and the eye aperture reaches its maximum at time nT, and by selecting an appropriate value, it is possible to accurately determine which side of the eye it is in any state. In this invention, two cosine phase comparison delay detection outputs are added and synthesized, but this is because when a signal containing noise is synthesized, the more the noises have no correlation with each other, the more the S/N ratio of the synthesized signal increases. In this way, the characteristics can be improved more than when differential detection that performs cosine phase comparison is used alone.

By the way, if the data code string detected in the delayed detection that performs cosine & phase comparison is bn, then bn is between the data code string an at the detector input, bn=an y an-, (yield is mod 2). (indicating addition) exists.

However, an-, is an delayed by one bit. Therefore, in order to match the detected data code string with the transmitted data code string, the transmitted data code string is subjected to 1-bit sum logical conversion in advance, and the carrier wave is FSKed with a modulation index of 0.5 using the output of the logical conversion and digital It may be transmitted as a frequency modulated signal. That is, in this invention, after performing 1-bit summation logic conversion on the transmitting side, FSK is performed, and on the receiving side, the received signal is subjected to delay detection by comparing two cosine phases with a delay time of T and a phantom, and the detected output is synthesized in the same phase. and decrypt it. FIG. 3 shows an embodiment of this invention. First, the transmitting side 11 will be explained. The signal output 13 of the data code generator 12 is input to one input terminal of the exclusive OR circuit 14, and its signal output 15 is divided into two, one of which enters a 1-bit delay circuit 16 and its delayed output signal 17 is input to one side of the exclusive logic circuit 14. Exclusive OR circuit 14
The 1-bit delay circuit 16 constitutes a 1-bit summation logic conversion circuit. The other half of the split signal 15 is input to a transmission baseband bandwidth limiting filter 18 . The output 21 of the carrier wave generator 19 is input to the FM converter 22 and is FM modulated by the output signal 23 of the transmit baseband bandwidth limiting filter 18, and its digital frequency modulated signal output 24 is transmitted from the transmit antenna 25.
Next, the receiving side 26 will be explained.

The received signal 28 received by the receiving antenna 27 enters the receiver 29 and its output 31 enters the cosine phase comparison delay detection circuits 32 and 33. The receiver signal output 31 is divided into four parts: one goes into a two-bit delay circuit 34, one goes into a one-bit delay circuit 35, one goes into a multiplier 36, and the last goes into a multiplier 37. The signal output 38 of the 2-bit delay circuit 34 is input to one input terminal of the multiplier 36, and the signal output 38 is input to one input terminal of the multiplier 36.
1 and the cosine phase are compared.

Also, the signal output 39 of the 1-bit delay circuit 35 is output to the multiplier 37.
is input to one input terminal of the signal 31, and is compared with the signal 31 in terms of cosine phase. The output 41 of the multiplier 36 is passed through a low pass filter 42
is input. Further, the output 43 of the multiplier 37 is inputted to a 1/2 bit delay circuit 44 in order to make it in phase with a signal 48 described later, and its signal output 45 is inputted to a low pass filter 46. The delayed cosine phase comparison delayed detection output 47 is input to the summation circuit 49 together with the signal output of the low-pass filter 42, that is, the 2-bit delayed cosine phase comparison delayed detection output 48, and is combined. The signal output 51 of the summation circuit 49 is input to a discriminating regenerator 52, and a code reproducing output 53 is obtained by determining whether it is above or below the threshold value. The 2-bit delay circuit 34, the multiplier 36, and the low-pass filter 42 form the cosine phase comparison delay detection circuit 32, and the 1-bit delay circuit 35, the multiplier 37, and the low-pass filter 46 form the cosine phase comparison delay detection circuit 33. has been completed.

Next, an example of experimental results of the communication system according to the present invention will be explained.

Figure 4 shows a modulation index of 0 with transmission baseband band limitation.
．． For a digital frequency modulated signal of 5, the delay time d =
Curve 54 shows the error rate characteristics of the conventional sine phase ratio comparison delayed detection method, where T and 7 = 2T.Curves 55 and 56 show the error rate characteristics of the cosine phase comparison delay detection method, when T and 7 = 2T. A curve 57 shows the error rate characteristics when the cosine phase comparison differential detection output is made in phase with the information signal and combined with a gain of 1:1. The horizontal axis of the figure is the reciprocal of the phantom B band width (BT), which is the standard for limiting the transmission baseband band.
The vertical axis indicates the value of signal energy versus noise density Eb/No per bit required to obtain an error rate of 10-3. In addition, standardization father old belt width BT of reception belt castle limit = 1
．． 25, and the bit rate is 1 ship bps. As shown in this figure, when strong transmission baseband bandwidth restrictions are applied, the Eb/No of cosine phase comparison delayed detection is smaller as compared to the subordinate sine phase comparison delayed detection, and the Eb/No of the latter It is clear that the characteristics of 2 are excellent, and by combining the two cosine phase comparison delayed detection outputs, the Hakama curve 57 is obtained, and for the same band limit, Eb/No is small, and cosine & The characteristics are further improved than when phase comparison differential detection is used alone. As explained above, according to the digital frequency modulation communication system according to the present invention, even when the transmitting side is subject to strong band restrictions, the deterioration of the identification error rate due to intersymbol interference and noise is small, and good communication quality can be ensured. I can do it.

Furthermore, since a stronger band restriction can be tolerated on the receiving side, differential detection can be identified with a higher signal-to-noise ratio, and quality can be improved. This method can be applied to a wide range of applications in general, in addition to mobile wireless systems, fixed wireless systems, and other systems that communicate in limited frequency bands.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the phase transition characteristics of a digital frequency modulation signal, Fig. 2 is a diagram showing an eye pattern of differential detection output under strong band limitation, and Fig. 3 is a diagram showing an embodiment of the digital frequency modulation communication system according to the present invention. Fig. 4 is a diagram showing an experimental example of the (BT)-1 versus required Eb/No characteristics of the transmission baseband bandwidth limit when demodulating a digital frequency modulation signal, and Fig. 5 corresponds to the transmission data. FIG. 3 is a diagram showing phase transition, phase difference, and cosine phase comparison delay detection output of a digital frequency modulation signal. 11: Transmission side, 12: Data code string generator, 14: Exclusive OR circuit, 16, 35: 1-bit delay circuit, 18:
Transmission baseband band limit filter, 22: FM converter, 19: Carrier wave generator, 25: Transmission antenna, 26: Receiving side, 27: Receiving antenna, 29: Receiver, 32, 33
: Cosine phase comparison delay detection circuit, 34: 2-bit delay circuit, 36, 37: Multiplier, 42, 46: Low-pass filter, 44: 1/2-bit delay circuit, 49: Addition circuit, 52
:Identification regenerator. O figure O figure 2 figure Ne 3 figure ice 4 figure juice 5 figure

Claims (1)

[Claims] 1 On the transmitting side, the digital information signal is subjected to 1-bit summation logic conversion, the summation logic conversion output is used to frequency modulate the carrier wave with a modulation index of 0.5, the frequency modulation output is transmitted, and the receiving side The received signals are differentially detected by two cosine phase comparison delay detectors, one with a delay time set to the repetition period of the digital information signal and the other with a delay time set to twice that, and these delay detection outputs are obtained. A digital frequency modulation communication system characterized in that a transmitted digital information signal is demodulated by adding and combining information signals in the same phase and identifying this combined signal at the time when its eye aperture reaches its maximum.