Multipath search processor for a spread spectrum multiple access communication system
First Claim
1. An integrated search processor receiving a signal comprised of a group of spread spectrum modulated call signals sharing a common frequency band, said integrated search processor comprising:
- a sample buffer for storing a limited number of data samples of said group of spread spectrum modulated call signals wherein each of said spread spectrum modulated call signals comprises a series of bits encoded in groups of a fixed length into a series of symbols having a transmission rate and wherein said data samples are stored at a rate corresponding to said transmission rate;
a PN sequence buffer for storing a limited number of PN sequence data chips wherein said PN sequence data chips correspond to a PN sequence used to modulate at least one call signal in said group of spread spectrum modulated call signals;
a despreader for correlating a portion of said data samples of said group of spread spectrum call signals stored in said sample buffer with a portion of said PN sequence data chips stored in said PN sequence buffer and for producing a correlated output corresponding to a single symbol; and
a transform engine for decoding said correlated output to produce an estimate of said series of bits wherein said transform engine decodes said correlated output at a rate higher than said transmission rate.
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Abstract
An integrated search processor used in a modem for a spread spectrum communications system buffers receive samples and utilizes a time sliced transform processor operating on successive offsets from the buffer. The search processor autonomously steps through a search as configured by a microprocessor specified search parameter set, which can include the group of antennas to search over, the starting offset and width of the search window to search over, and the number of Walsh symbols to accumulate results at each offset. The search processor calculates the correlation energy at each offset, and presents a summary report of the best paths found in the search to use for demodulation element reassignment. This reduces the searching process related workload of the microprocessor and also reduces the modem costs by allowing a complete channel element modem circuit to be produced in a single IC.
179 Citations
35 Claims
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1. An integrated search processor receiving a signal comprised of a group of spread spectrum modulated call signals sharing a common frequency band, said integrated search processor comprising:
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a sample buffer for storing a limited number of data samples of said group of spread spectrum modulated call signals wherein each of said spread spectrum modulated call signals comprises a series of bits encoded in groups of a fixed length into a series of symbols having a transmission rate and wherein said data samples are stored at a rate corresponding to said transmission rate;
a PN sequence buffer for storing a limited number of PN sequence data chips wherein said PN sequence data chips correspond to a PN sequence used to modulate at least one call signal in said group of spread spectrum modulated call signals;
a despreader for correlating a portion of said data samples of said group of spread spectrum call signals stored in said sample buffer with a portion of said PN sequence data chips stored in said PN sequence buffer and for producing a correlated output corresponding to a single symbol; and
a transform engine for decoding said correlated output to produce an estimate of said series of bits wherein said transform engine decodes said correlated output at a rate higher than said transmission rate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of receiving a signal comprised of a group of spread spectrum call signals sharing a common frequency band in a modem operating under control of a modem microprocessor, and isolating one of said call signals from among said group to determine a call signal strength at a path delay time offset from a zero offset reference time, said method comprising the steps of:
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storing PN sequence data bits in a FN sequence buffer;
storing a first received set of call signal samples in a sample buffer having a limited size;
despreading a first fixed length set of said call signal samples from said sample buffer corresponding to a first path delay time with a first set of PN sequence data bits from said PN sequence buffer to produce a first despread output;
storing a second received set of call signal samples in said sample buffer; and
despreading a second fixed length set of call signal samples from said sample buffer corresponding to a second path delay time with said first set of PN sequence data bits from said PN sequence buffer to produce a second despread output;
wherein said second fixed length set of call signal samples comprises a large number of the same call signal samples as said first fixed length set of call signal samples and wherein the length of said first and second received set of call signal samples is a fraction the fixed length of said first and second fixed length set of call signal samples. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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Specification