Characterizing the Impact of Feedback Delays on Wideband Rate Adaptation

Francis, Jobin and Mehta, Neelesh B (2015) Characterizing the Impact of Feedback Delays on Wideband Rate Adaptation. In: IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, 14 (2). pp. 960-971.

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Abstract

In contemporary orthogonal frequency division multiplexing (OFDM) systems, such as Long Term Evolution (LTE), LTE-Advanced, and WiMAX, a codeword is transmitted over a group of subcarriers. Since different subcarriers see different channel gains in frequency-selective channels, 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) maps the vector of SNRs into an equivalent flat-fading SNR, and is widely used to simplify this problem. 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. We derive a novel accurate approximation for the throughput as a function of feedback delay. We also propose a novel bivariate gamma distribution to model the time evolution of EESM between the times of estimation and data transmission, which facilitates the analysis. These are then generalized to a multi-cell, multi-user scenario with various frequency-domain schedulers. Unlike prior work, most of which is simulation-based, our framework encompasses both correlated and independent subcarriers and various multiple antenna diversity modes; it is accurate over a wide range of delays.

Item Type:	Journal Article
Publication:	IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS
Publisher:	IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Additional Information:	Copy right for this article belongs to the IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA
Keywords:	OFDM; adaptation; Exponential Effective SNR Mapping (EESM); feedback delay; scheduling; co-channel interference; bivariate gamma distribution
Department/Centre:	Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited:	01 Apr 2015 12:10
Last Modified:	01 Apr 2015 12:10
URI:	http://eprints.iisc.ac.in/id/eprint/51140

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