JPS5915223B2 - Space diversity receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a space diversity method for reducing the effects of fading that occurs in wireless communication lines, and mainly uses a transmission path where frequency selective fading occurs to transmit signals to a digitano. The present invention relates to a device that is highly effective when used in a transmission method.

Fading that occurs in wireless communication lines varies in frequency, depth, time, etc. depending on where the receiving antenna is installed. Taking advantage of this property, there is a method that reduces fading by installing two or more antennas in positions where there is little correlation between fading and combining or switching the signals received by each antenna. This is a so-called space diversity (SD) reception method. 15 Conventionally, in-phase synthesis SD using two antennas has been used to reduce thermal noise increase and momentary interruption due to fading in micro and wave FM lines.
reception method is applied.

Figure 1 shows its basic configuration. In FIG. 1, the signal e, 90 received by the antenna 1 is transmitted to the phase modulator 2 at a frequency fp.
The signal is phase modulated by the phase modulation (sensing) waveform A of , and enters the synthesizer 3. On the other hand, the signal e2 received by the antenna 4 passes through the phase shifter 5 and becomes e'. The signal e'1 from the antenna 1 is then added to the combiner 3 and combined with the signal e'1 from the antenna 1. 25e', and e
'.

If there is no phase difference between Only the amplitude change of the wave (frequency 2fd, H2) appears, and the fundamental wave f component becomes zero 30.

On the other hand, if there is a phase difference between e' and e'2, the amplitude change of the frequency fp appears in the two composite vectors as shown in FIG. 2b and c. The amplitude change of this fp(H2) is e'
It is approximately proportional to the phase difference between e'2 and e'2, and its polarity is reversed depending on whether e'1 is leading, 35 or lagging behind e'2. The signal with this amplitude modulation component enters the receiver 6, and its automatic gain control circuit 7 controls fp
The fluctuation components of are extracted. In the synchronous detection circuit 8, f
The polarity of the component is determined, the phase shifter 5 is controlled so that the F component becomes zero, and e'1 and E22 are combined in the same phase.

9 is a sine wave oscillator for driving the phase modulator 2 for phase difference detection.

Note that the method of determining phase lead/lag by phase modulation as shown in FIG. 2 is called a sensing method. Frequency selective fading generally occurs due to interference between multiple waves with path differences, and it is known that two waves are dominant among these multiple waves.

FIG. 3 shows a frequency selective fading model (two-wave model) that occurs due to the interference of two waves. Figure 4 shows the frequency-selective fading calculated using the two-wave model.
An example is shown, and it can be seen that large in-band amplitude deviations and delay deviations occur during single reception. When a digital signal is transmitted using such a transmission path, the waveform of the received signal is distorted and code errors occur. Furthermore, although FIG. 4 also shows the band characteristics during conventional in-phase synthesis, it can be seen that the improvement in the band characteristics is not perfect. Therefore,
Although conventional control methods can maximize the signal level, they are not suitable for improving the frequency characteristics, ie, waveform distortion, as described above. The symbols in FIG. 3 are as follows.

γ: Amplitude ratio between the main wave and the interference wave τ,: Delay time difference between the main wave and the interference wave in the antenna 4 τ2: Delay time difference between the main wave and the interference wave in the antenna 1 ω: Carrier wave angular frequency F1 (I, F2 (
C! )): Transfer function of single reception
2 (to), the output (a) of the phase shifter 5 is F1((j)
Exp(Jφ), and the output (b) of synthesizer 3 is X(C
i)=F1 (to) Exp(jφ)+F2 (to).

Also, Fig. 4 AO)a is a vector diagram of antenna 1, Fig. 4 A(
7) b shows the vector diagram of the antenna 4, and FIG. 4B shows the band characteristics for single and in-phase combination.The calculation conditions are as follows.

Center frequency F.

= 5G1Iz path difference τ1 = 4nsec Swing ratio γ = 0.9 In-phase condition band center (f = FO) In Figure 4B, curve a is F1 (to) due to antenna 4, curve b is F2 (to) due to antenna 1 , curve c shows the characteristics of in-phase synthesis according to the prior art.

Note that the present invention aims to obtain flat composite characteristics as shown by curve d. Since this conventional control method maximizes the level after synthesis, it is effective in improving the signal-to-thermal noise ratio of narrowband signals.

However, as shown in Figure 4B, the conventional in-phase synthesis method cannot achieve a sufficient effect in meeting the requirement to improve the in-band level deviation caused by frequency selective fading. There was a drawback. The present invention aims to realize a space diversity receiver that can reduce in-band level deviations and in-band delay deviations that occur in a frequency selective fading transmission path, and which is capable of reducing in-band level deviations and in-band delay deviations that occur in a frequency selective fading transmission path. It is characterized by using the waveform distortion generated in the road.

FIG. 5 is a diagram showing the concept of the present invention, and a and b show vector diagrams of each antenna reception signal, each consisting of a main wave and an interference wave.

