JPH0353620A - Equal gain synthesizing diversity receiver - Google Patents

Abstract

PURPOSE:To eliminate demodulation distortion and to improve the S/N based on an interference component due to a reflecting wave by using a tracking filter. CONSTITUTION:A narrow band tracking filter 20 is provided to the output of a synthesizer 13, and an output signal AF of an FM demodulator 10 is fed back to the tracking filter 20 to trace the center frequency of the tracking filter 20 to the instantaneous angular frequency of the output signal AF. Since the center frequency of the tracking filter 20 follows to the instantaneous angular frequency of the output signal AF, the output of the synthesizer 13 is only a desired FM modulation signal. Thus, the interference component due to a reflecting wave is eliminated and the generation of demodulation distortion is prevented and the S/N is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an equal gain combining diversity receiver, and particularly to an improvement incorporating a tracking filter to remove demodulation output distortion and improve S/N. do. [Summary of the Invention] In an equal gain combining or diversity receiving device, a tracking filter is provided on the output side of the combiner, and by feeding back the output signal of the demodulator to the tracking filter, the center frequency can be adjusted to the instantaneous value of the demodulated output signal. It is designed to follow the angular frequency. [Prior Art] Equal gain combining or diversity receivers combine multiple signals with phase differences received by multiple antennas into the same phase, and demodulate the combined signal, thereby eliminating the effects of multi-bus fading. The aim is to reduce this and obtain good reception conditions. Generally, when the antenna position changes, the phase of the carrier signal output from the antenna changes. This is due to the difference in propagation time on the radio wave propagation path.

Figure 3 shows the process by which fading occurs. In the figure, the radio waves sent out from the antenna S on the transmitting side are direct waves e
d■wed2 is the receiving antenna a, a? Sent to tena b. In addition, the reflected waves eu and eeu2 are also reflected from the antennas a and
Sent to antenna b. Assuming that each signal is as follows, eaz=Eaa cos(ωct+φ1(1)+01)
...(1) eux=Eua
cos(ωc(t-τ)+φm(at t-)+03)
...(2) ed, = Edbcos(ωct+φm(t
)+03)-(3)(!ua=Eub cos(ωc(
t-τ) + φ1 (t1τ) 10,) ... (4)
However, Eda is the amplitude of edx, θ is the initial phase of the carrier of adz, Eua is eth' *θ3 is euxE
db is ed2, θ, is edx 'Eub is e mountain 〃, θ. is the angular frequency of the carrier, τ is the delay time when it arrives after being reflected by a reflecting object, φm(t) is the modulation amount, and φo+(at t-) is the modulation component delayed by τ.

When the change in φm(t) is very small within the time τ, that is, when the following equation holds, φm(t)”F φ鳳(t−τ)
...(5) Based on this condition, the effect of multipath fading can be reduced in an equal gain combining diversity receiver by combining the carrier phase differences that occur between antennas a and antenna b in the same phase. I'm letting you do it. However, if φm(1) changes significantly within the delay time τ, the equation (5) cannot be satisfied, and the equal gain combining operation will be in a different state. Now, FIG. 5 shows a conventional system diagram of an equal gain combining diversity receiver, and FIG. 4 shows instantaneous frequency changes of the direct wave and reflected wave arriving at the antenna.

In Fig. 5, 1 and 2 are receiving antennas, 3 and l4
are front ends, 4 and l5 are IF filters, 5 and 6 are l-th mixers, 6 and l7 are band-pass filters, 7 and 18 are limiters 28 and 19 are second mixers,
9 is a low-pass filter, 10 is an FM demodulator, 11 is a limiter, l2 is a band-pass filter, and 13 is a combiner (adder). Further, FIG. 4 shows that the reflected wave S2 is delayed by a time τ compared to the direct wave S1, and at time tp, the instantaneous angular frequency of the direct wave S8 is ωD, and the reflection? The instantaneous angular frequency of S2 is ωU, and it can be regarded as two signals with different angular frequencies. Also, the difference between the two ωD−ωu (=
Δω〉 is. It changes over time due to FM modulation. Transforming equations (1) to (4) to show this state, e,
1■=EdB cos(ω■t+θ.) −(
6) Qu,:EuB eos(ω13 t+θ.)
・(7) edyo=EdbCOS(ωDt+OS)
-(S)eu. =Eub cos(ωut+θ1
-(9) However, θx: initial phase of instantaneous angular frequency of 8ch, ωD = ωU + Δωθ, :a11 θ3 : ed2 θ*: euz Signal ea obtained from antenna 1, signal eb obtained from antenna 2 are ea= e(1,+e+n=Eda cos(ωot10,)+E136 cos(ωut+02)...(10
) eb=ech+elli=Edb cos(ωDt+θ
z)+Eub cos(ωut+θ,)...(11)? In Figure 5, the radio waves received by antenna 1 are converted into IF signals by front end 3, and are also converted to IF signals by antenna 2.
The radio waves received at the front end 14 are similarly converted into IF signals, and are inputted to the equal gain combining or diversity section via the IF filter 4 and the IF filter 15. To simplify the following explanation, the IF signal ea in FIG.
, eb are expressed by equations (10) and (11), respectively.

