Telecommunications – Receiver or analog modulated signal frequency converter – Noise or interference elimination
Reexamination Certificate
1999-12-13
2001-05-15
Chang, Vivian (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Noise or interference elimination
C455S212000, C455S225000
Reexamination Certificate
active
06233443
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to frequency modulated radio transmission of voice signals, and particularly to the reduction of interference when more than one signal is received within the same bandwidth.
2. Statement of the Prior Art
The interception of frequency modulated, FM, voice signals in the presence of similar Interfering or cochannel signals, has long been a perplexing and difficult problem to solve. This problem encompasses the reception, separation and demodulation of one or more voice signals when more than one signal is present within the same modulation bandwidth. The nature of cochannel interference between a plurality of signals varies temporally and chaotically depending upon the presence and content of each modulated signal. An apparatus for the separation and demodulation of such signals would benefit from the ability to adjust to this temporal variation.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method and apparatus for separating and demodulating one or more frequency modulated signals from a plurality of such signals present in an overlapping modulation bandwidth.
It is a further object of the present invention to provide such separation and demodulation in a temporal manner to compensate for signal variations.
In one form, the present invention provides a method for reducing interference between multiple frequency modulated, FM, voice transmissions present in the same frequency bandwidth, comprising the steps of receiving a radio signal which includes a first FM voice signal to be demodulated along with one or more additional FM voice signals which are present within a modulation bandwidth of the first FM voice signal, detecting the presence of a carder frequency signal of the first FM signal and determining a lack of modulation of the detected carrier frequency signal by a voice signal, and squelching the received signal when the carrier signal is unmodulated.
In another form, the present invention provides an apparatus for reducing interference between multiple frequency modulated, FM, voice transmissions present in the same frequency bandwidth, comprising means for receiving a radio signal which includes a first FM voice signal to be demodulated along with one or more additional FM voice signals which are present within a modulation bandwidth of the first FM voice signal, means for detecting the presence of a carrier frequency signal of the first FM signal, means for determining a lack of modulation of the detected carrier frequency signal by a voice signal, and means for squelching the received signal when the carder signal is unmodulated.
In yet another form, the present invention provides an apparatus and method for determining the relative strength of a first frequency modulated, FM, signal having a carrier frequency signal and located within a transmission bandwidth in which one or more other FM signals are also present, comprising receiving transmission energy within the transmission bandwidth, demodulating the received transmission energy to an intermediate frequency signal, digitizing the intermediate frequency signal, digitally demodulating the intermediate frequency signal to a baseband signal, digitally measuring the power level of the baseband signal, digitally filtering the baseband signal to separate the carrier frequency signal of the first FM signal, digitally measuring the power of the separated carrier frequency signal, and comparing the measured power of the carrier frequency signal to the measured power of the baseband signal.
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Bhattacharya Sam
Chang Vivian
Kirkpatrick & Lockhart LLP
Transcept, Inc.
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