JPH03104322A - Urban noise elimination circuit - Google Patents

Abstract

PURPOSE:To eliminate an urban noise component by providing a 1st band pass filter extracting a frequency band around the frequency of a main signal, a 2nd band pass filter extracting a frequency band in the vicinity of the main signal and an inverse synthesis circuit applying constant amplitude inverse phase synthesis to the outputs of the 1st and 2nd band pass filters. CONSTITUTION:A pulse noise passing through a band pass filter 5 represents a pulse response. A similar response is obtained from a pulse noise passing through a band pass filter 6. When the pulse response outputs of the band pass filters 5, 6 are synthesized at a next stage inverse phase synthesis circuit 7, the output of the band pass filter 6 is set so that the peak of the pulse response of the band pass filter 5 is zero of the amplitude in the beat amplitude characteristic.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a wireless communication device used in wireless communication, particularly UHF band wireless communication, and particularly relates to a circuit for reducing the influence of urban noise on a wireless path. .

(Prior Art) In general, UHF band wireless communication is greatly affected by urban noise, such as car ignition noise, and it may be difficult to implement a line with wireless communication devices using digital modulation methods.

There are two broad categories of conventional methods for reducing the effects of urban noise. One is to increase the output on the transmitting side and improve the C/N, and the other is to narrow the receiving bandwidth.

[Problem to be solved by the invention] However, in the method of increasing the output on the transmitting side, 10 dB
If you want to improve the C/N of
This results in an increase of 0dB, compared to the IW output. It is necessary to change the scale of the device, such as requiring an output of 10W. In addition, in the method of narrowing the reception bandwidth,
In normal wireless communication equipment, the reception bandwidth has already been narrowed to its limit in order to increase channel division efficiency. Significant improvements cannot be expected, for example, in terms of receiving bandwidth in digital radio equipment. Band time rate (B
, T product) expression from 1.7 to 1.1, 20 log (1.1 / 1.7) = −
Only a C/N improvement of about 3.78 (dB) can be obtained.

The present invention is designed to significantly change the internal specifications of wireless devices, such as those mentioned above. Instead of an improvement method, a circuit is added to the human power section of the receiver to configure a circuit that removes urban noise components.In particular, compared to the conventional method of narrowing the reception band, the cancellation method is more effective. The purpose is to provide an urban noise removal circuit that can be expected to have significant improvement effects by adopting it.

[Means for Solving the Problems] The present invention transmits a received signal including a transmitted main signal to the same first signal.
, a branch circuit that branches to a second signal; a first bandpass filter that extracts a frequency band centered on the frequency of the main signal from the first signal; a second bandpass filter that extracts a frequency band near the main signal that does not include frequencies; and equal amplitude inverse synthesis of the output of the first bandpass filter and the output of the second bandpass filter; The present invention is characterized in that it includes a reverse phase synthesis circuit that removes noise from the received signal and outputs only the main signal.

(Function) The received signal is split into first and second signals, the first signal is input to the first filter that passes the frequency band of the main signal and the noise superimposed on it, and the second signal is input to the main signal. The signal is input to a second filter that passes nearby frequency bands that do not include the main signal.

At this time, by making the passband widths of the first filter and the second filter equal, the pulse response waveforms related to each noise become the same. Also. The noise that has passed through the first filter and the second filter has a certain frequency difference depending on the center frequency difference, but since they are originally responses from the same noise pulse, there is no phase uncertainty between the respective outputs. .

Therefore, for example, the noise fraction ω1 that has passed through the first filter
For example, when the noise component ω2 that has passed through the second filter is synthesized, a beat component with a certain period and a certain delay from the noise pulse is generated. Amplitude modulated noise waves are obtained.

