초록 ▼

A convolutional despreading method takes advantage of the algebraic structure of the spreading code and applies convolutional type decoding to received signal chip symbols to rapidly estimate code phase, preferably used for rapid acquisition of direct sequence spread spectrum signals. Modeled reduce

A convolutional despreading method takes advantage of the algebraic structure of the spreading code and applies convolutional type decoding to received signal chip symbols to rapidly estimate code phase, preferably used for rapid acquisition of direct sequence spread spectrum signals. Modeled reduced-state structures having branchword transitions are used to reduce metric computations. The reduced state structures and algebraic structures provide additive constraints for modifying convolutional sequential metric searching for improved speed of code phase determination. The convolution despreading method preferably uses a modified convolutional sequential search algorithm, such as, a modified Fano Tree convolutional sequential search, or, a modified Viterbi trellis convolutional sequential search. The method can also directly determine a modulated data stream, when present, to provide demodulated data without necessarily performing conventional cross correlation despreading. A metric state processors then functions as an ad hoc despreader. The convolutional despreading method is particularly useful in direct sequence spread spectrum systems where the use of chip spreading codes requires code phase determination for rapid acquisition of direct sequence spread spectrum signals.

대표청구항 ▼

1. A method for estimating a code phase of a linear code defined by a polynomial, generating the linear code by sequential shifting a code generator of M stages, the method comprising the steps,constructing a reduced state space by mapping the M stages into M-tuple length possible branchwords and by

1. A method for estimating a code phase of a linear code defined by a polynomial, generating the linear code by sequential shifting a code generator of M stages, the method comprising the steps,constructing a reduced state space by mapping the M stages into M-tuple length possible branchwords and by mapping the M-tuple length possible branchwords into transitions of the reduced state space of possible states each of N length defining N-tuple states conforming to the polynomial where N is less than M and where the possible branchwords define possible paths through the reduced state space extending from initial states through intermediate states to ending states, transmitting the linear code as transmitted symbols, receiving the transmitted symbols as received symbols received arbitrarily in time establishing the code phase relative in time, grouping the received symbols into received branchwords of M length, computing path metrics for the possible paths by searching from the initial states through the intermediate states to the ending states of the possible states within the reduced state space by metric comparison of the possible branchwords with the received branchwords, and estimating the code phase by selecting within the reduced state space one of the initial states having a preferred path of the possible paths to one of the ending states, which preferred path corresponds to a best metric of the computed path metrics.