3G wireless communications and beyond
Among the major factors limiting the performance of mobile wireless communication systems, fading of the signal coupled with the interference from transmitters using the same channel degrades the receiver's performance. However, significant improvements in the receiver's performance can be achieved by exploiting the channels' diversity, so as to effectively transmit the signal over multiple independently fading channels. Within the FLOWS project, funded by the Fifth Framework Programme, dedicated techniques for the joint exploitation of spatial, multipath and Doppler diversity were proposed for WCDMA systems. Wideband Code Division Multiple Access, the accepted technology for the next generation cellular networks, provides intrinsic protection against the multipath effects of the channel in highly loaded cells. On the other hand, Multiple-Input and Multiple-Output (MIMO) techniques provide an additional source of spatial diversity by creating, in the ideal case, independently fading channels between transmitter and receiver. Doppler spread caused by the rapidly time-varying channel with the fast motion of the mobile terminal was further regarded as an additional source of temporal diversity. Joint multipath-Doppler chip equalisation was proposed by project partners at the University of York as a means of optimally exploiting multipath and Doppler diversity for suppressing multi-access interference. The receiver designed with chip-level equalisation integrates two-dimensional (2D) matched filtering for combining the signal energy dispersed in the multipath delay and Doppler spread. The ultimate aim of this new processing technique was to reduce the transmission bit error rate (BER) sufficiently enough to allow a coding scheme to work more efficiently. Moreover, emphasis was laid on ensuring an implementation of the receiver technique with realisable complexity on existing devices. Its performance was evaluated over a wide range of channel models and more importantly, its compatibility with orthogonal frequency-division multiplexing (OFDM)-based standards. Besides providing high detection performance even in fully loaded multiuser scenarios, a simple implementation of a Universal Mobile Telecommunications System's (UMTS) receiver is promised.
