Linear Spreading Space-Time Block Codes: System Model and Optimization Criterion

We present a model of linear space-time block coded multiple input multiple output wireless systems for quasi-static frequency nonselective fading channels. The code is described by its set of spreading matrices. We give a condition on the spreading matrices in order not to degrade the mutual information compared to the uncoded case. The knowledge of the channel impulse response and the spreading matrices at the receiver defines the relationship between the received and transmitted symbol vectors via a positive semidefinite matrix R (k). We present a new criterion for optimizing linear space-time block codes based on the fact that all the entries of R (k) are sums of quadratic forms and that the intersubchannel interference is represented by the off-diagonal entries. This criterion aims at minimizing the peak value of the intersubchannel interference.