JPH01276827A - Random fm noise decreasing circuit - Google Patents

Abstract

PURPOSE:To decrease the influence of a random FM noise and to attain a high quality signal transmission by executing the product of a signal obtained through a delay compensating circuit and a signal to frequency-modulate a base band signal. CONSTITUTION:A carrier component is extracted by two-multiplying the frequency of a receiving signal by a multiplier 11. The output of the multiplier 11 is inputted to a band pass filter 12 in which a passband characteristic is a narrow band. After a base band signal obtained as the detection output of a frequency detector 13 passes through a coefficient multiplier 14, the signal is inputted to a frequency modulator 15 and a frequency modulation is executed. The product is executed for the output of the frequency modulator 15 and the output of a delay compensator 16 in a mixer 17, and after the outputs pass through a band pass filter 18, they are outputted to an output terminal 19. Thus, even when a quick phase fluctuation due to fading exists, a satisfactory detection characteristic can be obtained and a high quality radio signal transmission line can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for receiving and detecting digital signals used in mobile communications and the like.

[Conventional technology]

In a mobile communication system composed of a radio base station and a mobile station, deterioration of transmission quality occurs due to 7-anong caused by multiple propagation of radio waves.

The causes of transmission quality deterioration are: - A drop in the reception level; - A sudden phase change occurs even though the reception level is sufficiently high; and - Multiple signals with different propagation times are received. It can be roughly divided into three types depending on the situation.

Among these, the noise caused by sudden phase changes in ■ is called random FM noise, and along with the noise caused by receiving multiple signals with different propagation times in ■, it is a cause of errors in signal transmission. It becomes.

Diperity reception technology is one of the mitigation measures for such 7-acing, and it has been shown to be effective against (2) caused by a decrease in reception level and (2) random FM noise.

However, even with the above-mentioned diversity reception, the influence cannot be completely removed.

In contrast, conventionally, two carrier waves with different frequencies are prepared, only the first carrier wave is modulated, and the second carrier wave is simultaneously transmitted, and the receiving side uses the second carrier wave to generate random FMi sound. There is a way to reduce the
It is known as the uncl method (Reference ``J, G
ranlund.

'Topics in the design of
antenna for 5 cat-ter”,
Tech, Rep, Lincoln Labor
atoryMIT, Nov. 1956 J).

However, no method has been disclosed for reducing Hunghum FM noise without using a second carrier.

[Problem to be solved by the invention]

Dinotal phase change I$1! The signal is demodulated using phase detection methods such as synchronous detection and delayed detection.

In this case, especially when synchronous detection is used as the demodulation method, errors that are difficult to reduce occur because the phase of the recovered carrier wave cannot follow the rapid phase changes caused by aging, which poses a problem in terms of achieving high-quality transmission. there were.

Random FM2 below! A case will be described in which synchronous detection of the influence of sound is performed.

Figure tIS2 is a block diagram showing an example of a synchronous detection circuit, and shows a case where carrier wave recovery is added using a Costas loop.

The operation of the synchronous detection circuit 13 will be described below.

The received signal input to the detector input terminal 21 is input to the hybrid 22 , the 0 component of the output thereof is guided to the multiplier f, and the x/2 component is guided to the multiplier 25 . VCO(
Voltage Cot+Lrolled 0s-ci
The output of the llator) 30 is divided into two parts, one of which is input to the multiplier 23 and the other to the 71 unit 25 via the phase shifter 24, and the product of each is multiplied by the hybrid output signal. The output signal of the phase shifter 24 has a phase difference of π from the input signal.
/2. The outputs of the multiplier 23 and the multiplier 25 pass through the low-pass filters 26 and 27, respectively, and after removing the frequency component twice the carrier frequency, the outputs are sent to the in-phase component output terminal 31 and the quadrature component output terminal 3, respectively.
The detection signal is output to 2.

Further, the outputs of the low-pass filters 26 and 27 are multiplied by a multiplier 28. The output of the multiplier 28 passes through a loop filter 29 and is input as a DC voltage to the frequency control terminal of the VCO 30.

Next, the principle of synchronous detection will be explained using mathematical formulas.

The received signal applied to the detector input terminal 21 is "(t) r(t)" R(t) cos (ω is 1φ, (t) 10(t))... (1) put.

