REDUCED-COMPLEXITY EQUALIZATION WITH SPHERE DECODING

Techniques for spherical decision-feedback sequence estimation are disclosed. A received signal is equalized by forming a trellis comprising a plurality of stages, each stage corresponding to a symbol time and comprising a plurality of nodes, each having a node state. A most likely received symbol sequence is identified by evaluating cumulative state metrics for the nodes according to MLSE or DFSE criteria. The trellis is formed by selecting a set of fan-out branches for each node by identifying, of all possible state transition branches from the node to successor nodes in the succeeding stage, those state transition branches that have a spherical branch metric less than a pre-determined metric limit, and determining the cumulative state metric for each node as a function of the cumulative state metrics for predecessor nodes in the preceding stage and the spherical branch metrics for fan-out branches connecting the predecessor nodes to the node.