Abstract
A point-to-multipoint system consisting of an optical transmitter (known
as the central node) equipped with <i>K</i> apertures, and <i>K</i> users communicating over free-space optical (FSO) channels is considered.
It is assumed that each link suffers from weak-turbulence conditions. The
main goal of this paper is to analyze the performance of the system for various
multiuser diversity scheduling schemes in terms of the turbulence strength,
from the throughput and the latency perspectives. It is demonstrated that
for the proposed system with low turbulence strength, the greedy scheduling
scheme (i.e., the central node serves at each time slot the user with the
best channel characteristics) achieves the maximum system throughput among
various scheduling algorithms at the cost of a large latency. We extend the
well-known RF concepts of multiuser diversity to FSO communications. In particular,
we show that the Proportional Fair Scheduling with Exponential Rule (PFS/ER)
scheme achieves the minimum latency. In addition, the results demonstrate
that for point-to-multipoint FSO systems with low turbulence strengths, using
the proportional fair scheduling (PFS) has no diversity gain over other schemes.
Finally, two new scheduling algorithms are introduced to achieve a tradeoff
between the throughput and the latency in FSO-based systems.
© 2012 IEEE
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