Fundamental Rate-Reliability-Complexity Limits in Outage Limited MIMO Communications
Event details
| Date | 15.06.2011 |
| Hour | 14:15 |
| Speaker | Prof. Petros Elia, EURECOM |
| Location | |
| Category | Conferences - Seminars |
The work establishes fundamental limits with respect to rate, reliability and computational complexity, for encoding-decoding in a general setting of outage-limited MIMO communications. In the high-SNR regime, the limits are optimized over all encoders, all decoders, and all complexity regulating policies. The work then proceeds to explicitly identify encoder-decoder designs and policies, that meet this optimal tradeoff. In practice, the limits aim to meaningfully quantify different pertinent measures, such as the optimal rate-reliability capabilities per unit complexity and power, the optimal diversity gains per complexity costs, or the optimal number of numerical operations (i.e., flops) per bit. Finally the tradeoff's simple nature, renders it useful for insightful comparison of the rate-reliability-complexity capabilities for different encoders-decoders. In the same setting we identify the first ever lattice decoding solution that achieves both a vanishing gap to the error-performance of the exact solution of lattice decoding, as well as a computational complexity that is subexponential in the rate and in the problem dimensionality. This complexity behavior is rigorously demonstrated here for the first time, where it is also proven that for most common codes, the complexity cost for asymptotically optimal regularized lattice (sphere) decoding is exponential in the rate, and in many cases it in fact matches the complexity cost of ML (bounded) sphere decoding. In light of the fact that, prior to this work, a vanishing gap was generally attributed only to full lattice searches of exponential complexity, whereas subexponential complexity was generally attributed to early-terminated (linear) solutions having a performance gap that can be up to exponential in dimension and/or rate, the work constitutes the first proof that subexponential complexity need not come at the cost of exponential reductions in lattice decoding error performance. Finally, the performance and complexity guarantees in this work hold for the most general MIMO setting, for all reasonable fading statistics, all channel dimensions, and all lattice codes. Prof. Elia's homepage
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