A 772Mbit/s 8.81bit/nJ 90nm CMOS soft-input soft-output sphere decoder

Multiple-input multiple-output (MIMO) wireless transmission can approach its full potential in terms of spectral efficiency only with iterative decoding, i.e., by exchanging soft information between the MIMO detector and the channel decoder. Solving the soft-input soft-output (SISO) MIMO detection problem entails a very high complexity, which can typically be reduced only at the cost of a communication-performance penalty. The single tree-search (STS) sphere-decoding (SD) algorithm covers a wide range of this complexity-performance tradeoff. In this paper, we describe the silicon implementation of SISO STS SD. The 90 nm CMOS ASIC operates at a lower signal-to-noise ratio than other MIMO detectors. The maximum throughput is 772 Mbit/s at an energy efficiency of 8.81 bit/nJ.