认知无线电MIMO网络中干扰消除与用户调度技术研究
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摘要
无线通信的发展对无线频谱资源的需求相应增长，从而导致适用于无线通信的频谱资源变得日益紧张，成为制约无线通信发展的新瓶颈；另一方面，根据联邦通信委员会(Fcc，Feder a1 communlcatlon commlsslon)最近研究报告，已经分配给现有无线系统的频谱资源却在时间和空间上存在不同程度的闲置。认知无线电是一项富有潜力的革新性技术，可以有效解决上述问题，它通过频谱感知、根据射频环境调整系统参数等来实现动态频谱接入和智能的频谱分配。多入多出fMIM0，MuRiple-Input／Multiple-()utput)系统则被认为是另外一种提高频谱利用率的技术，它利用多天线带来的空间维数增加和空间分集来显著提高传输性能。将这两种技术应用于下一代无线通信，可使得无线系统获得更高数据吞吐量和服务质量、更高的频谱效率及功率效率和更广泛的业务等优点。围绕MIM0与认知无线电技术，该硕士论文主要研究认知MIM()无线网络中的干扰消除技术与用户调度算法，并且将MIM()技术和频谱共享技术集成到适合不同应用场景的实现方案中。本文具有如下创新点：
(1)针对认知MIM0下行广播网络中用户调度可能存在的公平性问题，本文提出一种改进的正比公平调度(PFs，Proportional Fair Scheduling)方案。为了减少多用户MIM()系统上行的反馈量，用户终端采取天线选择：迫零波束成形(zFBF Zero．1brcingBeaJnibrmlng)被使用来消除用户之间干扰。由于本文所研究的模型是主用户(Pu，Prlmarvusei‘)和次用户(cu，Secondasvuset或者cognltlVe user)共享频谱的系统，在每个时隙，接受服务的次用户要满足两个条件：1)与主用户信道要近似正交；2)次用户之间要满足信道近似正交。这种准则是为了降低用户之间的干扰，并且提高认知无线网络的吞吐量。最后，本文改进用户调度算法，考虑了公平性。仿真结果表明，所提出的方案能够以一定的和容量的损失来实现用户之间的公平调度。
(2)提出了一种适用于频谱共享的三阶段多跳蜂窝网下行传输方案，它涉及波束成形、MIM()中继策略、多用户调度与系统帧结构设计等。其研究结果显示：通过采用MIM0中继可获得高的主蜂窝系统和速率性能；所提出的三阶段的联合调度与传输方案可以兼顾主网络的高、低速率区用户的通信；当MIM0中继同时被用作为次用户网的基站，还可以有效支持近距离的次用户通信。
With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. According to the recent report of FCC(Federal Communication Commission), the spectrum is not utilized efficiently across time and frequency. To realize opportunistic spectrum access and intelligent resource allocation, Cognitive Radio (CR) technology is a promising and innovate radio technology which is capable of sensing spectrum and of adjusting the system parameters according to the radio environment. Multiple-Input/Multiple-Output (MIMO) system is another technique to increase spectrum utilization efficiency. It can enhance the system performance significantly with the increase of the spatial dimension and diversity by using multiple antennas. MIMO and CR are considered as two key technologies for the next generation wireless communication. By using these techniques, wireless systems will have higher data throughput and service quality, better spectrum and power efficiencies as well as wider range of business. Under the framework of MIMO and CR technologies, this thesis mainly investigates efficient joint beamforming and user scheduling algorithms to maximize the sum-rate throughput of the cognitive system and also gives the development of an extendable CR framework which combines the multi-antenna technology with spectrum sharing technology for different scenarios. The specific innovations of the thesis are as follows:
(1) According to the problem occurring in the cognitive MIMO downlink network that certain users may suffer unfairness based on certain user scheduling strategies, an improved Proportional Fair Scheduling (PFS) is proposed in this thesis. To reduce the feedback of the MIMO uplink, receiver antenna selection at each cognitive user is considered; Zero-forcing Beamforming (ZFBF) is utilized to cancel inter-user interference in the studied system. Furthermore, due to some cognitive radio users coexisting with a primary user, the system schedules the cognitive users based on the correlation between the users' channel matrices, which makes all selected cognitive users :1) near-orthogonal to the primary user; 2) near-orthogonal to each other. This criterion aims to achieving higher sum-rate of the CR network while reducing the multiuser interference. The simulation results show that the proposed scheme can realize the near fair resource allocation among all cognitive users at the expense of certain sum-rate loss.
(2) A three-stage multi-hop cellular downlink transmission scheme is proposed, which is designed for spectrum sharing and involves beamforming, MIMO relaying strategy, multi-user scheduling and system design of the frame structure. The research results show: a)by using MIMO relaying, the main cellular system can obtain high data speed performance; b)the proposed three-stage scheme of joint scheduling and transmission of the main network can take into account the high and low data rate zone user communications; c)when the MIMO relaying also be used as a secondary user network base station, it can effectively support the nearby secondary users’communications.
