Orthogonal designs optimize achievable dispersion for coherent MISO channels
Author(s)Polyanskiy, Yury; Collins, Austin Daniel
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This work addresses the question of finite block-length fundamental limits of coherently demodulated multi-antenna channels, subject to frequency non-selective isotropic fading. Specifically we present achievability bound for the channel dispersion - a quantity known to determine the delay required to achieve capacity. It is shown that a commonly used isotropic Gaussian input, which is only one of many possible capacity achieving distributions, is suboptimal. Optimal inputs minimizing channel dispersion turn out to include a family of modulation techniques known as orthogonal designs (in particular, Alamouti's scheme). For 8 transmit antennas numerical evaluation shows that up to 40% of additional penalty in delay is incurred by using isotropic codewords (compared to dispersion-optimal architecture exploiting transmit diversity).
DepartmentMassachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
Proceedings of the 2014 IEEE International Symposium on Information Theory
Institute of Electrical and Electronics Engineers (IEEE)
Collins, Austin, and Yury Polyanskiy. “Orthogonal Designs Optimize Achievable Dispersion for Coherent MISO Channels.” 2014 IEEE International Symposium on Information Theory (June 2014).
Author's final manuscript