JPS63266949A - Digital signal transmission method - Google Patents

Abstract

PURPOSE:To suppress the fluctuation of an envelope at band limit by using a chevron-shaped waveform for a phase transmission waveform in a time slot of a transmission signal to eliminate a discontinuous phase point in the same time slot. CONSTITUTION:The shape of the phase transition waveform in each time slot is the same as those of a 1st time slot and a (n+1)th time slot apart by a prescribed n-time slot and the entire waveform is shifted by theta according to sent information. That is, differential coding by n-time slot is applied. When the biphase system of 0 and pi as the theta is used, the information of 1 bit per time slot can be sent and when the quadruple system of 0, pi/2, pi, 3pi/4 as the thetais used, the information of 2 bits per time slot can be sent. Moreover, this method is used for the identical phase transition waveform in time slot.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital signal transmission method for transmitting digital signals on a multipath fading transmission path such as wireless transmission in urban areas.

BACKGROUND OF THE INVENTION In recent years, even in the field of mobile communications, digitalization is progressing due to improvements in confidentiality, sophistication of communications, and 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 of each wave composing a multipath becomes impossible to ignore with respect to the time slot length, waveform distortion and poor tracking of the synchronization system cause
The bit error rate characteristics deteriorate significantly.

Hereinafter, a first example of the above-mentioned conventional digital signal transmission method will be described with reference to the drawings.

FIG. 17 is a phase transition waveform diagram showing the phase transition of a transmission signal in the digital signal transmission method in the first conventional example.

T indicates the time slot length, which is the minimum unit for transmitting l data symbols. When the data is 1, the phase undergoes a π transition, and when the data is 0, no phase transition occurs. This signal format is called differentially encoded binary phase modulation.

To detect such a transmission signal, for example, delay detection having a delay line of l time slots can be used.

Now, as a typical example of multipath, consider what happens to the detected output signal under two-wave multipath with a propagation delay time difference τ that is not negligible compared to the time slot length. Note that waves that are ahead in time are called direct waves, and waves that are delayed are called delayed waves.

FIG. 18 is a diagram illustrating what happens to the detected output signal when the transmission signal shown in FIG. 17 is subjected to delay detection under two-wave multipath. Figure 18 (a
) shows the phase transition of the direct wave. On the other hand, the phase transition of the delayed wave delayed by the propagation delay time difference τ is as shown in FIG. 18(b). The detection output at a certain point in time is the vector inner product of the combined phase of the two waves at that time and the combined phase of the two waves one time slot before. For example, in FIG. 18(C), the detection output in the area B is the value of the Peltle inner product of the two-wave composite phase at B' and that at B.

FIG. 19 is a vector diagram illustrating the combined phase of the direct wave and the delayed wave in order to obtain the detection output at each time point of A to C. Note that the amplitude ratio of the direct wave and the delayed wave is ρ, and the phase difference is α. For example, in FIG. 19, the absolute value of the detection output at time B is Peltor OB' and Peltor O
This is the inner product of B, that is, the square of the line segment OB. Therefore,
Using the cosine theorem, etc., the detection output at each time point A to C in FIG. 18(C) is as follows.

A... UndefinedB...an (111" + 2 pcos
α) C... Undefined However, an (an=±1) is the data string being transmitted.

Regions A and C are undefined depending on the data values of previous and subsequent time slots, respectively. After delayed detection, a low-pass filter is usually inserted to remove harmonic components and unnecessary noise components, so the final detection output signal waveform is filtered to the solid line waveform in FIG. 18(C). The waveform becomes as shown by the dotted line in FIG. 18(C), and forms part of the eye pattern. Here, when ρ is close to 1 and α is close to π, the detection output in the region B, which is an effective detection output, becomes almost zero. Therefore, the eye is closed and the bit error rate characteristics are degraded. Also, at this time, the invalid detection outputs of areas A and C are much larger than the effective detection output of area B, so the eye fluctuates greatly in the time axis direction, making it impossible for the recovered clock to follow, and the bit error rate further increases. Significant deterioration (
For example, Onoue et al., “Bit error rate characteristics in Rayleigh fading with propagation delay time difference”, IEICE Technical Report, C5
8l-168, 1982, or Takai et al., “Analysis of instantaneous code errors due to multiple wave propagation and error generation mechanism based on bit synchronization system”, IEICE Technical Report, C583-15 translation, 1984.
).

