移动WiMAX系统的中继选择和切换机制研究
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摘要
无线宽带接入迅速发展的驱动力来自用户对宽带业务的需求。近些年来,各种无线宽带接入技术(Wi-Fi、WiMAX、Bluetooth、3G)的发展,使人们能够摆脱电话线的束缚,逐渐从固定走向移动。宽带无线接入技术以其成本低廉、不受地理环境的约束、支持用户的移动性等优点,将成为解决“最后一公里”接入问题的重要手段,是目前通信与信息技术领域发展最快的技术之一。
基于IEEE802.16系列标准的WiMAX技术加速了宽带无线网络“最后一公里”的部署,可以为DSL或有线宽带接入不能到达地区的用户提供便捷的解决方案,推动了全球宽带无线接入的发展。WiMAX能够提供高速的数据业务,并且具有频谱资源利用率高,覆盖范围大等特点。
下一代移动通信系统支持用户100Mbit/s～1Gbit/s的传输速率,如此高的速率对现有的蜂窝网络结构提出了许多现实的挑战。由于频率资源的紧张,大部分无线系统都将在大于2GHz频段上应用,如此高频段无线电信号的衰减比现有的1～2GHz频段要严重的多,小区边缘用户的服务质量就得不到保证。如果继续采取现有的网络结构将无法适应未来无线应用的要求,而Ad-hoc网络则是一种利用多个中间节点多跳转发将报文信息从源节点传递到目的节点实现节点之间通信的网络。移动多跳中继(Mobile Multihop Relay, MMR)网络综合了蜂窝网络和Ad-hoc网络的优点,通过负载均衡,路径分集等优势提高网络的抗干扰性,增强网络的稳健性。
IEEE802.16中继任务工作组将中继站的思想引入了IEEE802.16体系并形成了新的标准IEEE802.16j。IEEE802.16j并不是要建立一种包含多跳能力的mesh网络,而是对支持单跳的802.16d／e标准的扩展和补充使其拥有多跳通信的能力。通过在基站信号弱的地区布建成本相对低的中继站RS作为网络拓展负责将无线信号作一次或者多次转发,也就是说,无线信号要经过“多跳”才能到达终端。RS的引入可以扩大网络覆盖范围,提高数据吞吐量以及降低网络运营的成本等。
在移动通信系统中,切换是系统必不可少的过程,用户在蜂窝覆盖区内移动时其正在进行的呼叫有可能从一个小区覆盖区转移到另一个小区覆盖区,切换必须快而有效,否则将会影响用户在小区边界处的体验,而且还可能会对网络造成一定的负荷,降低系统的总体质量。在IEEE802.16j下的移动台MS可供选择的切换途径增多,既可以选择切换至某一中继站RS,或者切换至某一基站BS。在RS覆盖范围内,由于MS的移动性以及RS较小的覆盖范围,MS的切换更加频繁,切换控制更加复杂。
本文研究了在MMR网络中几种中继站的选择算法,并针对MMR网络提出一种基于路径损耗和SINR的改进最优中继选择算法与现有算法进行比较,仿真结果表明了在有效降低系统中断概率和提高网络的稳健性等方面所提方案的优越性；在某些情况下,由于资源调度或者是中继的负载均衡等原因可能无法得到最优中继的服务,在这种情况下就应该寻找次优中继或者第N个最优中继,通过对非最优中继选择策略下的系统中断性能以及误码率的分析研究了系统的分集级数与中继数目以及非最优中继N之间的关系。最后提出了在移动多跳中继网络中,通过考虑网络服务不同QoS需求的服务类型对切换门限值和迟滞电平的调整可以对移动台MS在多跳中继网络切换的执行进行干预,控制切换的层次和水平,有效降低不必要的切换次数,降低切换过程的“乒乓”效应,大大降低切换过于频繁引起的服务中断,保证了提供服务的连续性,提高了切换效率。
The rapid development of wireless broadband access driving force is the needs of users'broadband services. In recent years, various wireless broadband access technologies (Wi-Fi, WiMAX, Bluetooth,3G) enable people to shake off the shackles of telephone lines, and gradually from fixed to mobile. Broadband wireless access technology, with its low cost, without geographical constraints, support for user mobility and other advantages, which will become the important means of "last mile" access issues in communication and information technology is the fastest growing areas of the technologies.
WiMAX broadband wireless network technology based on IEEE802.16 series of standards accelerates the "last mile" deployment for DSL or cable access inaccessible areas to provide convenient solutions which promotes the global broadband wireless access development. WiMAX can provide high-speed data services and high resource utilization in the spectrum, a large coverage area and so on.
Next generation mobile communication system can support users'100Mbit/s-1Gbit/s transfer rate, such a high rate on the existing cellular network structure made many practical challenges. As the frequency resource constraints, most wireless systems will be greater than the 2GHz band applications, such a high frequency radio results to signal attenuation be more severe than the existing 1～2GHz band, cell edge users will not get the quality of service guarantee. Such a network will not be able to adapt to future wireless applications. The Ad-hoc networks are more intermediate nodes by means of a multi-hop packet of information which will be passed from the source node to destination node to achieve communication between the network nodes. Mobile Multi-hop relay (MMR) network integrates the advantages of cellular networks and Ad-hoc network to increase network interference and enhance network robustness through load balancing and path diversity advantages.
