In this work we present an iterative multiple-input multiple-output (MIMO) sphere decoding algorithm based on a proposed Constrained Metric-first search. The search strategy minimizes the number of required iterations as well as the variation in the number of iterations while overcoming the conventional metric-first memory requirements. Further complexity reduction is achieved through the use of a simplified distance norm and sorted QR-decomposition. The proposed algorithm is shown to be better suited for early termination schemes employed to guarantee high throughput as compared to traditional sequential sphere decoding. The decoder is synthesized to a standard TSMC 65nm CMOS process and shown to guarantee 750 Mbps throughput for a 4x4 16-QAM setup with close-to ML (Maximum Likelihood) performance and lower complexity than published decoders.
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