In this way, in order to reduce the deterioration of the error rate characteristics due to the deterioration of the eye pattern and the fluctuation of the eye in the time axis direction, the phase transition waveform of the transmission signal is devised to generate multiple types of detection outputs. A method has been proposed to improve the diversity effect by combining these multiple types of detection outputs.

An example of such a second conventional digital signal transmission method will be described below with reference to the drawings.

FIG. 20 is a phase transition waveform diagram showing the phase transition of a transmission signal in the second conventional digital signal transmission method.

One time slot of data is divided into a first half and a second half, and has a stepped waveform.

l The time of the time slot is T, and the time of the first half is TI.
, the time of the second half is shown as Tt, and the phase transition between the first half and the second half is shown as φ. Similar to the first conventional example, the information to be transmitted is based on the phase difference between adjacent time slots,
For example, one bit of information is transmitted by using 0 and π as possible values of this phase difference and assigning 0 and 1 correspondingly.

Next, it will be explained that the second conventional digital signal transmission method exhibits good error rate characteristics under multipath fading.

Since the second conventional digital signal transmission method is also a type of differential encoding phase modulation, detection is performed by differential detection using a delay line of l time slots. Figure 21 shows 2
21 is a diagram illustrating how a detection output signal becomes when the transmission signal of FIG. 20 is detected by a delay detector under wave multipath; FIG. FIG. 21(a) shows a phase transition between an arbitrary time slot of a direct wave and its adjacent time slot. On the other hand, the phase transition of the delayed wave delayed by the propagation delay time difference τ is the 21st
The result will be as shown in figure (b). As in the first conventional example, the detection output at a certain point in time is the vector inner product of the combined phase of the two waves at that time and the combined phase of the two waves l time slots ago.

FIG. 22 is a Peltle diagram illustrating the combined phase of the direct wave and the delayed wave in order to obtain the detection output at each time point of A-H. Note that the amplitude ratio of the direct wave and the delayed wave is ρ, and the phase of the carrier wave of the delayed wave viewed from the carrier wave of the direct wave is α. Second
From Figure 2, if the waveform is not deformed by the low-pass filter after detection, or if the cutoff frequency is sufficiently high compared to the data transmission speed, the detection output at each point A to E in Figure 21 (C) is It will look like this:

A, E... Undefined B, D... l+ρ2 +2ρCoS
αC...1+ρ2+2ρcos (α−φ) In areas A and E, the values are undefined depending on the data values of the previous and subsequent time slots. In reality, the cutoff frequency of the low-pass filter is selected low enough to prevent code amount interference, and the detected output signal after passing through the low-pass filter has the waveform of the solid line in Figure 21 (0). The 21st
A part of the eye pattern is formed as shown by the dotted line in Figure (C). The detection outputs of regions B, D, and region C are complementary and never become zero at the same time for any ρ or α, and the eye never closes. In addition, since at least one of these valid detection outputs will not become smaller than the invalid detection output in areas A or E, the fluctuation of the eye in the time axis direction is reduced, and the sign due to tracking failure of the recovered clock is reduced. There is also little deterioration in error rate. Therefore, the bit error rate characteristics are significantly improved and high-speed digital transmission becomes possible.

-g, under two-wave multipath, the detection output in each region of B-D is the transmission data string an (an=±1),
Assuming that the number of polyphases is m (m = 2.4.8...), and the complex product noise representing the received Peltle of the direct wave and delayed wave with fading is 5t (tl, 52 (11), as follows: Can be expressed.

B, D・ansin(π/11)・(ls+
+s, l") C...an 5in (57m) ・(l S, e
xp(jφ)+szl'')...■ The detection output in region C is the carrier wave phase of the direct wave further shifted by φ.Therefore, the modification of the digital signal transmission method in the second conventional example The good principle is a type of diversity that combines these different types of detection outputs.Assuming an appropriate diversity model, if the fading of the direct wave and delayed wave are independent and their averages are equal, then the average Calculating the error rate Pe, Pe = 1 2・(γ5in(57m)・5in(φ/2))
"r=slN ratio...■, and the optimal value of φ when not subject to band limitations is π (for example, Takai, "Multiple Wave Modulation/Demodulation System % Formula %"). Problems to be Solved by the Invention However, Since the digital signal transmission method in this second conventional example further has a phase □ discontinuity point within the time slot, when subjected to band limitation, the envelope fluctuation is significant and it is susceptible to nonlinear distortion. Since envelope fluctuations occur, the improvement effect decreases when the phase transition φ is made smaller than π, and nonlinearity resistance and improvement effect are not compatible. In addition, in the digital signal transmission method in this second conventional example, when T,=T, when the delay time difference τ exceeds 0.5 as τ/T, the region B and the region disappear, and the improvement effect is Lose. By setting T, #Tt, it is possible to improve even larger τ, but if the occupied bandwidth is further expanded and subjected to band limitation, the error rate characteristics will deteriorate significantly. In addition, the envelope line fluctuation also becomes larger, and there is a problem that it becomes weaker against nonlinear distortion.

