APP Processing for High Performance MIMO Systems

pwd One of the most demanding components in a multiple-input multiple-output (MIMO) receiver is the symbol detector. While linear cancellation techniques are typically used, the optimum maximum likelihood (ML) search algorithm combined with soft output processing, e.g., a posteriori probability (APP), offers superior performance and is feasible in current technology. An ASIC can be built for a 4x4 QPSK detector for HSDPA in less than 1.68 mm sup 2 in a 0.18mum process. A MLAPP search grows exponentially as the constellation size is increased. but it is still feasible to achieve near ML performance for 4x4 16QAM using "spherical" techniques in a complexity that remains a minor portion of the overall MIMO receiver.