JPS62152237A - Digital signal transmitting system - Google Patents

Abstract

PURPOSE:To prevent the waveform distortion due to a multi-path by mounting and transmitting alternately the same data to the first and second frequencies. CONSTITUTION:The first oscillating device 4 oscillates a frequency f1 and the second oscillating device 5 oscillates a frequency f2 respectively. Balance modulators 6 and 7 balance-modulate the differential coding data inputted to an input terminal 2 by the above-mentioned frequency. Switches 8 and 9 select alternately the output of the balance modulators 6 and 7, and output the signal modulated by the frequency f1 at the first half part of the same time slot and by the frequency f2 at the last half pat to a synthesizing device 10. At the receiving side, the sent signal is separated by the frequency, the first half part is delayed by the half time slot and synthesized with the last half part. Thus, since the part overlapped by the direct wave is decreased even when the delaying wave exists, the waveform distortion due to the multi-path can be miniaturized. The frequency and the time diversity effect can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a digital signal transmission system for wirelessly transmitting digital signals on multipath transmission lines in urban areas and the like.

BACKGROUND OF THE INVENTION In recent years, even in the field of mobile communications, digitization has been progressing in order to improve privacy, improve communication sophistication, and improve compatibility with surrounding communication networks. However, in urban areas where such demand is thought to be most concentrated, communication quality deteriorates significantly due to multipaths caused by reflection and diffraction from buildings and other structures.

In the case of digital transmission, when the propagation delay time difference between the respective waves constituting the multipath cannot be ignored with respect to the data time slot, code error susceptibility deteriorates significantly due to waveform distortion and tracking failure of the synchronization system.

Hereinafter, an example of the conventional digital signal transmission method described above will be described using examples of its modulation device and demodulation device, with reference to the drawings.

FIG. 8 shows a circuit configuration diagram of a modulation device using a conventional digital signal transmission system. In FIG. 8, 81 is a data input terminal, 82 is a Gaussian low-pass filter, 83 is an FM modulator, and 84 is a GMSK output terminal.

The operation of the conventional digital signal transmission modulation device configured as described above will be described below.

The N RZ (Non Return Zero) digital signal is baseband limited by a Gaussian low-pass filter 82 . The band-limited signal enters the FM modulator 83. The modulation index of the FM modulator is set to 0.5, and the baseband is band-limited by a Gaussian filter.
ing), G M S K (Gauss
ion Filtered MSK). GMSK has a constant envelope feature like MSK, and also has excellent spectral concentration and convergence.

As with MSK, demodulation of such a GMSK signal can be performed using either a synchronous detector or a frequency discriminator. An example of a conventional demodulator using the latter method will be described below with reference to the drawings.

FIG. 9 shows a circuit diagram of a conventional demodulator. In FIG. 9, 91 is an input terminal, 92 is an amplitude limiter, 93 is a monostable multi-bi break, 94 is a low-pass filter, and 95 is a demodulated signal output terminal.

The operation of the conventional demodulator configured as described above will be described below.

The GMSK signal input to the input terminal 91 is on the amplitude side @2
It is converted into a rectangular wave in S92. Furthermore, it is converted into a pulse train of a constant width by a monostable multi-by-break 93. Since the GMSK signal is a type of FM signal, the density of this constant width pulse train changes depending on the modulation signal. Therefore, by averaging this pulse train using the low-pass filter 94, changes in frequency can be extracted.

(For example, Miki, “Experimental study of GMSK frequency detection”
.

(IEICE Technical Report, C382-89, 1982) Problems to be Solved by the Invention However, in the above-mentioned system, the waveform distortion due to multipath is significant as described above, and the code error rate is significantly degraded. In particular, when we examine the relationship between signal S/N ratio and error rate, we find that the error rate does not decrease even if the S/N ratio is improved81.
jj! exists. Such code errors are called irreducible errors.