As a result, the signals eaweb input to the equal gain combination or diversity section are ωD and ωU, respectively, as shown in FIG. 6(a).
The signal has two angular frequencies. Also, in the equal gain combining diversity section, in-phase combining is performed for each of the instantaneous angular frequencies ωH and ωU, so the output of the limiter l1 is expressed as e■ by the following equation. e6=cosωlt 10cosωl′t101(12)
However, ωl is the instantaneous angular frequency obtained by in-phase combination of ωD, and ωi′ is the instantaneous angular frequency (=ωi−Δω) obtained by in-phase combination of ωU.

[Problem M to be solved by the invention] However, when the above co is mixed again by the first mixers 5 and 16, the products of ωD and ω1′ and ωU and ωl occur, and a new beat is generated. ．． The output ea1 of the first mixer 5 is eB1= e6X eo
...(13) The bandpass filter 6 passes the lower side wave of eat in the equation (l3), and also has a bandwidth Bω
, assuming that it is a narrow band filter with a center frequency ωC (=ωD - ω1), its output ea2 is ・eaz=Eda[cos{(ωD - (Ill)t+θ,
}+cos (((&)D-ω1')t+θ!}]10E
ua[cos((ωu-ωl) t10,)+cos(
(ωg-ωl')t+θ2}]...(14) However, ωD-ωl'=(ω0-ωl)+Δω, ωU-ω
l=(ω0-ω1)-Δω, ωU-ω1'=ωD-ω
It is l. ? The output ea■ of the transmitter 7 has the instantaneous spectrum shown in FIG. 6(b), and the amplitude of ea2 in equation (14) is
Assuming that ua is limited to 1, the output ea4 of the second mixer 8 is as follows: ea4=ea ” eaa = (cosωl t
+COS(1)L' t ) ●[cos((ωo ω
i)t+01)+cos((ω0'-ωl')t10,
}+cos((ωg-ωl)t10oz+cos((ω1
1-ωl')t+02)]...(15) Similarly, when calculating the output eb4 of the second mixer 19 for the signal input of eb, eb4=ebjeb3=(coSωlt+coSω1'
t)●[coS{(ωrω1)t10,}1008((
(IID-ωl')t+θ,)+cos((ωu-(+
)1) t10J+cos((ωu-(111')t+0
2}]...(l6) In the synthesizer 13, ea4 and eb of equations (15) and (16)
4 are synthesized in the same phase, extracted through a bandpass filter 12 that passes each lower side wave, and the amplitude component is limited to 1 by a limiter 11. is e(=cosωlt+cosωl't+eos((ωl
+Δω)t+θα)+Cos(<CIl1'+Δω)t
10a) +cos ((ωh-Δω)t-θα)10cos (((111'-Δω)t-θCl) +c
os (((Ill1Δω)t10−)+cos (
((111'+Δc.+)t-θp) +cos
(((Il1−Δω)t−θ− } +cos (
(ωl'+Δω)t+θ1)
-(17) However, θα=01-02, θp=02-0. ω1+Δω=ωl, ω1′−Δ
ω=ω1−2Δω. Here, the output spectrum of the limiter 11 is shown in Fig. 6 (c
).

As described above, the output of the limiter 11 has ωhωl+Δω
, ωl-Δω, ω1-2Δω are output, and for the desired wave ωl. Since an unnecessary spectrum is generated in the FM demodulator 10, the demodulated output AF obtained via the low-pass filter 9 includes demodulated distortion.

