【作者】 王首峰；

【导师】 张英海；

【作者基本信息】 北京邮电大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 认知无线电是通过与周围环境交互信息,以感知和利用所处空间中的可用频谱,并限制和降低对授权用户的干扰,提高现有授权频段频谱利用率的一种新兴技术。其中,频谱接入与频谱切换技术作为认知无线电的关键技术受到了学术界和产业界的广泛关注。论文着重研究了频谱空洞的差异对频谱接入与频谱切换技术的影响以及从用户控制信道的接入方法两方面的技术问题。本文分析了频谱空洞的频率、从用户所处无线环境、主从用户间干扰以及从用户业务匹配需求等因素对从用户利用频谱空洞的影响,并提出了相应的解决方案。基于对频谱接入和频谱切换技术的研究,本文提出了认知无线电控制信道的接入方案,该方案可以提高控制信道的可靠性和有效性。本文的主要研究如下：1.本文分析了频谱空洞在被从用户使用的过程中产生的不均匀特性,研究了频谱空洞不均匀性对从用户频谱接入和频谱切换的影响。基于论文对频谱空洞不均匀性的分析,本文提出了基于频谱空洞不均匀性的频谱接入方案。该方案将实现从用户有效地利用频谱空洞的容量作为优化目标,提出了从用户业务需求与频谱空洞容量匹配的原则来控制从用户的频谱接入。经理论推导和仿真分析证明,基于频谱空洞不均匀性的频谱接入方案在保证主用户通信质量的同时可以降低从用户的掉话率,并提高整个频段的频谱利用率。2.本文基于对频谱空洞时变特性的研究,提出了从用户主动切换方案及频谱空洞预留方案用来提高频谱切换的可靠性。在从用户主动切换方案中,从用户根据主用户占用频谱的统计规律预测其检测到的频谱空洞的可用时长,并将频谱空洞的可用时长作为触发切换的依据。当前正在使用的频谱空洞的可用时长较短时,从用户主动进行频谱切换并选择可用时长较长的频谱空洞作为其目标频谱空洞,减少了频谱切换的频度。在频谱空洞预留方案中,从用户通过为频谱切换预留频谱空洞来增加频谱切换的可靠性。仿真和数值分析验证了从用户主动切换方案和频谱空洞预留方案可以有效降低频谱切换掉话率。3.本文在分析频谱空洞不均匀性的基础上,研究了提高控制信道有效性和可靠性的方法,提出了一种快速控制信道接入方案。在该方案中,从用户使用不同频谱空洞依次传递控制信息,通过缩短从用户在每个频谱空洞上停留的时间达到降低控制信息传输时延的目的。该方案提出了从用户短时借用业务信道传输控制信息的方法,有效降低了主用户占用频谱空洞导致从用户控制信道中断的概率。方案优化了控制信道占用资源的比例,提供了更多资源供业务信道使用。仿真分析表明,该方案可以有效减少控制信道建立时间和控制信息传输时延,并且能够有效抵抗由主用户出现造成的控制信道中断。本文的主要贡献在于,在频谱接入与频谱切换技术研究中引入频谱空洞不均匀性的影响,加强了理论研究与潜在工程应用之间的联系。本文首先量化并利用了频谱空洞在频域和空域的差异,实现了匹配从用户业务需求与频谱空洞容量的频谱接入。其次基于频谱空洞时域的不均匀性,本文提出了预测频谱空洞可用时长的从用户主动切换方案和提高频谱切换可靠性的频谱空洞预留方案,从而保证了从用户业务质量。最后本文设计了一种快速控制信道接入方案,该方案降低了控制信息传输时延,提高了控制信道可靠性,进一步提高了频谱接入与频谱切换的可靠性。更多还原

【Abstract】 As an emerging technology that significantly improves the utilization of licensed frequency bands, cognitive radio exchanges information with its operational environment in order to utilize the spare licensed spectrum and can restrict its interference to guarantee the communication of licensed users. Among the key technologies in cognitive radio, spectrum access and spectrum handover have received extensive concern from both academia and industry.This dissertation focuses on two topics:the effects of spectrum holes’differences on spectrum access and spectrum handover, and the control channel access algorithms. A secondary user’s utilization of a spectrum hole is influenced by the frequency of the spectrum hole being used, the wireless environment where the secondary user stays, the interference from primary users and the service requirement of this secondary user. This research studies the differences of spectrum holes, and proposes new algorithms of spectrum access and spectrum handover to utilize these differences enhancing the performance of the secondary system. Based on the research of spectrum access and spectrum handover, the fast control channel selection algorithm is proposed to increase the reliability of control channel and the efficiency of control information exchange. The main contributions and innovations of this dissertation are as follows:1. The influence of the diversity of spectrum holes on spectrum access/spectrum handover is analyzed. According to the analysis, the spectrum access algorithm based on the diversity of spectrum holes is proposed which matches the service requirements of secondary users with the capacities of spectrum holes. The proposed scheme takes the capacity obtained by secondary users as the optimization target. Both the simulations and the evaluations prove that the proposed scheme can guarantee the communication of primary users, reduce the drop ratio of secondary users and increase spectrum utilization.2. Based on the research of time domain diversity of spectrum holes, the active spectrum handover scheme and the spectrum-hole reservation scheme are proposed to increase the reliability of spectrum handover. In active spectrum handover scheme, secondary users predict the duration of spectrum-hole availability according to the statistics of primary users’activity. The duration of spectrum-hole availability is used to trigger a spectrum handover. Secondary users perform the handover when the duration of spectrum-hole availability is too short, and choose the spectrum hole with long duration of availability as the target spectrum hole. The frequency of spectrum handover is reduced in active spectrum handover scheme. In the spectrum-hole reservation scheme, secondary users reserve spectrum holes for handovers to enhance the reliability of handovers. Simulations and evaluations prove that the two schemes can reduce the drop ratio effectively.3. The reliability of control channel is researched based on the analysis of the diversity of spectrum holes. The fast control channel selection algorithm is proposed to enhance the efficiency and the reliability of control channels. Secondary users use the spectrum holes alternitaively to transmit control information in the proposed algorithm. The dwelling time on each spectrum hole is shortened in the algorithm, and the delay of control information transmission is reduced. Secondary users can temporarily borrow the spectrum holes assigned for traffic channel to decrease the probability of control channel failure due to primary user’s reappearance. The algorithm optimizes the resource used for control channel, making more spectrum holes available for traffic channels. According to the simulations, the proposed algorithm can reduce the delay of the control channel build-up time and the delay of the control information transmission, and the algorithm can decrease the control channel failure probability.The research of this dissertation enhances the relation between theoretical study and potential engineering application, by introducing the diversity of spectrum holes into the research of spectrum access and spectrum handover. Firstly, the spectrum access algorithm matching secondary users’ service requirements and the capacities of spectrum holes is proposed, by quantizing and utilizing the diversity of spectrum holes in frequency domain and spatial domain. Secondly, the active spectrum handover scheme and the spectrum-hole reservation scheme are proposed to increase the reliability of spectrum handover. Thirdly, the fast control channel selection algorithm is proposed to enhance the efficiency and the reliability of control channels, increasing the reliability of both spectrum access and spectrum handover.更多还原