Due to this so-called irreducible error, in fact, la
! The data transmission speed in urban areas is severely limited, making high-speed transmission impossible.

In view of the above-mentioned problems, the present invention provides a digital signal transmission system that allows high-speed digital transmission on multipath transmission lines in urban areas and the like.

Means for Solving the Problems In order to solve the above problems, the digital signal transmission system of the present invention performs two-phase phase modulation on the signals of the first and second frequencies using the same data signal. These modulated signals are switched at a predetermined period within the time loft, and the signal output for a predetermined time is used as a transmission signal.

Operation As described above, the present invention transmits the same data alternately on the first and second frequencies. Therefore, when the image frequencies are received separately, the first or second wave becomes a burst-like signal whose width is narrower than the data signal time slot. In other words, even if a delayed wave exists, since it is an intermittent wave, there is little overlap with the direct wave, and it is less susceptible to waveform distortion due to multipath. Furthermore, since two frequencies are used, there is an effect of frequency diversity. Furthermore, a time diversity effect can be expected due to differences in transmission times of image frequencies. The effects described above enable higher-speed digital transmission than in the past on multipath transmission lines.

Embodiment Below, a digital signal transmission system according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows transmission signals of a digital signal transmission system in an embodiment of the present invention. The data has been differentially encoded in advance and is binary phase keyed (BPSK: B
Inary Phase 5hift Keying
> is applied. Since it is differentially encoded, more precisely, differential encoding B P S K (D P S K : D
iferentialPhase 5hirt Kc
ying ) modulation is applied.

However, the transmission signal is as shown in Figure 1 Transmission signal l.
The first half of the time slot is frequency r1, and the second half is frequency f.
Sent in 2. The transmission information includes, for example, the phase difference between fl-8 and f,-B in FIG.
It is expressed as the phase difference between A and f2-B. however,
The phase difference referred to here is 0" or 180°, and the systems with frequencies 1 and 12 transmit the same phase transition, that is, the same data. The transmission signal is the transmission signal shown in Figure 1. 2, the duty ratio may be even smaller than that of the transmission signal l.Also, the first
As shown in Figure Transmission Signal 3, each frequency may be transmitted a plurality of times within one time loft. As shown in the transmission signal 4 of FIG. 1, the duty ratio may be even smaller than that of the transmission signal 3.

Next, among these transmission signals, transmission signal 1 in FIG. 1 will be taken as an example to explain how a corresponding modulation device and demodulation device can be easily realized. moreover,
It will be explained that the digital signal transmission method of the present invention is resistant to multipath distortion.

FIG. 2 shows an example of a circuit configuration diagram of a modulation device that sends out a transmission signal of the digital signal transmission system of the present invention.

In FIG. 2, 1 is a first control signal input terminal, 2 is a data input terminal, 3 is a second control signal input terminal, 4 is a first oscillator, 5 is a second oscillator, and 6 and 7 are balanced modulators. , 8
and 9 is a high frequency switch, 10 is a multiplexer, and 11 is an output terminal.

The operation of the modulation device configured as described above will be explained below with reference to FIGS. 2 and 3.

The data has been differentially encoded in advance and is input to the data input terminal 2. The first oscillator 4 has a frequency f21. f...
The second oscillator 5 has a frequency f;! ! , f2 are generated and subjected to two-phase phase modulation by balanced modulators 6 and 7. On the other hand, a control signal as shown in FIG. 3 is applied to the first control signal input terminal 3 and the second control signal input terminal 3, and the balanced modulator 6 and 7 outputs are switched,
It is output to the output terminal 11. The output signal shown in FIG. 3 is the same as that shown in the transmission signal 1 of FIG. 1. In addition, transmission signals 2 to 4 in FIG.
A similar result can be obtained by changing the waveforms of the II+ control signal and the second control signal.

Next, an example of a demodulator for a digital signal transmission system according to an embodiment of the present invention will be described with reference to FIG.

FIG. 4 shows a circuit configuration diagram of the demodulator.

