JPS61177827A - Combined diversity receiver - Google Patents

Abstract

PURPOSE:To enable to lower frequency selective multi-path distortion by passing random phase component due to fading and modulation signal component of frequency selective multi-path distortion in a narrow band BPF connected to the output of the first mixer. CONSTITUTION:It is supposed that there is no multi-path in an antenna 1 and an FM wave in which frequency selective multi-path distortion is generated is inputted to an antenna 2. Received input signals are correlated with output signals 14 of a feedback circuit 30 by the first mixers 3, 4. The output of mixers 3, 4 is inputted to narrow band BPFs 20, 21 respectively. The band width of BPFs 20, 21 is large enough to pass phase distortion due to fading and frequency selective multi-path distortion component, and the output passes through limiters 7, 8 and mixed with input signals in the second mixers 9, 10. Receiving signals having multi-path distortion and output signals of the limiter 8 having multi-path distortion are mixed in the mixer 10. Multi-path distortion is removed from output of the mixer 10 and composed 11 with output of the mixer 9 and fed back to mixers 3, 4 through a BPF 12 and a limiter 13.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is a method of in-phase receiving signals from two or more antennas in order to improve reception quality in broadcast waves where fading and frequency-selective multipath distortion exist. The present invention relates to a combining diversity receiving device that performs combining.

[Conventional technology]

FIG. 4 shows, for example, Halpern (IEEII!
Trans, Commn, +Vo1. COI'1-
22. ? h8 1974 pp, 1099-110
6) is a conventional synthetic diversity receiving device shown in FIG. In the figure, 1.2 is a receiving antenna, 3.4 is a first mixer that takes the frequency of the difference between the received signal from this receiving antenna 1.2 and the output signal of a feedback circuit, which will be described later, and 5.6 is this first mixer. 1 narrow bandpass filter connected to the output of the mixer 3.4, 7.8 is the limiter, 9.10
1 is a second mixer that takes the frequency of the difference between the output signal of the limiter 7.8 and the output signal from the receiving antenna 1.2, 11 is a combiner that combines the outputs of the second mixer 9.10, and 30 is a combiner that combines the outputs of the second mixer 9.10. This is a feedback circuit that feeds back the output signal to the first mixer 3.4, and the feedback circuit 30 includes a bandpass filter 12 and a limiter 13. 14 is an output signal. Here, the narrow band pass filters 5 and 6 need to have a bandwidth that allows random phase components due to fading to pass and does not allow noise and modulation signal components to pass (for example, Miyagaki, Morinaga, Namekawa Communication Theory ( B)
Vol.

J63-B No. 1 pp, 9-161980), since this device has a structure that forms a feedback circuit, a narrow bandwidth of ±2 to 3 kHz is required for the receiving device to draw in the system. Bandwidth is required (for example, Japanese Patent Laid-Open No. 57-24134).

Next, the operation will be explained. Each of the received signals fcfn, fcZ LL of the receiving antenna 1.2 is supplied to a first mixer 3.4 and a second mixer 9,10.

Here, fc is the carrier frequency of the input signal, m(t) is the modulation signal, θ1. θ2 is a random phase due to fading. Also, at this time, the limiter 13 of the feedback circuit 30
The output signal 14 becomes foZ. fo is feedback circuit 3
0 output frequency.

In the first mixer 3.4, the correlation between the received signal and the output signal of the limiter 13 is taken, and the output is passed through a narrow band pass filter 5.6 and a limiter 7, which pass random phases due to fading and exclude modulated signal components. .8 respectively (fc-fo) ZLL, (f c-f
o) Becomes ZLL. The output of this limiter 7.8 is mixed in a second mixer 9.10 with the received signal from the feedforward circuit, and the output signals of the second mixer 9.10 are both of random phase θ1. It becomes fol Nitan with θ2 removed. After this output signal is combined by a combiner 11, it is applied to a bandpass filter 12 and a limiter 1.
3 and is returned to the first mixer 3.4.

(Problems to be Solved by the Invention) As described above, the conventional synthetic diversity receiver is configured to remove the random phase caused by fading, but in broadcast waves, in addition to the random phase caused by fading, Frequency-selective multipath distortion that distorts the amplitude and phase of the modulated signal component becomes a problem.However,
Conventional devices such as those described above do not take any countermeasures against this frequency-selective multipath distortion, and therefore there is a possibility that the multipath distortion may be removed by chance for received waves of a certain level. However, usually, for example, receiving antennas 1 and 2 each have an FM without the same degree of multipath distortion.
If an FM wave with multipath distortion is input, this multipath distortion cannot be reduced.

