The Research On The Transfer Protocol Of Cognitive Overlay Mode

With the number of wireless systems and services has grown exponentially, the availability of prime wireless spectrum has become severely limited. An important factor which leads to this phenomenon is the existing spectrum management strategy unreasonable. The cognitive radio (CR) is an effective way to solve this unreasonable. From the perspective of information theory, the cognitive radio approaches require different amounts of side information. Three CR network models are summarized in recent research, which are interweave, underlay, and overlay model. In the overlay model secondary users (SUs) can transmit at any power that is because the interference to primary users (PUs) can be offset by relaying the PU’s message. Thus, the overlay model has the best spectral efficiency. The cognitive overlay model faces enormous challenge, which is how to achieve the spectrum sharing between PUs and SUs, and thus become a hot issue. In order to improve the system outage performance and thoughput performance, transmission protocols in four kinds of feasibility scene of cognitive overlay model are studied, the main work and contributions of this dissertation are summarized as follows:The reliable communication of SUs is studied in two-phase cognitive radio overlay system model, which consists of a primary user and multiple secondary users. A two-phase cooperative transmission protocol based on best-relay selection for primary system is proposed in cognitive radio network. With the transmission quality of service (QoS) constraints of SUs, one of the SUs coexisting in the same spectrum as the PU can be selected to serve as a decode-and-forward (DF) relay for the primary system. The selection criterion is to maximize the signal to interference plus noise ratio for the primary system. The outage performance of the primary system is derived. The theoretical and simulation results show that the primary performance is improved and the access opportunity for secondary users is guaranteed. In addition, it indicates that the PU can achieve better outage performance as numbers of SUs increases.In the cognitive radio overlay model, a multi-hop transmission protocol based on parallel communication of SUs is proposed. The primary multi-hop network coexists with a set of SUs by cooperative spectrum sharing. The aim of the primary source is to communicate with the primary destination via a number of primary relays. Two opportunistic routing strategies are proposed. SUs may serve as extra DF relays for the primary network. When an SU acts as a relay for the PU, some other SUs that satisfy the condition for parallel communication are selected to simultaneously access the primary spectrum for secondary transmissions. A search algorithm is used to select SUs for the parallel communication is proposed. The energy consumption of the primary system is reduced by the cooperation of SUs. The throughput of the SUs and the PU is illustrated. The results demonstrate that the average throughput of the SUs is greatly improved, and the end-to-end throughput of the PU is slightly increased in the proposed protocol when the numbers of SUs are more than seven.The transmission protocol of cognitive radio overlay model based on two-path successive relaying (TPSR) is studied. The system model consists of a primary user and multiple secondary users. A spectrum sharing protocol with secondary user selection is proposed based on DF and TPSR. Two SUs, which can provide great primary outage performance, are selected to alternately help forward the primary packets, thus the PU continues its signal transmission without waiting or retransmission. With the cooperation of the two SUs, the primary system whose QoS is guaranteed is able to tolerate interference lower than a certain threshold. A third SU, which brings a low interference to the primary data transmission, is selected to access the spectrum band simultaneously when the former two are relaying. The outage performances of secondary and primary systems are illustrated. The results demonstrate that the primary outage performance is greatly improved and the secondary outage performance is also improved in the low secondary average transmit signal-to-noise ratio (SNR) region.In the cognitive radio overlay model, SU’s communications coexists with PU’s communications in the presence of an interferer is considered. The Hybrid automatic-repeat-request retransmission mechanisms are employed at primary and interfering links. A spectrum sharing protocol is proposed where the secondary system switches between cooperation and access. In the cooperation mode, the secondary transmitter forwards the interfering packet to the primary receiver, and this interfering packet can be exploited to interference mitigation at the primary receiver. Thus the performance of primary can be improved and credits are collected by secondary system. If the credits are collected enough, the secondary system will be operated in access mode, i.e. secondary data transmission is achieved over the primary spectrum, where the performance of primary is degraded and penalties are obtained. The credits are offsetted by the penalties. The primary throughput in the cooperation and the access, and the secondary throughput in the access, and the overall throughput of the primary and secondary system are derived. The results show that in the low primary SNR region, i.e., in the strong interference environment, the primary throughput of the proposed protocol is improved compared to conventional transmission protocol.