Blind spreading sequence discovery for DS-CDMA signal interception

Abstract

A scheme based on multiple signal classification (MUSIC) algorithm for blind discovery of spreading sequences of active users in a synchronous multiuser code division multiplex access (CDMA) is suggested. The scheme is blind in the sense that does not require prior knowledge of the spreading codes. Spreading codes and users power are acquired by the scheme. Eigenvalue decomposition (EVD) is performed on the received signal, and then all the valid possible signature sequences are projected onto the subspaces. However as a result of this process, some false answers are also produced and the ambiguity seems un-resolvable. Our approach is to apply a transformation derived from the results of the subspace decomposition on the received signal and then to inspect their statistics. It is shown the second order statistics of the transformed signal provides a reliable means for removing the false answers.