JPS62209950A - Digital signal transmitting method - Google Patents

Abstract

PURPOSE:To execute a highly speedy digital transmission in a multi-path transmission line by using a signal having the information transmitted to a phase difference between the respective first half part and last half parts of a time slot as a transmission signal. CONSTITUTION:Respective time slots of data are divided into the first half part and the last half part with the ratio of one type or plural types, the phase is inverted between the first half part and the last half part, the ratio of the first half part and the last half part in an optional time slot is respectively equal to the ratio of the first half part and the last half part in the time slot after the prescribed time slot only, and the signal having the information transmitted to the phase difference between respective first half part and the last half part of these both time slots away from the prescribed time slot only is used as a transmission signal. When delaying is detected, two types of the effective detecting output are obtained for a time slot, by one of the diversity effect obtained by synthesizing these outputs, a code error ratio under a multi- path is significantly improved and at the multi-path transmission line, a highly spedy digital transmission can be executed.

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 transmission path such as wireless transmission in urban areas.

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 a multipath cannot be ignored with respect to the data time front, the code error rate characteristics deteriorate significantly due to waveform distortion and poor tracking of the synchronization system.

An example of the above-mentioned conventional digital signal transmission method will be described below with reference to the drawings.

FIG. 12 shows a phase transition of a transmission signal in a conventional digital signal transmission method. T indicates one time slot of data. When the data is 1, the phase shifts by 180°, and when the data is 0, no phase shift occurs. This signal format is called differentially encoded two-phase phase modulation.

To detect such a transmission signal, for example, delay detection having a delay line of one time slot 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.

Note that waves that are ahead in time are called direct waves, and waves that are delayed are called delayed waves.

FIG. 13 is a diagram explaining what happens to the detection output signal when the transmission signal shown in FIG. 12 is subjected to delay detection under two-wave multipath. Figure 13 18
+ indicates 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 Figure 13).The detected output at a certain point is the combined phase of the two waves at that time, and one time slot. 1, which is the vector inner product with the composite phase of the previous two waves.
In Figure 3 (C1), the detection output in the section B is the value of the vector inner product of the two-wave composite phase at B' and that at B.

FIG. 14 illustrates the combined phase of the direct wave and 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. From FIG. 14, the detection outputs at each point A-C in FIG. 13 (C1) are as follows.

A... Undefined B= 1 + 13" + 2 Pcos a
C... In the undefined intervals A and C, the data values of the previous and subsequent time slots become undefined. After delayed detection, a low-pass filter is usually inserted to remove unnecessary noise components, so the final detected output signal waveform is as shown in Figure 13 (C).
The solid line waveform is filtered, resulting in a waveform as shown by the dotted line in Figure 13 (C1), which forms part of the eye pattern.By the way, when ρ is close to 1 and α is around 180'' , the detection output in section B, which is the effective detection output, is
It becomes zero. Therefore, the eye is closed and the bit error rate characteristics are degraded. Also, at this time, since the invalid detection outputs in sections A and C are much larger than the effective detection output in section B, the eye fluctuates greatly in the time axis direction, making it impossible for the recovered clock to follow, and the bit error rate becomes even worse. Significant deterioration. (For example, Onoue et al., “Bit error rate characteristics in Rayleigh fading with propagation delay time difference”, IEICE Technical Report, C38
1-168゜1982, or Takai et al., ``Analysis of instantaneous code errors caused by multiple wave propagation and error generation mechanism based on bit synchronization system'', IEICE Technical Report, C383-158゜Problems to be solved by the inventionHowever, In the above method, as mentioned above, the waveform distortion due to multipath is significant, and the code error rate is significantly degraded.In particular, when examining the relationship between the signal S/N ratio and the error rate, it is found that the S/N ratio There are regions where the error rate does not decrease even if the error rate is improved.Such code errors are called irreducible errors.

Due to such so-called irreducible errors, the actual data transmission speed in urban areas is severely limited, making high-speed transmission impossible.

