Processor for a radio receiver
First Claim
1. A processor system for a radio receiver, the processor system being adapted to process Direct Sequence Spread Spectrum (DS-SS) signals, said processor system having a demodulator, the demodulator comprising of a digitiser for digitising a received signal at a predetermined sample rate, said received signal comprising of a sequence of chips arriving at the processor at a known rate;
- and at least one correlator for correlating the digitised signal with a known signal, the correlator being arranged to have one tap per chip;
the digitiser being arranged to take a plurality of samples of each chip, at differing points thereon as compared to the sample points on an adjacent chip, and to have a sample rate that is not an integer multiple of the chip rate;
wherein the processor further incorporates a chip-matched filter (CMF) arranged to filter the output of the digitiser, and a sample selection unit (SSU) arranged to receive outputs from the CMF and to select, for input to each tap of the correlator, the CMF output nearest in time to a desired ideal time in relation to a timing reference point on the chip.
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Accused Products
Abstract
A processor for a radio receiver is adapted to process direct sequence spread spectrum (DS-SS signals), and includes a demodulator, digitizer, correlator, and chip-matched filter (CMF) wherein the digitizer sample rate is selected to take a plurality of samples of each incoming chip at differing points thereon compared to sample points on an adjacent chip and to sample the chip at a non-integer multiple of the chip rate, wherein the CMF is arranged to filter the output of the digitizer. A sample selection unit is arranged to select a single sample from the CMF for input to each tap of the correlator, the selected sample being chosen as that nearest in time to a desired ideal time in relation to a timing reference point on the chip. An improved correlation function results, leading to better tracking performance.
10 Citations
14 Claims
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1. A processor system for a radio receiver, the processor system being adapted to process Direct Sequence Spread Spectrum (DS-SS) signals, said processor system having a demodulator, the demodulator comprising of a digitiser for digitising a received signal at a predetermined sample rate, said received signal comprising of a sequence of chips arriving at the processor at a known rate;
- and at least one correlator for correlating the digitised signal with a known signal, the correlator being arranged to have one tap per chip;
the digitiser being arranged to take a plurality of samples of each chip, at differing points thereon as compared to the sample points on an adjacent chip, and to have a sample rate that is not an integer multiple of the chip rate; wherein the processor further incorporates a chip-matched filter (CMF) arranged to filter the output of the digitiser, and a sample selection unit (SSU) arranged to receive outputs from the CMF and to select, for input to each tap of the correlator, the CMF output nearest in time to a desired ideal time in relation to a timing reference point on the chip. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
- and at least one correlator for correlating the digitised signal with a known signal, the correlator being arranged to have one tap per chip;
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13. A method of processing a direct sequence-spread spectrum (DS-SS) signal comprising a sequence of chips received in a receiver, said chips being received at a known rate, the method comprising the steps of:
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a) digitising the signal at a sample rate at least twice the chip rate, wherein the sample rate is a non-integer multiple of the chip rate, such that successive chips are sampled at different points thereon; b) filtering the samples with a chip-matched filter (CMF), wherein the chip matched filter is substantially matched to the expected chip shape, the CMF providing an output sample for each input sample; c) selecting a single output of the CMF for each chip for input to a correlator; d) correlating the inputs provided by selection step c) with a reference signal; wherein the single output from the CMF nearest to an ideal desired timing point for each chip is chosen for input to the correlator. - View Dependent Claims (14)
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Specification