异构无线系统中的无线资源管理技术研究
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摘要
随着无线通信的快速发展,出现了多种不同无线网络并存的局面。为实现未来无线通信发展的最终目标,容纳急剧增加的移动通信用户,提供高质量的多媒体业务服务,不同类型相互重叠覆盖的各种无线通信网络就必然要融合到一起协同工作,形成一个统一的异构无线系统。无线资源管理技术是异构无线系统中的关键技术和研究热点,它涉及到的研究内容很广泛,包含了呼叫接入控制、切换控制、小区层选、负载控制、功率控制、分组调度、容量分析等领域。本文重点研究了层间呼叫双向溢出接入控制、切换和负载控制等内容。
首先对异构分层无线系统中的各种呼叫溢出技术作了统一的理论分析,并在建立的实际移动模型基础上对双向溢出呼叫接入控制方法进行了改进,兼顾了呼叫移动速度和小区覆盖面积。研究表明,快速和慢速呼叫双向溢出方法能够获得最大的信道利用率、最低的新呼叫阻塞率和切换呼叫掉线率。
在充分利用层间呼叫溢出技术的基础上,提出一种基于保护信道、队列缓冲和信道侵占的切换策略。相对于只采用保护信道的方案和同时采用保护信道与队列缓冲方案,提出的切换策略能显著降低快速和慢速实时切换业务的掉线率,同时快速和慢速非实时业务切换性能也能得到保证。
为降低热点地区的新呼叫阻塞概率和切换呼叫掉线率,并提高整个异构系统的利用率,本文对负载控制进行了深入研究,提出了几种流量均衡算法。
针对同层异构无线系统提出一种基于业务选择的流量均衡技术,采用半集中半分布式的非周期性流量控制机制。为了保证服务质量,流量均衡策略是只选择非实时性业务转移,设置的转移切换信号强度门限可以避免“乒乓”切换。仿真结果表明,新呼叫阻塞率和切换呼叫掉线率显著降低,系统利用率也得到了提高。
针对异构分层无线网络提出了3种基于逗留时间的流量均衡算法,建立了小区逗留时间计算模型。第一种是基于逗留时间的流量均衡算法,该算法的主要特点是一个流量均衡周期只选择一个呼叫,其新呼叫阻塞率和切换呼叫掉线率比随机选择流量均衡策略低。第二种是基于逗留时间的动态流量均衡算法,一个流量均衡周期内转移的呼叫数量将根据小区呼叫到达率和重叠覆盖小区的流量状态来确定,该算法的性能比第一种算法更好。第三种是基于逗留时间和业务的动态流量均衡算法,为了尽可能保证业务的QoS,该算法在第二种算法的基础上增加了业务类型,流量均衡过程中转移的呼叫只能为非实时业务,实时业务切换频率得以降低。
为进一步提高热点小区系统的信道利用率,结合信道借用和流量转移技术提出了一种混合动态流量均衡算法。信道借用用于与热点小区同类型的同构网络中,基于信道借用函数来选择信道借出小区。流量转移则采用基于逗留时间的动态流量均衡技术。每个流量均衡周期借用的信道数和转移的流量由热点小区的剩余可用信道数和新呼叫到达率来动态确定。研究表明,该混合流量均衡算法不仅能大大降低热点小区的新呼叫阻塞概率和切换呼叫掉线率,而且整个异构系统的信道利用率比基于逗留时间动态流量均衡算法高。
最后对全文进行总结,并指出今后需要进一步研究的工作。
With the rapid development of wireless communications, the various wireless networks will coexist. In order to relize the final goal of future wireless communications, accommodate mobile users increased enormously and offer multimedia traffic services with high quality, different wireless networks overlaid each other must be integrated to cooperate and form an uniform heterogeneous system. The radio resource management is a key technology and a research hotspot in the heterogeneous system. It includes many sub-areas such as call access control, handoff control, layer selection, load control, power control, packet schedule, capacity analysis and so on. The call access control (CAC) of bidirectional call-overflow, handoff, load control and others are emphatically studied in this thesis.
Firstly, various call-overflow schmems in the heterogeneous hierarchical wireless system are analysed with uniform theory. On the basis of real mobile model builded, the control method of bidirectional call-overflow is improved, the speed of call and size of cell are considered simultaneously. Simulation results show that the improved call-overflow scheme can gain maximum channel utilization, the lowest blocking probability of new calls and dropping probability of handoff calls.
