Heuristic algorithms for binary sequence assignment in DS-CDMA systems

For a given set of background interference signals, it is well known that the optimal sequence can be obtained by solving an eigenvalue problem. However, one usual practical constraint on the sequences is that the sequence elements should have a constant amplitude. We show that when the choice is limited to binary sequences, the sequence assignment problem is NP-hard. We propose a local search method to find suboptimal solutions. This method can also be applied when polyphase sequences are used. Performance evaluation when applied to multipath channels is made.