In view of the above problems, the present invention provides a digital signal transmission method that is resistant to band limitations and nonlinear distortion, and exhibits good characteristics even for larger τ/T.

Means for Solving the Problems In order to solve the above problems, the digital signal transmission method of the present invention provides that the phase transition waveform within one time slot of data is a chevron waveform, and the phase transition waveform within an arbitrary time slot is The transition waveform and the phase transition waveform in a time slot a given time slot later have the same shape regardless of the information being transmitted, and are at the same position in both time slots, separated by a given time slot. This method uses transmission signals in which information is transmitted based on the phase difference between them.

Operation The present invention uses the above-mentioned transmission signal and eliminates phase discontinuity points within a time slot, thereby making it possible to suppress envelope fluctuations during band limitation. In addition, multiple types of detection outputs can be obtained even for larger delay times τ,
Robust against band-limiting and non-linear distortion, with larger τ
/T also shows good error rate characteristics.

Embodiment Hereinafter, a digital signal transmission method according to an embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 is a phase transition waveform diagram showing an example of a phase transition waveform of a transmission signal in the digital signal transmission method of the present invention. Phase transition waveform ψ(t) within one time slot of data (
0<t<T) differs from the conventional phase modulation method in that it has a chevron-shaped waveform as shown by equation 0.

In Equation 0, the absolute values of the slopes of the two straight lines constituting the chevron waveform are equal, but they may be different, and the same effect can be obtained even if the position of the apex is not at the center of the time slot.

Then, the phase transition waveforms in each of the first time slot and the nth middle time slot, which are separated by a predetermined n time slots, have the same shape and are entirely shifted by θ according to the information to be transmitted. ing. That is, differential encoding of n time slots is performed.

For example, if we use a two-phase system with 0 and π as θ, 1 bit per time slot, θ as 0, π/2, π, 3π
A /2 four-phase system allows two bits of information to be sent per time slot. If θ is generally expressed, it will be as shown in the following equation.

However, the value of i indicates the Gray-encoded data value to be transmitted, and 0≦i S m, i F-Inte
It is ger. Therefore, if the phase transition waveform of the first time slot is ψ(1), the phase transition waveform of the l time slot in the nth time slot is expressed as ψ(t-nT)10.

Note that when the phase shift amount that carries information is expressed as the phase shift amount θa (t) from the absolute phase, the phase shift Iθa
(t) is a step-like function that has a constant value within each time slot, and is a data value sequence obtained by differentially encoding the gray-encoded data value sequence I Q (q E Integer) to be transmitted over n time slots. It can be expressed as follows using idq.

qg-Go m U(t-(q-1)T)) On the other hand, there may be multiple types of intra-time slot phase transition waveforms ψ(1). For n time slot differential encoding, up to n1ll! The intra-time slot phase transition waveform ψl (t), . . . , ψn (t) of fl can be selected.

ψr(t)=0(t≦O2t≧T, r z l N
n) −·−■, then the phase transition waveform of the transmission signal in the digital signal transmission method of the present invention! The general formula of (t) is expressed as q=-00m U (t-(q-1)T) )...■ using ■. The characteristics of the phase transition waveform of the transmission signal in the present invention are:
is in the first term of the equation, and the second term is the same as in conventional differentially encoded phase modulation. Note that some of the time slot phase transition waveforms ψ, (t), ψ2(1), ..., ψn (t) may be the same, or as a special case, all of them may be the same. It may be. In any case, it is sufficient that the intra-time slot phase transition waveforms ψ(tl) that are separated by n time slots match.Also, the value of n may be l, and in this case, the intra-time slot phase transition waveforms ψ([ ) is one type, and the intra-time slot phase transition waveforms of all time slots have the same shape.If the intra-time slot phase transition waveform ψ(1) is one type, the phase transition waveform diagram of the transmission signal (1) The ■formula becomes as follows.

q;-ω = Σ ψ(t-q?) q=-■ q=-00m -U (t-(q-1)T))...■The phase transition waveform ψ(1) within the time slot is As mentioned above, there may be multiple types. Figure 2 shows the maximum phase transition amount ψmaχ of ψCO
When there are a plurality of types, FIG. 3 shows a case where the phase transition direction is alternately leading and slowing.

