ABSTRACT
Opportunistic Scheduling
in Wireless Networks: An Overview of Issues
and Design Considerations
The exponential growth of
wireless internet systems in recent years
has created strong demand for new high data
rate wireless data services. Such systems
suffer from the limited resources due to
the limited bandwidth. Therefore, it is
important to develop techniques that utilize
the available bandwidth efficiently. One
way of utilizing the wireless resources
efficiently is by adopting a good scheduling
scheme. Good scheduling schemes in wireless
networks should opportunistically seek to
exploit channel conditions to achieve higher
network performance. By transmitting to
the best user in terms of channel condition
we are opportunistically scheduling users.
However, transmitting every time to the
best user introduces an important tradeoff
between wireless resource efficiency and
level of satisfaction among different users.
For example, allowing only users close to
the base station to transmit at high transmission
power may result in very high throughput,
but sacrifices the transmissions of other
users. Providing quality of service (QoS),
in particular meeting the data rate and
packet delay constraints of real-time data
users, is one of the requirements in emerging
highspeed data networks. In opportunistic
scheduling other considerations must be
taken into account, e.g., throughput, fairness,
queue delay, etc. In this tutorial, we present
an overview of multiuser opportunistic scheduling.
The tutorial begins by an overview of the
constraints of a wireless shared medium
and the relevant performance measures in
designing any scheduling scheme. The tutorial
then introduces various kinds of opportunistic
scheduling schemes (fair, semi-fair, and
non-fair). The tutorial then proceeds to
opportunist scheduling algorithms that make
use of multiple antennas. The tutorial also
covers practical considerations in opportunistic
scheduling such as the effect of parameter
estimation and quantization, limited feedback,
and channel correlation (in time, frequency,
and space). The tutorial ends with some
consideration of the opportunistic scheduling
in current wireless standards such as CDMA/HDR
and other IEEE 802 standards.