An optimised parallel tree search for multiuser detection with VLSI implementation strategy

Multiuser detection (MUD) strategies have the potential to significantly increase the capacity of wireless communications systems, but for these to be useful they must also be practical for implementation in VLSI circuits. In particular, while the maximum-likelihood (ML) solution is optimal in bit error rate, it cannot be directly implemented due to its exponential computational complexity. Lattice decoders, such as the sphere search, exhibit near-optimal ML performance with reduced complexity, but their application is still limited by computational requirements. Here, a number of optimisations are presented, designed to reduce the computational cost of the sphere search, in the context of VLSI implementation. We also propose parallel implementation strategies for such a detector. This is then combined with a single-pass tree search approach that can be designed to not significantly impair error-rate performance. While the design is targeted towards a MUD application, the concepts may also be applied to a multiple-input multiple-output (MIMO) system, or similar applications.