Least Squares Adaptive Algorithms Suitable for Multiplierless LMMSE Detection in 3Rd Generation Mobile Systems

Abstract:
This paper presents an evaluation of a simple adaptive FIR filter structure using a Hybrid-Logarithmic Number system (H-LNS) to minimize the complexity of a decentralized LMMSE receiver in the WCDMA downlink. Non-linear arithmetic operations can be executed efficiently with the H-LNS architecture without the necessity of fixed or floating point array multiplications. The use of Signed-LMS adaptive algorithms are included in this study since this significantly reduces the number of MAC operations required for conversion to and from the logarithmic domain. The multiplierless receiver has been simulated in Matlab(R) for the WCDMA-FDD downlink with macrodiversity, where the mantissa for each fractional logarithmic number was limited to 4,6 and 8 binary address bits. The results indicate that the Hybrid-Logarithmic Signed-LMS implementations are practical for slow fading channels, where the use of Log-Antilog conversion with small look up tables is feasible with only minimal reduction in the Signal to Noise Ratio.