Blind spreading sequence estimation algorithm for long‐code DS‐CDMA signals in asynchronous multi‐user systems
Jiang‐Hai Liang, Xiang Wang, Fenghua Wang, Zhitao Huang · IET Signal Processing · 2017
Despreading signal at receiver side requires prior knowledge of the spreading sequences in direct‐sequence code division multiple access (DS‐CDMA) system. However, the knowledge of spreading sequences is always unknown to the receiver in non‐cooperative communication. Therefore the receiver has to estimate the spreading sequences in a blind manner. This study presents a novel algorithm to estimate the spreading sequences for asynchronous long‐code (LC) DS‐CDMA signals. By investigating the projection characteristics of the signal subspace, the authors treat the spreading sequence estimation problem as a discrete optimisation search problem that can be solved efficiently by modern optimisation search methods. Moreover, they design a successive subspace deflation scheme to alleviate interference from other users. Numerical experiments demonstrate that the proposed algorithm provides good estimation of the spreading sequences for LC‐DS‐CDMA signals. Compared with the existing algorithms, the proposed algorithm exhibits much better performance in large system load scenario with low signal‐to‐noise ratio.