The present invention overcomes the above problems and provides a digital signal transmission method that enables 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 method of the present invention divides each time slot of data into a first half and a second half in one or more ratios, and The phase is reversed between the first half and the second half, and the ratio of the first half to the second half in any time slot is equal to the ratio of the first half to the second half in a time slot after a predetermined time slot, respectively. A signal containing information to be transmitted in the phase difference between the first half and the second half of these two time slots, which are separated by a predetermined time slot, is used as the transmission signal.

Operation The present invention uses the above-mentioned transmission signal to
When performing delayed detection, two types of effective detection outputs can be obtained for each time slot.

Then, by combining these outputs, a type of ubiquitous effect results in a significant improvement in the bit error rate under multipath conditions. Furthermore, if each time slot has multiple types of ratios between the first half and the second half, it is possible to obtain multiple types of valid detection output strings of two different types, which reduces burst errors and improves error correction. This can be simplified, and as a result, the bit error rate under multipath conditions can be further improved. The above-mentioned effects make it possible to perform digital transmission faster than before on a multipath transmission line.

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

FIG. 1 is a phase transition diagram showing the phase transition of a transmission signal in a digital signal transmission method according to a first embodiment of the present invention.

Transmission signals of the digital signal transmission method according to the first embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 1, one time slot of data is divided into a first half and a second half. The time of one time loft is shown as T, the time of the first half as T1, and the time of the second half as T2. There is always a phase transition as indicated by φ between the first half and the second half. The value of φ is 180@, and this phase transition is, in other words, a phase inversion.

Note that the ratio of T, and T is constant in all time slots, and its value may be arbitrary; of course, T,
, T2 may be equal.

6. Phase difference between the first half of a certain time slot and the first half after n time slots, and the same.6. Second part 5 1. ,,,) (phase difference, etc.), 5.2° The amount of phase shift is indicated by θ. Digital information is transmitted depending on the value of θ. For example, if a two-phase system with θ0 and 180# is used as the possible values of θ, 1 bit of information can be transmitted by assigning 0 and 1 to each of them. transmitted. Also, θ is 0", 90', 180°, 270'
If a four-phase system is used, two bits of information are transmitted. Furthermore, the value of θ is O", 45°, 90°...
8-phase system of..., similarly O'', 22.5°, 45@.

67.5°... 16-phase system, etc., which is a power of 2, polyphase, which is not a power of 2, and the interval between possible values of θ is not constant. good(
, θ may be any value as long as the value corresponds to the information to be transmitted. Note that the value of n may be arbitrary as long as it is a natural number.

As described above, the phase transition of the transmission signal in the digital signal transmission method in the first embodiment of the present invention is T, , T2 .
There are various values depending on the values of θ and n, but below, the second
An example is shown in FIG.

FIG. 2 shows an example of the phase transition of a transmission signal that transmits 1 bit of data per time loft corresponding to θ-0'', 180' when n-1.

Fig. 3 shows θ-0', 90 @ when nml.

180°, 270”, an example of a phase transition of a transmission signal transmitting 2 bits of data for l time slots is shown.

In Fig. 4, when n-1, θ-0@, 45'.

90', 135", 180', 225', 270"31
51, an example of the phase transition of a transmission signal for transmitting 3 bits of data for l time slots is shown.

Next, the reason why the digital signal transmission method of the present invention is strong against multipath distortion will be explained using an example.

In the following description, θ=0', 180
'That is, the explanation will be made using a two-phase system transmission signal as shown in FIG. 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.

Since the digital signal transmission method of the present invention is a type of differentially encoded phase modulation, detection is performed by delay detection using a delay line of n time slots. In the example of the transmission signal shown in FIG. 2, the signal is detected by delay detection using a delay line of one time slot.

An example of the configuration of the detection circuit is shown in FIG. However, the fifth
In the figure, l is an input terminal, 2 is a multiplier, 3 is a one-time loft delay device, 4 is a low-pass filter, and 5 is a detection output terminal.

Figure 6 shows that when a two-phase transmission signal as shown in Figure 2 is detected by the detection circuit shown in Figure 5,
FIG. 3 is a diagram illustrating how a detection output signal becomes.