However, in the latter case, the distance n between corresponding time slots is an even number. Further, the plurality of types may include, for example, a step-like waveform other than the chevron-shaped waveform.

FIG. 4 shows, for example, an intra-time slot phase transition waveform ψ([) or a #J neck ψIIIax=π chevron waveform, n=1, that is, one time slot differentially encoded.

FIG. 4 is a phase transition waveform diagram showing a specific example of a phase transition waveform of a transmission signal of the digital signal transmission method of the present invention, which is capable of transmitting 2 bits per time slot with a multiphase number m=4.

Next, a method for obtaining the above-mentioned transmission signal will be described with reference to an embodiment.

FIG. 5 is a configuration diagram of a transmission signal generation circuit of the digital signal transmission method in the first embodiment of the present invention. Fifth
In the figure, 501 is a data input terminal, 502 is a differential encoding circuit, 503 is an oscillator, 504 is a waveform generation circuit, and 502 is a differential encoding circuit.
05 is a quadrature modulator, and 506 is a transmission signal output terminal.

The digital data to be transmitted is transmitted through the data input terminal 501.
and is differentially encoded by the differential encoding circuit 502. Then, the waveform generation circuit 50. In II, modulation signals for the ■-axis and the Q-axis are generated in accordance with the differentially encoded data.

On the other hand, an oscillator 503 generates a carrier wave, and this carrier wave is modulated by the above-mentioned I-axis and Q-axis modulation signals in a quadrature modulator 505 to become a transmission signal, which is output from a transmission signal output terminal 506.

FIG. 6 shows an example of an internal circuit configuration diagram of the orthogonal modulator 505 in FIG. 5. In FIG. In Figure 6,
601 is a 90° phase shifter, 602 and 603 are balanced modulators, and 604 is a multiplexer. The carrier wave signal supplied from the oscillator 503 is modulated by the I-axis tone signal from the waveform generation circuit 504 using the balanced modulator 602, and becomes a single-axis modulated signal. On the other hand, the aforementioned carrier wave signal is shifted by 90 degrees by a 90 degree phase shifter, and is modulated by a Q-axis tone signal from a waveform generation circuit 504 using a balanced modulator 603 to become a Q-axis modulated signal. .

The two-wave modulated signals of the ■-axis and the Q-axis thus obtained are combined by a multiplexer 604 to become a transmission signal, which is a modulated signal, and is outputted from a transmission signal output terminal 506.

FIG. 7 shows an example of an internal circuit configuration diagram of the differential encoding circuit 502 in FIG. 5. In FIG.

701 and 704 are Gray code conversion circuits, 702 is an adder, and 703 is a delay device. Polyphase number m (m=2゜4
．． 8...), that is, in the case of m phase, it is input to the Gray code conversion circuit 701 as a p-bit parallel data value string, as shown in equation 0. The gray coded data value sequence iq enters the adder 702;
The output is added modulo nl to data delayed by n time slots, that is, n clocks in the delay device 703. Then, by further converting the output of the adder 702 in a Gray code conversion circuit 704, the input p-bit parallel data value string is Gray coded, and n
A differentially encoded p-bit parallel data value sequence idq of the time slot is obtained.

FIG. 8 shows the waveform generation circuit of FIG. 5, taking as an example a four-phase system in which the phase transition waveform 'I' (t) is expressed by equation 0.

504 shows an example of an internal circuit configuration diagram of 504.

801 is a single-axis data input terminal, 802 is a data clock output terminal, 803 is a Q-axis data input terminal, 804 and 806 are shift registers, 805 is a binary counter, 80
7 is read-only memory (hereinafter abbreviated as ROM)
, 80B is a clock generator, 809 and 810 are digital-to-analog converters (hereinafter abbreviated as D/A converters),
811 and 812 are low-pass filters, 813 is a ■-axis modulation output terminal, and 814 is a Q-axis modulation output terminal. In the case of a four-phase system, what is the output idq of the differential encoding circuit 502? This is bit parallel data, and its upper bits and lower bits are input from the ■-axis data input terminal 801 and the Q-axis data input terminal 803, respectively. Each input data string is transferred to shift registers 804 and 806.
The modulation data of the current time slot and the modulation data of the time slots before and after it are obtained. That is, in the example of FIG. 8, shift registers 804 and 8
Qd of 06 is the modulation data of the current time slot, and modulation data for three time slots before and after QexQg and Qa-'-QC are obtained. On the other hand, in the ROM 807, the modulation waveforms of the ■-axis and the Q-axis are written in accordance with the modulation data, and in the example of FIG. 8, each time slot is formed by 16 sample points. ROM807
Addresses A4 to A17 are used as select signals to determine which modulation waveform to select, and modulation data for the current and three previous and previous time slots described above are input.

