JPH0746798B2 - Digital signal transmission method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital signal transmission method for transmitting a digital signal in a multipath transmission line such as wireless transmission in an urban area.

2. Description of the Related Art In recent years, even in the field of mobile communication, digitization is progressing due to improvement of confidentiality, sophistication of communication, and compatibility with peripheral communication networks. However, in urban areas where such demand is considered to be most concentrated, communication quality is significantly deteriorated due to multipath due to reflection and diffraction by buildings and other structures. In the case of digital transmission, if the propagation delay time difference between the waves forming the multipath cannot be ignored with respect to the data time slot, the waveform error and the tracking failure of the synchronous system will significantly deteriorate the code error rate characteristic.

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

FIG. 8 shows a phase transition of a transmission signal in the conventional digital signal transmission method. T indicates one time slot of data. When the data is 1, the phase transitions by 180 °,
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, differential detection having a delay line of one time slot can be performed.
Now, let us consider, as a typical example of multipath, what happens to the detection output signal under the multipath of two waves having a propagation delay time difference τ that cannot be ignored compared to time slots. In addition, the wave that precedes in time is a direct wave,
The delayed wave is called the delayed wave.

FIG. 9 is a diagram for explaining what a detection output signal looks like when a transmission signal as shown in FIG. 8 is subjected to delay detection under a two-wave multipath. FIG. 9 (a) shows
This shows the phase transition of the direct wave. On the contrary,
The phase transition of the delayed wave delayed by the propagation delay time difference τ is
It becomes like FIG. 9 (b). The detection output at a certain time point 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. 9 (c), the detection output in the section B is 2 at the time of B '.
It is the value of the vector inner product of the wave synthesis phase and that of B.

FIG. 10 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 C.
The amplitude ratio of the direct wave and the delayed wave was ρ, and the phase difference was α. From FIG. 10, the detection output at each time point A to C in FIG. 9 (c) is as follows.

A: undefined B: 1 + ρ ² + 2ρ cosα C: undefined In sections A and C, the data values of the previous and subsequent time slots are undefined. After differential detection, a low-pass filter is usually inserted to remove unnecessary noise components, so the final detection output signal waveform is shown in FIG. 9 (c).
The waveform of the solid line is filtered to form a waveform as shown by the dotted line in FIG. 9C, which constitutes a part of the eye pattern. By the way, when ρ is close to 1 and α is around 180 °, the detection output in the section B, which is an effective detection output, becomes almost zero. Therefore, the eye is closed and the code error rate characteristic deteriorates. Further, at this time, since the invalid detection output of the sections A and C is much larger than the valid detection output of the section B,
The eye greatly fluctuates in the time axis direction, the reproduced clock cannot follow, and the code error rate further deteriorates. (For example, Onoe et al., "Code Error Rate Characteristic in Rayleigh Fading with Propagation Delay Time Difference", IEICE Tech.
8, 1982, or Takai et al., "Analysis of instantaneous code error due to multiple wave propagation and error generation mechanism based on bit synchronization system",
(Technical Report, CS83-158, 1984) Problems to be Solved by the Invention However, in the method as described above, the waveform distortion due to multipath is significant as described above, and the code error rate is significantly deteriorated. In particular, examining the relationship between the signal S / N ratio and the error rate, there is a region where the error rate does not decrease even if the S / N ratio is improved. Such a code error is called an irreducible error. Due to such so-called irreducible errors, the actual data transmission rate in urban areas is greatly limited, and high-speed transmission is impossible.

In view of the above problems, the present invention provides a digital signal transmission method capable of high-speed digital transmission in a multi-pulse transmission line such as an urban area.

Means for Solving the Problems In order to solve the above-mentioned problems, the digital signal transmission method of the present invention divides each time slot of data into a first half part and a second half part at a plurality of ratios, and the first half part and the second half part. Between the parts, there are phase transitions of multiple kinds, and the directions of the phase transitions are all advanced or delayed in each time slot. The ratio and the amount of phase transition are equal to the ratio and the amount of phase transition of the first half and the latter half of the time slot after the predetermined time slot, respectively, and the time slots of both of them are separated by the predetermined time slot. A signal having information to be transmitted in a phase difference between the first half portion and the second half portion is used as a transmission signal.

Action The present invention, by using the transmission signal as described above,
When performing differential detection, two types of effective detection outputs can be obtained for each time slot. Then, due to one kind of diversity effect by combining these outputs, the code error rate under multipath is significantly improved. Further, in each time slot, it is possible to obtain two different sets of effective detection outputs, only the type of phase transition angle and the type of ratio of the first half part and the second half part,
Burst errors are reduced, error correction can be simplified, and the code error rate under multipath is further improved. Due to the effects as described above, digital transmission at a higher speed than ever can be performed on a multipath transmission line.

