On the SNR exponent of hybrid digital-analog space time coding
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We consider the transmission of a real i.i.d. "analog" source over a quasi-static M-input N-output MIMO fading channel. The relevant performance criterion is end-to-end average quadratic distortion D versus channel SNR, for given spectral efficiency , defined as the ratio of the source bandwidth over the channel bandwidth. We define the distortion SNR exponent a ( ) as the largest a = -limsnr1 logD/ log snr, over all possible source-channel coding schemes. We find a closed form upperbound on a (), a lower bound asep() achievable by separated (tandem) source-channel coding, and a tighter lower bound ahybrid() achievable by hybrid digital analog space-time coding. In particular, we completely determine a ( ) for the scalar fading channel and for the case 2M, for any M, N M. Explicit and simple constructions of hybrid space-time codes achieving ahybrid() are also given.
