Pulse or digital communications – Receivers – Interference or noise reduction
Patent
1994-02-01
1998-01-20
Chin, Wellington
Pulse or digital communications
Receivers
Interference or noise reduction
375346, 455295, 455296, 341118, H04B 110
Patent
active
057107998
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention generally relates to cross polarization interference cancelers and cross polarization interference eliminating apparatuses using the same, and more particularly to a cross polarization interference canceler which mutually cancels interference of one channel with respect to another channel in a system such as a radio communication system which forms two channels in parallel using carriers which have the same frequency but have mutually orthogonal planes of polarization, and to a cross polarization interference eliminating apparatus which uses such a cross polarization interference canceler.
BACKGROUND ART
An orthogonal polarization sharing system which forms two channels (co-channels) with suppressed interference by making two carriers having the same frequency have mutually orthogonal planes of polarization is an advantageous system from the point of view of effectively utilizing the radio frequency, and is thus employed in transmission apparatuses such as digital multiplexed wireless installations. In such a transmission apparatus, a deviation is introduced in the plane of polarization due to a distortion of a propagation path caused by rain or the like, and each channel receives the interference from the other channel. Hence, a cross polarization interference canceler is provided at a receiving end to suppress such interference.
FIG. 1 shows an example of the construction of a receiver part of a transmission apparatus which uses the orthogonal polarization sharing system. In FIG. 1, a receiving antenna 91 is connected to an input of a polarization branching filter 92, and one output of the polarization branching filter 92 is connected to an input of a demodulator 94.sub.1 via a frequency converter 93.sub.1. One output of the demodulator 94.sub.1 supplies a first demodulated signal to a latter stage via a cross polarization interference canceler 95.sub.1. The other output of the polarization branching filter 92 is connected to an input of a demodulator 94.sub.2 via a frequency converter 93.sub.2, and one output of the demodulator 94.sub.2 supplies a second demodulated signal to a latter stage via a cross polarization interference canceler 95.sub.2. The other output of the demodulator 94.sub.1 is connected to the other input of the demodulator 94.sub.2, and the other output of the demodulator 94.sub.2 is connected to the other input of the demodulator 94.sub.1. Various signals related to the suppression of the interference described above are exchanged between the demodulator 94.sub.1 and the cross polarization interference canceler 95.sub.1 and between the demodulator 94.sub.2 and the cross polarization interference canceler 95.sub.2. The demodulators 94.sub.1 and 94.sub.2 have the same construction, and the cross polarization interference cancelers 95.sub.1 and 95.sub.2 have the same construction.
FIG. 2 shows the construction of the cross polarization interference canceler and the demodulator. In the demodulator 94.sub.1 (94.sub.2), an intermediate frequency signal from the frequency converter 93.sub.1 (93.sub.2) is applied to an input of a hybrid 102 via an AGC amplifier 101. A first output of the hybrid 102 is connected to one input of a multiplier 103.sub.1, and a second output of the hybrid 102 is connected to one input of a multiplier 103.sub.2. An output of the multiplier 103.sub.1 is connected to an input of an analog-to-digital (A/D) converter 106.sub. 1 via a lowpass filter 104.sub.1 and an AGC amplifier 105.sub.1, to an output of an amplifier 107.sub.1, and to a first differing polarization output terminal. An output of the multiplier 103.sub.2 is connected to an input of an analog-to-digital (A/D) converter 106.sub.2 via a lowpass filter 104.sub.2 and an AGC amplifier 105.sub.2, to an output of an amplifier 107.sub.2, and to a second differing polarization output terminal. A third output of the hybrid 102 is connected to an input of a hybrid 108, and first and second outputs of the hybrid 108 are respectively connected to inputs of a multiplier 109. A
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Chin Wellington
Fujitsu Limited
Shankar Vijay
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