The present invention has been made in view of the above points, and is a synthetic diversity receiving device that can reduce random phases caused by fading of broadcast waves, reduce frequency selective multipath distortion, and not impair diversity effects. The purpose is to obtain.

[Means for solving problems]

The synthetic diversity receiving device according to the present invention uses a narrowband pass filter connected to the output of the first mixer to pass random phase components due to fading and to pass modulated signal components having frequency selective multipath distortion. This is to allow it to pass through.

[Effect]

In the present invention, the run due to fading is reduced, and the diversity effect is not impaired.

〔Example〕

Before explaining the present invention in detail, the reason why frequency-selective multipath distortion is not reduced in conventional devices will be specifically explained.

FIG. 5(a) shows the spectrum of an FM wave modulated with a sine wave modulation signal when there is no multipath.

fc is the carrier frequency and fm is the frequency of the modulated signal, and this figure shows the carrier spectrum 15, the upper side wave 16a and the lower side wave 16b of the fundamental wave of the modulated signal.

An upper wave 17a and a lower wave 17b of the second harmonic of the modulated signal are shown. FIG. 5(bl) shows a vector diagram of an FM wave related to FIG. 5(a). For simplicity, only the fundamental wave of the modulation signal is considered, but generality is not lost. When the FM wave shown in FIG. 5 (al) is input to the receiving antenna 1.2, the spectrum of the output 14 of the feedback circuit 30 also becomes the same spectrum as shown in FIG. 5 (Jl). However,
The carrier frequency fc has been converted to an output frequency fo, which is shown in FIG. 5(C).

Now, assume that an FM wave is input to the receiving antenna 2 when there is a frequency-selective multipath. The spectrum of the FM wave at this time is shown in Figure 5 (d), and the vector diagram is shown in Figure 5 + e).
Shown below. At this time, the first mixer 3.degree. 4 correlates the received signal with the output 14 of the feedback circuit 30. The Vex diagram and spectrum of the output of the first mixer 3 in a system without multipath are shown in FIGS. 5(f) and 5(g). In addition, the vector diagram at the output of the first mixer 4 in a system with multipath is shown in Figure 5 (hl).The spectrum at this time is shown in Figure 5 (11);
18 shows the spectrum of (fc-fo), 19a shows the spectrum of the multipath distortion component of the upper side wave, and 19b shows the spectrum of the multipath distortion component of the lower side wave.

Here, since the bandwidth of the narrow band pass filter 6 is the bandwidth for excluding the modulated signal component, the distortion component 19a of FIG.
, 19b are not passed. Therefore, the output signals of the second mixers 9 and 10 are the same signals as the received input signals, and distortion components are not removed. The output signals of the second mixer 9.10 are combined by a combiner 11, and the output vector thereof is shown in FIG. 5 (Jl).

This shows that there is no multipath reduction effect.

In this way, if the bandwidth of the narrow bandpass filter 6 is set to such a bandwidth that the modulated signal component is removed, multipath distortion will not be reduced.

Therefore, in the present invention, the bandwidth of the narrow band pass filter 6 is configured to pass not only random phases due to fading but also frequency selective multipath distortion components.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In Fig. 1, the same reference numerals as in Fig. 4 indicate the same or equivalent parts, and 20.21 accurately reflects the random phase due to fading, and at the same time passes frequency-selective multipath distortion components. is a narrow bandpass filter with a bandwidth that rejects the viroft signal.

Next, the operation will be explained. When the FM wave in the absence of multipath is input to the receiving antenna 1°2 as shown in FIG. 5 (al), the operating principle is the same as that shown in FIG. 14 is the same as the receiver's power, and its spectrum is shown in Figure 5 (C1). Now, suppose that an FM wave with frequency-selective multipath distortion is input to the receiving antenna 2. At this time, the FM The wave spectrum and vector diagram are shown in Fig. 5(d) and (e).The above received input signal is transmitted to the first mixer 3.4.
Correlation with the output signal 14 of the feedback circuit 30 is thus taken. The vector diagram and spectrum at the output of the first mixer 3 in a system without multipath distortion are shown in Fig. 5(f), fgl
It will not be shown to you. Also, the first part of the system with multipath distortion
The vector diagram and spectrum at the output of mixer 4 are
The signals are shown in FIGS. 5(h) and (1), and these signals are input to narrow band pass filters 20 and 21, respectively. The narrow band pass filter 21 filters multipath distortion components 19a, 19 as well as random phase components of fading.
b, and are input to the second mixer lO via the beam mink 8. A second mixer 10 receives a received signal with multipath distortion and a limiter 8 with multipath distortion components.
The second mixer 1 is mixed with the output signal of the second mixer 1.
An output of 0 is a signal from which multipath distortion has been removed. Second
Figure (a) shows how multipath distortion is removed by the second mixer 10 in a vector diagram. Therefore, the spectrum of the signal at the output of the second mixer 10 is as shown in FIG. 2(b).