(1)针对认知MIM0下行广播网络中用户调度可能存在的公平性问题，本文提出一种改进的正比公平调度(PFs，Proportional Fair Scheduling)方案。为了减少多用户MIM()系统上行的反馈量，用户终端采取天线选择：迫零波束成形(zFBF Zero．1brcingBeaJnibrmlng)被使用来消除用户之间干扰。由于本文所研究的模型是主用户(Pu，Prlmarvusei‘)和次用户(cu，Secondasvuset或者cognltlVe user)共享频谱的系统，在每个时隙，接受服务的次用户要满足两个条件：1)与主用户信道要近似正交；2)次用户之间要满足信道近似正交。这种准则是为了降低用户之间的干扰，并且提高认知无线网络的吞吐量。最后，本文改进用户调度算法，考虑了公平性。仿真结果表明，所提出的方案能够以一定的和容量的损失来实现用户之间的公平调度。
(2)提出了一种适用于频谱共享的三阶段多跳蜂窝网下行传输方案，它涉及波束成形、MIM()中继策略、多用户调度与系统帧结构设计等。其研究结果显示：通过采用MIM0中继可获得高的主蜂窝系统和速率性能；所提出的三阶段的联合调度与传输方案可以兼顾主网络的高、低速率区用户的通信；当MIM0中继同时被用作为次用户网的基站，还可以有效支持近距离的次用户通信。
With the advent of new high data rate wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. According to the recent report of FCC(Federal Communication Commission), the spectrum is not utilized efficiently across time and frequency. To realize opportunistic spectrum access and intelligent resource allocation, Cognitive Radio (CR) technology is a promising and innovate radio technology which is capable of sensing spectrum and of adjusting the system parameters according to the radio environment. Multiple-Input/Multiple-Output (MIMO) system is another technique to increase spectrum utilization efficiency. It can enhance the system performance significantly with the increase of the spatial dimension and diversity by using multiple antennas. MIMO and CR are considered as two key technologies for the next generation wireless communication. By using these techniques, wireless systems will have higher data throughput and service quality, better spectrum and power efficiencies as well as wider range of business. Under the framework of MIMO and CR technologies, this thesis mainly investigates efficient joint beamforming and user scheduling algorithms to maximize the sum-rate throughput of the cognitive system and also gives the development of an extendable CR framework which combines the multi-antenna technology with spectrum sharing technology for different scenarios. The specific innovations of the thesis are as follows:
(1) According to the problem occurring in the cognitive MIMO downlink network that certain users may suffer unfairness based on certain user scheduling strategies, an improved Proportional Fair Scheduling (PFS) is proposed in this thesis. To reduce the feedback of the MIMO uplink, receiver antenna selection at each cognitive user is considered; Zero-forcing Beamforming (ZFBF) is utilized to cancel inter-user interference in the studied system. Furthermore, due to some cognitive radio users coexisting with a primary user, the system schedules the cognitive users based on the correlation between the users' channel matrices, which makes all selected cognitive users :1) near-orthogonal to the primary user; 2) near-orthogonal to each other. This criterion aims to achieving higher sum-rate of the CR network while reducing the multiuser interference. The simulation results show that the proposed scheme can realize the near fair resource allocation among all cognitive users at the expense of certain sum-rate loss.
(2) A three-stage multi-hop cellular downlink transmission scheme is proposed, which is designed for spectrum sharing and involves beamforming, MIMO relaying strategy, multi-user scheduling and system design of the frame structure. The research results show: a)by using MIMO relaying, the main cellular system can obtain high data speed performance; b)the proposed three-stage scheme of joint scheduling and transmission of the main network can take into account the high and low data rate zone user communications; c)when the MIMO relaying also be used as a secondary user network base station, it can effectively support the nearby secondary users’communications.
引文
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[5] Mitola个J. Cognitive radio for flexible mobile multimedia communications [J].Journal Mobile Networks and Applications, 2001, 6 (5): 435-441.
[6] Mitola J, MAGUIRE G Q Jr. Cognitive radio: Making software radios more personal [J]. IEEE Personal Communications, 1999, 6 (4):13-18.
[7] J. Mitola,“Cognitive radio: An integrated agent architecture for software defined radio,”Ph.D. dissertation, KTH, Stockholm,Sweden, Dec. 2000.
[8] Notice of proposed rule making and order [R]. FCC Et Docket no. 03-322, 2003.
[9] HAYKIN S. Cognitive radio: Brain-empowered wireless communications [J]. IEEE Journal on Selected Areas in Communications, 2005, 23 (2): 201-220.
[10] F. N. Hatfield and P. J. Weiser,“Property rights in spectrum: taking the next step,”in Proc. IEEE Int. Symp. New Frontiers Dynamic Spectr. Access Networks, vol. 1, Baltimore, MD, USA, Nov. 2005, pp. 43–55.
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