Here, R(t) is the amplitude of the received signal, ω is the carrier wave angular frequency, and φ, (t) is the phase component due to modulation. Also, θ
(1) is a phase based on 7 asons, which varies randomly in the ray IJ-7 asons received by the received signal via the moving propagation path. At this time, the multiplier fL unit 23 and c
/25 input r+(t) and rib) are respectively rl(t)=r(tl r2(t)=R(t) 5in(cm L+φ,
(shi)+θ(L)]...(2) The output of the VCO is given by the following equation.

u(t)=U(L)cosn(ωt+ψ(t)
) -------(3) U(t) rise ψ(1) are amplitude and phase, respectively. This time, multiplier 2
The inputs ul(t) and 2(1) of 3 and 25 are respectively u+(t)=U(t) u,(t)=U(t) 5in(ω + ψ(t)
) −・−・・−(4) is given.

Therefore, the outputs of the in-phase component output terminal 31 and the quadrature component output terminal 32 are respectively d+(t)=D+(t) cos (φm(t
) 10 〇 (t:)−φ (L))do(t)” D
g(t) sin(φM(t)+θ(1)−ψ(t))]・
...(5) It becomes.

In addition, by using the detection output of equation 1 (5) that controls the oscillation frequency of the VCO to be kept constant using the DC signal voltage obtained by passing the output of the Ml generator 28 through the loop filter 29, clock regeneration is possible. Then, a demodulated signal can be obtained by performing code identification.

By the way, in equation (5), unless θ(t)=ψ(L), the demodulation characteristics will deteriorate. In this method, the frequency of the recovered carrier wave is kept constant, but because a loop filter is inserted, the phase φ(1) of the recovered carrier wave cannot follow the phase fluctuation θ(1) due to 7 aging. Under this condition, an error that is difficult to reduce occurs in a region where the received input voltage is large, and the magnitude of the error is more than an order of magnitude larger than that of frequency detection, although it depends on the constant of the loop filter (
Literature “K, D&1koku et al, w”
High-speed digital tran
mission experiments i
n 9 2 0 MHz urban an
d suburban mobile radio
channels, IEEE Tra
ns.

Vehic, Technol, e VT-31w
pp. 70-75, May 1982 J).

In view of these conventional problems, the present invention theoretically reduces the influence of the random FM noise on the receiving side,
The purpose is to provide a method for high quality signal transmission.

[Means to solve the problem]

According to the invention, the above object is achieved by the means described in the claims.

That is, the present invention obtains a signal from which a modulated phase component is removed by multiplying or multiplying the received signal in a dinotal phase modulation signal receiving section, and extracts the signal from the signal using a bandpass filter and converts the frequency The baseband signal obtained by the detection is made into a signal with a magnitude that is a reciprocal of the multiplication number, and the baseband signal is subjected to frequency modulation using the signal to obtain a frequency modulated signal, and the received signal is passed through the bandpass filter. This is a random FM noise reduction circuit that multiplies the frequency modulation signal and a signal obtained through a delay compensation circuit having delay characteristics equivalent to those caused by frequency detection and frequency modulation.

[For production]

Using the characteristics of the digital phase signal itself, 7
A carrier wave component including phase fluctuation is extracted from the modulated signal that has received the Ason, and the extracted signal is frequency-detected.The resulting signal is further subjected to frequency modulation, and the received signal is multiplied by the received signal. A signal is obtained by removing seven aging-induced fluctuation components from the phase term of the modulated signal.

〔Example〕

PIS1 diagram is a block diagram showing one embodiment of the present invention, and is a block diagram showing an embodiment of the present invention.
s shift keying) signal is demodulated.

In the figure, the received signal input to the input terminal 10 is 2
and is input to the upstream delay compensation circuit 16 of the transmitter 11. The multiplier 11 extracts the carrier wave component by doubling the frequency of the received signal. The output of the multiplier 11 is input to a bandpass filter 12 having a narrow passband characteristic.

The output of the bandpass filter 12 is input to the frequency detector 13 and detected.The baseband signal obtained as the detection output of the frequency detector 13 is input to the frequency modulator 15 after passing through the coefficient unit 14 and is frequency modulated. The output of the zero frequency modulator 15 and the output of the delay compensator 16 are sent to the mixer 17.
After being multiplied by the odor and passing through the bandpass filter 18,
The signal is output to the output terminal 19 thereof. 16 is the delay characteristic of the bandpass filter 12, the frequency detector 13, and the coefficient unit 14.
, which is a circuit that compensates for the delay in the frequency modulator 15.

