Unquantized and Uncoded Channel State Information Feedback in Multiple Antenna Multiuser Wireless Systems

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The potential and promise of multiple antenna techniques has now resulted in widespread considerations for the use of these in a variety of contexts: for wide area wideband wireless transmission in next generation cellular systems; for local area hot-spot data service overlays in cellular systems; for emerging short-range wireless LAN networks; for promoting efficient spectrum sharing in the unlicensed bands; and a variety of collaborative techniques in wireless adhoc networks. A key attribute required of any multiple antenna technique to be successful, in any of the above contexts, is the need for reliable and efficient channel state information (CSI). Delay requirements imposed by wireless applications and the time variations in the channel, require not only reliability in CSI information, but also that the feedback of such information be fast and frequent. This project studies the fundamental limits of CSI feedback schemes that can be used in multiple antenna multiuser wireless communication systems. A fundamental issue studied is if it is necessary for reliable CSI feedback to be optimally quantized and encoded in a Shannon theoretic sense? Specifically, unquantized and uncoded (UQ-UC) CSI feedback schemes are studied, that have the attractive feature of avoiding the delays due to quantization and coding, while still being optimal in certain situations relating to the uplink and downlink of wireless channels. In cases where such "zero-delay" schemes are sub-optimal, enhancements that can substantially improve performance are studied via (a) performance bounds for UQ-UC CSI feedback in FDD and TDD systems, (b) CSI feedback receivers, (c) information capacity of transmitter optimization in multiple antenna multiuser systems, and (d) comparative evaluation of UQ-UC CSI feedback with practical coded transmission.