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

FIG. 1 is a phase transition diagram showing a phase transition of a transmission signal in the digital signal transmission method of the present invention. The transmission signal of the digital signal transmission method 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 portion and a second half portion. The time of one time slot is shown as T, the time of the first half is shown as T ₁₁ , T ₂₁ , T ₃₁ , and the time of the latter half is shown as T ₁₂ , T ₂₂ , T ₃₂ . Then, there is always a phase transition as indicated by φ _{1 to} φ ₃ between the first half portion and the second half portion. The direction of these phase transitions is constant in all time slots, but there are multiple types of transition amount depending on the time slot. That is, in FIG. 1, the positive phase axis may be either the advanced phase or the delayed phase, and the phase transition direction is always the advanced phase or the delayed phase. On the other hand, in this example, there are three types of phase transition amounts indicated by φ ₁ , φ ₂ , and φ ₃ . Note that the number of types of phase transition amount is 3 in this example.
Although it is a type, it can be arbitrarily selected, and some may be duplicated. Also, the ratio of the first half and the second half,
T ₁₁ : T ₁₂ , T ₂₁ : T ₂₂ or T ₃₁ : T ₃₂ are also 3 in this example.
Although it is a type, it can be arbitrarily selected, and some may be duplicated. However, as shown in FIG. 1, the phase transition amounts and ratios in both time slots separated by n time slots must be equal. Therefore, n
Can be arbitrarily selected as long as it is equal to or larger than the number of types of pairs of phase shift amount and ratio. Of course, n is an integer of 2 or more.

The location of the phase transition in a time slot and the location of the phase transition in the time slot after n time slots are
Since the ratios of the first half and the second half of both time slots are equal, they are in the same position in each time slot. Further, the phase difference between the first half portion and the second half portion of both time slots is equal because the phase transitions in both time slots are in the same amount and in the same direction. In FIG. 1, for example, the phase difference between the second time slot and the (n + 2) th time slot is θ as shown in the figure, and the location of the phase transition is at the same position in each time slot. Digital information is transmitted according to the value of the phase difference θ between the time slots separated by n time slots. For example, if a two-phase system of 0 ° and 180 ° is used as a possible value of θ, 1-bit information is transmitted by assigning 0 and 1 correspondingly. Also,
If a four-phase system of 0 °, 90 °, 180 °, 270 ° is used as θ,
Two bits of information are transmitted. Furthermore, as the value of θ, 8-phase system of 0 °, 45 °, 90 ° ..., 0 °, 22.5 °,
45 °, 67.5 ° ... 16-phase system such as a power-of-two polyphase system, those that use only some of the above angles, and those that are not a power-of-two system, and The interval of possible values of θ may not be constant, and the value of θ 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 present invention is T ₁₁ , T ₁₂ , T ₂₁ , T ₂₂ , T ₃₁ , T _32, ...
_Although there are various values depending on the values of ₁ , φ ₂ , φ _3, ..., θ, n, examples are shown in FIGS. 2 to 4 below.

Figure 2 shows that n = 2, φ ₁ = 45 °, φ ₂ = 135 °, and the ratio of the first half and the second half is T ₁₁ : T ₁₂ and T ₂₁ : T ₂₂ when θ = 0. An example of phase transition of a transmission signal for transmitting 1-bit data for one time slot is shown corresponding to ° and 180 °.

FIG. 3 shows that n = 2, φ ₁ = 45 °, φ similarly to the case of FIG.
₂ = 135 °, the ratio of the first half to the second half is T ₁₁ : T ₁₂ and T
₂₁ : Corresponding to θ = 0 ° and 180 ° for 2 types of T ₂₂ , 1
The example of the phase transition of the transmission signal which transmits 1-bit data about a time slot is shown. In the transmission signal of the digital signal transmission method of the present invention, the phase difference between the first half and the second half of adjacent time slots, to be exact, the initial phase difference can be freely selected. The initial phase difference in the case of FIG. 3 is 45
Deviated by ° or 135 °.

In Fig. 4, n = 2, φ ₁ = 45 °, φ ₂ = 135 °, and the ratio of the first half and the second half is T ₁₁ : T ₁₂ and T ₂₁ : T ₂₂ when θ = 0. Corresponding to °, 90 °, 180 °, 270 °, 2 bits per 1 time slot like (0,0), (1,0), (1,1), (0,1) respectively. The example of the phase transition of the transmission signal which transmits data is shown. In this case, as in the case of offset four-phase phase modulation, for example, θ = 0 °, 90 °,
It may be one that takes only part of the angle of the four-phase system, such as 270 °.

