JPH0323742A - Signal system detecting method - Google Patents

Abstract

PURPOSE:To detect a specific signal system even in fast digital transmission by detecting the fact that the change of a sampled phase is always kept constant at every symbol. CONSTITUTION:In an example in which a signal vector obtained by performing synchronization detection on a digital angle modulation wave (MSK wave) capable of performing cycle detection is sampled with a clock synchronized with the symbol, a white circle shows the example of only a direct wave, and a black circle shows the example of a wave on which a delay wave is superimposed, and those examples correspond to a case where all the signal systems are symbols '1'. At such a case, when the signal vector of the direct wave transits in sequence of 11 12 13 14 11 in a counterclockwise direction, the signal vector of a superimposed wave transits in sequence of 15 16 17 18 15 in the counterclockwise direction. When the change of the phase of the signal vector of the direct wave is always equal to that of the phase of the signal vector of the delay wave, the change of the phase of the signal vector of the superimposed wave is always equal. In such a manner, transmission information can be demodulated correctly even in fast digital communication, and the specific signal system can be detected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal sequence detection method, and in particular, in a time division multiple access (TDMA) communication system under a multiple propagation path environment, the present invention relates to a signal sequence detection method. The present invention relates to a method for detecting a specific signal sequence such as a preamplifier from detectable digital angle modulated waves.

As is well known, in the TDMA communication system. The transmitted and received waves are burst-like. In order to receive such a burst-like received wave, a preamble is provided in the received wave before the transmission information including the data to be actually transmitted. In other words, the receiving section of each station recognizes the arrival of the received wave by detecting this preamble. It is designed to demodulate the data contained in the received waves. Generally, a demodulated signal obtained by synchronously detecting (demodulating) this received wave includes an in-phase component (I channel signal) and a quadrature component (Q channel signal). Therefore, this demodulated signal is called a signal vector.

[Prior Art] Conventionally, this type of signal sequence detection method is as follows. A clock is recovered from the in-phase and quadrature components of the demodulated signal, and the recovered clock is used to make a decision on each of the in-phase and quadrature components of the demodulated signal at the optimal decision point. This is done by comparing the reproduced signal sequence with a specific signal sequence to be detected after reproduction.

[Allml that the invention tries to solve? In the conventional signal sequence detection method described above, in high-speed digital communication, not only the preamble but also the transmitted information may not be correctly demodulated due to the influence of propagation delay.

below. An explanation will be given by taking the MSK method as an example of the modulation method. The MSK wave is. As is well known, cosφ(t)cosω
It is expressed as c t +slnφ(t)s1nωct.

Here, ωC is the angular frequency of the carrier wave, and eOsφ(
t). sinφ(1) are the in-phase component and quadrature component of the input signal, respectively. φ(1) is the phase of the signal vector.

A delayed wave with an amplitude ratio a that is delayed by the time to with respect to the direct wave of the MSK wave is a cosφ(t tg) eoli
ω( (t t■) +a sinφ(t-tg
) slnωc (t to). Therefore, the wave (superimposed wave) in which the direct wave and the delayed wave are superimposed is (cosφ(1) + a cos(φ (t-to
)1ωcto)]cosω(t+[sinφ(
t) 10as1n (φ(t-to)1ωc t
o)] s1nωct is poorly expressed.

This will be explained below using drawings. FIG. 2 shows an example in which a signal obtained by synchronously detecting an MSK wave is sampled using a clock synchronized with a symbol. In the same figure. The I axis shows the in-phase component, and the Q axis shows the orthogonal component. The signal locus of the MSK wave changes on the circumference, and naturally the sample values also lie on this circumference. The phase of the signal vector of the MSK wave is . As a symbol “
When 1° is inputted, it changes by (π/2), and when “0” is inputted, it changes by (1π/2). Therefore, if the sample is to be sampled using a clock synchronized with the symbol, the sampled signal must be fixed at a fixed position, as shown by the circle in FIG. However, when sampling a wave in which a direct wave and a delayed wave are superimposed due to the influence of propagation delays in multiple propagation paths, the sampled value no longer exists at a fixed position on the circumference.

Figure 2(b) shows "ttoto" based on the position of point 1.
This is an example in which a signal sequence called ``00'' is sampled using a clock whose symbol is a superimposed direct wave and delayed wave of the MSK wave.The white circle is an example of only the direct wave, and 1-2-3
The vector transitions in the order of -2→3→2→1→4.