When these are combined, if the signal of the antenna 2 is shifted by a phase shift amount φ=130 as shown in the example shown in the figure, the interference waves can be eliminated as shown in c of the figure. As a result, only the main wave 1 and the main wave 2 with no delay time difference remain in the combined signal, and the band characteristics become flat. (See the broken line in Figure 4b) Therefore, it can be seen that if the interference waves received by each antenna are combined so that they have opposite phases, the in-band amplitude characteristics and delay characteristics will become flat and waveform distortion can be removed. . FIG. 6 shows an embodiment of the present invention, in which 1 and 4 are antennas, 2
is a phase modulator, 3 is a combiner, 5 is a phase shifter, 6 is a receiver,
7 is an automatic gain control circuit, 8 is a synchronous detection circuit, 9 is a sensing oscillator, 10 is a detection circuit, 11 is a discriminator, 12 is a waveform distortion detection circuit, 13 is a switching circuit, and 14 is a drive circuit. The signals received by the antenna 1 or 4 are passed through a phase modulator 2 or a phase shifter 5, respectively, combined using a combiner 3, and applied to a receiver 6.

In the receiver 6, an automatic gain control circuit 7 is used to remove amplitude fluctuations, and a digital signal is extracted in addition to a detection circuit 10 and a discriminator 11. On the other hand, the discriminator input signal a and output signal b are applied to a waveform distortion detection circuit 12 to obtain a signal c proportional to the waveform distortion generated in the transmission path. The relationship between the phase shift amount of the phase shifter 5 and the waveform distortion is as shown in FIG. 7a, and there are two stable points where the waveform distortion is minimum. Since the signal received from the antenna 1 is phase modulated by the phase modulator 2, the amount of phase shift changes periodically. As a result, the waveform distortion signal c shown in FIG. A signal is generated. The synchronous detection circuit 8 determines whether the output signal S of the sensing oscillator 9 and the waveform distortion signal c are in phase or out of phase, determines the drive direction of the phase shifter,
The phase shifter is moved toward the stable point by , and the phase is stabilized at the point where the waveform distortion is minimized. Note that R indicates residual waveform distortion, and the arrow in FIG. 7a indicates the direction of the armature of the phase shifter. Among the stable points shown in FIG. 7, stable point 1 indicates the case where the interference wave is eliminated, and stable point 2 indicates the case where the main wave is eliminated.

Generally, the level of the interference wave is smaller than that of the main wave, so when the interference wave converges to stable point 1, the signal level after synthesis becomes higher than when it converges to stable point 2. Therefore, it is desirable to converge to stable point 1. On the other hand, the 4 marks in the figure indicate stable point B when performing conventional in-phase synthesis control where the combined signal level is maximum, and generally the phase shift amount at this point is stable point B.
is closer to the phase shift amount at stable point 1 than the phase shift amount at stable point 1. Therefore,
Immediately after starting control, switch 13 is switched to automatic gain control circuit 7.
After connecting the switch 13 to the waveform distortion detection circuit 1 and performing conventional in-phase synthesis control to maximize the synthesized signal level,
By connecting it to the 2 side and performing the control described above, it is possible to converge to the stable point 1 close to the in-phase synthesis point. By performing the control described above, it becomes possible to make the interference waves have opposite phases and cancel each other out, thereby reducing in-band level deviation,
In-band delay deviation is reduced, enabling good digital transmission. FIG. 8 shows an embodiment of the waveform distortion detection circuit,
15 is a delay circuit, 16 is a subtraction circuit, 17 is a binary conversion circuit, 18 is a low-pass filter having band characteristics equivalent to the transmission line, 19 is a sampling circuit, 20 is a full-wave rectifier circuit, and 21 is a low-pass filter. shows a range filter.

If the transmitted digital signal is polygonal, the discriminator 1
The binary signal obtained from 1 is added to the binary one-to-multiple conversion circuit 17 and the low-pass filter 18 to produce a signal identical to the transmitted waveform distortion-free signal, and the received waveform is converted using the subtraction circuit 16. Only the difference signal from the distorted signal, that is, the waveform distortion component, is extracted and added to the sampling circuit 19. Only the waveform distortion occurring at the sampling time is extracted, and the full-wave rectifier circuit 20
The absolute value of the waveform distortion is obtained, and the harmonic components are removed by the low-pass filter 21 to obtain the output c corresponding to the desired waveform distortion. Note that when the detected digital signal is binary (for example, 4PSK), it is not necessary to use the binary one-to-multiple conversion circuit 17.

Furthermore, if the low-pass filter 18 has the same frequency characteristics as the transmission path (including the transmission filter and reception filter),
The sample circuit 19 can be omitted. Furthermore, when relaying digital signals, a modulator is used to perform binary one-to-multiple conversion and low frequency conversion, so the circuits 17 and 18 in FIG. 8 are not necessary in such a case. FIG. 9 shows another embodiment of the waveform distortion detection circuit, in which 22 represents a pattern determination circuit, and 23 represents a comparison circuit.