The reference clock generated by the clock generator 808 is stored in the addresses AO to A3 of the ROM 807 by the binary counter 80.
The frequency divided by 5 is added and becomes a read signal of the modulated waveform. ROM807 output X0NX7 and YO~Y
7 are D/A converters 809 and 810, and low-pass filters 811 and 81 for removing aliasing components, respectively.
2 is converted into an analog signal and becomes a modulation signal for the ■-axis and Q-axis. In addition, when performing multi-phase modulation such as an eight-phase system, shift registers equal to the number of p in equation 0 are prepared, and corresponding ROM addresses are required.

Next, the modulation waveform for each time slot written in the ROM 807 will be explained. Basically, from the phase transition waveform A+11 of the transmission signal determined from the differentially encoded data value sequence idq to be transmitted using the formula 0, the modulation waveforms Ml(t), MO( t).

Ml (t) = cos A(1) MO(t)
= sin A(t) ・'・
(2) However, as it is, it becomes a broadband signal, so if the impulse response of the band-limiting filter is set as h(t) and band-limiting is performed using this filter, the equation 0 becomes as shown in the following equation.

+L.

+j.

Various types of frequency characteristics can be used for the band-limiting filter as long as it is a low-pass type, such as a cosine square type and a Gaussian type. The impulse response h(t) also changes accordingly. - As an example, the cutoff angular frequency ω. , denotes the impulse response h (t) of a cosine-squared filter with roll-off coefficient γ.

...■ The ROM 807 in Fig. 8 stores the modulation waveforms Ml(t), M
Q (t) is written. [Phase] Integral range of equation (
-to.

[. ) is selected to be approximately the spread range of tl, and in the example of Fig. 8, it is 3 time slots before and after, and to calculate the phase transition waveform A (1) from equation 0, 3 time slots before and after are selected.
Requires time slot modulation data.

Therefore, all the modulation data patterns of the current and three time slots before and after are calculated and written in the ROM 807 using the [phase] formula, and the modulation data for the current and three time slots before and after are calculated and written in the ROM 807.
7 addresses A4 to A17 select which modulation waveform to select.

Phase transition waveform! As shown in equation (1), it is almost the same when there are multiple types of intra-time slot phase transition waveform ψ(1), and modulation of the I-axis and Q-axis for one time slot using the [phase] equation. Waveforms Ml(t), MQ(t
All you have to do is write l to ROM. However, the [phase] expression! (
When calculating 1) from equation 0, it is further necessary to know what value r (1≦ran) of the current intra-time slot phase transition waveform ψr (t) is. Therefore, the waveform data to be written to the ROM is calculated not only for the current modulation data pattern and the several time slots before and after, but also for r, which indicates the number of the phase transition waveform ψr (t) in the current time slot. Write it down. Accordingly, the internal circuit configuration diagram of the waveform generating circuit 504 in FIG. 5 needs to be as shown in FIG. 9. In FIG. 9, 801 is an I-axis data input terminal, 802 is a data clock output terminal, 803 is a Q-axis data input terminal, 804 and 806 are shift registers, 805 is a binary counter,
808 is a clock generator, 809 and 810 are D/A
converter, 811 and 812 are low pass filters, 81
3 is an I-axis modulation output terminal, and 814 is a Q-axis modulation output terminal, and the above structure is exactly the same as that shown in FIG. What is different from the configuration in FIG. 8 is the 2 of 901 indicating the current value of r.
A forward counter is added, and addresses of AlB and A19 are added to the ROM 902 in order to select a waveform based on the value of r. Note that the period of the binary counter 901 is n, and in the example of FIG. 9, n=4.

Next, a method of detecting a transmitted signal in the digital signal transmission method of the present invention as described above will be explained.

In the digital signal transmission method of the present invention, the detection method uses a delay detector having a delay line of n time slots. A brief explanation will be given below.