Note that it is also possible to use a mixer instead of the frequency doubler and take the product of the received signal itself.

Next, the operation shown in FIG. 1 will be explained using mathematical formulas.

When the received signal is expressed by equation (1), by passing the output of the multiplier 11 through the bandpass filter 12, w+(t)=R''(t) cos(2ωt+2φ5(
t)+20(t)]...(6) A signal is obtained. Here, in BPSK, 0 (mark) φ lI (shi) =
...... (7) Since π (space), equation (6) can be expressed as 豐+(t)"R"(L)cos(2ωt+2θ(
0]...(8) It is assumed that the passband width of No. 12 is narrow enough to allow the carrier wave component to pass with a center angular frequency of 2ω.

When formula (8) is detected by a frequency detector with a center frequency of 2ω, w(L) = (1/2π) d(2θ(t) )/dt・
...(9) A detected signal is obtained. Here, dx/clt is frequency modulated using a signal obtained by multiplying Equation (9) representing the time differential of X by k using the coefficient multiplier 14, and then u(L)=U(t
) cos (ωLt+2 kr f m(L)dt ψL(t) ) ・・・・・・ (10)
The fH number is obtained. Here, ω is the carrier wave angular frequency and ψ1(t) is the phase given by the carrier wave oscillator.

The mixer 17 converts the signals given by equations (10) and (1) into JTi! When multiplied, v(L) = V (t) cos ((ω+ωL> t
+φm(t) 10(t)+ 2 kπf■(t)dt+
ψL(t) )+cos((ω−ωL) t+φ−(1
) 10(1)-2kff f 5i(t)dt-ψL(
t) )...(11) By passing the signal given by equation (11) through a bandpass filter with a center angular frequency ω-ω, the following signal is obtained: v(t)-V (t) cos ((ω −ωL)
t+-1(1) 10 〇 (t)-2krfso(t)a
t −ψ+−(1))・・・・・・(12) Obtain the signal. Here, the coefficient of the coefficient multiplier is set to = 1/2, and θ (t) = 2 is given by f(t(t)/2)dt
Using the relationship, Equation (12) becomes %Equation %(1). Equation (13) includes the phase term ψL(t) of the oscillator, which fluctuates gradually over time, as a phase term other than the modulation component.
is included, but the rapidly changing phase term θ(1) due to aging is not included.

Therefore, by performing detection on the output of 18, a detected output signal having good detection characteristics can be obtained.

It is easily shown that the present invention is also applicable to multilevel dinotal phase-modulated signals such as QPSK.
In PSK, the frequency can be multiplied by 4 using the multiplier shown in FIG. 1, and the carrier frequency component can be extracted.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to obtain good detection characteristics even when there is a rapid phase fluctuation due to aging, and there is an advantage that a high quality radio signal transmission path can be realized.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of the configuration of a synchronous detection circuit. 10...Input terminal, 11...
Multiplier, 12, 18...Band pass filter, 13...Frequency detector, 1
4...Coefficient unit, 15...Frequency modulator, 16...Delay compensator,
17 ・・・・・・ Mixer, 21 ・・・・・・
Detector input terminal, 22...Hybrid, 23, 25, 28...
・ Multiplier, 24 ... Phase shifter,
26. 27 ・・・・・・ Low pass filter, 29
...Loop filter, 30 ...
・・vCO131・・・・Common mode component output terminal,
32... Orthogonal component output terminal,
33...In-phase detection circuit

Claims (1)

[Claims] In the receiving section of the digital phase modulation signal, a signal from which the modulated phase component is removed is obtained by multiplying or multiplying the received signal, and a signal extracted from the signal by a bandpass filter is frequency-detected. The baseband signal is a signal having a magnitude that is a reciprocal of the multiplication number, frequency modulation is performed on the baseband signal using the signal to obtain a frequency modulation signal, and the received signal is subjected to frequency detection based on the delay characteristics of the bandpass filter. A random FM noise reduction circuit characterized in that a signal obtained through a delay compensation circuit having a delay characteristic equivalent to a delay characteristic caused by frequency modulation is multiplied by the frequency modulated signal.