APP Processing for High Performance MIMO Systems
21 September 2003
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 proces sing, 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^2 in a 0.18um process. An MLAPP search grows exponentially as the con stellation 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.