Research On Dynamic Spectrum Access Based On Hierarchical Access Model

The explosive growth of wireless communications was plagued with spectrum scarcity. In order to ease spectrum scarcity, spectrum efficiency should be improved to make the limited spectrum support more data transmission. Dynamic spectrum access, which allows more than one wireless system to share the same spectrum band, can significantly improve the spectrum efficiency and plays an important role in the alleviation of spectrum scarcity problem. Cognitive radio is the core technology to realize dynamic spectrum access. This paper focuses on the hierarchical access model in dynamic spectrum access, and concerns three technical issues of cognitive radio:spectrum sensing, spectrum analysis and decision making, and spectrum allocation.1. Spectrum SensingOn the issue of spectrum sensing, this paper focuses on the decision fusion technology in cooperative spectrum sensing and seeks for the solution to the reliability estimation of spectrum sensing nodes. In this paper, a cooperative spectrum sensing scheme based on detection reliability statistics (CSS-DRS scheme) is proposed, in which fusion center estimates the sensing reliability of each node by means of probability statistics. In CSS-DRS scheme, fusion center takes the sensing reliability of each node into consideration when combining the local decisions of sensing nodes. Compared with the existing schemes, the CSS-DRS scheme can improve the sensing reliability in cognitive radio without increasing the system transmission overhead.2. Spectrum Analysis and Decision Making On the issue of spectrum analysis and decision making, this paper focuses on the analysis of time domain characteristics of spectrum holes and seeks for the solution to time domain statistical prediction of spectrum occupancy. In this paper, a dynamic prediction scheme of spectrum occupancy (DP-SO scheme) for hierarchical access is proposed, which analyses the time domain statistical characteristics of authorized spectrum based on the transient probability distribution of Markov chain. Spectrum Decision is made according to the analysis result of the DP-OS scheme. Compared with the existing schemes, the proposed DP-SO scheme considers the impact of initial state on the spectrum occupancy in a queuing process, and therefore provides more reliable prediction results.3. Spectrum AllocationOn the issue of spectrum allocation, this paper focuses on the non-cooperative completely limited power control in centralized cognitive radio network. In this paper, a downlink power control scheme based on asynchronous search (DPC-AS scheme) is proposed to deal with inter-cell interference of cognitive radio system. In DPC-AS scheme, each base station adjusts the downlink transmission power respectively aims at optimizing the total channel capacity. The power control process corresponds to an asynchronous search towards the direction of gradient ascent in hypersurface of channel capacity. So the total channel capacity will converge to local maximum after several loops of power control. Compared with the existing schemes, the DPC-AS scheme improves the system throughput and brings down the transmission power of base station.