The black circle mark is (COSωC”O*sln tI)c t
o ) − (f d/2, -(d/2), a-(T/
This is an example of a wave (superimposed wave) in which a delayed wave of 2.to-T (1/T is the symbol rate) is superimposed. For example, when the direct wave transitions from 1 to 2. At the timing of point 2. The vector of the direct wave at the timing of point 1 is rotated by ωcto and multiplied by a to the vector of the direct wave, and the result becomes vector 5 of the superimposed wave. Similarly, the vector changes in the order of 5→7→6→7-46→9→8. Like this example. If the delay is longer than the sampling interval and the amplitude of the delayed wave is large, it is difficult to reproduce the data correctly. If you cannot reproduce the data correctly like this. The disadvantage is that the preamble cannot be detected.

Furthermore, in order to compensate for this drawback caused by intersymbol interference in multiple propagation paths, a method called transmission path equalization has been employed. however. Even if data can be reproduced correctly using this method, there is a problem in that it takes time to detect a specific signal sequence.

Furthermore, even when there is no effect of propagation delay, conventional methods perform clock recovery, which has the disadvantage that data cannot be correctly recovered unless a stable clock is obtained.

[Means and Effects for Solving the Problems 1] The signal sequence detection method according to the present invention detects not an arbitrary signal sequence but a specific signal sequence, such as a preamble, which is not affected by propagation delay. The present invention attempts to eliminate the problems of the prior art by selecting the signal sequence of , and is characterized in that it does not require clock recovery or transmission line equalization. Here, a signal sequence that is not affected by propagation delay refers to a signal sequence in which the changes in the phase of the signal vector obtained by synchronously detecting the modulated wave at each sampling time interval T are always the same. .

below. The principle of the present invention will be explained first with reference to FIG. 3 and later with reference to FIG. 4.

Referring to Figure 3, similar to Figure 2, the signal vector obtained by synchronously detecting the MSK wave is sampled with a clock synchronized with the symbol. , (COSωCiO+s1n ω( to
) −(I/2, =f/2). a-J] 7/2
, t. This is an example of a wave in which a delayed wave called II-T is superimposed. (
a> is the case where all the signal sequences are symbols "1", (b> is the case where all the signal sequences are symbols "Om").

In Figure 3(a), the signal vector of the direct wave is 11→
When transitioning counterclockwise in the order of 12 → 13 → 14 → 11. The signal vector of the superimposed wave is 15→16→17→1
Transition counterclockwise in the order g-15. In this way, if the changes in the phase of the direct wave signal vector and the changes in the phase of the delayed wave signal vector are always equal, then the changes in the phase of the superimposed wave signal vector are also always equal.

Similarly, regarding FIG. 3(b), for the clockwise transition of the signal vector of the direct wave from 21 to 24 to 23 to 22 to 21, the signal vector of the superimposed wave is 25-28-27-
It exhibits a clockwise transition of 26→25.

Figure 4 is similar to Figure 2. Unlike the case in Figure 3, this is a sample of the signal vector obtained by synchronously detecting the MSK wave using a clock whose frequency is slightly different from the clock synchronized with the symbol, and is displayed over a short period of time. , the signal sequence is all symbols "1". The signal vector of the direct wave transitions counterclockwise in the order of 31 → 32 → 33 → 34, but the 8 sampling clock is not synchronized with the symbol. The sample value is f,
It does not exist on the Q axis. Also, over time. The sample values move slowly around the circumference. However, the change in the phase of the signal vector every two sample time intervals T is always (π
/2), so it appears to be fixed at four points on the I-Q plane.

Therefore, the signal vector of the superimposed wave is also 35-3 6-3
The signal vector transitions counterclockwise as 7-38→35, and the change in the phase of the signal vector for each sample time interval T is always (π/2). All signal sequences are symbol “O”
The same is true in the case of ``.The change in the phase of the signal vector for each sampling time interval T is always (1π/2).

As explained above, if the changes in the phase of the direct wave signal vector obtained by synchronously detecting the modulated wave at each sampling time interval T are always the same, then the changes in the phase of the superimposed wave signal vector are also always the same. Moreover, since only the phase change is focused, even if the sampling clock is not completely synchronized with the symbol, it is sufficient that the frequency synchronization can be achieved within a certain accuracy.

The signal sequence detection method according to the present invention converts the phase of a signal vector obtained by synchronously detecting a received wave into a symbol.
sample over a finite number of consecutive symbols with a sampling rate equal to the rate. A specific signal sequence is detected by detecting that the phase difference between a certain sampled phase value and a sampled phase value one symbol before becomes a predetermined phase difference.

