Abstract
Orthogonal
Frequency Division Multiplexing (OFDM) has recently been proposed as a modulation
technique for optical networks, because of its good spectral efficiency, flexibility,
and tolerance to impairments. We consider the planning problem of an OFDM
optical network, where we are given a traffic matrix that includes the requested
transmission rates of the connections to be served. Connections are provisioned
for their requested rate by elastically allocating spectrum using a variable
number of OFDM subcarriers and choosing an appropriate modulation level, taking
into account the transmission distance. We introduce the Routing, Modulation
Level and Spectrum Allocation (RMLSA) problem, as opposed to the typical Routing
and Wavelength Assignment (RWA) problem of traditional WDM networks, prove
that is also NP-complete and present various algorithms to solve it. We start
by presenting an optimal ILP RMLSA algorithm that minimizes the spectrum used
to serve the traffic matrix, and also present a decomposition method that
breaks RMLSA into its two substituent subproblems, namely 1) routing and modulation
level and 2) spectrum allocation $({\rm
RML}+{\rm SA})$, and solves them sequentially. We also propose
a heuristic algorithm that serves connections one-by-one and use it to solve
the planning problem by sequentially serving all the connections in the traffic
matrix. In the sequential algorithm, we investigate two policies for defining
the order in which connections are considered. We also use a simulated annealing
meta-heuristic to obtain even better orderings. We examine the performance
of the proposed algorithms through simulation experiments and evaluate the
spectrum utilization benefits that can be obtained by utilizing OFDM elastic
bandwidth allocation, when compared to a traditional WDM network.
© 2011 IEEE
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