FIG. 10 shows a circuit configuration diagram of a delay detector in the case of a two-phase system. In FIG. 10, 1001 is an input terminal, 1002 is a multiplier, 1003 is a low-pass filter, 1004 is an n time slot delay device, and 1005 is an output terminal. In the n time slot delayer 1004, the signal is delayed by n time slots, but the carrier waves are in phase at the input and output. The low-pass filter 1003 not only removes the frequency component twice the carrier wave generated by the multiplier 1002, but also serves to synthesize multiple types of detection outputs, which will be described later. The frequency characteristic of the low-pass filter 1003 is half the symbol transmission rate 1/T, that is,
A so-called Nyquist filter having a cutoff frequency of 1/2T and oddly symmetrical attenuation characteristics with respect to this frequency is desirable.

FIG. 11 shows a circuit configuration diagram of a delay detector in the case of a four-phase system. In FIG. 11, 1101 is an input terminal, 1102 and 1106 are multipliers, 1103 is a -45° phase shifter, 1105 is a +45° phase shifter, 1104 is an n time slot delay device, and 1107 and 1108 are low-pass filters. , 1109 is an output terminal A, and 1110 is an output terminal B. What is different from the case in FIG. 10 is -45° phase shifter 1103 and +45° phase shifter 11.
05, delay detection is performed on two axes orthogonal to each other, and 2-bit parallel data is demodulated.Other operations are the same as in the case of FIG. 1θ.

FIG. 12 shows a circuit configuration diagram of a delay detector in the case of an eight-phase system. In FIG. 12, 1201 is an input terminal, 1202 to 1205 are multipliers, 1206 is an n time slot delayer, 1207 is a -22,5° phase shifter, 1
208 is a 22.5° phase shifter, 1209 is a +67.5° phase shifter, 1210 is a -67.5° phase shifter, 1211 to 12
14 is a low pass filter, 1215 is a comparator, 1216
is output terminal A, 1217 is output terminal C, and 1218 is output terminal B. In this case, furthermore, phase shifters 1207 to 1
21O performs delayed detection on three axes shifted by 45° and demodulates 3-bit parallel data. Note that the comparator 1215 detects whether the polarities of both inputs match or do not match.

Next, it will be explained that the digital signal transmission method of the present invention exhibits good error rate characteristics under multipath fading.

FIG. 13 shows the expected intra-time slot phase transition waveform ψ(
Regarding 1), similar to FIG. 21, it is a diagram illustrating how the detection output signal becomes under two-wave multipath. As in the case of Fig. 21, the detection forces are roughly divided into F, G, ~G3. )(are classified into five areas, area F
and H is a region of invalid detection output whose polarity does not necessarily match the transmitted data value. The regions B, C, .D in FIG. As shown by the solid line in FIG. 13(C), three different types of detection outputs appear. Second
As in the case of FIG. 1, the solid line waveform in FIG. 13(C) is further filtered to form a part of the eye pattern as shown by the dotted line in FIG. 13(C1).

The detection output in areas 01 to G is: Area G; +s, l'') Area G2; an sin = (l S+ exp U °2ψ
max...@region G,; 10Sg bi) Therefore, it can be seen that the error rate characteristics are improved under multipath fading due to a kind of diversity effect by combining different detection outputs. Note that as the delay time difference τ increases, regions G1 and G disappear, but region G has different detection outputs that continuously change within the region itself due to changes in the parameter. The diversity effect is not lost. In other words, the improvement effect is not lost even for a larger delay time difference τ.

Next, taking a representative example of the digital signal transmission method of the present invention, an example of the average error rate characteristics under two-wave Rayleaf aging with a delay time difference will be shown.

FIG. 14 shows the average error rate characteristics with respect to the S/N ratio when the intra-time slot phase transition waveform is a four-phase system using ψwax of FIG. 1 or equation 0 as a parameter. For comparison, the same graph also shows the case of four-phase phase modulation, which is a conventional digital signal transmission method. 1st
As shown in Figure 4, quadrature phase modulation produces irreducible errors that cannot be alleviated even if the S/N ratio is increased, but in the digital signal transmission system of the present invention, such a phenomenon does not occur, and the error rate is significantly reduced. It can be seen that the characteristics are improved.

Similarly, FIG. 15 shows 4
The average error rate characteristics in the case of a phase system are shown with respect to the delay time difference τ. It can be seen that if ψmax is set to 180° or more, a significant improvement is achieved in the range of 0 and τ/T<0.7.

If ψwax is increased, the occupied bandwidth will increase, so it is appropriate to select ψma to be about 180°. Note that when τ/T=0 or τ/T>0.7, the improvement effect disappears, and the characteristics are close to those of quadrature phase modulation.

