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ROPAS:一种基于认知无线电的移动超宽带网络跨层架构

ROPAS: Cross-Layer Cognitive Architecture for Mobile UWB Networks

  • 摘要: 目前的一些实验表明很多在超高频(UHF)带宽内的授权频谱的利用率很低。另一方面,对宽带服务的需求,如一些集成了语音、数据和音乐的应用,揭露了无线频谱资源的缺乏问题。认知无线电(CR)可以调和频谱利用率低和频谱资源缺乏这两者之间的矛盾。CR检测到频谱的未被使用的部分,并将这部分带宽动态地分配给未授权的用户,同时满足低发射功率的要求。这个低发射功率的要求使得超宽带(UWB)通信设备成为理想的授权UHF频谱的使用者。但是,在不增加对现有授权用户干扰的情况下,将带宽动态地分配给未授权的UWB用户,是目前面临的一个挑战。在本文中,作者针对授权UHF带宽内的UWB通信问题,提出了一个全新的Rake优化和具有节能意识的调度(ROPAS)架构。因为UWB通信容易受到多径效应的影响,所以使用耙式接收器(rake receiver)来实现路径多样性。在ROPAS架构下开发一个优化的耙式接收器的基本思想来源于减少耙式接收器的每个耙指(rake finger)在权值推算过程中的乘法和加法的次数,以此来降低计算复杂度。认知无线电用于将信道动态地分配给请求的用户,同时限制每个子频带的平均发射功率。基于认知无线电的跨层设计涉及物理层和MAC层之间的信息共享。以前提出的动态信道分配策略没有结合功率控制,以降低对授权用户的干扰。本文提出的结合了功率控制的动态信道分配策略在将子频带分配给未授权用户的同时,保证对授权用户的干扰在容许的范围内(美国联邦通信委员会对UWB通信提出的频谱模板的要求是-41.3 dBm/MHz)。此外,采用一种基于优先级的调度策略,将一个帧间隔内的最大并行发送数定义为一个优化问题。问题的最优解基于发送方和接收方之间的距离、位误码率和应用的请求频率。该优化问题还采用一种区分技术,将用户的请求标以不同的优先级。这样可以通过调节UWB网络要求的功率限制和数据发送速率,保证公平性和较高的吞吐率。

     

    Abstract: The allocation of bandwidth to unlicensed users, withoutsignificantly increasing the interference on the existing licensedusers, is a challenge for Ultra Wideband (UWB) networks. Ourresearch work presents a novel Rake Optimization and Power AwareScheduling (ROPAS) architecture for UWB networks. Since UWBcommunication is rich in multipath effects, a Rake receiver is usedfor path diversity. Our idea of developing an optimized Rakereceiver in our ROPAS architecture stems from the intention ofreducing the computation complexity in terms of the number ofmultiplications and additions needed for the weight derivationattached to each finger of the Rake receiver. Our proposed work usesthe Cognitive Radio (CR) for dynamic channel allocation among therequesting users while limiting the average power transmitted ineach sub-band. In our proposed novel ROPAS architecture, dynamicchannel allocation is achieved by a CR-based cross-layer designbetween the PHY and Medium Access Control (MAC) layers.Additionally, the maximum number of parallel transmissions within aframe interval is formulated as an optimization problem. Thisoptimal decision is based on the distance parameter between atransmitter-receiver pair, bit error rate and frequency of requestby a particular application. Moreover, the optimization problemimprovises a differentiation technique among the requestingapplications by incorporating priority levels among userapplications. This provides fairness and higher throughput amongservices with varying power constraint and data rates required for aUWB network.

     

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