text: We present an analytical framework to assess the link layer throughput of multichannel Opportunistic Spectrum Access (OSA) ad hoc networks. Specifically, we focus on analyzing various combinations of collaborative spectrum sensing and Medium Access Control (MAC) protocol abstractions. We decompose collaborative spectrum sensing into layers, parametrize each layer, classify existing solutions, and propose a new protocol called Truncated Time Division Multiple Access (TTDMA) that supports efficient distribution of sensing results in “K out of N” fusion rule. In case of multichannel MAC protocols, we evaluate two main approaches of control channel design with 1) dedicated and 2) hopping channel. We propose to augment these protocols with options of handling secondary user (SU) connections preempted by primary user (PU) by 1) connection buffering until PU departure and 2) connection switching to a vacant PU channel. By comparing and optimizing different design combinations, we show that 1) it is generally better to buffer preempted SU connections than to switch them to PU vacant channels and 2) TTDMA is a promising design option for collaborative spectrum sensing process when K does not change over time.
  @cite_48: We analyze the performance of a wireless system consisting of a set of secondary users opportunistically sharing bandwidth with a set of primary users over a coverage area. The secondary users employ spectrum sensing to detect channels that are unused by the primary users and hence make use of the idle channels. If an active secondary user detects the presence of a primary user on a given channel, it releases the channel and switches to another idle channel, if one is available. In the event that no channel is available, the call waits in a buffer until either a channel becomes available or a maximum waiting time is reached. Spectrum sensing errors on the part of a secondary user cause false alarm and mis-detection events, which can potentially degrade the quality-of-service experienced by primary users. We derive system performance metrics of interest such as blocking probabilities. Our results suggest that opportunistic spectrum sharing can significantly improve spectrum efficiency and system capacity, even under unreliable spectrum detection. The proposed model and analysis method can be used to evaluate the performance of future opportunistic spectrum sharing systems.
  @cite_55: We develop a general framework for analyzing the performance of an opportunistic spectrum sharing (OSS) wireless system at the session level with Markovian arrivals and phasetype service times. The OSS system consists of primary or licensed users of the spectrum and secondary users that sense the channel status and opportunistically share the spectrum resources with the primary users in a coverage area. When a secondary user with an active session detects an arrival of a primary session in its current channel, the secondary user leaves the channel quickly and switches to an idle channel, if one is available, to continue the session. Otherwise, the secondary session is preempted and moved to a preemption queue. The OSS system is modeled by a multi-dimensional Markov process. We derive explicit expressions for the related transition rate matrices using matrix-analytic methods. We also obtain expressions for several performance measures of interest, and present both analytic and simulation results in terms of these performance measures. The proposed OSS model encompasses a large class of specific models as special cases, and should be useful for modeling and performance evaluation of future opportunistic spectrum sharing systems.
  @cite_26: Cognitive radio (CR) is a promising technology for increasing the spectrum capacity for ad hoc networks. Based on CR, the unlicensed users will utilize the unused spectrum of the licensed users in an opportunistic manner. Therefore, the average spectrum usage will be increased. However, the sudden appearance of the licensed users forces the unlicensed user to vacate its operating channel and handoff to another free one. Spectrum handoff is one of the main challenges in cognitive ad hoc networks. In this paper, we aim to reduce the effect of consecutive spectrum handoff for cognitive ad hoc users. To achieve that, the licensed channels will be used as operating channels and the unlicensed channels will be used as backup channels when the primary user appears. Therefore, the number of spectrum handoff will be reduced, since unlicensed bands are primary user free bands. A Markov chain model is presented to evaluate the proposed scheme. Performance metrics such as blocking probability and dropping probabilities are obtained. The results show that the proposed scheme reduces all the aforementioned performance metrics.
summary: In later works, assumptions on the OSA network model became more realistic. Specifically, Markovian analysis of SU traffic buffering on the event of PU arrival was presented for a SU exponential service time @cite_48 and for a SU phase-type service time @cite_55 . Unfortunately the impact of spectrum sensing detection time overhead on the OSA network performance was not investigated and the connection arrangement process for new SU arrivals, i.e. method to select and access a channel for a new sender-receiver pair, was assumed to be performed by a centralized entity. A different option of the above model has been analyzed in @cite_26 , with only PU channels dedicated to the OSA network and with a mixture of PU and SU exclusive channels. SU connection buffering was not allowed, however, SU connections were able to switch to an empty SU exclusive channel on the event of channel preemption by the PU.