That is, assuming equal amplitude and simultaneous combination, the combined wave is exp (iω, t) + exp (iω2t
)−exp (iω+t) +exp (iω
, t −iω, t+iω2 t) ””eXp(iω+ t) (1 +exp (
lω2 t-iω,t)) -Aexp (iω, t) Therefore, when ω2-ω, -Δω, the noise amplitude characteristic is IA I = l (1+exp (iω2t-i
cc＞+t) )=11+expiΔωt=I1+cosΔωt+i stnΔωt− J
l(1+cosΔωt) 2+sln2Δωt}−J
It shows a beat-like amplitude characteristic of (2+2 cos Δωt}. Therefore, Δωt - π
Under the condition of +2nπ (n-0.1.2.3...), the amplitude can be zero. Urban noise or equivalent pulsed noise can be removed by realizing this condition by reverse phase synthesis so that it is satisfied at the peak position of the signal that has passed the first filter.

(Example) Embodiments 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 of application to a small-capacity multiplex digital communication path in the UHF band, assuming a two-way communication line.

In this embodiment, an urban noise removal circuit 10 is inserted between the antenna 1 and the transceiver 13 using two circuit generators (CIR) 2.3.

The urban noise removal circuit 10 includes a branching circuit 4 that branches a received signal into two, and bandpass filters 5 and 6 that pass only signals of predetermined frequencies from among the branched received signals.
and an anti-phase synthesis circuit 7 for anti-phase synthesis of the output signals from the bandpass filters 5 and 6.

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

First, a main signal for communication and urban noise arrive from the antenna 1 in the figure, and are input to the urban noise removal circuit 10 via the CIR 2.

In the urban noise removal circuit 10, the inputted main signal and urban noise are divided into two by a branch circuit 4, and each is inputted to band pass filters 5 and 6. Here, the band pass filters 5.6 have different band center frequencies as shown in FIG. 2, but their pass band widths are the same. Further, here, the band center frequency of the band pass filter 5 is set to be the same as the band center frequency ω1 of the main signal, and its bandwidth is set to Δω3, which is sufficiently wider than the main signal bandwidth. Further, the band-pass filter 6 is a band-passing filter having a band center at a frequency ω2 that is offset from the band center frequency ω1 of the band-pass filter 5 by Δω, and a bandwidth ΔωB. At this time Δ
ω−ΔωB is the main signal bandwidth Δω. Make it bigger. That is, the bandpass filter 6 is configured not to pass the main signal. The main signal passes through the bandpass filter 5 and also passes through the next-stage negative phase synthesis circuit 8, and then reaches the wireless communication device 13 at CIR3. During this time, this circuit does not make any changes to the received signal. because. This is because the received signal band is outside the filter passing frequency of the bandpass filter 6, as shown in FIG.

Regarding the insertion loss in the branch circuit 4, it is necessary to estimate 3 dB in the worst case, but in the case where the frequency difference Δω in the branch circuit 4 is large and the pass band frequencies of the band pass filters 5 and 6 are not weighted. It is also possible to consider configurations such as the following, and it is also possible to create a circuit with even lower loss.

On the other hand, expanding the explanation of urban noise, the pulse noise that has passed through the band pass filter 5 exhibits a pulse response as shown in FIG. That is, the response wave is obtained in a form that is amplitude-modulated to the component of the center frequency ω1 of the bandpass 5, and its amplitude change. That is, the envelope line is determined by the band characteristics of the band pass filter 5. Similarly, a similar response can be obtained for pulse noise passing through the bandpass filter 6.

In other words, the ω2 component is modulated, and the shape of its envelope is exactly the same as that passed through the band-pass filter 5.

When the pulse response outputs of the bandpass filters 5 and 6 are combined in the next-stage negative phase synthesis circuit 7, the peak of the pulse response of the bandpass filter 5 (the peak of the envelope) is in the beat-like amplitude characteristic described above. , the point where the amplitude becomes zero, 1-(π+2nπ
)/Δω. Here, pulses are input to the bandpass filters 5 and 6 at the same time, and the responses of each bandpass filter are obtained. Therefore, assuming that the electrical lengths of the bandpass filters 5 and 6 are equal, each ω1 and ω2 in the response waveform are in phase. Therefore, in order to make the peak of the response waveform zero, the output of the bandpass filter 6 is set to 18
By combining through a 0'' phase shifter 9, anti-phase combination is realized.