IEEE802.16 Relay Task Group introduced relay station into IEEE802.16 system and formed a new standard IEEE802.16j. IEEE802.16j doesn't establish a multi-hop mesh network but expands single-hop 802.16d/e standards to support the capacity of multi-hop communications. Weak signal in a network go through "multi-hop" to reach the end by relay station. RS can expand the network coverage, increase data throughput and reduce network operating costs.
In the mobile communication system, the user moves in the cellular coverage area and its ongoing call may be transferred from one cell coverage area to another cell coverage area. Handoff should be quickly and effectively, otherwise will affect the user experience in the district boundaries, but also may cause certain network load and reduce the system's overall quality. Mobile station under the IEEE802.16j has much choice of handoff means, the option to switch to a relay station or switch to a base station. Within the coverage area of the RS, MS switch more frequently because of MS's mobility and less coverage of the RS, Handoff control will be more complex.
In this paper, several relay station selection algorithms in the MMR networks are researched, and we propose improved optimal relay selection algorithm based on path loss and SINR which are compared with existing algorithms. Simulation results show that the system is reduced disruption probability and improve the robustness of the network. In some cases, due to resource scheduling or load balancing and other reasons MS may not get the best relay services. In this case, we should look for second-best relay or the Nth-best relay, and we research the system performance such as interruption and bit error rate performance under the Nth-best relay selection strategy. Finally, in the mobile multi-hop relay network, we propose an improved handoff algorithm to adjustment MS handoff procedure on the handoff threshold and hysteresis level by considering QoS requirements of different service types. This handoff algorithm effectively improves the handoff efficiency, reduces the unnecessary handoff, reduces the handoff "ping-pong" effect and greatly reduces the handoff service interruptions to ensure continuity of services.
基于IEEE802.16系列标准的WiMAX技术加速了宽带无线网络“最后一公里”的部署,可以为DSL或有线宽带接入不能到达地区的用户提供便捷的解决方案,推动了全球宽带无线接入的发展。WiMAX能够提供高速的数据业务,并且具有频谱资源利用率高,覆盖范围大等特点。
下一代移动通信系统支持用户100Mbit/s～1Gbit/s的传输速率,如此高的速率对现有的蜂窝网络结构提出了许多现实的挑战。由于频率资源的紧张,大部分无线系统都将在大于2GHz频段上应用,如此高频段无线电信号的衰减比现有的1～2GHz频段要严重的多,小区边缘用户的服务质量就得不到保证。如果继续采取现有的网络结构将无法适应未来无线应用的要求,而Ad-hoc网络则是一种利用多个中间节点多跳转发将报文信息从源节点传递到目的节点实现节点之间通信的网络。移动多跳中继(Mobile Multihop Relay, MMR)网络综合了蜂窝网络和Ad-hoc网络的优点,通过负载均衡,路径分集等优势提高网络的抗干扰性,增强网络的稳健性。
IEEE802.16中继任务工作组将中继站的思想引入了IEEE802.16体系并形成了新的标准IEEE802.16j。IEEE802.16j并不是要建立一种包含多跳能力的mesh网络,而是对支持单跳的802.16d／e标准的扩展和补充使其拥有多跳通信的能力。通过在基站信号弱的地区布建成本相对低的中继站RS作为网络拓展负责将无线信号作一次或者多次转发,也就是说,无线信号要经过“多跳”才能到达终端。RS的引入可以扩大网络覆盖范围,提高数据吞吐量以及降低网络运营的成本等。
在移动通信系统中,切换是系统必不可少的过程,用户在蜂窝覆盖区内移动时其正在进行的呼叫有可能从一个小区覆盖区转移到另一个小区覆盖区,切换必须快而有效,否则将会影响用户在小区边界处的体验,而且还可能会对网络造成一定的负荷,降低系统的总体质量。在IEEE802.16j下的移动台MS可供选择的切换途径增多,既可以选择切换至某一中继站RS,或者切换至某一基站BS。在RS覆盖范围内,由于MS的移动性以及RS较小的覆盖范围,MS的切换更加频繁,切换控制更加复杂。
本文研究了在MMR网络中几种中继站的选择算法,并针对MMR网络提出一种基于路径损耗和SINR的改进最优中继选择算法与现有算法进行比较,仿真结果表明了在有效降低系统中断概率和提高网络的稳健性等方面所提方案的优越性；在某些情况下,由于资源调度或者是中继的负载均衡等原因可能无法得到最优中继的服务,在这种情况下就应该寻找次优中继或者第N个最优中继,通过对非最优中继选择策略下的系统中断性能以及误码率的分析研究了系统的分集级数与中继数目以及非最优中继N之间的关系。最后提出了在移动多跳中继网络中,通过考虑网络服务不同QoS需求的服务类型对切换门限值和迟滞电平的调整可以对移动台MS在多跳中继网络切换的执行进行干预,控制切换的层次和水平,有效降低不必要的切换次数,降低切换过程的“乒乓”效应,大大降低切换过于频繁引起的服务中断,保证了提供服务的连续性,提高了切换效率。
The rapid development of wireless broadband access driving force is the needs of users'broadband services. In recent years, various wireless broadband access technologies (Wi-Fi, WiMAX, Bluetooth,3G) enable people to shake off the shackles of telephone lines, and gradually from fixed to mobile. Broadband wireless access technology, with its low cost, without geographical constraints, support for user mobility and other advantages, which will become the important means of "last mile" access issues in communication and information technology is the fastest growing areas of the technologies.
