Channel fragmentation in dynamic spectrum access systems

Abstract

Dynamic Spectrum Access systems exploit temporarily available spectrum ('white spaces') and can spread transmissions over a number of non-contiguous sub-channels. Such methods are highly beneficial in terms of spectrum utilization. However, excessive fragmentation degrades performance and hence off-sets the benefits. Thus, there is a need to study these processes so as to determine how to ensure acceptable levels of fragmentation. Hence, we present experimental and analytical results derived from a mathematical model. We model a system operating at capacity serving requests for bandwidth by assigning a collection of gaps (sub-channels) with no limitations on the fragment size. Our main theoretical result shows that even if fragments can be arbitrarily small, the system does not degrade with time. Namely, the average total number of fragments remains bounded. Within the very difficult class of dynamic fragmentation models (including models of storage fragmentation), this result appears to be the first of its kind. Extensive experimental results describe behavior, at times unexpected, of fragmentation under different algorithms. Our model also applies to dynamic linked-list storage allocation, and provides a novel analysis in that domain. We prove that, interestingly, the 50% rule of the classical (non-fragmented) allocation model carries over to our model. Overall, the paper provides insights into the potential behavior of practical fragmentation algorithms.

Spectrum Allocation and QoS Provisioning Framework for Cognitive Radio With Heterogeneous Service Classes

“…The channel allocation procedure begins with the maximum s = s max and is repeated for descending values, down to minimum s = s min . Starting the allocation from s max is aimed towards minimizing the number of unused fragments at the end of allocation procedure for efficient use of the spectrum [23], [24].…”

A performance analysis of channel fragmentation in dynamic spectrum access systems

“…Our main result is a proof that, even if fragments can be arbitrarily small, the system remains stable in the sense that the average total number of fragments remains bounded. Within the class of dynamic fragmentation models, includ-This paper is a revision for journal publication of the conference paper [3]. All of the results herein can be found in [3].…”

“…Within the class of dynamic fragmentation models, includ-This paper is a revision for journal publication of the conference paper [3]. All of the results herein can be found in [3].…”

“…Further details on Dynamic Spectrum Access Networks can be found in[3], which also contains an extensive review of related work.…”