Spreading Codes for Multiuser Estimation in Non Coherent and Non Cooperative Environments

The need for a more efficient and reliable use of available radio resources has led to the developement of Spread Spectrum based communication networks, like WCDMA. Even though the Spread Spectrum signals are inherently robust, and provide significant level of security, it has been shown that the use of interference suppression techniques can result in a substantial performance improvement. This paper proposes an overview of interference suppression techniques used in combination with different sets of spreading codes. The focus of the paper is on Direct Sequence SS systems, and on the choice of proper spreading codes, in a blind asynchronous environment. Particular attention is devoted to analyzing the performance of spreading codes based on their cross correlation properties, in a multiple users scenario. Eigenvalue estimation and Maximum Likelihood estimation techniques are used to evaluate the robustness of the system, in the presence of Additive White Gaussian Noise.