JP2619719B2 - Urban noise elimination circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a radio communication device used for radio communication, particularly for UHF band radio communication, and more particularly to a circuit for reducing the influence of city noise on a radio path.

(Prior Art) In general, in UHF band wireless communication, the influence of city noise typified by automobile ignition noise and the like is large, and it may be difficult to realize a line in a wireless communication device or the like using a digital modulation method.

There are two major methods for reducing the effects of urban noise that have been implemented in the past. One is a method of improving the C / N by increasing the output on the transmission side, and the other is a method of narrowing the reception bandwidth.

[Problem to be solved by the invention] However, the method of increasing the output on the transmission side requires a 10 dB C
In order to expect the / N improvement, the transmission output will be increased by 10 dB relatively, and a 1 W output will require a 10 W output, requiring a change in equipment scale. or,
In the method of reducing the reception bandwidth, in a normal wireless communication device, the reception bandwidth is already narrowed to the limit in order to increase the channel division efficiency, so that a significant improvement cannot be expected. For example, the reception bandwidth is expressed as a band time rate (BT product) expressed by a digital wireless device from 1.7 to 1.
Even if it is changed to 1, only a C / N improvement of about 20log (1.1 / 1.7) = –3.78 (dB) can be obtained.

According to the present invention, a circuit for removing an urban noise component is configured in such a manner as to be added to an input section of a receiving apparatus in place of the improvement means, as described above, in which the internal specifications of the wireless apparatus are largely changed. In particular, the adoption of the cancellation method in comparison with the conventional method of narrowing the reception bandwidth,
The purpose of the present invention is to provide an urban noise elimination circuit that can be expected to improve.

[Means for Solving the Problems] The present invention converts a received signal including a transmitted main signal into the same received signal.
1, a branch circuit for branching to a second signal, a first band-pass filter for extracting a frequency band centered on the frequency of the main signal from the first signal, and a main signal from the second signal. A second band-pass filter for extracting a frequency band in the vicinity of the main signal that does not include the frequency of the first band-pass filter, and an output of the first band-pass filter and an output of the second band-pass filter having equal amplitudes and opposite phases. , An anti-phase combining circuit for removing noise from the received signal and outputting only the main signal.

(Operation) The received signal is branched into first and second signals, and the first signal is input to a first filter that passes a main signal and a frequency band of noise superimposed on the main signal, and the second signal is converted to a main signal. The signal is input to a second filter that passes a frequency band that is near and does not include the main signal. At this time, by making the pass bandwidths of the first filter and the second filter equal, the pulse response waveforms of the respective noises become the same. Also, the noise that has passed through the first filter and the second filter respectively has a frequency component difference corresponding to the center frequency difference, but originally has the same noise pulse response. There is no. Therefore, when synthesizing passed through the first filter for example noise component omega ₁ and the example of the noise component omega ₂ passes through the second filter, at a constant period, the beat component which is constant delay from further noise pulses, amplitude-modulated A noise wave is obtained.

That is, if equal to the amplitude-simultaneous synthesis, synthesis _{wave, exp (iω 1 t) +} exp (iω 2 t) = exp (iω 1 t) + exp (iω 1 t-iω 1 t + iω 2 t) = exp ( iω ₁ t) {1 + exp (iω ₂ t−iω ₁ t)} = Aexp (iω ₁ t) Therefore, when the amplitude characteristic of the noise is ω ₂ −ω ₁ = Δω FIG. Therefore, under the condition of Δωt = π + 2nπ (n = 0, 1, 2, 3,...), The amplitude can be zero. This condition
Urban noise or equivalent pulse noise is removed by realizing reverse phase synthesis so as to be satisfied at the peak position of the signal that has passed through the first filter.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

 FIG. 1 shows a specific embodiment of the present invention.

FIG. 1 shows an example in which a phase-directional communication line is assumed and the system is adapted to a small-capacity multiplex digital communication channel in the UHF band.

This embodiment uses two circulators (CIRs) 2 and 3 between the antenna 1 and the transmitter / receiver 13 to provide an urban noise elimination circuit.
10 is inserted.

The urban noise elimination circuit 10 includes a branch circuit 4 for branching a received signal into two, and band-pass filters 5 and 6 for passing only signals of a predetermined frequency from the branched received signals.
And an anti-phase synthesizing circuit 7 for synthesizing the output signals from the band-pass filters 5 and 6 in anti-phase.

 The operation of the urban noise synthesis circuit 10 will be described below.

First, the main signal for communication and the city noise arrive from the antenna 1 in the figure and are transmitted via the CIR 2 to the city noise elimination circuit 10.
Is input to

In the city noise elimination circuit 10, the input main signal and city noise are divided into two by the branch circuit 4 and input to the band-pass filters 5 and 6, respectively. Here, the bandpass filters 5, 6
Differs in the band center frequency as shown in FIG.
The pass bandwidths are equal. Also, here
Band center frequency the same city as the band center frequency omega ₁ of the main signal of the band-pass filter 5, the bandwidth of the or keep a sufficiently wide [Delta] [omega _B from the main signal bandwidth. Further bandpass filter 6 has a bandwidth centered on the frequency omega ₂ was detuned by [Delta] [omega than the band center frequency omega ₁ of the band-pass filter 5, a band passing filter bandwidth [Delta] [omega _B. At this time, Δω−Δω
_B is kept set to be larger than the bandwidth [Delta] [omega _s of the main signal. That is, the bandpass filter 6 is set so as not to pass the main signal. The main signal passes through the band-pass filter 5 and also passes through the next-stage antiphase combining circuit 8, and then reaches the wireless communication device 13 by the CIR3. During this time, the circuit does not change the received signal. This is because the reception signal band is outside the filter pass frequency of the band pass filter 6, as shown in FIG.