As described above, according to this embodiment, by making the intra-time slot phase transition waveform into a chevron waveform, a larger τ
Furthermore, since there are no phase discontinuities within the time slot, envelope fluctuations during band limitation can be reduced, and characteristics against band limitation and nonlinear distortion are improved.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 16 is a configuration diagram of a transmitting circuit of a digital signal transmission method according to a second embodiment of the present invention.

In FIG. 16, 501 is a data input terminal; 1601
1 is a transmission signal generation circuit, and the above configuration is exactly the same as the configuration shown in FIG. 5 in the first embodiment. 1602~
1604 Hani system's first antenna to antenna, 1605
~1607 is a system level adjuster, 1608~161
0 is the 1st delay device to the 11th delay device of the 11th system.

Note that the level adjusters 1605 to 1607 may have an amplification effect. Also, the detection method on the receiving side is the first one.
10 to 12, which are shown as examples of the present invention, delay detection is carried out for delayed time slots.

The digital signal transmission method configured as above will be explained below using FIG. 15, FIG. 16, and Equation 0.

FIG. 15 shows the average error rate characteristics when the transmission signal of the present invention, which is the output signal of the transmission signal generation circuit 1601, propagates through a two-wave Rayleigh fading path with a delay time difference τ and is received and detected. As mentioned above. Now, the delay time difference τ of the propagation path, so-called delay dispersion, is the time slot length T
Assume that it is smaller than . This condition corresponds to a case where delay dispersion is small in a campus or the like, or a case where the transmission speed is slow. In this way, when τ/T is close to 0, the ◎Bujin side changes less with respect to a change of 2, and the diversity effect due to combining different types of detection outputs as described in the first embodiment decreases. do. For this reason, as shown in FIG. 15, as τ/T approaches 0, the error rate characteristics are no longer improved. Therefore, the improvement range of τ/T is O
If a delay within the range of ~0.7 is given in advance on the transmitting side, the error rate characteristics will be improved due to the diversity effect.

In Fig. 16, the delay devices 1608 to 1610 give the above-mentioned delays on the transmitting side.Including the delay due to the path difference from each antenna, on the receiving side, the waves that arrive first and the waves that arrive last It is necessary to set the time difference τ- of the waves to τm/T so that it does not exceed the maximum improvement range (about 0.7) of τ/T determined by the intra-time slot phase transition waveform ψ1laX. Level adjuster 1605
~1607 sets the average level of waves with fading from each antenna to be approximately equal during reception. 1st
-Thirdly, it is necessary to install the antennas separately or use antennas with different planes of polarization so that the fading of the paths from each antenna to the receiving point are uncorrelated with each other. The simplest and most useful case is when k = 2. In this case, the time difference τ between the waves arriving from the two antennas is τm/T, and the best point of the error rate determined by ψIIIax is It is desirable to select a value of about 0.3 to 0.4.

As described above, in the second embodiment of the present invention, by transmitting the same transmission signal from different antennas with a time difference, a diversity effect can be obtained even when τ/'r is small, and the error rate characteristics can be improved.

This diversity is useful in making the receiving side equipment more compact and portable since only one antenna is required on the receiving side.

Effects of the Invention As described above, the present invention uses a chevron-shaped waveform as the phase transition waveform within the time slot of the transmission signal, thereby eliminating phase discontinuities within the time slot, suppressing envelope fluctuations during band limitation, and improving the bandwidth. Improved performance against limitations and nonlinear distortion. Furthermore, multiple types of detection outputs can be obtained even for larger delay times τ, and good error rate characteristics can be obtained even for larger τ/T.

[Brief explanation of drawings]

