Algorithms and VLSI architectures for RLS-based time reference beamforming in mobile communications

We propose the use of RLS-based techniques for adaptive antenna signal processing in mobile communications, where systems are required to operate reliably in the presence of strong interference and under time-varying propagation conditions. We present several practical schemes for implementing digital beamformers employing training sequences for initial weight adaptation and either periodically inserted pilot symbols or decision-feedback for weight updating during subsequent data transmission. The QRD-RLS algorithm was chosen for adaptive control of the array due to its robust numerical properties and because it lends itself well for parallel processing as required in high speed applications, e.g., mobile broadband systems (MBS). It is demonstrated how to map this algorithm onto a highly efficient systolic array architecture entirely consisting of identical processing elements which rely on CORDIC arithmetic to carry out all the required computations, thus enabling very economic VLSI implementations. Additionally, a fast method for joint reference signal synchronisation and array adaptation as well as a simple scheme which allows one to control multiple independent beams in parallel are discussed. Both of these fit very nicely with the proposed hardware concepts and can be exploited advantageously for multipath diversity combining or for the concurrent reception of several spatially distributed users sharing the same frequency and/or time slot. Results of bit-true computer simulations are included to illustrate the performance of the proposed techniques.