In FIG. 4, 31 is an input terminal, 32 and 33 are balanced modulators, 34 is a one time slot delay device, and 35 is a 90
36 is a half-time loft delay device, 37 and 38 are low-pass filters, 39 is a multiplexer, 310 is a band-limiting filter, and 311 is a demodulated signal output terminal.

The operation of the demodulator configured as described above will be described below.

two transmission frequencies f1 and f2 and a data transmission rate f,
It is assumed that there is a relationship between them as shown in the following equation, where n is an integer.

fl f2 = (2n 1)xf, /4 +
＋・＋・■ If T is the time slot length, T = 1 / f, ,
,,"°°■. However, if we multiply both sides of the 0 equation by 2πT, we get the following equation.

2πf IT 2 ''' 2 T = (2n-1)
The phase relationship between the signal of f2 and the signal of f2 shows that they are further shifted from each other by 90''.

In FIG. 3, it is assumed that a signal α as shown in the following equation is input manually to the input terminal 31.

α=ancosω, t+bncosω2
t -e...■ However, an and bn are data strings (an=±1, bn=±1), ω1=2πf1, ω
2=2πr2. In other words, the signal α has two frequencies f
1 and r2 are shown.

Furthermore, the delay time T1 of the l time slot delay device 34
cos (ω, 1+ωHT I) ”CO5ω1 t
......If there is a relationship of
...■. Therefore, from equations (2) and (2), the output signals α and β of the balanced modulator 32 are as follows.

α・β =aeO5ω1 t' an-(CO5ω!t±
a cosa+ t eb sinω2Ln
l n-1+bco
sω2 L' an-1CO9ω1t±b C
O3a)2L'1)1-15Inω2L='
A (anan-1(1+ cos 2ω, 1)±a
n b n −I S in (ωr + ω2)
t±a n b n-l5 j n (ω1-ω2)
t”b n a n-lCo5(ω, +ω2)t+
bna, -1cos(ω1-ω2)t± b (+
b rl-1s+n 2 ω21 ) ・
...■Here, if the frequency component of 2ω3.01±ω2.2ω2 is removed by the low-pass filter 37, the output signal T of the low-pass filter 37 is expressed by the following formula % Boot row a, If the signal γ is differentially encoded, the output signal γ becomes a demodulated data string. In this way, f,,f2,
Set the condition of 0 expression on f, and! Time slot delay device 34
By performing delay detection with a relation of the equation 0 to the delay time T, the modulated data sequence an for the carrier wave of frequency f1 is
Only the demodulated signal can be obtained.

Demodulation of the modulated data sequence bn for a carrier wave with a frequency of "2" can be performed in the same manner. By further shifting the output signal of the time slot delayer 34 by 90 degrees,
The output signal δ of the 0° phase shifter 35 is expressed as 6δ2b n-(cos ω2 t ± a
n −+ sin ω, 1−・・・・■ Therefore,
From equations 0 and 0, the output signals α and δ of the balanced modulator 33 are similarly expressed by the following equations.

α・δ = Vz (bnbrl-1(1+ cos 2ω21)
±bnan-, 5in(ω1 +ω2)t±b na
n-1S 1 n (ω1-ω2)t” a n b
n 4 Co5(ω1-+ω2)t” a B tl
n-I Co5("1-ω2)t, ±a na
n-1tr t n 2ω, t l ・・−
...131i) Here, if the frequency components of 2ω1, ω1±ω2.2ω2 are removed by the low-pass filter 3B, the output signal ε of the low-pass filter 38 is ε=%
bnbn-1...0, and if the data string bn is differentially encoded, it is a modulated data string for the carrier wave of frequency f2. Only the demodulated signal can be obtained.

