Abstract
Frequency channels are assigned in wireless local-area network (WLAN) mesh
networks subject to strict cochannel interference constraints. Since Wi-Fi may be freely
used by other networks, added interference may eventually invalidate the original
frequency assignment, making full link activation impossible. In this paper, we address
this problem by selectively installing supplementary free-space optical (FSO) links when
radio-frequency (RF) link performance has deteriorated. To minimize cost, the number of
FSO links that are needed should be as small as possible. We first formulate the channel
assignment problem with the objective of maximizing the number of simultaneous link
activations while satisfying cumulative RF interference constraints. A proof is given
for the NP-completeness of the joint frequency assignment and FSO link placement
problem. We then propose an efficient heuristic to solve the channel assignment problem
using a genetic algorithm. Results are then presented for various mesh networks which
show that the proposed algorithm has good results compared with the computed bounds. The
presented results show that the use of FSO links permits WLAN mesh network deployment in
interference-prone situations.
© 2008 IEEE
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