1 to 4 are phase transition waveform diagrams showing examples of phase transition waveforms of transmission signals in the digital signal transmission method of the present invention, and FIG. 5 is transmission of the digital signal transmission method in the first embodiment of the present invention. 6 is a circuit diagram of the signal generation circuit, FIG. 6 is a circuit diagram of the orthogonal modulator 505 in FIG. 5, FIG. 7 is a circuit diagram of the differential encoding circuit 502 in FIG. 5, and FIGS. FIG. 9 is a circuit configuration diagram of the waveform generation circuit 504 in FIG.
θ diagrams to FIG. 12 are circuit configuration diagrams of the detector of the digital signal transmission method in the embodiment of the present invention, and FIG. 13 is an explanation explaining the detection output signal under two-wave multipath of the digital signal transmission method of the present invention. Figures 14-15 are 2
Characteristic diagram showing the average error rate characteristics of the digital signal transmission method of the present invention under wave ray leaf aging, No. 16
FIG. 17 is a circuit configuration diagram of a transmitting circuit of a digital signal transmission method according to the second embodiment of the present invention, and FIG. 17 is a phase transition waveform diagram showing a phase transition of a transmission signal of a digital signal transmission method according to the first conventional example. FIG. 18 is an explanatory diagram illustrating the detection output signal under two-wave multipath in the digital signal transmission method in the first conventional example, and FIG. A Peltle diagram showing the composite phase, FIG. 20 is a phase transition waveform diagram showing the phase transition of the transmission signal in the digital signal transmission method in the second conventional example, and FIG. 21 shows the phase transition waveform diagram in the digital signal transmission method in the second conventional example. FIG. 22, which is an explanatory diagram illustrating a detection output signal under two-wave multipath, is a Peltle diagram showing the combined phase of a direct wave and a delayed wave to obtain the detection output of FIG. 21. 501... Data input terminal, 502...
・Differential encoding circuit, 503... Oscillator, 504
... Waveform generation circuit, 505 ... Quadrature modulator, 506 ... Transmission signal output terminal, 601.
...90゛phase shifter, 602.603...
Balanced modulator, 604... Multiplexer, 701...
... Gray code conversion circuit, 702 ... Adder, 703 ... Delay device, 704 ... Gray code conversion circuit, 801 ... I-axis data Input terminal, 802... Data clock output terminal, 80
3...Q-axis data input terminal, 804, 806.
...Shift register, 805.901...
・Binary counter, 807, 902... Read only memory (ROM>, 808...
Clock generator, 809.810...Digital-to-analog converter (D/A converter), 811,812.
1003.110? , 1108°1211-1214
...Low pass filter, 813...■
Axis modulation output terminal, 814... Q-axis modulation output terminal, 1001°1101.1201... Input terminal, 1002.1102.1106.1202-1205
・・・・・・Multiplier, 1004.1104.1206・
...=n time slot delay device, 1005...
・Output terminal, 1109.1216...Output terminal AS1110.1218...Output terminal B, 12
17...Output terminal C, 1103...-
45° phase shifter, 1105...+45° phase shifter,
1207...-22,5° phase shifter, 1208.
...+22.5' phase shifter, 1209...
+67.5° phase shifter, 1210...-67,5
° Phase shifter, 1215... Comparator, 1601...
...Transmission signal generation circuit, 1602...1st
Antenna, 1603...Second antenna, 1604.
...Second antenna, 1605-1607...
・Level adjuster, 1608...First delay device, 1
609...Second delay device, 1610...
・No. 11 delay device. Name of agent: Patent attorney Toshio Nakao (1 person) Figure 0o4 Figure 11 Figure 12F2! l 萬 13 Figure To 7-=l H-7-- '' Sho II No. 17 Data string 7.・O・12./1・1.7,・′・2
, To Ding--←-Ryo--H-Ryo-←--Ding Yiichi←-T-
÷−7−→ (C) Neka −111−−−：Go====upper knee 1st
9 prison irises data string -------1,・O・5,7.・7
,,, ,,?・1, ------1=7←←TjT
→←T→ 360°−−−−−−−−−−−−−−−−−
−−−−−−−−−−−−−−−−−−−−−−
-1T: To Tel -S ゐ Q~
+%J. Fig. 22 C' O°゛・, 7pa・・′180+φ 1----f mark, 7・. 〇

Claims (6)

[Claims] (1) In a transmission device that transmits digital data,
The phase transition waveform within one time slot of data is a chevron waveform, and the phase transition waveform within an arbitrary time slot and the phase transition waveform within a time slot after a predetermined time slot are the information to be transmitted. Digital signal transmission characterized by using a transmission signal that has the same shape regardless of the time slot, and has information transmitted in the phase difference between the same positions of both time slots, which are separated by a predetermined time slot. Method. (2) The digital signal transmission method according to claim (1), wherein the chevron waveform is composed of two straight lines each having a different slope. (3) The digital signal transmission method according to claim (1), wherein the peak of the chevron waveform is located at the center of the time slot. (4) The digital signal transmission method according to claim (1), wherein the phase difference is an angle obtained by equally dividing 2π by a number that is a power of 2. (5) The digital signal transmission method according to claim (1), wherein the transmission signal is detected by delay detection using a delay line capable of obtaining a delay corresponding to a predetermined time slot. . (6) The digital signal transmission method according to claim (1), wherein the predetermined time slot is one time slot.