In the case of the first transfer signal 1, the same differentially encoded data string is transmitted at the frequency f1 in the first half of the data time slot, and at the frequency [2] in the second half. Therefore, each time the demodulated signal corresponding to the former is delayed by a half time slot in the half time loft delay device 36, the same data strings sent by the image frequency are frequency-separated and received, and the demodulated signals 43 corresponding to each are received at the same timing. It can be synthesized with A band-limiting filter 310 limits the band of each demodulated signal synthesized by the multiplexer 39 to an extent that allows the data signal to pass, and removes noise components. Regenerate the clock component from the demodulated signal obtained in this way,
By instantaneously identifying the demodulated signal, the data string is decoded.

Note that the first transmission signal 2 is demodulated in the same manner, but the first transmission signal 3 and the transmission signal 4 are demodulated in the same manner.
By making the delay time of the half-time slot delay device 36 in FIG. 4 equal to the time for one transmission of frequency f1 or r2, demodulation can be performed in exactly the same way.

Next, the reason why the digital signal transmission system of the present invention exhibits excellent code error stability against multipath distortion will be explained in the fifth section below.
This will be explained using FIGS. 7 to 7.

In the demodulation process, as described above, the carrier frequencies f1 and 12 are received separately and then combined, so first, consider the effects of multipath distortion on the transmission system of the frequency r. Furthermore, as a multipath model, a typical two-wave model will be considered. Waves that are ahead in time are called direct waves, and waves that are delayed are called delayed waves.

FIG. 5 is a diagram illustrating how the demodulated signal of the transmission system with the frequency fl becomes under two-wave multipath. FIG. 5 ta+ shows an example of phase transition of a direct wave. The amplitude becomes zero in the second half of the time slot.

On the other hand, compared to time slots,
The phase transition of the delayed wave delayed by the propagation delay time difference τ is
The result will be as shown in Fig. 5 fbl. As mentioned above, the demodulation method is one time slot delayed detection, so the demodulated output at a certain point is the vector inner product of the composite phase of the two waves at that time and the composite phase of the two waves for one time slot. . For example, in FIG. 5(C), the demodulated output in section B is B'
It is the value of the vector inner product of the two-wave composite phase at the time of B and that at the time of B. However, the half time slot delay device 3 in FIG.
The time delay caused by 6 and the distortion of the demodulated signal waveform caused by the low-pass filter 37 will not be considered here to simplify the explanation.

FIG. 6 illustrates the combined phase of the direct wave and delayed wave at each time point A' to E' and A to E. In addition,
The amplitude ratio of the direct wave and the delayed wave was set to ρ, and the phase difference was set to φ. 6th
From the figure, the demodulated outputs at each time point A to E in FIG. 5<c+ are as follows.

A... O B... l C... 1+ρ2+2ρcos φD...
・・・ ρ2 E・・・・・・ 0 Depending on the values of ρ and φ, even if the demodulated output may be zero in the section C, the demodulated output will definitely be zero in the section B or D. Never. In this way, there is little deterioration of the eye pattern due to multipath.

The same holds true for the f2 frequency system.

However, the phase difference ψ between the direct wave and the delayed wave at the frequency 01 of f2 has no correlation with the phase difference φ at rl, and is generally different. In other words, the value of demodulated output in section C is
It is generally different from that of the fl strain. Therefore, as described above, by the half time loft delay device 36 of FIG.
By combining both demodulated outputs at the same time,
In section C, a diversity effect can be expected.

To be precise, this ubiquity effect is a frequency diversity effect.

FIG. 7 is a diagram showing such a frequency diversity effect. In FIG. 7(a) and FIG. 7(bl), demodulated output 1 is the demodulated output of the system with frequency r1,
The demodulated output 2 is the demodulated output of the frequency f2 system. Both have a timing loss due to the half-time loft delay device 36. By combining the demodulated output 1 and the demodulated output 2, a composite waveform as shown by the solid line in FIG. 7+C) is obtained.

Furthermore, by passing this composite waveform through a band-limiting filter 310, a demodulated signal output as shown by the dotted line C1 in FIG. 7 is obtained.

