A METHOD AND DEVICE FOR DESPREADING AN OFFSET SIGNAL

摘要

A method and a device are disclosed for despreading incoming signals in a receiver for DS-CDMA systems (DS-CDMA = Direct Sequence Code Division Multiple Access) using Offset-QPSK spreading as the transmitting spreading format combined with arbitrary data modulation formats, such as BPSK and QPSK data modulation formats. The receiver has a PN generator (3; 11) for generating a unique PN sequence signal ¢s(k)! divided into a real and an imaginary component. The input sampled complex valued numbered signal is divided into inphase and quadrature components. The invention is characterized in that the inphase and the quadrature components (yI and yQ) of the input signal are downsampled to provide either two complex samples per chip period or one complex sample per chip period in which later case the downsampling instants are delayed by a quarter of a chip period. Each downsampled complex signals is correlated with the corresponding segments of the complex PN sequence signal of the receiver. The correlation values obtained for odd and even complex samples of the downsampled input signal are summed, in the case when two samples per chip are provided after downsampling.