In this paper, we introduce the novel use of linear spatial precoding basedon fixed and known parameters of multiple-input multiple-output (MIMO) channelsto improve the performance of space-time coded MIMO systems. We derive linearspatial precoding schemes for both coherent (channel is known at the receiver)and non-coherent (channel is un-known at the receiver) space-time coded MIMOsystems. Antenna spacing and antenna placement (geometry) are considered asfixed parameters of MIMO channels, which are readily known at the transmitter.These precoding schemes exploit the antenna placement information at both endsof the MIMO channel to ameliorate the effect of non-ideal antenna placement onthe performance of space-time coded systems. In these schemes, the precoder isfixed for given transmit and receive antenna configurations and transmitterdoes not require any feedback of channel state information (partial or full)from the receiver. Closed form solutions for both precoding schemes arepresented for systems with up to three receiver antennas. A generalized methodis proposed for more than three receiver antennas. We use the coherentspace-time block codes (STBC) and differential space-time block codes toanalyze the performance of proposed precoding schemes. Simulation results showthat at low SNRs, both precoders give significant performance improvement overa non-precoded system for small antenna aperture sizes.
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