ITR/SI(CISE): MIMO Processing and Space-time Coding with Interference

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ITR Small ProposalCCR-0112501Blum, RickTransmit and receive antenna arrays used to form multiple-input multiple-output (MIMO) channels have shown great potential in isolated, single link communications without cochannel interference.Provided the same number of transmit and receive antennas are used, recent research has shown that capacity scales linearly with the number of transmit antennas. This result has created an incredibleflurry of interest among researchers. While these MIMO systems have received extensive study for cases without cochannel interference, cases with cochannel interference have received much lessattention. Further, new simulation results indicate that cochannel interference can significantly degrade the overall capacity when MIMO channels are used in a cellular system in the same manner in whichthey are used for cases without interference. The investigators study the properties of MIMO systems withinterference to develop new methods of using MIMO which adapt the transmission scheme to the interference environment. These new methods, called stream control algorithms, transmit several different streams, each one using a different transmit weight vector. The maximum number of streams that can be transmitted is equal to the minimum of the number of transmit and receive antennas. The exact number of streams chosen depends on the current sensed state of the interference environment. Preliminary results indicate that significant performance gains can be achieved in this manner. Using the well developed theory of power control, distributed algorithms are being developed to control the number of streams employed in a cellular system with cochannel interference. The use of space-time coding is also being studied in conjunction with stream control. Wireless channels with frequency selective fading, various correlation structures, and other practical degradations are being studied.