Space-time coding and spatial multiplexing are prime candidates for achieving high data rates and link quality in multiple input multiple-output (MIMO) wireless links. However, both the schemes assume no channel knowledge at the transmitter. In a number of applications, channel knowledge can be made available at the transmitter. A natural question to ask is how to use these channel estimates to further optimize the transmitter. There can be several ways to linearly or non-linearly optimize the transmitter and receiver depending on channel knowledge. In this thesis, we consider linear optimization schemes at the transmitter (precoding) and receiver (decoding) to improve performance of MIMO systems. We consider a number of designs depending on the performance criteria and degree of channel knowledge at the transmitter.; First, assuming perfect channel knowledge at the transmitter and receiver, and a flat-fading channel, we propose a generalized linear block precoding and decoding scheme based on the weighted mean square error criteria, assuming a total power constraint at the transmitter. The optimum design forces transmission only on the eigenmodes of the MIMO channel, for any set of error weights. The power allocation on the eigenmodes depends on the error weights, which can be varied depending on the application. The weighted MMSE criteria thus provides a unified framework for designing jointly optimal linear precoders and decoders, assuming perfect channel knowledge at the transmitter.; Next, we derive optimal linear precoders and decoders for other optimization criteria such as the pairwise error probability (PEP) criteria, and constraints such as the peak power constraint. In the latter case, we find that the eigenmode transmission need not be the optimum strategy.; Next, we show how to extend the linear precoder and decoder framework to delay spread channels and multicarrier systems employing OFDM modulation. In the former case, we employ block transmission with guard symbols inserted between data blocks to prevent inter-block interference. In OFDM modulation, redundancy is added in the form of a cyclic prefix to handle delay spread. We then present a novel Finite Impulse Response (FIR) precoder structure to pre equalize the MIMO channel with delay spread assuming a zero-forcing constraint and subject to a transmit power constraint.; Finally, we consider the design of precoders assuming partial channel knowledge at the transmitter and perfect channel knowledge at the receiver. In this context, we develop an optimum linear precoder for a space-time coded system, assuming knowledge of only the transmit antenna correlations.
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