Figure 6 (al 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, which cannot be ignored compared to the time slot, is the phase transition of the 5th wave. It looks like figure fbl.The detection output at a certain point is:
This is the vector inner product of the composite phase of the two waves at that time and the composite phase of the two waves n time slots ago. For example, in Figure 6 (
In C), the detection output in the section B is the value of the vector inner product of the two-wave composite phase at B' and that at B.

FIG. 7 illustrates the combined phase of the direct wave and the delayed wave in order to obtain the detection output at each time point A to E.

Note that the amplitude ratio of the direct wave and the delayed wave is ρ, and the phase difference is α. From Fig. 7, if the waveform is not deformed by the low-pass filter 4, or if the cut-off frequency is sufficiently high compared to the data transmission rate, the demodulated output at each time point A-H of C1 (Fig. 6) is as follows. It becomes like this.

A... Undefined B... 1+ρN +'lρcos α
・Old・・■C・・・・・・ 1+ρ2−2ρCOSα
・・・・・・■D・・・・・・ 1+ρ3+2ρc
osα . . . ■ E . . . In the undefined intervals A and E, the value becomes undefined depending on the data values of the previous and subsequent time slots, respectively. Depending on the values of ρ and α, even if the detected signal in any one of sections B, D, and C becomes zero, the other does not become zero. In reality, the cutoff frequency of the low-pass filter 4 is selected to be low enough to prevent code amount interference. Therefore, the detected output signal after passing through the low-pass filter 4 is filtered by the waveform shown by the solid line in FIG. As mentioned above, sections B and D and section C produce complementary detection outputs, so
The eye never closes. In addition, at least one of these valid detection outputs will not become smaller than the invalid detection outputs in sections A or E, so 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.

As described above, the digital signal transmission method of the present invention is less susceptible to waveform distortion due to multipath due to a kind of diversity effect by combining the different detection outputs of sections B and D and section C. As a result, the bit error rate characteristics are significantly improved over the conventional system in a multipath transmission path, and high-speed digital transmission becomes possible.

In addition, in this explanation, as shown in Fig. 2, θ-0''
, 180°, that is, a two-phase system transmission signal, has been explained as an example, but the bit error rate characteristics can be significantly improved by using exactly the same principle for transmission signals of other values. For example,
When θ is 4 phases, 1 time slot delay device 3 in Fig. 5 is used.
It is necessary to connect a 90" phase shifter to the output of the As described above, the output has two types of effective detection outputs, and the bit error rate characteristics are significantly improved due to a kind of diversity effect by combining both outputs.

Furthermore, for polyphase systems such as 8-phase and 16-phase, the number of detection axes increases, but the detection output of each detection axis is exactly the same as described above, and the bit error rate characteristics are significantly improved. . Regarding the ratio of T and T2, the interval B,
The lengths of C and D vary, but other than that, the explanation is exactly the same as above.

That is, the digital signal transmission method in the first embodiment of the present invention using a transmission signal that undergoes a phase transition as shown in FIG. T2. θ, n (7) Regardless of the difference between each flight, the bit error rate is lower than that of the conventional method in multipath transmission channels due to a type of diversity effect by combining two different effective detection outputs. The characteristics are significantly improved and high-speed digital transmission becomes possible.

A digital signal transmission method according to a second embodiment of the present invention will be described below with reference to the drawings.

FIG. 8 is a phase transition diagram showing the phase transition of a transmission signal in the digital signal transmission method according to the second embodiment of the present invention. below,
Transmission signals of the digital signal transmission method according to the second embodiment of the present invention will be explained using FIG.

As shown in FIG. 8, one time slot of data is divided into a first half and a second half, similar to the first embodiment. 1
Time slot time is T, first half time is TII”
The time for the second half of a' is T1□.

Indicated as T4. There is always a phase transition as indicated by φ between the first half and the second half.

φ is 180'', ie, phase inversion.

The above is exactly the same as the first embodiment.

The difference from the first embodiment is that there are multiple types of ratios between the first half and the second half for each time loft.For example, in the case of FIG. 8, T1):TII or T,
:T, there are two types.

