Research On Cross-layer Opportunistic Cognitive Routing For Spectrum-Aware Based Crahns

Cognitive Radio Networks(CRNs) have been receiving significant research attention recently due to their ability to solve issues associated with spectrum congestion and under-utilization. Due to the dynamicity of spectrum availability in Cognitive Radio Ad Hoc Networks(CRAHNs), design of protocols and schemes at different layers of the CRNs’ stack has been challenging. In this dissertation, aiming at CRAHNs in a harsh electromagnetic environment, we focus on the cross-layer cooperation and optimization for cooperative sepectrum sensing and routing in CRAHNs, combining channel selection strategies with routing selection strategies, coupling cooperative spectrum sensing technology in the Physical(PHY) layer and the scheduling mechanism in the Medium Access Control(MAC) layer with routing schemes in the Network layer, and propose a opportunistic cognitive routing protocol(DCSS-OCR) that exploits a Dual Collaborative Spectrum Sensing(DCSS) scheme to improve the accuracy of spectrum availability and the efficiency of transmission capability. The simulation results experimentally and theoretically reveal the benefits of the proposed schemes to improve effectively the end-to-end Quality of Service(Qo S) and spectrum usage in CRAHNs. The dissertation content and contributions are summaried as follows:Considering the complex issues of CRAHNs in a harsh electromagnetic environment, such as hidden terminal and shadow fading problems, a dynamic and variable time-division multiple-access(DV-TDMA) scheduling mechanism is proposed to combine with a dual collaborative spectrum sensing(DCSS) model, because cooperative spectrum sensing has been shown to be an effective method to mitigate the impact of hidden terminal and shadow fading in CRNs. Moreover, this dissertation derives closed-form expressions of the average sensing time and the amount of time slots for DCSS scheme, and addresses the critical range of time slot length. Finally, an optimized algorithm to minimize the average sensing time is deduced and its feasibility verified by the theoretical analysis and simulations. The simulation results indicate that the proposed DCSS scheme is more beneficial to cognitive radio users in less ideal electromagnetic environments, compared to the single cooperative spectrum sensing(SCSS) scheme, the shortening of the average sensing time by as much as 11.5% while still meeting the average detection error rate requirement of less than 1%.Considering the open issue of cross-layer cooperation, this dissetation studies the optimal cross-layer scheme for the Opportunistic Spectrum Access(OSA), and proposes an optimization of MAC frame structure and a multi-objective optimized algorithm for OSA to enhance the accuracy and time agility of spectrum sensing, and the throughput of CRAHNs. Moreover, an optimal energy detection threshold and an optimal throughput are also deduced by minimizing the average detection error ratio of the entire network. Finally, the simulated results indicate that the performance of the optimized DCSS method outperforms the DCSS scheme without optimization and the SCSS scheme while still meeting the average detected error ratio requirement of less than 1%.Considering the instability of routing in multi-channels and multi-hops CRAHNs, Opportunistic Cognitive Routing(OCR) coupled with cooperative spectrum sensing in that networks is investigated. Recognizing the spectrum dynamics and the problems of hidden terminal and shadow fading in CRAHNs, the dissertation proposes an opportunistic cognitive routing protocol(DCSS-OCR) that exploits a DCSS scheme to improve the accuracy of spectrum availability to discover and establish the opportunity routing. Solutions to select the best channel and the optimal routing path are designed. Moreover, a DCSS-OCR model is builded, which considering jointly the accuaracy of spectrum sensing, the link availability and the shortest path, to reach an effective routing in space and frequency domains. Finally, effcient routing metrics are proposed and deduced, including link availability probability, breakage probability, path access opportunity, expected link average transmission delay and average path delay.Finally, taking explicitly into account the unique dynamic characheristics of CRAHNs, an optimal routing metric is proposed and validated. Performance evaluation is conducted through simulations, and the results reveal that routing access opportunity, breakage probability and the average transmission delay of link and the path using the proposed DCSS, compared with those using the SCSS scheme and non-cooperation sensing(NCS) scheme, are closer to the practical value of routing establishment. Besides, it is observed that the number of available channels, the number of next hop cognitive routing node and routing hop counts also affect the successful rate of routing establishment. Therefore, the simulations validate the accuracy and optimality of the proposed shemes.In the end, the research is summarized in this dissertation, and the guidelines for routing are pointed out in CRAHNs.