As described above, the bandwidth of the narrow band pass filters 20 and 21 allows random phase components due to fading to pass,
In addition, the frequency-selective multi-path distortion is reduced by being set to pass the frequency-selective multi-path distortion component.

Next, the upper limit of the bandwidth of this narrow band pass filter 20.21 will be explained. When the filter 20.21 passes a distortion component of Hz (period: approximately 52 μsec) to the pilot signal 19 of the FM broadcast, the filter 20.
The bandwidth of 21 is 38KHz, and the group delay time of the filter is 1.
It becomes 5 to 30 psec. Above pyro 7) Signal 19Kl
The distortion component of lz passes through the narrow band pass filter 20.21 and is input to the second mixer 9.10.
10 attempts to cancel out the Hz distortion component in the pilot signal 19 of the received signal inputted via the feedforward circuit, but the signal inputted via the filter 20.21 is delayed by the delay of the filter 20.21. The signal is delayed by the amount of time compared to the received signal that has passed through the feedforward circuit. At this time, a 19KHz pilot signal (period is approximately 52μ
sec), the influence of a group delay time of 15 to 30 μsec is large (not only cannot cancel out the distortion components, but also may cause adverse effects due to phase shift. Therefore, the band of the narrow band pass filter 20. The width shed is set to a bandwidth that eliminates the viroft signal.

Moreover, FIG. 3 shows the probability of falling below the relative level in this device, the line 22 shows the theoretical value in the case of one antenna, that is, without guidance, and the O mark shows the actual value.

Moreover, the line 23 indicates the theoretical value of equal gain combining diversity. As is clear from the experimental results, the composite diversity receiving apparatus composed of the filters having the bandwidth of this embodiment has a diversity effect.

In this way, according to this embodiment, the narrow band pass filter 20
．． 21 bandwidth to pass the modulated signal component, and FM
Since the broadcast pilot signal of 19 KHz is not passed, it is possible to reduce random phase due to fading and frequency selective multipath distortion, and the ubiquity effect is not impaired.

Note that the synthetic diversity receiving device according to the present invention may be connected to a receiver that uses an intermediate frequency, and the same effects as in the above embodiments can be obtained.

〔Effect of the invention〕

As described above, according to the synthetic diversity receiving device according to the present invention, the bandwidth of the narrow bandpass filter connected to the output of the first mixer allows random phase components due to fading to pass, and frequency-selective multipath distortion Since even modulated signal components having 100 kHz are passed through, it is possible to reduce random phase due to fading and reduce frequency selective multipath distortion.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a synthetic diversity receiving device according to an embodiment of the present invention, FIG. 2(a) (bl is a diagram for explaining the frequency selective multipath distortion reduction effect of the device, and FIG. 3 is A diagram showing the cumulative probability distribution of the reception level of the device, FIG. 4 is a block diagram of a conventional synthetic ubiquitous receiving device, and FIGS. It is a figure showing that there is no reduction effect. 1.2...Reception antenna, 3.4...First mixer, 9.10...Second mixer, 11...Synthesizer, 1
2...Band pass filter, 13...Limiter, 20
．． 21... Narrow band pass filter, 30... Feedback circuit. Note that the eaves numbers in the middle of the figure indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A first mixer that mixes each of the received signals from at least two or more antennas and a signal from a feedback circuit to be described later; and a first mixer that is connected to the output of each of the first mixers and is connected to the output of each of the first mixers to generate randomness due to fading in the received signal. a narrow band pass filter having a bandwidth that allows the phase component and the main component of the modulation signal to pass; a second mixer that mixes the output signal of each of the narrow band pass filters and each of the received signals; A combining diversity receiver comprising: a combiner that combines outputs; and a feedback circuit that feeds back the output signal of the combiner to the first mixer. (2) The composite diversity receiver according to claim 1, wherein the upper limit of the bandwidth of the narrow band pass filter is set so as not to pass a 19 KHz pilot signal of FM broadcasting.