Fast Optimal and Suboptimal Any-Time Algorithms for CDMA Multiuser Detection Based on Branch and Bound

Fast Optimal and Suboptimal Any-Time Algorithms for CDMA Multiuser Detection Based on Branch and Bound J. Luo, K. Pattipati, P. Willet, and G. Levchuk A fast optimal algorithm based on the branch and bound (BBD) method is proposed for the joint detection of binary symbols of users in a synchronous code-division multiple-access channel with Gaussian noise. Relationships between the proposed algorithms (depth-first BBD and fast BBD) and both the decorrelating decision-feedback (DF) detector and sphere-decoding algorithm are clearly drawn. It turns out that a decorrelating DF detector corresponds to a “one-pass” depth-first BBD; sphere decoding is, in fact, a type of depth-first BBD, but one that can be improved considerably via tight upper bounds and user ordering, as in the fast BBD. A fast any-time suboptimal algorithm is also available by simply picking the “current best” solution in the BBD method. Theoretical results are given on the computation complexity and the performance of the current best suboptimal solution.