Research On Dynamic Spectrum Allocation, Spectrum Access, Resource Optimization Based On Spectrum Characteristics In Cognitive Radio

Cognitive Radio is intended to improve spectrum efficiency by reusing the spectrum resource shared between the primary system and the cognitive system. Therefore, cognitive radio has been thought to be the best way to relief the problem of spectrum shortage and has been paid more and more attentions. However, how to make cognitive system have an effective utilization of the spectrum resource becomes an important priority.Firstly, traditional dynamic spectrum allocation mechanisms focus on avoiding interference among cognitive networks in order to share spectrum effectively among these cognitive networks, but they do not guarantee the reliability of the cognitive system; secondly, traditional spectrum access mechanisms are applied under spectrum sensing errors or interference temperature limit required by the primary system, these mechanisms are designed to avoid interference to the primary system while ignoring system performance of cognitive system; thirdly, there are multi-dimensional characteristics of spectrum resource in cognitive system, but traditional resource optimization methods just consider parts of these characteristics, how to combine these multi-dimensional characteristics and realize an optimum match between spectrum resources and radio services need to be deeply researched. Therefore, in order to make cognitive system re-use spectrum resources effectively, the thesis researches these three mechanisms mentioned above and makes some innovations listed as follows. The innovations about dynamic spectrum allocation mechanisms are shown as following:To deal with the call dropping problem caused by the instability of spectrum resource in cognitive network, a dynamic spectrum allocation mechanism based on risk-sharing has been proposed in this thesis. By this mechanism, the call dropping rate is reduced while the stability of the cognitive system is improved, in a way of sharing the risk of spectrum reoccupation by the primary system.When the above mentioned mechanism is applied to the broadband cognitive system with various channel bandwidths, the cognitive system will have more overhead. Therefore, a self-adaptive dynamic spectrum allocation mechanism is proposed. The mechanism can determine the threshold of system stability for each cognitive network, according to the distribution of services types, and then optimization theory is referred to achieve a better trade-off between spectrum stability and continuity. The mechanism can improve system stability as well as reduce system overhead.To deal with the frequent spectrum handoff problem caused by the instability of spectrum in cognitive network, a new spectrum assignment mechanism intra cognitive cell is proposed in this thesis. The mechanism is based on adaptive radio multi-homing and mapping scheme between traffic flows and spectrum resource.The innovations about spectrum accessing mechanisms are shown as following:For sensing errors in spectrum sensing mechanism, a spectrum access mechanism based on spectrum prediction is put forward. In this mechanism, a new method of spectrum prediction based on Support Vector Mechanism (SVM) is proposed. This method can predict spectrum occupied or idle more effectively, and judge the correctness of spectrum sensing results accordingly, in order to eliminate the harmful effect caused by sensing errors in the cognitive network. This mechanism is applied to the scenario in which cognitive and primary networks share the primary spectrum in temporal.For the interference temperature limit required by the primary system, a spectrum access mechanism based on uplink and downlink interference models and power control on multi-users is put forward, it can guide cognitive terminals in different locations to access the spectrum and to transmit in a certain power. It can suppress interference to the primary system and guarantee the communication in the cognitive system. This mechanism is applied to the scenario in which cognitive and primary networks share the primary spectrum in spatial.The innovation about resource optimization method is shown as following:For multi-dimensional characteristics of spectrum and diversity of services in cognitive system, a resource optimization method based on joint descriptions of spectrum characteristics has been given. The method can establish relational matching between spectrum resource and services, and in this matching, service type, location of cognitive terminals, interference temperature limited, spectrum space between the cognitive transmitter and the primary transmitter, and spectrum instability are considered comprehensively. The method can make cognitive system use spectrum resource effectively.A summary is given at the end of this thesis, where the future research directions related to this thesis are also pointed out.