JPH03932B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a method for removing unnecessary signals of the other party when wireless stations in close proximity to each other interfere with each other.
This relates to a signal-to-noise ratio improvement circuit.

When attempting to transmit information by placing it on a carrier wave,
There are often interfering signals around that carrier frequency. Mutual interference in mobile broadband radars and between two adjacent stations in spread spectrum mobile communication systems is an important problem in the use of spread spectrum. Conventionally, circuits for removing such interference waves include those using PLL (Phase-Lock-Loop) and those configured with filters.
It can only remove interference waves with a relatively narrow band. Also, a circuit that combines linear and nonlinear amplifiers has been proposed, but this circuit has the drawback that it is almost ineffective in removing interference waves when the input noise amplitude approaches the Lehre distribution.

The present invention is a type of device that effectively combines linear and nonlinear amplifiers, and aims to eliminate the above-mentioned drawbacks and provide an SN ratio improvement circuit that can effectively eliminate and suppress interference waves regardless of the input noise amplitude distribution. That is.

Embodiments of the SN ratio improvement circuit according to the present invention will be described below with reference to the drawings.

In Fig. 1, the information signal S(t) cos {ω ₀ t+θs
(t)} strong interference signal I(t)cos{ω ₀ t+θ _I (t)
}
The carrier wave information signal X containing a mixture of carrier wave information signals is input through an input terminal 1 to an envelope detection circuit 2, a limiter circuit 4, and a substantially linear amplifier 7 (which operates substantially as a linear amplifier). First, in the limiter circuit ₄ , the signal A signal D containing a substantially constant carrier wave is taken out. Further, the output A whose envelope has been detected by the envelope detection circuit 2 further passes through a low-pass filter 3, and the amplitude modulation circuit 6 (or multiplier) modulates the amplitude of the signal D using this output B. . At this time, low-pass filter 3
plays an important role in suppressing interference waves. The amplitude modulated output E and the substantially linear output F of the amplifier 7 are applied to a difference circuit 8, and a difference signal Z between the two signals is sent to an output terminal 9.
is output to.

Let us theoretically consider the circuit shown in FIG. 1 above. The input X in FIG _. 1 can be _expressed as _: At this time, the envelope detection circuit output A is A=√ ² () + ² () + 2 ()・(
) × {() − _I ()}……(2). Let us now consider a case where the interference signal is relatively large compared to the information signal. Therefore, S(t)≪I(t)...(3) holds true. In this case, equation (2) is approximately A≒I(t)+S(t) cos {θs(t)−θ _I (t)
}
...It can be expressed as (4). Here, as shown in Figure 2, the interference signal has an amplitude I(t) and a frequency band of S(t)cos{θs(t)-θ
_I
Consider a case where the frequency band is very small compared to the frequency band of (t)}. Such cases often occur when the information signal or interference signal is subjected to high-speed phase modulation or frequency modulation. In such a case, if the envelope detection signal A is passed through an appropriate low-pass filter 3, most of the component of the second term on the right side of equation (4) can be removed. At this time, output B can be approximately expressed as A≒i(t)...(5).

On the other hand, _the signal
The output D when extracting only the vicinity of is approximately expressed by the main component of the hard limiter output. becomes. Considering the conditions of equation (3), equation (6) approximately becomes D≒3/4 [cos {ω ₀ t+θ _I (t)}+S(t)/2I(
t)×cos {ω ₀ t+θs(t)}−S(t)/2I(t)×
cos {ω ₀ t＋2θ _I (t)−θs(t)}]
...(7) becomes. Output D is amplitude modulated by the output B signal. Therefore, the output E after modulation can be found by multiplying equation (5) by equation (7).

E≒3/4 [I(t)cos{ω ₀ t+θ _I (t)}+S(t
)/2×cos {ω ₀ t+θs(t)}−S(t)/2×cos
{ω ₀ t＋2θ _I (t)−θs
(t)}] ...(9) Final output Z obtained at output terminal 9 in Figure 1
is a difference signal between the output E and the signal F obtained by passing the input signal X through a substantially linear amplifier. At this time,
When the amplification degree of the nearly linear amplifier 7 is adjusted so as to remove the interference signal as much as possible, _the output Z becomes
(t)cos{ω ₀ t+2θ _I (t)−θs(t)} (10). Here, when calculating the signal-to-noise ratio (abbreviated as SIR) of input X and output Z, we find that the input SIR (=
Rin) is Rin=<S ² >/<I ² >. However, <> indicates the average value. Further, the SIR (=Rout) of the output Z becomes Rout=<S ² >/<S ² >=1 from equation (10). Therefore, the degree of improvement I in the input and output SIR is as follows: I=Rout/Rin=<I ² >/<S ² >, and the smaller the input SIR, the greater the improvement can be expected.

As explained above, according to the signal-to-noise ratio improvement circuit of the present invention, effective processing is performed by combining linear and non-linear amplifiers. It can remove unnecessary signals from the station.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the SN ratio improving circuit according to the present invention, and FIG. 2 is an explanatory diagram showing the characteristics of an envelope detection signal of an input signal. 1...Input terminal, 2...Envelope detection circuit, 3...
...Low pass filter, 4...Limiter circuit, 5...
...Bandpass filter, 6...Amplitude modulator, 7...
Almost linear amplifier, 8...differential circuit.

Claims (1)

[Claims] 1 A signal obtained by passing a carrier wave information signal containing interference waves through a limiter circuit and a harmonic removal filter is amplitude-modulated by the output of passing an envelope detection signal of the carrier wave information signal through a low-pass filter. , an SN ratio improvement circuit that outputs a difference signal between this amplitude modulated wave output and an output obtained by amplifying the carrier information signal with a nearly linear amplifier.