Method and apparatus for fast acquisition and multipath search in a spread spectrum system
First Claim
1. A method for searching for a direct sequence spread spectrum (DS-SS) signal, said method comprising the steps of:
- (a) receiving a first signal, said first signal spread by at least a PN code sequence having a chip period;
(b) generating a second signal from said first signal, said second signal being a digital signal;
(c) generating a third signal from said first signal, said third signal being a digital signal spaced a predetermined portion of said chip period in phase from said second signal;
(d) generating said PN code sequence at a first phase;
(e) defining a correlation period and dividing each of said second and third signals into a first and second plurality of N subdwells, respectively, within said correlation period, wherein the N subdwells included in each of said first and second plurality of N subdwells are sequential in time, and wherein an xth subdwell of said first plurality of N subdwells, and an xth subdwell of said second plurality of N subdwells are substantially concurrent in time;
(f) correlating said second signal with at least said PN code sequence at said first phase over a zth subdwell of said first plurality of N subdwells to generate a first phase correlation result for the zth subdwell of said first plurality of N subdwells;
(g) correlating said third signal with at least said PN code sequence at said first phase over a (z+1 )th subdwell of said second plurality of N subdwells to generate a first phase correlation result for the (z+1 )th subdwell of said second plurality of subdwells;
(h) repeating steps f and g, increasing the value of z by at least 2 for each repetition of both steps and storing the first phase correlation result for each repetition of steps f and g, until the end of said correlation period has been reached; and
(i) generating a detection statistic for said PN code sequence at said first phase from the first phase correlation results of steps f, g, and h.
1 Assignment
0 Petitions
Accused Products
Abstract
Early and on-time signals are generated from a received CDMA signal for each PN code phase being searched, and the early and on-time signals are each divided into a number of subdwells sequentially in time. A correlation is then performed for each PN code phase search, on subdwells of the early and on-time signals for that PN code phase in a staggered manner in time, by alternating the correlation between the early and on-time signals during each sequential subdwell correlation. A detection statistic for the PN code phase is then generated from the correlation result. In an embodiment of the invention, two PN code phases are searched simultaneously by staggering the subdwell correlations in an alternate fashion between the early and on-time signals, so that each PN code phase uses a different set of subdwell correlations. In an alternative embodiment, a single PN code phase is searched by alternating the correlation between the early and on-time signals during each sequential subdwell correlation.
19 Citations
24 Claims
-
1. A method for searching for a direct sequence spread spectrum (DS-SS) signal, said method comprising the steps of:
-
(a) receiving a first signal, said first signal spread by at least a PN code sequence having a chip period; (b) generating a second signal from said first signal, said second signal being a digital signal; (c) generating a third signal from said first signal, said third signal being a digital signal spaced a predetermined portion of said chip period in phase from said second signal; (d) generating said PN code sequence at a first phase; (e) defining a correlation period and dividing each of said second and third signals into a first and second plurality of N subdwells, respectively, within said correlation period, wherein the N subdwells included in each of said first and second plurality of N subdwells are sequential in time, and wherein an xth subdwell of said first plurality of N subdwells, and an xth subdwell of said second plurality of N subdwells are substantially concurrent in time; (f) correlating said second signal with at least said PN code sequence at said first phase over a zth subdwell of said first plurality of N subdwells to generate a first phase correlation result for the zth subdwell of said first plurality of N subdwells; (g) correlating said third signal with at least said PN code sequence at said first phase over a (z+1 )th subdwell of said second plurality of N subdwells to generate a first phase correlation result for the (z+1 )th subdwell of said second plurality of subdwells; (h) repeating steps f and g, increasing the value of z by at least 2 for each repetition of both steps and storing the first phase correlation result for each repetition of steps f and g, until the end of said correlation period has been reached; and (i) generating a detection statistic for said PN code sequence at said first phase from the first phase correlation results of steps f, g, and h. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
-
-
13. An apparatus for searching for a CDMA signal, said apparatus comprising:
-
a receiver for receiving a first signal, said first signal spread by a PN code sequence having a chip period; a converter for converting said first signal into a second and a third signal, said second and third signals being digital signals spaced a predetermined portion of said chip period apart in phase; a PN code generator for generating said PN code sequence at a first phase; first control circuitry for defining a correlation period and dividing each of said second and third signals into a first and second plurality of N subdwells, respectively, within said correlation period, wherein the N subdwells included in each of said first and second plurality of N subdwells are sequential in time, and wherein the xth subdwell of said first plurality and the xth subdwell of said second plurality are substantially concurrent in time;
a correlator for correlating said second signal by at least said PN code sequence at said first phase over the zth subdwell of said first plurality of N subdwells to generate a first phase correlation result for the zth subdwell of said first plurality of subdwells, and further for correlating said third signal by at least said PN code sequence at said first phase over the (z+1)th subdwell of said second plurality of subdwells to generate a first phase correlation result for the (z+1)th subdwell of said second plurality of subdwells;second control circuitry for causing said correlator to generate said first phase correlation result for the zth subdwell of said first plurality of N subdwells and the (z+1)th subdwell of said second plurality of N subdwells, for incrementing the value of z by at least 2, and for repeating the correlation of the zth subdwell of said first plurality of N subdwells and the (z+1)th subdwell of said second plurality of N subdwells until the end of said correlation period is reached; a memory device for storing the first phase correlation results generated for each correlation performed in said correlator; and third control circuitry for generating a detection statistic for said PN code sequence at said first phase, from the first phase correlation results stored in said memory device, when said multiplier has reached the end of said correlation period. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
-
Specification