On the basis of making the best of call-overflow scheme, a handoff strategy based on guard channel, queuing and channel preemption is proposed. Simulation results show that compared with the scheme of only guard channel adopted and the scheme of both guard channel and queuing used, the proposed handoff scheme can dramatically decrease the dropping probabilities of fast and slow real-time traffic, and guarantee the performance of fast and slow nonreal-time handoff traffic.
In order to decrease the call blocking probability (CBP) and call dropping probability (CDP), heighten the utilization of overall heterogeneous system, the load control is researched and several load balancing algorithms are proposed.
A load balancing scheme based on traffic selection is proposed for the heterogeneous wireless system composed of same layer wireless networks, in which non-periodical load control mechanism of half-centralization and half-distribution is employed. For the sake of QoS guaranteed, only nonreal-time traffic are selected to transfer. A handoff signal strength threshold for transfer is set to avoid ping-pong handoff. Simulation results show that the CBP and CDP are greatly decreased, system utilization is also enhanced.
For the heterogeneous hierarchical syetem, three load balancing algorithms based on sojourn time are proposed. A model is used to calculate the cell sojourn time. The first algorithm is called load balancing algorithm based on sojourn time, only one call can be selected to transfer from overloaded cell to under-loaded cell overlaid per load balancing period. This algorithm has lower CBP and CDP than those of random selection algorithm.
The second is a dynamic load balancing algorithm, in which the number of transferred calls in a load balancing period is calculated according to call arrival rate and the workload states of overlaid cells with the hot spot cell. The second algorithm outperforms the first algorithm. The third algorithm is based on the second algorithm and considers the type of call service. Only nonreal-time traffic calls can be transferred in the third load balancing algorithm, so the handoff frequency of real-time traffic in the third algorithm is lower than those of other two load balancing algorithms.
In order to further increase the channel utilization of hotspot cell system, a hybrid dynamic load balancing algorithm is proposed based on the combination of channel borrowing scheme and load transfer scheme. The hotspot cells can borrow channels from homogeneous cells with light workload in the compact pattern. At the same time, some ongoing calls can be transferred from hotspot cells into the overlapping heterogeneous cells with light workload according to certain conditions. The total number of channels borrowed and ongoing calls transferred per load balancing period is computed by the remainder available channels and new calls arrival rates of hotspot cell. Simulation results show that the proposed hybird dynamic load balancing algorithm can decrease CBP, CDP of hot-spot cell system and overall heterogeneous system, and the system utilization of overall heterogeneous system is increased accordingly.
Finally, it concludes the dissertation briefly, and the future research work is indicated.
首先对异构分层无线系统中的各种呼叫溢出技术作了统一的理论分析,并在建立的实际移动模型基础上对双向溢出呼叫接入控制方法进行了改进,兼顾了呼叫移动速度和小区覆盖面积。研究表明,快速和慢速呼叫双向溢出方法能够获得最大的信道利用率、最低的新呼叫阻塞率和切换呼叫掉线率。
在充分利用层间呼叫溢出技术的基础上,提出一种基于保护信道、队列缓冲和信道侵占的切换策略。相对于只采用保护信道的方案和同时采用保护信道与队列缓冲方案,提出的切换策略能显著降低快速和慢速实时切换业务的掉线率,同时快速和慢速非实时业务切换性能也能得到保证。
为降低热点地区的新呼叫阻塞概率和切换呼叫掉线率,并提高整个异构系统的利用率,本文对负载控制进行了深入研究,提出了几种流量均衡算法。
针对同层异构无线系统提出一种基于业务选择的流量均衡技术,采用半集中半分布式的非周期性流量控制机制。为了保证服务质量,流量均衡策略是只选择非实时性业务转移,设置的转移切换信号强度门限可以避免“乒乓”切换。仿真结果表明,新呼叫阻塞率和切换呼叫掉线率显著降低,系统利用率也得到了提高。
针对异构分层无线网络提出了3种基于逗留时间的流量均衡算法,建立了小区逗留时间计算模型。第一种是基于逗留时间的流量均衡算法,该算法的主要特点是一个流量均衡周期只选择一个呼叫,其新呼叫阻塞率和切换呼叫掉线率比随机选择流量均衡策略低。第二种是基于逗留时间的动态流量均衡算法,一个流量均衡周期内转移的呼叫数量将根据小区呼叫到达率和重叠覆盖小区的流量状态来确定,该算法的性能比第一种算法更好。第三种是基于逗留时间和业务的动态流量均衡算法,为了尽可能保证业务的QoS,该算法在第二种算法的基础上增加了业务类型,流量均衡过程中转移的呼叫只能为非实时业务,实时业务切换频率得以降低。
为进一步提高热点小区系统的信道利用率,结合信道借用和流量转移技术提出了一种混合动态流量均衡算法。信道借用用于与热点小区同类型的同构网络中,基于信道借用函数来选择信道借出小区。流量转移则采用基于逗留时间的动态流量均衡技术。每个流量均衡周期借用的信道数和转移的流量由热点小区的剩余可用信道数和新呼叫到达率来动态确定。研究表明,该混合流量均衡算法不仅能大大降低热点小区的新呼叫阻塞概率和切换呼叫掉线率,而且整个异构系统的信道利用率比基于逗留时间动态流量均衡算法高。
最后对全文进行总结,并指出今后需要进一步研究的工作。