For the first transmission signals 2 to 4, the demodulated signal outputs can be output in exactly the same way by appropriately selecting the delay time of the half-time slot delay device 36 and combining both demodulated outputs at the same timing. can get.

As described above, in the digital signal transmission method of the present invention, each wave of frequencies r and r is intermittent, so even if a delayed wave exists, there is little overlap with the direct wave, and the waveform due to multipath Not susceptible to distortion. Furthermore, there is an effect of frequency diversity due to the two frequencies. Also, −frequency f,
The system with frequency 12 and the system with frequency 12 are time-shifted, and a time diversity effect can also be expected. As a result of the above-mentioned effects, code error susceptibility is significantly improved over the conventional system in a multipath transmission path, and high-speed digital transmission becomes possible.

In addition, V1 diagram transmission signal 2 and transmission signal 4 have a narrower signal existence section than transmission signal 1 and transmission signal 3, and the section where the direct wave and delayed wave overlap is reduced, improving the characteristics against multipath distortion. Effects of the Invention As described above, the present invention performs two-phase phase modulation of first and second frequency signals using the same data signal, and switches these modulated signals at a predetermined period within one data time slot. By using a signal that is output for a predetermined period of time as a transmission signal, it becomes possible to perform digital transmission at a higher speed than before on a multipath transmission line.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a transmission signal of the digital signal transmission method in an embodiment of the present invention, FIG. 2 is a block diagram of an example of a modified J11 device of the digital signal transmission method of the present invention, and FIG. 3 is a schematic diagram of the same signal. 4 is a block diagram of an example of a demodulation device for the digital signal transmission method of the present invention, and FIGS. 5 to 7 show signals for explaining that the digital signal transmission method of the present invention is resistant to multipath distortion. The schematic diagrams, FIGS. 8 and 9, are block diagrams of a modulation device and a demodulation device of a conventional digital signal transmission system. ■...First control signal input terminal, 2...
data input terminal, 3... second control signal input terminal, 4... first oscillator, 5... second oscillator, 6. 7. 32゜33...Balanced modulator, 8,9...High frequency switch, 10.39.
...Multiplexer, 11...Output terminal, 31.
...Input terminal, 34...1 time slot delayer, 35...90゛phase shifter, 36...
...Half time slot delayer, 37.38...
-Low pass filter, 310...Band limit filter, 311...Demodulated signal output terminal. Name of agent Patent attorney Toshio Nakao 1 person - Edge size Figure 5 Figure 6 Figure 7r5 A 8CD Figure 48

Claims (7)

[Claims] (1) In a transmission device that transmits digital data, two-phase phase modulation is performed on first and second frequency signals using the same data signal, and these modulated signals are modulated at a predetermined period within one data time slot. A digital signal transmission method characterized by using a signal that is switched and output for a predetermined period of time as a transmission signal. (2) The predetermined period is half of one time slot of the data to be transmitted, and the data is transmitted once each on the first and second frequencies during one time slot. The digital signal transmission method described in item 1. (3) The predetermined period is an integer fraction of one time slot of the data to be transmitted, and the data is transmitted multiple times each at the first and second frequencies during one time slot. The digital signal transmission method described in scope 1. (4) The predetermined time is the time obtained by dividing one time slot of data to be transmitted by the total number of times data is transmitted on the first or second frequency within one time slot. The digital signal transmission method according to scope 2 or 3. (5) A patent claim characterized in that the predetermined time is less than the time obtained by dividing one time slot of data to be transmitted by the total number of times the data is transmitted on the first or second frequency within one time slot. The digital signal transmission method according to item 2 or 3. (6) The digital signal transmission method according to claim 4 or 5, wherein the data signal is differentially encoded. (7) Claims 1 or 4 or 5 or 6, characterized in that the difference between the first and second frequencies is an odd multiple of one-fourth of the data transmission rate. Digital signal transmission method described in section.