Multi-stage CDMA synchronization with parallel execution
First Claim
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1. A synchronization method for synchronizing a receiver with a transmitted signal, comprising the steps of:
- selecting a frequency channel and receiving a signal;
filtering, amplifying and sampling the signal to generate signal samples for processing;
processing said samples using a first code to detect correlation with said first code;
upon detection of correlation with said first code, processing said same signal samples using a timing identified by said detected correlation and at least one second code to detect correlation with said at least one second code;
upon detection of correlation with said at least one second code, processing said same signal samples using a code related to said second code to decode transmitted information; and
testing for correct decoding of said information to verify correct synchronization.
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Abstract
Methods and systems for time synchronizing a receiver to a spread spectrum signal are described. Exemplary embodiments of the present invention provide for at least a two step process in which, at a first step, a number of candidate synchronization frequencies or timings are identified, followed by confirming one of the candidates as a correct synchronization state at a second or final step. According to the present invention, the confirmation step may be performed at the same time as the step of identifying further candidates by processing the same received signal samples in different ways.
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Citations
28 Claims
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1. A synchronization method for synchronizing a receiver with a transmitted signal, comprising the steps of:
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selecting a frequency channel and receiving a signal;
filtering, amplifying and sampling the signal to generate signal samples for processing;
processing said samples using a first code to detect correlation with said first code;
upon detection of correlation with said first code, processing said same signal samples using a timing identified by said detected correlation and at least one second code to detect correlation with said at least one second code;
upon detection of correlation with said at least one second code, processing said same signal samples using a code related to said second code to decode transmitted information; and
testing for correct decoding of said information to verify correct synchronization. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for synchronizing a receiver with a transmitted signal, comprising the steps of:
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selecting a frequency channel and receiving a signal;
filtering, amplifying and sampling the signal to generate signal samples for processing;
processing said samples using a first code to detect correlation with said first code; and
after detecting said correlation with said first code, continuing to process further signal samples to detect further correlations with said first code while processing said same further signal samples to detect a second code.
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22. A method for synchronizing a receiver with a transmitted signal comprising the steps of:
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sequentially tuning said receiver to successive frequency channels and measuring received signals strength on said channels;
forming said frequency channels into a first list for testing in a prioritized order;
tuning said receiver to the channel in said first list with highest priority and receiving a signal;
starting a timer to record time spent tuned to said channel and to compare the recorded time with a time-out value;
filtering, amplifying and sampling the received signal to generate signal samples for processing;
processing said signal samples using a first code to detect correlation with said first code;
upon detecting correlation with said first code, recording in a second list the timing position within said signal samples of each such detected correlation;
if said second list contains one or more entries, processing said signal samples to detect correlation with at least one second code at the corresponding recorded timing position; and
if said timer reaches said time-out value, retuning said receiver to the channel of next highest priority in said first list and resetting said timer.
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23. A receiver for detection of synchronisation with a transmitter, comprising:
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filtering, amplifying and conversion means for receiving signals and producing signal samples for processing;
correlation means for correlating said signal samples with a first code using time-shifts between said received signal samples and said first code and for correlating said same signal samples with at least one second code at specified time-shifts;
first detection means for detecting time shifts at which correlation with said first code exceeds a first threshold and recording said time-shifts in a first memory;
control means for specifying the time-shifts to said correlation means for performing correlations with said at least one second code based on the time-shifts recorded in said first memory;
second detection means for detecting when a correlation with said at least one second code specified by said control means exceeds a second threshold and for recording the associated at least one second code and time-shift in a second memory;
confirmation means for processing said same signal samples using a code based on said second code to decode information and performing a decoding error check; and
deletion means for deleting records from said second memory when said confirmation means indicates decoding error.
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24. A method of synchronizing a receiver with a transmitted signal, said transmitted signal comprising a first and second repeated coded pattern having a determined repetition period, comprising the steps of:
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selecting a frequency channel and receiving a signal;
filtering, amplifying and sampling the signal to generate signal samples for processing;
correlating said signal samples with said first coded pattern using different timing shifts in said repetition period between said first coded pattern and said signal samples to produce a first correlation value for each time shift;
accumulating correlation values that correspond to the same time shift in successive repetition periods in corresponding timing bins;
detecting when the cumulative value in one of said timing bins exceeds the value in another of said timing bins by more than a first threshold and recording the timing bin number in a first memory;
when said memory contains at least one timing bin number, correlating said same signal samples with said second repeated code pattern using timing shifts corresponding to said recorded timing bin numbers and producing corresponding second correlation values; and
accumulating said second correlation values in a number of second bins, each corresponding to an entry recorded in said first memory while continuing to accumulate said first correlation values in said timing bins.
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25. A method for transmitting a Code Division Multiple Access signal comprising the steps of:
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transmitting paging information having a repetitive frame structure on a given frequency using a first spread-spectrum access code, said paging information being used to address specific receivers;
transmitting traffic information to individual receivers on said same given frequency using one of a set of second spread spectrum access codes assigned to each receiver, said traffic transmissions overlapping in time with said paging information; and
periodically transmitting a narrowband signal having substantially narrower bandwidth than said traffic and paging transmissions with a periodicity related to said repetitive frame structure. - View Dependent Claims (26, 27)
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28. A method for time-synchronizing a receiver with a transmitted signal and determining a coarse frequency error estimate, comprising the steps of:
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computing correlations between received signal samples and known symbols included in said transmitted signal at periodic intervals, using several time-shifts between said received signal samples and said known symbols corresponding to early and late timing postulates;
combining successive correlations corresponding to the same timing postulate using a combining method with no frequency error compensation to obtain first cumulative correlations;
combining correlations made with successively later timing postulates using a combining method compensated for a receiver frequency that is relatively high compared to the transmitted signal frequency to obtain second cumulative correlations;
combining correlations made with successively earlier timing postulates using a combining method compensated for a receiver frequency that is relatively low compared to the transmitted signal frequency to obtain third cumulative correlations; and
determining the largest of said first, second and third correlations to determine a timing and a coarse frequency error estimate.
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Specification