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

In the following description, as an example of the transmission signal of the digital signal transmission method of the present invention, θ = 0 °, 180 °, that is, a two-phase system transmission signal as shown in FIG. 2 or 3 will be used. In addition, as a multipath model, a typical 2
Consider a wave model. Direct wave that precedes in time,
The delayed wave is called the delayed wave.

The digital signal transmission method of the present invention is detected by differential detection using a delay line of n time slots. An example of the structure of the detection circuit is shown in FIG. However, in FIG. 5, 1 is an input terminal, 2 is a multiplier, 3 is an n time slot delay device, 4 is a reduction pass filter, and 5 is a detection output terminal.

FIG. 6 is a diagram for explaining what a detection output signal looks like when these transmission signals are detected by the detection circuit of FIG. 5 under a two-wave multipath. Figure 6 (a)
FIG. 4 shows the phase transition of an arbitrary time slot of a direct wave and a time slot after the n time slots. The locations of the phase transitions in both time slots are at the same positions in the respective time slots, and the magnitudes of the phase transitions are the same and are indicated by φ. 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 as shown in FIG. 6 (b). The detection output at a certain time point is a vector inner product of the combined phase of the two waves at that time and the combined phase of the two waves n time slots before. For example, in FIG. 6 (c), the detection output in the section B is the value of the vector inner product of the two-wave combined phase at B'and that at B.

FIG. 7 shows a combined phase of the direct wave and the delayed wave in order to obtain the detection output at each time point A to E.
The amplitude ratio of the direct wave and the delayed wave was ρ, and the phase difference was α. Further, the phase axes of FIGS. 6A and 6B may be positive or may be in the advanced phase, but are set in the advanced direction. As shown in FIG. 7, when the waveform is not deformed by the low-pass filter 4 or the cutoff frequency is sufficiently higher than the data transmission rate, the demodulation outputs at the respective points A to E in FIG. become that way.

A: undefined B: 1 + ρ ² + 2ρ cosα ・ ・ ・ C: 1 + ρ ² + 2ρ cos (α ± φ) ・ ・ ・ D: 1 + ρ ² + 2ρ cosd ・ ・ ・ E: undetermined In the sections A and E, time slots before and after respectively It is undefined depending on the data value of. Depending on the values of ρ and α, even if the detection signal in any of the sections B, D, and C becomes zero, the other does not become zero. The compound symbols in the equation are + when the phase transition φ is late and − when it is advanced.
For example, in FIG. 6 or 7, since φ is a phase advance, the compound double sign of the equation is − at this time.

In practice, the cutoff frequency of the low-pass filter 4 is selected low enough to prevent intersymbol interference. Therefore, the detection output signal after passing through the low-pass filter 4 is as shown in FIG.
The waveform of the solid line is filtered to form a part of the eye pattern as shown by the dotted line in FIG. 6 (c). As described above, the sections B and D and the section C generate complementary detection outputs, so that the eye does not close. Further, at least one of these effective detection outputs does not become smaller than the ineffective detection output in the section A or E, so that fluctuations of the eye in the time axis direction are reduced and the code due to the poor tracking of the reproduction clock is reduced. There is little deterioration in the 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 different detection outputs of the sections B and D and the section C. Furthermore, since there are multiple types of ratios of the first half part and the second half part of the time slot that indicate the location of the phase transition, the section showing the effective detection output.
There are a plurality of B, C, and D component ratios. When this component ratio changes, the error rate characteristic mainly changes with respect to the propagation delay time difference τ. In particular, by intentionally changing the ratio of the first half portion and the second half portion of the time slot from 1: 1, either the section B or the section D and the section C are provided for a multipath transmission line having a longer delay time difference. It can be made to exist and the error rate characteristic can be improved (see IEICE technical report SAT86-23). This means, conversely, that higher-speed transmission can be performed on the same transmission line (with a constant delay time difference). Also, since there are multiple types of φ values,
The detection output of the section C exists in the number of times. Therefore,
Even if the error rate of a time slot with a certain phase transition amount and ratio deteriorates under a specific multiple wave condition, the error rate of a time slot with a phase transition amount and ratio other than this phase transition amount and ratio does not necessarily deteriorate. . That is, it is less likely that a burst error will occur in the transmitted data string, and error correction can be simplified.
As described above, the code error rate characteristic in the multipath transmission line is remarkably improved as compared with the conventional method, and high-speed digital transmission becomes possible.