With the rapid development of wireless communications, the various wireless networks will coexist. In order to relize the final goal of future wireless communications, accommodate mobile users increased enormously and offer multimedia traffic services with high quality, different wireless networks overlaid each other must be integrated to cooperate and form an uniform heterogeneous system. The radio resource management is a key technology and a research hotspot in the heterogeneous system. It includes many sub-areas such as call access control, handoff control, layer selection, load control, power control, packet schedule, capacity analysis and so on. The call access control (CAC) of bidirectional call-overflow, handoff, load control and others are emphatically studied in this thesis.
Firstly, various call-overflow schmems in the heterogeneous hierarchical wireless system are analysed with uniform theory. On the basis of real mobile model builded, the control method of bidirectional call-overflow is improved, the speed of call and size of cell are considered simultaneously. Simulation results show that the improved call-overflow scheme can gain maximum channel utilization, the lowest blocking probability of new calls and dropping probability of handoff calls.
On the basis of making the best of call-overflow scheme, a handoff strategy based on guard channel, queuing and channel preemption is proposed. Simulation results show that compared with the scheme of only guard channel adopted and the scheme of both guard channel and queuing used, the proposed handoff scheme can dramatically decrease the dropping probabilities of fast and slow real-time traffic, and guarantee the performance of fast and slow nonreal-time handoff traffic.
In order to decrease the call blocking probability (CBP) and call dropping probability (CDP), heighten the utilization of overall heterogeneous system, the load control is researched and several load balancing algorithms are proposed.
A load balancing scheme based on traffic selection is proposed for the heterogeneous wireless system composed of same layer wireless networks, in which non-periodical load control mechanism of half-centralization and half-distribution is employed. For the sake of QoS guaranteed, only nonreal-time traffic are selected to transfer. A handoff signal strength threshold for transfer is set to avoid ping-pong handoff. Simulation results show that the CBP and CDP are greatly decreased, system utilization is also enhanced.
For the heterogeneous hierarchical syetem, three load balancing algorithms based on sojourn time are proposed. A model is used to calculate the cell sojourn time. The first algorithm is called load balancing algorithm based on sojourn time, only one call can be selected to transfer from overloaded cell to under-loaded cell overlaid per load balancing period. This algorithm has lower CBP and CDP than those of random selection algorithm.
The second is a dynamic load balancing algorithm, in which the number of transferred calls in a load balancing period is calculated according to call arrival rate and the workload states of overlaid cells with the hot spot cell. The second algorithm outperforms the first algorithm. The third algorithm is based on the second algorithm and considers the type of call service. Only nonreal-time traffic calls can be transferred in the third load balancing algorithm, so the handoff frequency of real-time traffic in the third algorithm is lower than those of other two load balancing algorithms.
In order to further increase the channel utilization of hotspot cell system, a hybrid dynamic load balancing algorithm is proposed based on the combination of channel borrowing scheme and load transfer scheme. The hotspot cells can borrow channels from homogeneous cells with light workload in the compact pattern. At the same time, some ongoing calls can be transferred from hotspot cells into the overlapping heterogeneous cells with light workload according to certain conditions. The total number of channels borrowed and ongoing calls transferred per load balancing period is computed by the remainder available channels and new calls arrival rates of hotspot cell. Simulation results show that the proposed hybird dynamic load balancing algorithm can decrease CBP, CDP of hot-spot cell system and overall heterogeneous system, and the system utilization of overall heterogeneous system is increased accordingly.
Finally, it concludes the dissertation briefly, and the future research work is indicated.
引文
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