  In conventional wireless systems, unless a contiguous frequency band with
width at least equal to the required bandwidth is obtained, multimedia
communication can not be effected with the desired Quality of Service. We
propose here a novel channel allocation technique to overcome this limitation
in a Cognitive Radio Network which is based on utilizing several non-contiguous
channels, each of width smaller than the required bandwidth, but whose sum
equals at least the required bandwidth. We present algorithms for channel
sensing, channel reservation and channel deallocation along with transmission
and reception protocols with two different implementations based on $FDM-FDMA$
and $OFDM-FDMA$ techniques. Simulation results for both these implementations
show that the proposed technique outperforms the existing first-fit and
best-fit~\cite{b109, b110} allocation techniques in terms of the average number
of attempts needed for acquiring the necessary number of channels for all
traffic situations ranging from light to extremely heavy traffic. Further, the
proposed technique can allocate the required numbers of channels in less than
one second with $FDM-FDMA$ ($4.5$ second with $OFDM-FDMA$) even for $96\%$
traffic load, while the first-fit and best-fit techniques fail to allocate any
channel in such situations.