In this example, there are two types of ratios, but any type of ratio can be selected. Note that there may be some overlap. However, as shown in FIG. 8, the ratios of the first half and the second half within both time slots, which are separated by n time slots, must be equal. Therefore, n must be a number of types of ratios. Of course, n is a natural number.

The location of the phase transition φ in a certain time slot and the location of the phase transition φ in the time slot after n time slots are determined by the location of the phase transition φ within the time slot, since the ratio of the first half and the second half of both time slots is equal. They are in the same position. Also, the phase difference between the first half and the second half of both time slots is equal, which means that
This is exactly the same as the first embodiment. In FIG. 8, for example, the phase difference between the first time slot and the fi+l time slot is θ, as shown, and the location of the phase transition φ is at the same position within each time slot. As in the first embodiment, digital information is transmitted by the value of the phase difference θ between time slots separated by n time slots. For example, a two-phase system with Oo and 180" as possible values of θ If θ is used, 1 bit of information is transmitted by assigning O and 1 to each bit. Also, as θ, O'' and 90''.

If a 180", 270" (7) four-phase system is used, 2-bit information is transmitted. Furthermore, the value of θ is 0'',
8-phase systems of 4'5', 90', etc., as well as lG phase systems of 00°22.5", 45', 67.5", etc. The value of θ may be a polyphase system, an angle that uses only some of the above angles, a polyphase system that is not a power of 2, or a system where the interval between the possible values of θ is not constant. may be any value as long as the value corresponds to the information to be transmitted.

As described above, the phase transition of the transmission signal in the digital signal transmission method of the second embodiment of the present invention is T1)'"I!'T
a' Ta...There are various values depending on the values of θ and n, examples of which are shown in FIGS. 9 to 1) below.

In Figure 9, when n=2, the ratio between the first half and the second half is “I”.
When there are two types: I:TII and T, :T, θ-06,18
An example of a phase transition of a transmission signal for transmitting data of one via for one time slot is shown.

In Figure 10, n=2 and the ratio of the first half to the second half is T.
II"l! and T, :Trl, θ=O", 9
0'', 180@, and 270'', an example of a phase transition of a transmission signal for transmitting 2-bit data for l time slots is shown.

In Figure 1), n=2, and the ratio between the first half and the second half is "
When there are two types of II"II and T2I:Ta, θ=O', 4
5', 90°, 135°, 180"225', 270@
, 315'', an example of phase transition of a transmission signal for transmitting 3-bit data for l time slots is shown.

In the second embodiment, as in the first embodiment, the location of the phase transition φ in a certain time slot and the location of the phase transition φ in the time slot after n time slots are respectively They are in the same position. Therefore, the ninth
Taking the two-phase system transmission signal as shown in the figure as an example, the fifth
By using the detection circuit as shown in the figure, in the second embodiment as well, the sixth embodiment can be obtained in exactly the same way as explained using FIGS. 6 to 7 in the first embodiment.
The detected waveform shown in Figure fcl is obtained. The detection outputs in sections B to D are the same as those shown in equations 0 to 0. As in the first embodiment, depending on the values of ρ and α, even if the detected signal in any one of sections B, D, and C becomes zero, the other does not become zero.

As described above, in the second embodiment as well, the digital signal transmission method of the present invention uses a kind of diversity effect by combining the different detection outputs of sections B and D and section C to improve the waveform due to multipath. Not susceptible to distortion. Since there are multiple ratios between the first half and the second half of the time slot, which indicate the location of the phase transition φ, there are multiple composition ratios of sections B, C, and D that indicate effective detection outputs. Therefore, under specific multiplexed wave conditions, even if the error rate of a time slot with a certain ratio deteriorates, the error rate of time slots other than this ratio does not necessarily deteriorate, and burst errors occur in the transmitted data string. Error correction can be simplified.