Note that the insertion loss in the branch circuit 4 must be estimated at 3 dB at worst. However, in the branch circuit 4, when the frequency difference Δω is increased and the pass band frequencies of the band-pass filters 5 and 6 are not weighted, etc. It is also conceivable that the circuit has a lower loss.

On the other hand, when the description of the urban noise is expanded, the pulse noise that has passed through the band-pass filter 5 has a pulse response as shown in FIG. That is, the response wave is obtained in the form of being amplitude-modulated to the component of the center frequency ω ₁ of the band pass 5, and the amplitude change, that is, the envelope is determined by the band characteristic of the band pass filter 5. Similarly, a similar response is obtained for pulse noise passing through the band-pass filter 6. In other words, the form is obtained by modulating the component of ω ₂ , and the shape of the envelope is exactly the same as that after passing through the band-pass filter 5.

When the pulse response outputs of the band-pass filters 5 and 6 are combined by the reverse-phase combining circuit 7 at the next stage, the peak of the pulse response (the envelope peak) of the band-pass filter 5 has the beat-like amplitude characteristic described above. The point where the amplitude becomes zero, t = (π + 2nπ) /
The output of the bandpass filter 6 is set so as to be Δω. Here, a pulse is input to the band-pass filters 5 and 6 at the same time, and the response of each band-pass filter is obtained. Therefore, if the electrical lengths of the band-pass filters 5 and 6 are equal, Ω _{1 in} response waveform
And ω ₂ are in phase. Therefore, in order to reduce the peak of the response waveform to zero, the output of the band-pass filter 6 is combined via the 180 ° phase shifter 9 to realize reverse-phase combining. In FIG. 1, a variable 180 ° phase shifter is used in order to absorb irregularities in the electrical lengths of the bandpass filters 5 and 6 or imperfections in other circuits.

In the above, the concept of antiphase combining has been described with reference to FIGS. 1 to 3. Next, specific values will be adopted for frequencies in the UHF band to explain the pulse noise canceling ability. .

Here, examples 1, 2, and 3 in which the band bands of the band-pass filters 5 and 6, the detuning frequency thereof, the transmission / reception duplexer bandwidth of the transmission / reception device 10, and the main signal bandwidth are determined as shown in Table 1. State.

When the response envelope waveform of the output 12 from the antiphase combining circuit 7 of each embodiment is calculated under the conditions shown in Table 1, the form shown in FIG. 4 is obtained. FIG. 4 shows a transient response from the noise peak point for comparison. A response having an amplitude of 10 indicates a response when no out-of-phase synthesis is performed, that is, an output 11 of the band-pass filter 5.

When evaluating the noise amplitude suppression at this stage, Becomes

Next, the noise enters the transmission / reception duplexer 14 of the transmission / reception device 13, and a band-pass filter (band-pass filter 5
When the waveform response after passing through is calculated, it becomes as shown by the solid line in FIGS. 5, 6, and 7, and the suppression amount is Becomes Here, especially, it can be seen that a large improvement effect can be obtained for a communication channel having a small main signal bandwidth and a large influence of urban noise.

5 to 7, the output of the band-pass filter 5 and the output of the antiphase combining circuit are also shown.

As described above, according to the present invention, in the case of a small-capacity digital multiplex radio apparatus inserted between a radio apparatus and an antenna, city noise suppression of about 10 dB can be achieved.

Therefore, compared to the method of increasing the transmission output,
It is economical and has no radio administration problems. In addition, a communication path near a city where the problem of urban noise is often a short circuit distance, and if carelessly increasing the transmission output, there is a danger of receiver saturation, but according to the present invention,
Since there is no change in the input level of the receiver, it is also advantageous in circuit design.

(Effects of the Invention) According to the present invention, a branch circuit for branching a received signal into first and second signals, a first pass band filter for passing a main signal of the first signal, and a second With a second band-pass filter that blocks the passage of the main signal among the signals, and an anti-phase synthesis circuit that synthesizes the outputs of the first and second band-pass filters with equal amplitudes in anti-phase, the configuration is simple. It is possible to remove city noise included in the received signal.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of an urban noise elimination circuit according to the present invention, FIG. 2 is a diagram for explaining characteristics of a band-pass filter, and FIG. 3 is a band-pass filter of FIG. FIG. 4 is an envelope waveform showing the pulse noise response of the antiphase combining circuit of FIG. 1, and FIGS. 5, 6, and 7 are FIG.
3 shows pulse noise responses of the band-pass filter of the duplexer shown in the figure, and is an envelope waveform showing the cases of Embodiment 1, Embodiment 2 and Embodiment 3, respectively. 1… Antenna, 2,3… Circulator, 4… Branch circuit, 5,6… Bandpass filter, 7… Negative phase synthesis circuit, 8…
Synthesizing circuit, 9: Variable type 180 ° phase shifter, 10: Urban noise elimination circuit, 11: 5 band-pass filter 5 output, 12: Negative phase synthesizing circuit output, 13: Transceiver, 14: Transmission / reception Duplexer band-pass filter, 15 ... Transmit / receive duplexer output.

Claims (1)

(57) [Claims] 1. A branch circuit for branching a UHF band received signal including a transmitted main signal into the same first and second signals, in a city noise removing circuit employed in a UHF band wireless communication device.
A first band-pass filter for extracting a frequency band centered on the frequency of the main signal from the first signal;
A second band-pass filter having a pass bandwidth equal to that of the first band-pass filter and extracting a frequency band near the main signal that does not include the frequency of the main signal from the second signal; An anti-phase synthesizing circuit for synthesizing the output of the filter and the output of the second band-pass filter with equal amplitude in reverse phase, removing pulsed urban noise in the UHF band reception signal, and outputting only the main signal; An urban noise elimination circuit, comprising: