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This paper considers spatial multiplexing (SM) systems with precoding. The precoder is derived from the singular value decomposition (SVD) of the available channel state information at the transmitter (CSIT) and the receiver is a function of the precoder and the current channel. With perfect CSIT, the MR X MT fiat-fading MIMO channel can be decomposed into min(MT, MR) parallel spatial subchannels. However in practice, the available CSIT suffers from delay-induced error due to the channel temporal variations. Using this outdated CSIT for precoding in SM systems causes interference among the subchannels. Performance of the decorrelator, minimum mean squared error (MMSE) and successive interference cancelation (SIC) receivers is analyzed as the reliability of the available CSIT varies. Explicit expressions for the signal to interferenceplus-noise ratio (SINR) and the mean squared error (MSE) are derived. Simulation results are provided to illustrate the significant performance gain achieved by precoding even with a moderate amount of correlation between the available outdated channel estimate and the current channel.

A method based on recursive computation of the expected number of attempts and successes during the collision resolution phase of a protocol is introduced for the design of near-optimum protocols for multiple access collision channels with ternary and binary feedback. With this approach it is possible to circumvent the extremely difficult and still unsolved problem of finding the protocol which achieves the highest throughput among all protocols by settling for a near-optimum solution. The key to the design of our protocols is to approximate the originally infinite dimensional optimization problem by a one dimensional optimization problem. In the ternary feedback our proposed protocol achieves a throughput virtually identical to the highest throughput reported today. Several forms of binary feedback are considered and protocols are introduced that achieve the highest throughput of any known protocols.