Telecommunications – Receiver or analog modulated signal frequency converter – With wave collector
Patent
1988-03-14
1990-01-09
Griffin, Robert L.
Telecommunications
Receiver or analog modulated signal frequency converter
With wave collector
342381, 455272, H04B 106
Patent
active
048933503
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an interference cancellation system which cancels undesired interference waves in the direction of side lobes of a receiver antenna.
BACKGROUND OF THE INVENTION
An interference cancellation system cancels undesired waves which are received by a high gain antenna positioned in the direction of a desired signal, by combining the desired signal with an undesired signal received by another antenna positioned in the direction of the undesired wave, the same amplitude and opposite phase.
FIG. 5 shows a prior interference cancellation system. In FIG. 5, an output signal of a main antenna (1) (which is called a main signal) is converted to an intermediate frequency signal by a local oscillator (5) and a mixer or a combiner (3). An output signal of an auxiliary antenna (2) which is called a reference signal is, after being converted to an intermediate frequency signal by a local oscillator (5) and a mixer (4), combined with a weighting signal w which is the output of a weight control circuit (8) in a variable complex weight circuit (7), so that a presumed signal of an undesired signal included in a main signal is provided. The numeral (6) is a combiner which functions to subtract the presumed undesired signal from the main signal. The output of the combiner (6) is the output of the interference cancellation system. The reference signal is multiplied with the output signal of the interference cancellation system in the multiplier (10). The numeral (9) is a low-pass filter, and the combination of the multiplier (10) and the low-pass filter (9) provides a correlation circuit. The output of the correlation circuit is applied to the variable complex weight circuit (7) through the weight control circuit (8) so that a correlation loop is provided. The correlation loop senses a residual component of an undesired signal included in the output signal.
DRAWBACKS OF A PRIOR ART
In the above structure, when both the desired signal and undesired signal are wideband signals, a mutual spectrum density function is spread over a wide frequency range. Further, since those signals are random signals, the average of a correlation value is not constant, but deviates. Therefore, a prior correlation circuit with a multiplier (10) and a low-pass filter (9) is not enough for providing an accurate correlation value, and an undesired signal is not sufficiently cancelled. This fact is the problem in a prior interference cancellation system.
SUBJECT OF THE INVENTION
An object of the present invention is to overcome the disadvantage of the prior art.
It is also an object of the present invention to provide an excellent interference cancellation system irrespective of the bandwidth and/or modulation system of a signal, by using the power of an output signal.
The important feature of the present invention is the use of a feedback loop which adjusts phase and amplitude of a reference signal so that the signal power contained in the desired signal band (which is called inband power) becomes minimum.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a first embodiment of the present invention,
FIG. 2 is a modification of the first embodiment,
FIG. 3 is a second embodiment of the present invention,
FIG. 4 is a third embodiment of the present invention, and
FIG. 5 is a block diagram of a prior interference cancellation system.
PREFERRED EMBODIMENTS OF THE INVENTION
The theoretical explanation of the present invention is summarized as follows. Assuming that d is a desired signal component, and i is an undesired signal component, and n is a noise component, a main signal x is expressed as follows. component n.sub.a. When the ratio i.sub.a
.sub.a in an auxiliary antenna is sufficiently large, y is expressed as follows. signal, and is the phase difference which relates to the difference in the propagation path length. An output signal z of the interference cancellation system is expressed as follows by using the above symbols. is expressed as follows. ]+E[.vertline.1-w.multidot.K.vertline.
REFERENCES:
patent: 3978483 (1976-08-01), Lewis et al.
patent: 4075633 (1978-02-01), Lewis
patent: 4742568 (1988-05-01), Furuya
Baba Noboru
Minamisono Kenichi
Watanbe Fumio
Yasunaga Masayuki
Griffin Robert L.
Kokusai Denshin Denwa Co. Ltd.
Kuntz Curtis
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