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Impact of feedback delays on EESM-based wideband link adaptation: Modeling and analysis
, N.B. Mehta
Published in Institute of Electrical and Electronics Engineers Inc.
2014
Pages: 3952 - 3957
Abstract
In orthogonal frequency division multiplexing (OFDM) systems, such as long term evolution (LTE) and WiMAX, a codeword is transmitted over a group of subcarriers. Since the subcarriers see different channel gains in a frequency-selective channel, the modulation and coding scheme (MCS) of the codeword must be selected based on the vector of signal-to-noise-ratios (SNRs) of these subcarriers. Exponential effective SNR mapping (EESM) simplifies this problem by mapping the vector of SNRs into a single, equivalent flat-fading SNR. We develop a new analytical framework to characterize the throughput of EESM-based rate adaptation in such wideband channels in the presence of feedback delays, which make the choice of the MCS partially outdated by the time data transmission takes place. To this end, we first propose a novel bivariate gamma distribution to model the joint statistics of EESM at the times of estimation and data transmission. We then derive a novel expression for the throughput as a function of feedback delay. Our framework works for both correlated and independent subcarriers and for various multiple antenna diversity modes, and is accurate over a wide range of delays. © 2014 IEEE.
About the journal
JournalData powered by Typeset2014 IEEE Global Communications Conference, GLOBECOM 2014
PublisherData powered by TypesetInstitute of Electrical and Electronics Engineers Inc.