In this description, a two-phase system transmission signal such as θ = 0 °, 180 ° as shown in FIG. 2 or 3 has been described as an example, but transmission using another value as the value of θ. The bit error rate characteristic of a signal is remarkably improved by the same principle. For example, when θ is a multi-phase system such as a 4-phase system or an 8-phase system, a 90 ° phase shifter is further connected to the output of the 1-time-slot delay device 3 in FIG. 5, and this output signal is used as a reference signal for quadrature. It is necessary to perform differential detection on the axis as well. However, although the configuration of the detection circuit becomes complicated, the detection output of each detection axis is exactly the same as the above description.
The code error rate characteristic is remarkably improved due to a kind of diversity effect which has effective detection outputs of a kind and combines them. Then, these two types of effective detection output sets exist only for the types of sets of the phase transition amount and the ratio of the first half portion and the second half portion, and the burst error is reduced. 4
By increasing the number of phases and 8 phases, the transmission rate can be doubled or tripled for the same time slot length, and good error rate characteristics can be exhibited at higher transmission speeds. You can

That is, the digital signal transmission method of the present invention using the transmission signal having the phase transition as shown in FIG. 1 is T ₁₁ , T ₁₂ ,
T ₂₁ , T ₂₂ , T ₃₁ , T ₃₂ …, φ ₁ , φ ₂ , φ ₃ …, θ, n can be freely selected, and regardless of the difference in their respective values, all of them are two effective types that are different from each other. In the multipath transmission line, a diversity effect is obtained by synthesizing different detection outputs, and a burst error mitigation effect is obtained by having a set of two types of effective detection outputs of multiple types depending on time slots. The code error rate characteristic is significantly improved over the method, and high-speed digital transmission becomes possible.

As described above, according to the present invention, each time slot of data is divided into a first half portion and a second half portion at a plurality of types of ratios, and phase shifts of a plurality of types of angles are provided between the first half portion and the second half portion. , The direction of the phase transition is all advanced or all delayed in each time slot, the ratio of the first half and the second half in any time slot and the amount of phase transition, and the time after the predetermined time slot. The ratio of the first half part and the second half part in the slot and the amount of phase transition are equal to each other, and are separated by the predetermined time slot,
By using a signal that has information to be transmitted in the phase difference between the first half part and the second half part of both of these time slots as a transmission signal, it is possible to perform digital transmission at a higher speed than before in a multipath transmission line. .

In particular, the present invention contributes to the improvement of characteristics in a multipath transmission line, the magnitude of the phase transition of a predetermined angle in a time slot, and the parameter of the position in the time slot represented by a predetermined ratio. There are multiple types of combinations, each of which can be arbitrarily selected, and it is possible to set optimal parameters according to other constraint conditions such as transmission path conditions. Faster,
Higher quality transmission is possible.

[Brief description of drawings]

FIG. 1 is a phase transition diagram of a transmission signal of the digital signal transmission method of the present invention, FIGS. 2, 3 to 4 are phase transition diagrams of an example of the transmission signal, and FIG. 5 is a phase transition diagram of FIG. FIG. 3 is a block diagram of an example of a detection circuit corresponding to a transmission signal of the digital signal transmission method of the present invention, and FIGS. 6 and 7 show that the digital signal transmission method of the present invention is resistant to multipath distortion. FIG. 8 is a waveform diagram of a detection output signal and a vector diagram showing a composite phase of multipath waves, FIG. 8 is a phase transition diagram of a transmission signal of a conventional digital signal transmission method, FIG. 9 and FIG.
FIG. 10 is a waveform diagram of a detection output signal and a vector diagram showing a composite phase of multipath waves, which explains that the conventional digital signal transmission method is weak against multipath distortion. 1 ... input terminal, 2 ... multiplier, 3 ... n time slot delay device, 4 ... low pass filter, 5 ... detection output terminal.

Claims (5)

[Claims] 1. A transmission device for transmitting digital data, wherein each time slot of data is divided into a first half portion and a second half portion at a plurality of types of ratios, and phases of a plurality of types of angles are provided between the first half portion and the second half portion. A transition, the direction of the phase transition is, in each time slot, all advanced or all delayed, the ratio of the first half part and the second half part and the phase transition amount in any time slot, The first half portion and the second half portion in the time slot after the predetermined time slot are equal to each other in the ratio and the phase shift amount, respectively, and are separated by the predetermined time slot, and the first half portion of each of the both time slots is separated. And a transmission signal having information to be transmitted in the phase difference between the latter half portions is used to transmit only the predetermined time slot. Digital signal transmission method characterized in that it is detected by the differential detection using a delay line capable of delaying. 2. The digital signal transmission method according to claim 1, wherein the phase difference is either 0 or 180. 3. The digital signal transmission method according to claim 1, wherein the phase difference is any of 0, 90, 180, and 270. 4. The digital signal transmission method according to claim 1, wherein the phase difference is one of angles obtained by dividing 360 into eight. 5. The digital signal transmission method according to claim 1, wherein the phase difference is one of angles obtained by dividing 360 into 16.