SINR maximizing space-time filtering for asynchronous DS-CDMA

摘要

Direct sequence code division multiple access (DS-CDMA) is a corentechnology for wireless access that is proposed for future generationn(3G) mobile and personal communication systems. The use of anbase-station antenna array is strongly endorsed in these systems,nbecause of its capabilities of filtering out the interference in thenspace domain. This paper considers space-time one shot single usernreceivers for DS-CDMA, based on a multiple input single output timeninvariant linear filter. The optimization of the filter response isnperformed jointly in the space and time domains yielding maximalnsignal-to-interference-plus-noise ratio. Using this framework, anspace-time noise whitening matched filter (ST-NWMF) for DS-CDMAndemodulation is introduced. It is shown that combined spatio-temporalnfiltering, taking advantage of the fact that the multiple accessninterference is colored in the space as well as time domains, can reducenthe effects of strong interference components and improves thenperformance. Simpler suboptimal space-time linear receivers, consistingnof a single temporal LT filter following the antenna array, are alsonconsidered. It is shown that such a filter approaches the ST-NWMF in thenlimit, when the M chip waveform has a flat spectrum with no excessnbandwidth and N the observation interval is infinite. These schemes,noptimal as well as suboptimal, for large observation intervals arensuitable also for DS-CDMA systems employing long sequencenspreading