Method and apparatus for multipath parameter estimation in spread-spectrum communications systems
First Claim
1. A method of characterizing a secondary signal propagation path relative to a main signal propagation path, said method comprising:
- (a) receiving a first multipath signal that includes a main path signal received through said main signal propagation path and a secondary path signal through said secondary signal propagation path;
(b) comparing a magnitude of said secondary path signal with a magnitude of said main path signal to determine a relative magnitude of said secondary path signal to said main path signal;
(c) identifying corresponding symbols in said main and secondary path signals;
(d) comparing said corresponding symbols in said main path and secondary path signals to determine a relative time offset between said secondary path signal and said main path signal; and
(e) comparing corresponding symbols in said main and secondary path signals to determine a relative phase of said secondary path signal to said main path signal;
wherein said relative magnitude, time offset, and phase determined for said first multipath signal are used to improve reception performance for a subsequent multipath signal received through said main and secondary signal propagation paths.
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Abstract
A training method provides an advantageous technique for estimating secondary propagation path parameters based on learning propagation path characteristics for a selected number of secondary propagation path signals. In a multipath environment, a received radio signal comprises multiple received signals, each received through a different signal propagation path. The strongest multipath signal is deemed the main path signal, while the remaining multipath signals are termed secondary path signals. In some types of direct-sequence, spread spectrum communications systems, significant secondary signals must be canceled from the received multipath signal to achieve desired receiver performance, while in other types of systems, such secondary signals may be used to enhance the signal-to-noise ratio of the received signal. In either case, the various multipath signals must be accurately characterized. The training method includes a course search technique that yields initial identification of the significant secondary path signals, and further includes techniques for characterizing the magnitude, phase, and path delay, all relative to the main path signal for secondary path signal of interest. The training method employs differential decoding and sample phase slicing to improve parameter estimation accuracy, and further includes phase correlation operations to determine secondary path delay, where such delays may have delay spreads that exceed a transmitted signal symbol period.
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Citations
36 Claims
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1. A method of characterizing a secondary signal propagation path relative to a main signal propagation path, said method comprising:
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(a) receiving a first multipath signal that includes a main path signal received through said main signal propagation path and a secondary path signal through said secondary signal propagation path;
(b) comparing a magnitude of said secondary path signal with a magnitude of said main path signal to determine a relative magnitude of said secondary path signal to said main path signal;
(c) identifying corresponding symbols in said main and secondary path signals;
(d) comparing said corresponding symbols in said main path and secondary path signals to determine a relative time offset between said secondary path signal and said main path signal; and
(e) comparing corresponding symbols in said main and secondary path signals to determine a relative phase of said secondary path signal to said main path signal;
wherein said relative magnitude, time offset, and phase determined for said first multipath signal are used to improve reception performance for a subsequent multipath signal received through said main and secondary signal propagation paths. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
(a) generating a first sample of said subsequent multipath signal;
(b) offsetting said first sample of said subsequent multipath signal from a later sample of said subsequent multipath signal by said relative offset time, (c) applying said secondary path coefficient associated with said secondary path signal to said first sample; and
(d) subtracting said first sample from said later sample to substantially remove an effect of said secondary path signal in said subsequent multipath signal on said later sample.
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16. The method of claim 15 further comprising searching said first multipath signal to identify one or more additional secondary signals contained in said received multipath signal to identify associated one or more secondary signal propagation paths.
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17. The method of claim 16 further comprising:
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(a) determining said complex coefficients and said relative time offsets for a selected number of said one or more additional secondary path signals;
(b) generating a number of first samples of said subsequent multipath signal;
(c) offsetting said first samples of said subsequent multipath signal from a later sample of said subsequent received multipath signal by respective ones of said relative offset times;
(d) applying respective ones of said secondary path coefficients associated with said selected number of one or more additional secondary path signals to respective ones of said first samples; and
(e) subtracting said first samples from said later sample to substantially remove an effect of said selected number of one or more secondary path signals in said subsequent multipath signal on said later sample.
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18. A method of processing a received multipath signal that includes a main path signal and at least one secondary path signal, said method comprising:
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(a) while receiving a first portion of said received multipath signal;
(i) measuring signal magnitudes for two or more signals within said received multipath signal to identify a strongest signal as said main path signal, and at least one next-strongest signal as said at least one secondary path signal; and
(ii) calculating a relative magnitude, phase, and time offset for said at least one secondary path signal relative to said main path signal; and
(b) while receiving a second portion of said received multipath signal;
(i) generating at least one estimated secondary path signal corresponding to said at least one secondary path signal using said relative magnitude phase, and time offset; and
(ii) combining said at least one estimated secondary path signal with said received multipath signal to substantially cancel said at least one secondary path from said received multipath signal. - View Dependent Claims (19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A method of estimating propagation parameters for at least one secondary signal propagation path, said method comprising:
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receiving a first signal through multiple signal propagation paths, including a main propagation path and at least one secondary propagation path;
selectively despreading said first signal to identify a main and at least one secondary path signal associated with receiving said first signal through said main and at least one secondary signal propagation path;
comparing symbol sequence concurrently received in said main and at least one secondary path signals determine propagation path parameters for said at least one secondary signal propagation path relative to said main signal propagation path;
subsequently receiving a second signal through said main and at least one secondary signal propagation paths; and
applying said propagation path parameters to said second signal to substantially cancel an effect of a least one secondary signal associated with receiving said second signal through said at least one secondary signal propagation path.
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36. A system for compensating a received multipath signal comprising:
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a means for receiving a first multipath signal;
a means for identifying a strongest signal within said first multipath signal as a main propagation path signal corresponding to a main signal propagation path and identifying one or more next-strongest sills within said first multipath signal as one or more secondary propagation path signals corresponding to one or more secondary signal propagation paths;
a means for comparing a portion of said main propagation path signal to concurrent portions of each of said secondary propagation path signals to determine a relative phase, magnitude, and time offset for said secondary propagation path signals to said main propagation path signal;
a means for receiving a second multipath signal;
a means for creating secondary signal estimates for said second multipath signal corresponding to one or more secondary propagation path signals received through said one or more secondary signal propagation paths based on said relative phase, magnitude, and time offsets determined for said second propagation path signals in said first multipath signal; and
a means for subtracting said secondary signal estimates from said second multipath signal to substantially remove an effect of said one or more secondary path signals associated with said second multipath signal from said second multipath signal.
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Specification