Enabling Dynamic Spectrum Access in 4G Networks and Beyond

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Virginia Tech

As early as 2014, mobile network operators' spectral capacity will be overwhelmed by the demand brought on by new devices and applications. To augment capacity and meet this demand, operators may choose to deploy a Dynamic Spectrum Access (DSA) overlay. Spectrum regulation is following suit, with regulators attempting to incorporate spectrum sharing through the design of spectrum access rules that support DSA. This dissertation explores the idea of DSA applied to Long Term Evolution Advanced (LTE+) networks. This idea is explored under functional, architectural, and spectrum policy aspects.

Under the functional and architectural aspects of this topic, the signaling and functionality required by such an overlay have not yet been fully considered in the architecture of an LTE+. This dissertation presents a Spectrum Accountability framework to be integrated into LTE+ MacroNet and HetNet architectures, defining specific element functionality, protocol interfaces, and signaling flow diagrams required to enforce the rights and responsibilities of primary and secondary users. We also identify and propose three DSA management frameworks for LTE+ HetNets: Spectrum Accountability Client Only, Cell Spectrum Management, and Domain Spectrum Management. Our Spectrum Accountability framework may serve as a guide in the development of future LTE+ network standards that account for DSA.

We also quantify, through simulation and integer programs, the benefits of using DSA channels to augment capacity under a scenario in which LTE+ network can opportunistically use TV and GSM spectrum. In our first experiment, we a consider a scenario where three different operators share the same cell site with LTE+ equipment and a Dynamic Spectrum Access (DSA) band to augment spectral capacity. Our experiments show that throughput can increase by as much as 40%. We develop integer programs to model the assignment of spectrum channels to both a MacroNet and HetNet. In our selected scenario, we observe TV white spectrum provides the largest gain in performance for both Nets: 27% for MacroNet and 9% increase for the HetNet over our measured ranges. Although the gains in using opportunistic use of GSM is more modest, 10% and 2% for the Macro and HetNet, respectively, we believe that these gains will significantly increase as operators continue to migrate users to LTE+, thus freeing up portions of the bands currently used for GSM service. In our final analytical model, we create integer program sets to represent the different three DSA management frameworks for LTE+ HetNets and compare their results.

Under the spectrum policy aspects, this dissertation develops a decision-theoretic framework for regulators to assess the impacts of different spectrum access rules on both primary and secondary operators. We analyze access rules based on sensing and exclusion areas, which in practice can be enforced through geolocation databases. Our results show that receiver-only sensing provides insufficient protection for primary and co-existing secondary users and overall low social welfare. On the other hand, combining sensing information of only the transmitter and receiver of a communication link provides dramatic increases in system performance. The performance of using these link end points is relatively close to that of using many cooperative sensing nodes associated to the same access point and large link exclusion areas. We hope these results will prove useful to regulators and network developers in un and developing rules for future DSA regulation.

Long Term Evolution Advanced, Cellular Networks, Dynamic Spectrum Access