High throughput downlink cellular packet data access with multiple antennas and multiuser diversity

This paper presents a discussion of MIMO (multiple-input multiple-output) system designed to exploit multiuser diversity, with the principal goal of increasing throughput of delay tolerant data services to nomadic and mobile users in cellular systems. We consider the downlink of a cellular packet data access scheme with a base station transmit antenna array and users equipped with a single receive antenna. We show that it can be preferable to transmit to several users simultaneously using the transmit antenna array even with sub-optimal signaling. This is in contrast to single antenna systems exploiting multiuser diversity and using link adaptation, in which the average throughput per sector is maximized, when in any packet time slot transmission occurs only to one user experiencing the best channel conditions at the time. We propose several scheduling algorithms and compare their performance to the throughput achievable with precoding and perfect channel state information at the transmitter. We show that the capacity scaling typical to MIMO systems can be achieved even with single-antenna mobile receivers, but only a fraction of that capacity can be achieved with limited channel knowledge at the transmitter, when multiuser diversity is exploited.