Technical Program

Paper Detail

Paper:	SPCOM-L8.3
Session:	MIMO STC and Decoding
Time:	Friday, May 19, 17:10 - 17:30
Presentation:	Lecture
Topic:	Signal Processing for Communication: MIMO space-time code design, analysis and decoding algorithms
Title:	Outage Probability of OSTBC: Optimal Transmit Strategy and Suboptimality of Odd Number of Transmit Antennas
Authors:	Eduard Jorswieck, Aydin Sezgin, Holger Boche, Fraunhofer Institute for Telecommunications, Germany
Abstract:	Orthogonal space-time block codes (OSTBC) are an efficient mean in order to exploit the diversity offered by the wireless multiple-input multiple-output (MIMO) channel. It was shown that the Alamouti scheme, an OSTBC for two transmit antennas, achieves the capacity of such MIMO channels with one receive antenna. However, by increasing the number of transmit antennas, the transmission rate of the OSTBC is monotonically decreasing. Recently, this rate reduction was characterized completely. Using a recent result on the properties of Gaussian quadratic forms, we show two key results: Assume the transmitter has not channel state information. We show that for given rate and SNR it is optimal to use a subset of all available antennas with equal power allocation. Further on, we show that an OSTBC for an odd number of transmit antennas is always outperformed by an OSTBC for either the next lower or the next higher even number of transmit antennas. Finally, the impact of spatial correlation with uninformed transmitter is characterized. We illustrate the theoretical results by numerical simulations. The theoretical and simulation results show the suboptimality of the OSTBC for an odd number of antennas with respect to the outage probability minimization.