Frequency Reference Compensation
First Claim
1. A frequency reference compensation system, comprising:
- a downconverter for mixing a received signal with a local oscillator signal to provide a downconverted signal, the downconverted signal being output from said downconverter;
a demodulator interfaced with said downconverter for determining a frequency offset between a frequency of said downconverted signal and a predetermined frequency of the downconverted signal, said demodulator providing a frequency control signal representative of said frequency offset;
an accumulator coupled to said demodulator for accepting each said frequency offset so determined and accumulating values indicative of said frequency offsets;
a comparator coupled to said accumulator for comparing said accumulated values to a predefined threshold and following a complete reception of said received signal adjusting said frequency control signal to define an adjusted frequency control signal based on said comparison;
a voltage controlled oscillator interfaced with said comparator for accepting said adjusted frequency control signal and for generating a reference signal having a reference frequency based on said frequency offset; and
a frequency synthesizer coupled to said voltage controlled oscillator and having an input of said reference signal and generating said local oscillator signal based on said reference frequency thereby adjusting said frequency of said downconverted signal to minimize the frequency offset.
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Accused Products
Abstract
The present invention provides a frequency tracking and compensation system and methods for minimizing the frequency offset between remote and local units of a communications system. The system of the present invention resides in the local unit and comprises a downconverter, a digital transceiver, a processor, a reference oscillator and a frequency synthesizer. The downconverter mixes a signal received from the remote unit with a local oscillator (LO) signal generated by the frequency synthesizer. The frequency of the LO signal is based on the frequency of a reference signal generated by the reference oscillator. The system of the present invention utilizes the digital transceiver to determine a frequency offset of the received signal without comparing the received signal to the reference signal. The processor then utilizes the frequency offset to adjust the frequency of the reference signal. The method of the present invention accumulates the frequency offsets and compares the accumulated offset to a predetermined threshold. The reference frequency is adjusted if the accumulated offset exceeds the threshold. In one embodiment, the reference frequency is adjusted after complete reception of each call.
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Citations
18 Claims
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1. A frequency reference compensation system, comprising:
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a downconverter for mixing a received signal with a local oscillator signal to provide a downconverted signal, the downconverted signal being output from said downconverter; a demodulator interfaced with said downconverter for determining a frequency offset between a frequency of said downconverted signal and a predetermined frequency of the downconverted signal, said demodulator providing a frequency control signal representative of said frequency offset; an accumulator coupled to said demodulator for accepting each said frequency offset so determined and accumulating values indicative of said frequency offsets; a comparator coupled to said accumulator for comparing said accumulated values to a predefined threshold and following a complete reception of said received signal adjusting said frequency control signal to define an adjusted frequency control signal based on said comparison; a voltage controlled oscillator interfaced with said comparator for accepting said adjusted frequency control signal and for generating a reference signal having a reference frequency based on said frequency offset; and a frequency synthesizer coupled to said voltage controlled oscillator and having an input of said reference signal and generating said local oscillator signal based on said reference frequency thereby adjusting said frequency of said downconverted signal to minimize the frequency offset. - View Dependent Claims (2, 3, 4, 5, 11)
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6. In a communications system having at least one remote unit and at least one local unit which transmit signals therebetween in the form of calls, a method of adjusting a frequency of a reference signal of said at least one local unit to track a frequency of a signal being transmitted from said at least one remote unit, said signal so transmitted defining a remote signal, comprising the steps of:
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generating a local oscillator signal based on said reference signal; mixing said remote signal with said local oscillator signal to produce a downconverted signal; determining, upon the completion of each call, a frequency offset defining a difference between a frequency of said downconverted signal and a predetermined frequency of said downconverted signal; and adjusting the frequency of said reference signal after any said call, but not during any said call, based on said frequency offset to minimize said frequency offset thereby eliminating signal distortion of the downconverted signal when the frequency of said reference signal is so adjusted. - View Dependent Claims (7, 8, 9)
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10. The method of claim 10, wherein said predetermined threshold being based upon an expected frequency of said calls.
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12. A method of minimizing frequency offset between a remote unit and a local unit wherein a number of transmissions between said remote and local units define a call, comprising the steps of:
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transmitting a signal from said remote unit to said local unit such that said local unit receives said transmitted signal, said transmitted signal having a predetermined operating frequency; determining, upon the completion of each call, a frequency offset indicative of a difference between said predetermined operating frequency and a frequency of said transmitted signal as received by said local unit; and adjusting, upon the completion of each call, the frequency of a local reference signal generated by said local unit based on said frequency offset to minimize said frequency offset thereby eliminating signal distortion of said transmitted signal while said transmitted signal is being received by said local unit. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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Specification