Incidentally, in FIG. 1, a variable 1800 phase shifter is used in order to absorb irregularities in the electrical lengths of the bandpass filters 5.6 and other circuit imperfections.

Above, the concept of reversed phase synthesis has been explained with reference to Figures 1 to 3. Next, the pulse noise canceling ability will be explained using specific values for the UHF band frequency.

Here, we will discuss Examples 1.2 and 3 in which the bandpass of the bandpass filter 5.6, its detuning frequency, the duplexer bandband of the transmitter/receiver 10, and the main signal bandband are determined as shown in Table 1. state

Margin below Table 1 becomes.

Next, the waveform response after the noise enters the duplexer 14 of the transmitter/receiver 13 and passes through the bandpass filter (which has the same characteristics as the bandpass filter 5) in the duplexer 14 is calculated as shown in FIGS. This is shown by the solid line in Figure 7. When the response envelope waveform of the output 12 is calculated, the amount of suppression becomes the form shown in FIG. For comparison, Figure 4 shows the transient response from the time of the noise peak. Also, the amplitude 1
．． The response that is 0 is the response when reverse phase synthesis is not performed. The output 11 of the bandpass filter 5 is shown.

At this stage, noise amplitude suppression is evaluated. Especially here. It can be seen that a significant improvement effect can be obtained for communication channels where the main signal bandwidth is small and the influence of urban noise is large.

Note that the output of the bandpass filter 5 and the output of the anti-phase synthesis circuit are also shown in FIGS. 5 to 7.

As explained above, the present invention enables urban noise suppression of about 10 dB in the case of a small capacity digital multiplex radio device inserted between a radio device and an antenna.

Therefore, compared to methods such as increasing the transmission output. It is economical and there are no problems regarding radio wave administration.

Furthermore, communication channels near cities where urban noise is a problem often have short line distances, and if the transmission output is carelessly increased, there is a risk of receiver saturation. Since there is no change in level, it is also advantageous in line design.

(Effects of the Invention) According to the present invention, a branch circuit that branches a received signal into first and second signals, a first bandpass filter that passes the main signal of the first signal, and a second It is equipped with a second bandpass filter that blocks the main signal from passing through the signal, and an antiphase synthesis circuit that combines the outputs of the first and second bandpass filters with equal amplitude and inverse phase. It is possible to eliminate urban noise caused by noise.

2 is a diagram for explaining the characteristics of the bandpass filter shown in Fig. 1, Fig. 3 is a pulse response waveform of the bandpass filter shown in Fig. 1, and Fig. 4 is a diagram for explaining the characteristics of the bandpass filter shown in Fig. 1. Envelope waveforms showing the pulse noise response of a certain circuit, and FIGS. 5, 6, and 7 show the pulse noise responses of the bandpass filter of the duplexer shown in FIG. 1, respectively. 7 is an envelope waveform showing the case of Example 3.

1...Antenna, 2.3...Circulation evening, 4.
... Branch circuit, 5.6... Bandpass filter. 7...
・Negative phase combination circuit, 8... combination circuit, 9... variable type 1
80° phase shifter, 10... Urban noise removal circuit, 11...
・Band-pass filter 5 output, 12... Output of anti-phase combination circuit, 13... Transmitting/receiving device, 14... Transmitting/receiving duplexer band-pass filter, 15... Transmitting/receiving duplexer output.

[Brief explanation of drawings]

Fig. 1 shows an example of the urban noise removal circuit of the present invention. Fig. 6 shows an example of band-pass filter characteristics.
ω-tension 2: C ・8 X 1G 'Example 2 Fig. 7

Claims (1)

[Claims] 1. A branch circuit that branches a received signal including the transmitted main signal into the same first and second signals, and a branch circuit that extracts the same wave number band centered on the frequency of the main signal from the first signal. 1 band-pass filter, a second band-pass filter that extracts a frequency band near the main signal that does not include the frequency of the main signal from the second signal, and an output of the first band-pass filter and the An urban noise removal circuit comprising: an anti-phase synthesis circuit that performs equal-amplitude anti-phase synthesis with the output of a second band-pass filter, removes noise in the received signal, and outputs only the main signal.