Adaptive Complexity Equalization for the Downlink in WCDMA Systems

We consider the issue of terminal reconfigurability in the downlink of WCDMA. For the purpose of optimizing power consumption in mobile terminals, we propose an adaptive-complexity equalization algorithm, which adapts the equalization length to the environment. A simple approach in WCDMA systems consists of computing the equalizer coefficients in frequency domain, and carry out channel equalization in time domain. The equalizer can be easily computed in frequency domain from channel estimates, which are generally obtained through pilot symbols. In our work, we decouple the task of adaptive complexity equalization in two parallel operations: variable length equalization and equalization length control. We propose a practical scheme to reduce equalization complexity by prewindowing in frequency domain and performing IFFT of variable length. An element of length control monitors the equalizer coefficients, updating the equalizer length at each stage. Both simulation and experimental results in outdoor-to-indoor scenarios show good performance and significant power savings with respect to full length equalization.