The steady growth in demand for spectrum has increased research interest in dynamic spectrum access schemes. This thesis studies some challenges in dynamic spectrum access based on two strategies: open sharing and hierarchical access. (1) In the open sharing model, the channels are allocated based on an auction process, taking into account the propagation characteristics of the channels, termed as channel heterogeneity. Two distributed dynamic spectrum access schemes are evaluated, sequential and concurrent. We show that the concurrent accessmechanismperforms better in terms of channel utilization and energy consumption, especially in wireless cellular network with an energy constraint. (2) In the hierarchical model, we assess the opportunities for secondary access in the radar band at 5.6GHz. The primary user is a meteorological radar and WLANs are the secondary users. The secondary users implement an interference protection mechanism to protect the radar, such that the WLAN’s transmission is regulated by an interference threshold. We evaluate the aggregate interference caused to the radar from multiple WLANs transmitting. We derive a mathematicalmodel to approximate the probability distribution function of the aggregate interference at the primary user, considering two cases: when secondary users are homogeneously distributed, and when they are heterogeneously distributed. The heterogeneous distribution of secondary users is modeled using an annulus sector with a higher density, called a hot zone. Finally, we evaluate opportunities for secondary access when WLANs employ an interference protection mechanism that considers the radar’s antenna pattern, such that temporal opportunities for transmission exist. The analytical probability distribution function of the interference is verified showing a good agrement with a Monte Carlo simulation. We show that the aggregate interference is sensitive to the propagation environment, thus in the rural case interference is more severe when compared to the urban case. In the evaluation of the hot zonemodel, we observe that the heterogenous distribution of secondary users has impact on the aggregate interference if the hot zone is near to the radar. The mathematical framework presented in this thesis can easily be adapted to assess interference to other types of primary and secondary users. / QC 20110523
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-33791 |
| Date | January 2011 |
| Creators | Tercero Vargas, Miurel |
| Publisher | KTH, Kommunikationssystem, CoS, Stockholm : KTH Royal Institute of Technology |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Trita-ICT-COS, 1653-6347 ; 1105 |
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