Synchronization preamble correlation detector and frequency estimator
First Claim
1. A synchronization preamble correlation detector for a spread spectrum receiver adapted to operate in the presence of frequency offsets in a received signal from a nominal signal frequency, comprising:
- means for providing reference synchronization (sync) preamble signal;
receiver means for providing the received sync preamble signal;
a plurality of subcorrelator circuits responsive to said reference preamble signal and said received preamble signal, each adapted to provide a subcorrelator signal indicative of the extent of matching between respective predetermined portions of said reference signal and said received signal; and
a plurality of frequency sensitive channels each respectively adapted to match a predetermined frequency offset subband, each channel comprising;
(i) means for providing predetermined phase corrections to said subcorrelator signals in dependence upon the frequency offset subband to which the respective channel is adapted to match so as to provide phase corrected subcorrelator signals; and
(ii) means for combining said phase corrected subcorrelator signals and providing a channel output signal.
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Accused Products
Abstract
A device is disclosed which simultaneously performs sync preamble correlation detection and frequency offset estimation functions for a spread spectrum receiver. The device performs a parallel frequency search, executed by a plurality of frequency sensitive circuit channels connected in parallel. These parallel circuit channels first apply phase corrections to the subcorrelator outputs and then linearly reintegrate the corrected outputs. In each channel the phase corrections applied to each successive subcorrelator output vary with the frequency offset subregions to which the channel is designed to match. By applying approximated phase corrections of 0°, 90°, 180° or 270° in lieu of the exact phase corrections required to remove the phase shift, the need for multiplication operations in the reintegration process is eliminated, as well as the need for storing large numbers of weighting coefficients. As a result, the reintegration process involves only addition and subtraction operations and the non-linear integration process is eliminated. The detector also establishes an estimate of the input signal frequency offset at the time of detection of the preamble correlation.
249 Citations
18 Claims
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1. A synchronization preamble correlation detector for a spread spectrum receiver adapted to operate in the presence of frequency offsets in a received signal from a nominal signal frequency, comprising:
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means for providing reference synchronization (sync) preamble signal; receiver means for providing the received sync preamble signal; a plurality of subcorrelator circuits responsive to said reference preamble signal and said received preamble signal, each adapted to provide a subcorrelator signal indicative of the extent of matching between respective predetermined portions of said reference signal and said received signal; and a plurality of frequency sensitive channels each respectively adapted to match a predetermined frequency offset subband, each channel comprising; (i) means for providing predetermined phase corrections to said subcorrelator signals in dependence upon the frequency offset subband to which the respective channel is adapted to match so as to provide phase corrected subcorrelator signals; and (ii) means for combining said phase corrected subcorrelator signals and providing a channel output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A synchronization preamble correlation detector for a spread spectrum radio frequency (RF) receiver, wherein the frequency offset of a received signal is within a frequency uncertainty bandwidth, comprising:
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means for providing a reference synchronization preamble signal; means for providing a received preamble signal; a number, N, of subcorrelator circuits, each responsive to said received signal and said reference signal and adapted to provide a subcorrelator signal indicative of the correlation between respective predetermined chips of said received signal and said reference signal; a number, k, of frequency sensitive channels responsive to said subcorrelator signals, each of said channels adapted to match a predetermined frequency region within said frequency uncertainty bandwidth and comprising; (i) means for providing successive predetermined phase shifts to said subcorrelator signals in dependence upon said frequency regions so as to provide phase corrected subcorrelator signal; and (ii) means for reintegrating said phase corrected subcorrelator signals and providing a channel output signal. - View Dependent Claims (9, 10, 11)
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12. A synchronization preamble correlation detector for a spread spectrum radio frequency (RF) receiver, wherein the frequency of a received signal is within a frequency uncertainty bandwidth, comprising:
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means for providing a reference synchronization (sync) preamble signal; means for providing a reference sync preamble signal; a number, N, of subcorrelator means, each responsive to said received signal and said reference signal and adapted to provide a subcorrelator signal indicative of the extent of correlation between respective predetermined portions of said reference signal and said received signal; a number, k, of frequency sensitive primary channels responsive to the subcorrelator output signals, each respectively adapted to match a predetermined frequency offset subband within the frequency uncertainty bandwidth, each channel comprising; first phase correction means responsive to the output signals of a first predetermined set of said subcorrelator means and adapted to provide predetermined phase corrections to said subcorrelator signals; second phase correction means responsive to the output signals of a second predetermined set of said subcorrelator means, and adapted to provide predetermined phase corrections to subcorrelator signals; first summing means adapted to sum the phase corrected outputs from said first set of subcorrelators and provide a first primary composite signal; second summing means adapted to sum the phase corrected outputs of said second set of subcorrelators and provide a second primary composite signal; and third summing means adapted to sum said first composite signal and said second composite signal and provide a primary channel output signal; and at least one frequency sensitive derivative channel adapted to match a predetermined frequency offset subband within the frequency uncertainty bandwidth, said derivative channel responsive to said first and said second composite signals of a predetermined one of said primary channels, said derivative channel comprising; a third phase correction means adapted to apply a phase correction to said first composite signal in dependence upon the frequency relation of the respective frequency offset subbands of said primary channel and the derivative channel; and fourth summing means for summing the phase corrected first composite signal and said second composite signal to provide a derivitive channel output signal. - View Dependent Claims (13, 14, 15, 16, 17)
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18. A synchronization preamble correlation detector and frequency estimator for a spread spectrum radio frequency (RF) receiver, wherein the frequency of the received signal is within a frequency uncertainty bandwidth, comprising:
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means for providing a reference synchronization (sync) preamble signal; means for providing a received sync preamble signal; a plurality of subcorrelator circuits responsive to said reference preamble signal and said received preamble signal, each adapted to provide a subcorrelator signal indicative of the extent of correlation between respective predetermined chips of said reference signal and said received signal; a plurality of frequency sensitive channels each respectively adapted to match a predetermined frequency offset subband within said frequency uncertainty bandwidth, each channel comprising; means for providing approximated predetermined phase corrections to said subcorrelator signals in dependence upon the frequency offset subband to which the respective channel is adapted to match, said means adapted to provide phase corrections of 0°
, 90°
, 180°
or 270°
in dependence upon which of these values is closest to the phase correction for exact phase compensation; andmeans for combining said phase corrected correlator signals and providing a channel output signal; and estimating means for estimating the frequency of signals received by said spread spectrum receiver, comprising means for determining that channel whose output is indicative of the highest correlation.
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Specification