The pattern determination circuit 22 is used to determine only a specific code sequence (pattern) from the transmitted signal, and the received signal containing the corresponding waveform distortion is extracted by the sampling circuit 19 and sent to the comparison circuit 23. In addition, by comparing the signal waveform with a previously stored signal waveform that does not include waveform distortion, it is possible to extract only the waveform distortion. Incidentally, FIG. 6 is a diagram showing the principle configuration, and the following configuration can be cited as a modification of FIG. 6.

Even if the four-sensing phase modulator 2 and the phase shifter 5 are connected in series to the same antenna path, the same effect can be obtained.

Furthermore, if the phase shifter 5 can be driven at high speed, phase modulation can be applied at the same time as the phase shift, so the role of the phase modulator 2 can be replaced by the phase shifter 5. ◎ Although Fig. 6 shows an example of the high frequency synthesis method, the same signal detection and processing as shown in Fig. 6 is also used in the intermediate frequency synthesis method in which the received signals of antennas 1 and 4 are converted to intermediate frequency bands and then synthesized. 〇◎ The larger the maximum phase shift amount of the phase modulator shown in FIG. 6, the more the signal-to-noise power ratio of the control signal can be improved.

However, excessive phase shift may cause unnecessary phase fluctuations and amplitude fluctuations in the transmission signal, resulting in deterioration of transmission quality. Therefore, as shown in FIG. 10, by adding a new path for detecting control information and performing sensing, it is possible to improve the signal-to-noise power ratio of the control signal without deteriorating the main signal. is possible. @ In the above explanation, the switch 13 was switched to the automatic gain control circuit 7 side only immediately after control started, but when the output signal level of the synthesizer 3 is detected and it becomes below a preset value, Forcibly switch to the automatic gain control circuit side,
An embodiment is also possible in which the received signal level is not lowered below a required value. In FIG. 10, part of the input signal is branched by branch circuits 24 and 25, one of which is used for demodulating the digital signal, and the other used for extracting the control signal.

Since the phase modulator 2 is located outside the main signal system, it is possible to apply deep phase modulation as necessary. Although the main text has been explained using a two-wave model as an example of frequency-selective fading, the configuration of the present invention controls the waveform distortion to a minimum even when there are many interfering waves. By using , it is possible to minimize interference waves and obtain the same effect.

As explained above, according to the configuration of the present invention, it is possible to always eliminate the interference wave component that causes in-band amplitude and delay deviation due to fading in an opposite phase state, and improve the in-band level characteristics and delay. Characteristics can be flattened at the same time. In wideband waveform transmission such as digital transmission methods using microwave bands, intersymbol interference increases due to in-band level deviation and delay deviation that occur during fading, and error rate characteristics significantly deteriorate. Therefore, by applying the space diversity reception method according to the present invention, it is possible to suppress the occurrence of in-band deviations during fading, which greatly contributes to improving the transmission quality of wideband digital signals in fading propagation paths. .

As a result, it becomes possible to increase relay distance, increase transmission capacity, and make effective use of frequencies, thereby reducing digital signal transmission costs.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional in-phase synthesis space diversity device, Figure 2 is the principle of phase difference detection by sensing,
Figure 3 is a diagram explaining the concept of the two-wave model, Figure 4 is a diagram showing frequency characteristics calculated using the two-wave model, Figure 5 is a conceptual diagram explaining the basic operation of the present invention, and Figure 6 7 is a diagram showing the operation of the control circuit, and FIGS. 8 and 9 are examples of the configuration of the waveform distortion detection circuit 12 shown in FIG. 6. FIG. 10 shows an embodiment of the present invention in which a sensing system for control is installed separately from the main signal transmission system. 1, 4... Antenna, 2... Phase modulator, 3, 31... Combiner, 5... Phase shifter, 6, 61... ... Receiver, 7, 71 ... th dynamic gain control circuit, 8 ... Synchronous detection circuit, 9 ...
...sensing oscillator, 10,101...
Detection circuit, 11... Discriminator, 12...
Waveform distortion detection circuit, 13... Complete switching circuit, 14
...Drive circuit, 15...Delay circuit, 1
6... Subtraction circuit, 17... Binary one-to-multiple conversion circuit, 18... Low-pass filter, 19...
... Sample circuit, 20 ... Full wave rectifier circuit, 21
...Low pass filter, 22...Pattern judgment circuit, 23...Comparison circuit, 24, 25...
...Branch circuit.

Claims (1)

[Claims] 1 Phase-modulate at least one of the two systems of digital reception signals with a low frequency for sensing, process at least one of both reception waves with a phase shifter, and then combine the two systems,
In a space diversity receiving device that detects a signal f_p corresponding to the low frequency from among the composite waves and controls the phase shifter according to the signal, a pulse waveform generated in a transmission line from the composite digital signal. After controlling the phase shift amount of the phase shifter so that the signal f_p included in the composite wave is minimized, the signal f_p included in the output of the waveform distortion detection circuit is A space diversity receiving device comprising means for controlling the amount of phase shift of the phase shifter so that a control signal corresponding to a frequency signal is minimized.