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PARTIAL FEEDBACK MULTI-USER SCHEDULING
IN MULTI-ANTENNA SYSTEMS
Ahmad Suhail Salim
Electrical Eng. Dept., King Fahd University of Petroleum and Minerals (KFUPM)
P.O. Box 7626, Dhahran 31261Saudi Arabia
Keywords: MIMO, MIMO Scheduling, Partial Feedback.
Abstract: In this paper we consider the greedy scheduling algorithm that routes transmission of users’ packets based
on their reported CSI in the uplink channel to the user with the best instantaneous channel conditions. We
propose a scheduling scheme that relies on reporting partial feedback of the CSI. We compare the proposed
scheme to the one that uses perfect channel information at the base station, we will see that the proposed
scheme has significantly less complexity at the expense of a loss in the system’s capacity.
1 INTRODUCTION
In order to support services requiring high data rates
such as the Internet while ensuring the quality of
service (QoS), the spectral efficiencies of the next
generation of wireless networks has to be greatly
enhanced. The concept of multiple-input multiple-
output (MIMO) systems introduced in the mid 1990s
demonstrated that using multiple antenna elements
at both the receiver and the transmitter can result in
enormous capacity gains. Since then, various MIMO
architectures have been proposed such as space-time
block coding and smart antenna beamforming.
In multiuser environments, independence of
fading among users, called multiuser diversity, can
be exploited to increase the system capacity. Two
critical targets of packet scheduling are to maximize
the system capacity (throughput) and to offer
fairness among users. This is accomplished by
tracking the instantaneous channel quality of the
users in the system and schedule transmissions to the
user who has the best channel quality at any given
time. In this case the system is ‘riding the peaks’ of
channel qualities of all the users at all times.
In the case of greedy scheduling, the scheduling
scheme maximizes the system capacity through the
use of multiuser diversity. Specifically, each spatial
channel is allocated to a user with the best channel
condition for each time slot. Therefore, some users
in adverse channel conditions may not be served,
causing unfairness among users. While in the round
robin scheduling (RRS) scheme was studied for
MIMO cellular systems operated in a cyclic fashion
regardless of the channel conditions, and thus
achieves fairness among users.
Much of the work on multi-user MIMO channels
has assumed that the transmitter and receivers all
know the channel exactly. Accurate CSI may be
easy to obtain when the channel is changing slowly
(e.g., as in indoor scenarios), but it is much more
difficult in situations where the channel is changing
rapidly. An analysis of the penalty for using
imperfect or outdated feedback of channel
information would be of significant benefit to
system designers.
In this paper we propose a scheduling algorithm
that would require the users to report part of their
CSI back to the transmitter, where it then will decide
to route the transmission to the user with the best
effective SNR The key reason for this idea is to
reduce the traffic in the feedback path, so then it can
be used for other purposes, but the question is does
this sacrifice worth it, and what are the effects of
using such scheme on the capacity of the system,
and is it tolerable or not, such questions and other
more will be further discussed in this paper.
2 SYSTEM MODEL
The model we consider applies to the downlink of a
multiuser MISO wireless packet data system as
illustrated in Figure 1, where we assumed having a
single BTS of multi transmit antennas that provides
data services to M users, each of which is equipped
157
Salim A. (2010).
PARTIAL FEEDBACK MULTI-USER SCHEDULING IN MULTI-ANTENNA SYSTEMS.
In Proceedings of the International Conference on Wireless Information Networks and Systems, pages 157-160
DOI: 10.5220/0002966401570160
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