〔Example] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a flowchart showing the procedure of a signal sequence detection method according to an embodiment of the present invention.

The phase φ(1) of the signal vector obtained by synchronously detecting the received wave is symbol ◆Sampling equal to the rate●Ray 1' (1./T), and sampling starts from time 1-0 (step 101, 102, 103, 10
4), Phase difference Δ between the sampled phase value φ(T) and the phase value sampled one symbol before) φ<0>
φ1 is determined (step 105). It is checked whether the obtained phase difference Δφ1 matches the phase change reference value (predetermined phase difference) Δφc (step 106), and if it does not match, the next sampling is performed and the process continues ( Steps 110, 103, 104) If they match, check how many times the matches continued (Step 1)
07). If the number of matches i is less than the length n of the specific signal sequence to be detected. Next sampling is performed and processing continues (steps 111, 103, 104). If the number of matches i is n or more, it can be seen that a specific signal sequence has been detected (step 108). If the next specific signal sequence is detected, sampling is performed again (NO in step 109); otherwise, the process ends (Yes in step 109).

In the above procedure, the value that the phase change reference value Δφc should take is (when detecting a signal sequence in which all symbols are '1' when the modulation method is the MSK method).
π/2), and when detecting a signal sequence in which all symbols are "0", it is .pi./2). or. The modulation method is
G using a Gaussian filter as a baseband filter ε
In the case of the MSK method, the above MS. This is similar to that of the K method.

on the other hand. In the modulation method, if three symbols 01# are input in succession, the phase of the signal vector will be (π/2
) increases. If three symbols MO" are input in succession, the phase of the signal vector decreases by (π/2) per symbol. If the symbol "01" and the symbol "1" are input alternately, the phase of the signal vector will not change. Tamed
Regarding the FM method. The reference value Δφc is (π/
2) When detecting a signal sequence in which all symbols are “O” (1π/2), symbol “0” and symbol “1” are detected.
The value is 0 when detecting a signal sequence in which `` and `` are alternately continued.

or. In the above procedure, the number of times that the obtained phase difference Δφi matches the predetermined phase difference and Δφc is as follows. If there is a delayed wave, the length may be less than the length of the specific signal sequence to be detected due to intersymbol interference.

In such a case, the length of the specific signal sequence to be detected is made as long as possible so that the number of times i that the obtained phase difference Δφi and the predetermined phase difference Δφc match is several times less than that. However, countermeasures such as assuming that a specific signal sequence has been detected may be taken.

[Effects of the Invention] As explained above, the present invention samples the phase of a signal vector obtained by synchronously detecting a received wave at a sampling rate equal to the symbol rate, and the change in the sampled phase corresponds to the symbol. By detecting that each time is always constant. Transmission path equalization is also used in high-speed digital transmission. A demodulator with a simple configuration that does not require clock recovery. This has the effect of being able to detect a specific signal sequence.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the procedure of a signal sequence detection method according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example in which a signal vector obtained by synchronous detection of an MSK wave is sampled with a clock synchronized with a symbol. , (a) shows an example of only direct waves, and (b) shows an example of direct waves and superimposed waves. Figure 3 is a diagram showing an example in which the signal vector obtained by synchronously detecting the MSK wave to be detected is sampled with a clock synchronized with the symbol. b
) shows an example when the signal sequence is all symbols "01",
Fig. 4 is a diagram showing, over a short period of time, the signal vector obtained by synchronously detecting the MSK wave to be detected, sampled with a clock whose frequency is slightly shifted from the clock synchronized with the symbol. . Figure 2 Figure 1 Figure 3

Claims (1)

[Claims] 1. Corresponding to symbols "1" and "0" to be transmitted, the phase of the carrier wave is in a first direction and in a second direction opposite to the first direction, respectively. A modulated wave changed by a predetermined angle is received as a received wave, and a change in phase of a signal vector obtained by synchronously detecting the received wave from among the received waves is the same at every sampling time interval T. A method for detecting a specific signal sequence corresponding to a symbol pattern, the method comprising: sampling the phase of the obtained signal vector at a sampling rate (1/T) equal to the symbol rate; Obtain the value φ[kT], determine the phase difference Δφi between the sampled phase value φ[kT] and the phase value φ[(k-1)T] sampled one symbol before, and calculate the determined position. Phase difference φi and predetermined phase difference Δφc
calculate the number of times i that are consecutively equal, determine whether the calculated number of times i reaches a predetermined number of times n, and when the counted number of times i reaches the predetermined number of times n; , when the specific signal sequence is detected.