A Comparison of Scheduling Strategies for MIMO Broadcast Channel with Limited Feedback on OFDM Systems

Ermanna Conte,Stefano Tomasin,Nevio Benvenuto

doi:10.1155/2010/968703

Abstract

We consider a multiuser downlink transmission from a base station with multiple antennas (MIMO) to mobile terminals (users) with a single antenna, using orthogonal frequency division multiplexing (OFDM). Channel conditions are reported by a feedback from users with limited rate, and the base station schedules transmissions and beamforms signals to users. We show that an important set of schedulers using a general utility function can be reduced to a scheduler maximizing the weighted sum rate of the system. For this case we then focus on scheduling methods with many users and OFDM subcarriers. Various scheduling strategies are compared in terms of achieved throughput and computational complexity and a good tradeoff is identified in greedy and semiorthogonal user selection algorithms. In the greedy selection algorithm, users are selected one by one as long as the throughput increases, while in the semiorthogonal approach users are selected based on the channel correlation. An extension of these approaches from a flat-fading channel to OFDM is considered and simplifications that may be useful for a large number of subcarriers are presented. Results are reported for a typical cellular transmission of the long-term evolution (LTE) of 3GPP.

Highlights

Generation wireless cellular systems are expected to support high-quality multimedia services; this motivates the interest in multiantenna (MIMO) systems, where both spatial diversity and multiplexing can be used to increase the achievable throughput
This paper has provided an overview of scheduling problems for multiuser downlink MIMO orthogonal frequency division multiplexing (OFDM) systems
We first have shown that scheduling according to a wide class of utility functions can be reduced to a scheduling problem aiming at maximizing the weighted sum rate of the system, under a proper choice of the weighting function

Summary

Introduction

Generation wireless cellular systems are expected to support high-quality multimedia services; this motivates the interest in multiantenna (MIMO) systems, where both spatial diversity and multiplexing can be used to increase the achievable throughput. Nonlinear dirty paper coding scheme achieves the system capacity, it has a high computational cost [2], and simpler solutions have been investigated. Linear beamforming has been shown [3] to achieve a large part of dirty paper coding capacity; in particular, zero forcing beamforming matched to an opportunistic scheduling is widely used [3]. Benefits of MIMO are obtained only by a proper scheduling of transmissions, which opportunistically exploits channel conditions in order to increase throughput, while ensuring quality of service (QoS). A similar problem to multiuser MIMO scheduling can be found in other transmission systems, such as multicarrier code- or frequency-division multiple access [18]

Methods

Results

Conclusion