WiMAX broadband wireless network technology based on IEEE802.16 series of standards accelerates the "last mile" deployment for DSL or cable access inaccessible areas to provide convenient solutions which promotes the global broadband wireless access development. WiMAX can provide high-speed data services and high resource utilization in the spectrum, a large coverage area and so on.
Next generation mobile communication system can support users'100Mbit/s-1Gbit/s transfer rate, such a high rate on the existing cellular network structure made many practical challenges. As the frequency resource constraints, most wireless systems will be greater than the 2GHz band applications, such a high frequency radio results to signal attenuation be more severe than the existing 1～2GHz band, cell edge users will not get the quality of service guarantee. Such a network will not be able to adapt to future wireless applications. The Ad-hoc networks are more intermediate nodes by means of a multi-hop packet of information which will be passed from the source node to destination node to achieve communication between the network nodes. Mobile Multi-hop relay (MMR) network integrates the advantages of cellular networks and Ad-hoc network to increase network interference and enhance network robustness through load balancing and path diversity advantages.
IEEE802.16 Relay Task Group introduced relay station into IEEE802.16 system and formed a new standard IEEE802.16j. IEEE802.16j doesn't establish a multi-hop mesh network but expands single-hop 802.16d/e standards to support the capacity of multi-hop communications. Weak signal in a network go through "multi-hop" to reach the end by relay station. RS can expand the network coverage, increase data throughput and reduce network operating costs.
In the mobile communication system, the user moves in the cellular coverage area and its ongoing call may be transferred from one cell coverage area to another cell coverage area. Handoff should be quickly and effectively, otherwise will affect the user experience in the district boundaries, but also may cause certain network load and reduce the system's overall quality. Mobile station under the IEEE802.16j has much choice of handoff means, the option to switch to a relay station or switch to a base station. Within the coverage area of the RS, MS switch more frequently because of MS's mobility and less coverage of the RS, Handoff control will be more complex.
In this paper, several relay station selection algorithms in the MMR networks are researched, and we propose improved optimal relay selection algorithm based on path loss and SINR which are compared with existing algorithms. Simulation results show that the system is reduced disruption probability and improve the robustness of the network. In some cases, due to resource scheduling or load balancing and other reasons MS may not get the best relay services. In this case, we should look for second-best relay or the Nth-best relay, and we research the system performance such as interruption and bit error rate performance under the Nth-best relay selection strategy. Finally, in the mobile multi-hop relay network, we propose an improved handoff algorithm to adjustment MS handoff procedure on the handoff threshold and hysteresis level by considering QoS requirements of different service types. This handoff algorithm effectively improves the handoff efficiency, reduces the unnecessary handoff, reduces the handoff "ping-pong" effect and greatly reduces the handoff service interruptions to ensure continuity of services.
引文
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[2]3GPP TR 25.999.Technical Specification Group Radio Access Network; HSPA Evolution (FDD) 2008
[3]IEEE Std 802.16e-2005:IEEE Standard for Local and Metropolitan Area Networks Part 16:Air Interface for Fixed Broadband Wireless Access Systems Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands.2005.
[4]IEEE Std 802.11-1997. Information Technology-telecommunications And Information exchange Between Systems-Local And Metropolitan Area Networks-specific Requirements-part 11:Wireless Lan Medium Access Control (MAC) And Physical Layer (PHY) Specifications.1997
[5]NI W, SHEN G, JIN S. Cooperative relay approaches in IEEE802.16j. IEEE802.16 Broadband Wireless Access Working Group[R]. C802.16j-07/258r1,2007
[6]David Chen, I-Kang Fu, Mike Hart and Wendy Wong, "Channel Models and Performance Metrics for IEEE 802.16j Relay Task Group", Contribution of IEEE 802.16 Broadband Wireless Access Working Group:IEEE C80216j-06/020, May 2006.
[7]IEEE 802.16e/D5-2004, Part 16:Air Interface for Fixed and Mobile Broadband Wireless Access Systems-Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands, Nov.,2004.
[8]W. Honcharenko, J. P.Kruys, D. Y. Lee, et al. Broadband Wireless Access. IEEE Communications Magazine, Jan.1997,35(1):20-26.
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