Open Access

Scheduling for Multiuser MIMO Downlink Channels with Ranking-Based Feedback

EURASIP Journal on Advances in Signal Processing20082008:854120

Received: 28 June 2007

Accepted: 26 January 2008

Published: 20 February 2008


We consider a multi-antenna broadcast channel with more single-antenna receivers than transmit antennas and partial channel state information at the transmitter (CSIT). We propose a novel type of CSIT representation for the purpose of user selection, coined as ranking-based feedback. Each user calculates and feeds back the rank, an integer between 1 and W + 1, of its instantaneous channel quality information (CQI) among a set of W past CQI measurements. Apart from reducing significantly the required feedback load, ranking-based feedback enables the transmitter to select users that are on the highest peak (quantile) with respect to their own channel distribution, independently of the distribution of other users. It can also be shown that this feedback metric can restore temporal fairness in heterogeneous networks, in which users' channels are not identically distributed and mobile terminals experience different average signal-to-noise ratio (SNR). The performance of a system that performs user selection using ranking-based CSIT in the context of random opportunistic beamforming is analyzed, and we provide design guidelines on the number of required past CSIT samples and the impact of finite W on average throughput. Simulation results show that feedback reduction of order of 40‐50% can be achieved with negligible decrease in system throughput.

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Authors’ Affiliations

Wireless Networking and Communications Group, Department of Electrical and Computer Engineering, The University of Texas at Austin
France Telecom Research and Development
Mobile Communications Department, Eurecom Institute


© Marios Kountouris et al. 2008

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.