Radio receiver
AssigneeGS IP Limited Liability Company
InventorsMorgan James Colmer, Martin John Brennan
Life of this patent
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Abstract
A radio receiver comprising: an antenna for receiving a radio frequency signal amplitude modulated with an audio frequency signal; a digitizer for periodically sampling the radio frequency signal and generating a digital reception signal representative of the amplitude of the radio frequency signal; and a demodulator for demodulating the digital reception signal to generate a representation of the audio frequency signal.
Claims42
A radio receiver, configured for operation in a radio system in which a plurality of radio channels are transmitted at frequencies spaced apart by a predetermined channel spacing, the radio receiver comprising:
- an antenna configured to receive a radio frequency signal amplitude modulated with an audio frequency signal;
- a digitiser configured to sample the radio frequency signal and to generate a digital reception signal representative of the amplitude of the radio frequency signal;
- a demodulator configured to demodulate the digital reception signal to generate a representation of the audio frequency signal, wherein the demodulator comprises a local oscillator configured to generate a first local oscillator signal at a reception frequency of the radio receiver, a first mixer configured to mix the first local oscillator signal with the digital reception signal to form a first demodulated signal, and a second mixer configured to mix a second local oscillator signal with the digital reception signal to form a second demodulated signal, wherein the second local oscillator signal is at the reception frequency of the radio receiver and having a quadrature phase relationship with the first local oscillator signal, wherein the demodulator further comprises a filter configured to filter the demodulated signals to thereby generate first and second filtered demodulated signals, the filter having a peak response in the region of the reception frequency of the radio receiver and having nulls in its response in a region of frequencies spaced apart from the reception frequency of the radio receiver by the predetermined channel spacing;
- and
- a beat cancellation device configured to form a beat-cancelled signal by processing the first filtered demodulated signal and/or and the second filtered demodulated signal to at least partially cancel from at least one of the first filtered demodulated signal and/or and the second filtered demodulated signal a beat frequency resulting from the mixing of the local oscillator signals with the digital reception signal,
- wherein the radio receiver is configured for operation in a radio system in which a plurality of radio channels are transmitted at frequencies spaced apart by a predetermined channel spacing, and the demodulator further comprises a filter configured to filter the first demodulated signal, the filter having a peak response in the region of the reception frequency of the receiver and having nulls in its response in a region of frequencies spaced apart from the reception frequency of the receiver by a channel spacing.
A radio receiver for operation in a radio system in which a plurality of radio channels are transmitted at frequencies spaced apart by a predetermined channel spacing, the radio receiver comprising:
- an antenna for receiving a radio frequency signal;
- a demodulator for demodulating a signal derived from the radio frequency signal to form a demodulated signal;
- and
- a filter for filtering the demodulated signal, the filter having a peak response in a region of a reception frequency and having nulls in its response in a region of frequencies spaced apart from the reception frequency by the predetermined channel spacing, and the filter being configured to decimate the demodulated signal in hardware, and being configured to filter the decimated signal in software at an audio sample rate.
A method for cancelling a beat frequency use in a radio receiver configured to receive a radio signal, forming a first demodulated signal by mixing a signal derived from the received radio signal with a first local oscillator signal, and forming a second demodulated signal by mixing the signal derived from the received radio signal with a second local oscillator signal having a quadrature relationship with the first local oscillator signal, the method comprising repeatedly performing:
- determining the modulus of the first demodulated signal;
- determining the modulus of the second demodulated signal;
- comparing the modulus of the first demodulated signal with the modulus of the second demodulated signal;
- determining a quotient by dividing the greater lesser of the moduli of the first demodulated signal and the second demodulated signal by the lesser greater of the moduli of the first demodulated signal and the second demodulated signal;
- determining a cancellation factor having the value of the reciprocal of the cosine of the arctangent of the quotient;
- and forming a beat-cancelled signal by multiplying one of the first and second demodulated signals by the cancellation factor.
A method for use in a radio receiver configured to receive a radio signal, the method comprising:
- forming a first demodulated signal by mixing a signal derived from the received radio signal with a first local oscillator signal;
- forming a second demodulated signal by mixing the signal derived from the received radio signal with a second local oscillator signal having a quadrature relationship with the first local oscillator signal;
- evaluating a trigonometrical relationship between signals derived from the first and second demodulated signals to determine a beat frequency;
- generating a correction factor from a trigonometric function of the determined beat frequency;
- and
- applying the correction factor to the first demodulated signal or the second demodulated signal to thereby cancel the beat frequency from the first demodulated signal or the second demodulated signal.
Dependencies are inferred from the claim text.