MIMO techniques for high data rate radio communications

MIMO wireless transceivers employ multiple antennas and advanced digital signal processing to achieve higher data rates and superior link reliability compared to their single-antenna counterparts. After a simplified overview of general MIMO theory, this paper presents a 2times2 MIMO 5 GHz WLAN transceiver implemented in 90 nm CMOS. Crosstalk between the different MIMO channels is shown to have a detrimental effect on MIMO performance. Such crosstalk can occur at the radio channel, between the antennas, and at the radio IC. Several architectural and circuit techniques are described that minimize crosstalk between the multiple radio chains co-existing on the same silicon die. Measurements results demonstrate the increased data rate of the fabricated system compared with a conventional single-antenna system. The paper concludes with some interesting scenarios for future MIMO evolution, including collaborative, directional and 60 GHz phased-array communications.