Look-ahead sphere decoding: algorithm and VLSI architecture

Multiple-input-multiple-output (MIMO) systems are recognised as a key enabling technology in high-performance wireless communications; however, the implementation of high-throughput MIMO detectors still is a critical task. Among known MIMO detectors, sphere decoder algorithm (SDA) is capable of optimal performance with acceptable processing complexity. The study presents an improved SDA, which enables significant throughput increase at a very limited additional complexity and with no degradation in terms of bit error rate performance. The modified detection method, called LASDA (look-ahead SDA), is based on formal algorithm transformations, namely look-ahead, retiming and pipelining, and requires a modified tree search strategy. The VLSI design of LASDA detector supporting a 4 × 4 MIMO channel with 16 QAM modulation is detailed in the study for a 130 nm CMOS standard cell technology: synthesis results show that the proposed solution achieves an average throughput of 380 Mbps at a signal-to-noise ratio of 22 dB (Rayleigh fading channel), with an occupied silicon area of 0.18 mm². Comparisons with a number of previous implementations are also provided.