In this explanation, as in the first embodiment, two-phase transmission signals such as θ O'' and I80'' as shown in FIG. 9 are used as examples, but other values of θ may be used. The bit error rate characteristics are significantly improved by the same principle in transmission signals that use values of 0. For example, if θ is a 4-phase system,
In the case of a multi-phase system such as a phase system, it is necessary to further connect a 90@phase shifter to the output of the 1-time-sloft delay device 3 shown in Fig. 5, and perform delay detection on the orthogonal axis using this output signal as a reference signal. be. However, although the configuration of the detection circuit becomes complicated,
As described above, the detection output of each detection axis has two types of effective detection outputs, and by combining the two, a kind of ubiquitous effect results in a significant improvement in the bit error rate characteristics. These two types of valid detection output sets exist only in the types of sets of the amount of phase transition, the direction of phase transition, and the ratio between the first half and the second half, and burst errors are reduced.

That is, in the digital signal transmission method of the second embodiment of the present invention using a transmission signal that undergoes a phase transition as shown in FIG. 8, TII, TII, T, -Tn=θ.

Regardless of the difference in the 6 values of n, all 2 different from each other
It has a kind of diversity effect by combining the effective detection outputs of different species. In addition, since there are multiple ratios between the first half and the second half, the burst error reduction effect by having multiple types of effective detection output sets further improves the bit error rate characteristics in a multipath transmission path. This is a significant improvement and enables high-speed digital transmission.

Effects of the Invention As described above, the present invention allows each time slot of data to be
It is divided into a first half and a second half according to the type or ratio of multiple types, and the phase is reversed between the first half and the second half,
The ratio of the first half to the second half in any time slot is equal to the ratio of the first half to the second half in a time slot after a given time slot, and the ratio between these two parts separated by the given time slot is equal. By using a signal containing information to be transmitted in the phase difference between the first half and the second half of a time slot as a transmission signal, it becomes possible to perform digital transmission at a higher speed than before on a multipath transmission path.

[Brief explanation of drawings]

FIG. 1 is a phase transition diagram of a transmission signal of the digital signal transmission method in the first embodiment of the present invention, FIGS. 2 to 4 are phase transition diagrams of an example of the transmission signal, and FIG. 5 is a phase transition diagram of an example of the transmission signal. Alternatively, FIG. 9 is a configuration diagram of an example of a detection circuit corresponding to the transmission signal of the digital signal transmission method of the present invention, and FIGS. 6 and 7 are FIG. 8 is a waveform diagram of the detection output signal and a vector diagram showing the composite phase of the multipath wave, which explains the strong 9 to 1) is a phase transition diagram of an example of the transmission signal, FIG. 12 is a phase transition diagram of a transmission signal of the conventional digital signal transmission method, and FIGS.
FIG. 4 is a vector diagram showing a waveform diagram of a detection output signal and a composite phase of multipath waves, explaining that the conventional digital signal transmission method is susceptible to multipath distortion. 1... Input terminal, 2... Multiplier, 3...
. . . n time slot delay device, 4 . . . low pass filter, 5 . . . detection output terminal. - Annual figure 2 Figure 3 Figure 7 District Year figure 9 - T→ 1 1 1 1To 1T121T21) Ta21 To 1T
I21 lower 2+ 1 Ta2 l Fig. 10 IT, 1) T121T2, 1 221T1. lT12I
Ta1) T221, heat T, a l Ta1) T2L1
-1 Tokaizuka
: β

Claims (5)

[Claims] (1) In a transmission device that transmits digital data, each time slot of data is divided into a first half and a second half at a rate of one or more types, and the phase is reversed between the first half and the second half. The ratio of the first half to the second half in a timeslot is equal to the ratio of the first half to the second half in a timeslot after a given timeslot, and the ratio between these two parts separated by this given timeslot is A digital signal transmission method characterized by using a transmission signal in which information to be transmitted is present in a phase difference between the first half and the second half of each slot. (2) The digital signal transmission method according to claim (1), wherein the phase difference is either 0° or 180°. (3) Claim (1) characterized in that the phase difference is any one of 0°, 90°, 180°, and 270°.
Digital signal transmission method described in Section 2. (4) The digital signal transmission method according to claim (1), wherein the phase difference is any angle obtained by dividing 360° into 8. (5) The digital signal transmission method according to claim (1), wherein the phase difference is any angle obtained by dividing 360° into 16.