[Object of the Invention] Therefore, the object of the present invention is to eliminate demodulation distortion based on interference due to reflected waves by using a tracking filter in an equal-gain combining or diversity receiving device to improve S/
The goal is to improve N. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a tracking filter on the output side of the combiner and feeds back the output signal of the demodulator to the tracking filter, thereby improving the output signal. The gist is that the instantaneous angular frequency follows the center frequency of the tracking filter. [Operation] Since the center frequency of the tracking filter follows the instantaneous angular frequency of the demodulated output signal, its output is only the desired FM modulation signal. Therefore, interference components due to reflected waves are removed, and demodulation distortion can be prevented. [Examples] The present invention will be described below with reference to examples shown in the drawings. FIG. 1 shows an embodiment of an equal gain combining or diversity receiving apparatus according to the present invention. In the same figure, the same reference numerals as in FIG. 5 represent the same or similar circuits, and the structure different from that in FIG.
The demodulated output signal AF is fed back to the tracking filter so that its center frequency follows the instantaneous angular frequency of the demodulated output signal.

Next, the operation of the above embodiment will be explained. In FIG. 1, radio waves input to an antenna 1 are converted into an IF frequency by a front end 3 and then outputted via an IF filter 4. The output signal is input to the first mixer 5 and multiplied by the feedback signal from the limiter 11. The bandpass filter 6 passes only the lower side wave of the output of the first mixer 5, and the output signal is inputted to the second mixer 8 after the amplitude fluctuation component is removed by the limiter 7. The second mixer 8 multiplies the signal with the output signal of the IF filter 4 and outputs the product. In addition, the input signal of the antenna 2 is also sent to the front end 14, the IF filter 15, the first mixer 16, the bandpass filter 17, the limiter 18, and the second mixer l.
9 performs a similar operation. Second mixer 8,1
The output signals of 9 are in-phase synthesized by a synthesizer 13 and input to a narrowband tracking filter 20. In the narrow band tracking filter 20, the center frequency of the filter follows the instantaneous angular frequency ωl of the feedback signal for the direct wave, and the output signal is sent to the first mixer 5, 16 for feedback after the amplitude component is removed by the limiter 11. It becomes a signal. Further, the output signal is inputted to the FM demodulator 10 and outputted as a demodulated output signal via the low-pass filter 9. Further, this demodulated output signal is fed back as a control signal for the narrowband tracking filter 20. FIG. 2 shows the amplitude and phase characteristics of the narrowband tracking filter 20. In the same figure, ω. is the feedback angular frequency without modulation, ωdeV is the maximum frequency deviation, and ω
1 is ω. Move within 1ωdeV≦ωL≦ω010ωdev. At this time, the center frequency of the filter 20 also operates to follow ωl. The phase at this time is constant, so the delay time of the filter is O. That is. FM demodulator 1
0. Assuming that the input/output response delay of the low-pass filter 9 is very small, the demodulated signal corresponding to the FM modulation signal input to the FM demodulator 10 instantly passes through the low-pass filter 9.
It is output from The instantaneous voltage output from the low-pass filter 9 represents the instantaneous frequency of the FM modulation signal.
Therefore, if the center frequency of the tracking filter 20 is determined by the output signal of the low-pass filter 9, only the desired FM modulation signal can be obtained at the output of the tracking filter 20. Since the tracking filter 20 has characteristics of a narrowband filter, the filter itself has a large delay time. However, due to the control operation of the tracking filter, the center frequency follows the input frequency of the filter 20, so the filter 20 is always used at the "O" point of the phase characteristic as shown in FIG. It turns out. Therefore, unless there is a delay in the control of the filter 20, the delay time will be "O". Therefore, the operation of the first mixers 5 and 16 fully satisfies the conventional equal gain combining diversity function shown in FIG. As a result, even if there is an unnecessary signal other than the desired signal on the input side of the tracking filter 20, the output will be
Only the desired signal can be obtained. [Effects of the Invention] As explained above, according to the present invention, the output distortion in equal gain synthesis based on the frequencies of the direct wave and the reflected wave can be reduced to a low range, and the S/N can be reduced because the tracking filter removes noise outside the imperial range. Improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is an amplitude phase characteristic diagram of a narrowband tracking filter, Fig. 3 is a radio wave propagation path diagram, and Fig. 4 is an instantaneous angular frequency change of an FM wave. FIG. 5 is a block diagram of a conventional equal-gain matching or diversity receiver, and FIG. 6 is an instantaneous spectrum diagram at each point of the receiver.

Claims (1)

[Claims] In an equal gain combining diversity receiving device comprising a combiner that combines signals from each front end received by a plurality of antennas in phase, and a demodulator that demodulates the combined signal from the combiner, the output of the combiner A tracking filter is provided on the side, and the center frequency of the tracking filter is configured to follow the instantaneous angular frequency of the output signal by feeding back the output signal of the demodulator to the tracking filter. Gain combining diversity receiver.