CORDIC-based LMMSE equalizer for Software Defined Radio

Abstract

In Code Division Multiple Access (CDMA) systems, the orthogonality of the spreading codes used to achieve multiple access over a channel is severely degraded due to multi-path interference. Expensive equalization techniques are needed to recover the transmitted signal. The Linear Minimum Mean Square Error (LMMSE) equalizer is a sub-optimal equalizer that is a good compromise between computational complexity and communication system performance. It uses computationally-intensive matrix inversion operations to perform equalization. In this paper, we address the computational challenges of implementing the LMMSE equalizer on Software Defined Radio (SDR) platforms. SDR platforms are favored by the wireless industry due to their significant benefits of reduced development costs and accelerated time-to-market. We present COordinate Rotation DIgital Computer (CORDIC) Instruction Set Architecture (ISA) extensions that speed up the LMMSE equalization algorithm. The costs and benefits of the ISA extensions are evaluated on the Sandbridge Sandblaster 3000 (SB3000) low-power, multithreaded SDR processor. The proposed ISA extensions provide significant performance improvements with little hardware overhead, while improving the accuracy of the LMMSE Equalizer.