With the traditional static spectrum management, a significant portion of the licensed spectrum is underutilized in most of time while the unlicensed spectrum is over-crowded due to the growing demand for wireless radio spectrum from exponential growth of various wireless devices. Dynamic Spectrum Access utilizes the wireless spectrum in a more intelligent and flexible way. Cognitive radios are a promising enabler for Dynamic Spectrum Access because they can sense and access the idle channels. With cognitive radios, the unlicensed users (SUs) can opportunistically identify and access the vacant portions of the spectrum of the licensed users (PUs). In cognitive radio networks (CRNs), multiple idle channels may be available to SUs. If two or more SUs want to communicate with each other, they must select a channel which is available to all of them. The process of two or more SUs to meet and establish a link on a commonly-available channel is known as rendezvous. 1) Multiple Radios for Fast Rendezvous in CRNs: The existing works on rendezvous implicitly assume that each cognitive user is equipped with one radio (i.e., one wireless transceiver). As the cost of wireless transceivers is dropping, this feature can be exploited to significantly improve the rendezvous performance at low cost. We investigate the rendezvous problem in CRNs where cognitive users are equipped with multiple radios and different users may have different numbers of radios. We first study how the existing rendezvous algorithms can be generalized to use multiple radios for faster rendezvous. We then propose a new rendezvous algorithm, called role-based parallel sequence (RPS), which specifically exploits multiple radios for more efficient rendezvous. Our basic idea is to let the cognitive users stay in a specific channel in one dedicated radio and hop on the available channels with parallel sequences in the remaining general radios. We prove that RPS provides guaranteed rendezvous (i.e., rendezvous can be completed within a finite time) and derive the upper bounds on the maximum time-to-rendezvous (TTR) and the expected TTR. The simulation results show that i) multiple radios can cost-effectively improve the rendezvous performance, and ii) the proposed RPS algorithm performs better than the ones generalized from the existing algorithms. 2) Efficient Channel-Hopping Rendezvous Algorithm Based on Available Channel Set: All the existing rendezvous algorithms that provide guaranteed rendezvous (i.e., rendezvous can be achieved within finite time) generate channel-hopping (CH) sequences based on the whole channel set. However, some channels may be unavailable (e.g., being used by the licensed users) and these existing algorithms would randomly replace the unavailable channels by the available ones in the CH sequence. This random replacement is not effective, especially when the number of unavailable channels is large. We design a new rendezvous algorithm, called Interleaved Sequences based on Available Channel set (ISAC), that attempts rendezvous on the available channels only for faster rendezvous. ISAC constructs an odd subsequence and an even subsequence and interleaves these two subsequences to compose a CH sequence. We prove that ISAC provides guaranteed rendezvous. We derive the upper bounds on the maximum time-to-rendezvous to be O(
| Identifer | oai:union.ndltd.org:hkbu.edu.hk/oai:repository.hkbu.edu.hk:etd_oa-1213 |
| Date | 28 August 2015 |
| Creators | Yu, Lu |
| Publisher | HKBU Institutional Repository |
| Source Sets | Hong Kong Baptist University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Open Access Theses and Dissertations |
| Rights | The author retains all rights to this work. The author has signed an agreement granting HKBU a non-exclusive license to archive and distribute their thesis. |
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