2 research outputs found
Performance of Hybrid-ARQ in Block-Fading Channels: A Fixed Outage Probability Analysis
This paper studies the performance of hybrid-ARQ (automatic repeat request)
in Rayleigh block fading channels. The long-term average transmitted rate is
analyzed in a fast-fading scenario where the transmitter only has knowledge of
channel statistics, and, consistent with contemporary wireless systems, rate
adaptation is performed such that a target outage probability (after a maximum
number of H-ARQ rounds) is maintained. H-ARQ allows for early termination once
decoding is possible, and thus is a coarse, and implicit, mechanism for rate
adaptation to the instantaneous channel quality. Although the rate with H-ARQ
is not as large as the ergodic capacity, which is achievable with rate
adaptation to the instantaneous channel conditions, even a few rounds of H-ARQ
make the gap to ergodic capacity reasonably small for operating points of
interest. Furthermore, the rate with H-ARQ provides a significant advantage
compared to systems that do not use H-ARQ and only adapt rate based on the
channel statistics.Comment: 28 pages, 11 figures, accepted at IEEE Trans. Communication
Hybrid ARQ in Multiple-Antenna Slow Fading Channels: Performance Limits and Optimal Linear Dispersion Code Design
This paper focuses on studying the fundamental performance limits and linear
dispersion code design for the MIMO-ARQ slow fading channel. Optimal average
rate of well-known HARQ protocols is analyzed. The optimal design of space-time
coding for the MIMO-ARQ channel is discussed. Information-theoretic measures
are used to optimize the rate assignment and derive the optimum design
criterion, which is then used to evaluate the optimality of existing space-time
codes. A different design criterion, which is obtained from the error
probability analysis of space-time coded MIMO-HARQ, is presented. Examples are
studied to reveal the gain of ARQ feedback in space-time coded MIMO systems