On Outage and Capacity for Orthogonal Transmit Diversity
Transmit diversity; space-time codes; orthogonal transmit diversity (OTD); outage probability
Assuming that only the receiver has perfect channel state information, we analyze the orthogonal transmit diversity (OTD). First, we consider the case of fast fading or <i>ergodic</i> channels. We demonstrate that for a single receive antenna, OTD does not result in a capacity loss. This is not the case when there are multiple receive antennas. Then, we consider block fading or <i>non-ergodic</i> channels. We propse a new, simple, and asymptotically tight upper bound for the outage probability in multiple transmit and single receive antenna systems. Assuming equal power distribution, we also demonstrate that for non-ergodic channels and a single receive antenna, OTD preserves the achievable outage probability. However, in the case of multiple receive antennas, OTD increases the achievable outage probability. In short, regardless of the nature of fading, OTD is optimal only in the case of a single receive antenna.
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- ECE Publications