IP化基站无线Mesh组网构架

无线网状网（WMN）融合了无线局域网（WLAN）和Ad Hoc网络的性能优势,具有容量大、速率高、覆盖范围广等特点,成为宽带无线接入的一种有效手段,可以灵活地应用于多种无线环境。目前,蜂窝移动通信系统中各基站间的有线连接,使得传统的蜂窝移动通信系统难以满足部署方便、成本低廉、高可扩展性、高可靠性等指标。为适应下一代移动通信网络扁平化、简单化的发展趋势,IP化基站的无线Mesh组网架构是可选方案之一。支持IP化基站自组织的关键技术包括按需的基站自组织技术、联合无线资源调度机制、路由技术、安全技术、网络管理技术等。     

A resource estimation and call admission algorithm for wirelessmultimedia networks using the shadow cluster concept

The shadow cluster concept can be used to estimate future resource requirements and to perform call admission decisions in wireless networks. Shadow clusters can be used to decide if a new call can be admitted to a wireless network based on its quality-of-service (QoS) requirements and local traffic conditions. The shadow cluster concept can especially be useful in future wireless networks with microcellular architectures where service will be provided to users with diverse QoS requirements. The framework of a shadow cluster system is completely distributed, and can be viewed as a message system where mobile terminals inform the base stations in their neighborhood about their requirements, position, and movement parameters. With this information, base stations predict future demands, reserve resources accordingly, and admit only those mobile terminals which can be supported adequately. The shadow cluster concept involves some processing and communication overheads. These overheads have no effect on wireless resources, but only on the base stations and the underlying wireline network. It is shown how base stations determine the probabilities that a mobile terminal will be active in other cells at future times, define and maintain shadow clusters by using probabilistic information on the future position of their mobile terminals with active calls, and predict resource demands based on shadow cluster information. In addition, a call admission algorithm is introduced, which uses current traffic and bandwidth utilization conditions, as well as the amount of resources and maximum allowable “dropping probability” being requested. Performance results showing the advantages of the shadow cluster concept are also included     

Resource management implications and strategies for SDR clouds

This paper analyzes the computing resource management implications of SDR base stations implemented as SDR clouds. SDR clouds describe distributed antennas that connect to a data center for digital signal processing. The data center employs cloud computing technology, providing a virtualized computing resource pool. The service area of a single SDR cloud may be a metropolitan area with a high user density. Hence, the data center will execute thousands of SDR applications in parallel, providing wireless communications services to several radio cells. Whenever a user initiates or terminates a wireless communications session, computing resources need to be allocated or deallocated in real time. We therefore propose a hierarchical resource management. This paper justifies such an approach and analyzes different resource management strategies. The results indicate the need for strategies that can dynamically adapt to the given user traffic distribution.     

Least squares algorithms for time-of-arrival-based mobile location

Localization of mobile phones is of considerable interest in wireless communications. In this correspondence, two algorithms are developed for accurate mobile location using the time-of-arrival measurements of the signal from the mobile station received at three or more base stations. The first algorithm is an unconstrained least squares (LS) estimator that has implementation simplicity. The second algorithm solves a nonconvex constrained weighted least squares (CWLS) problem for improving estimation accuracy. It is shown that the CWLS estimator yields better performance than the LS method and achieves both the Crame/spl acute/r-Rao lower bound and the optimal circular error probability at sufficiently high signal-to-noise ratio conditions.     

Actual call connection time characterization for wireless mobile networks under a general channel allocation scheme

Actual call connection time (ACCT) is the total time that a mobile user engages in communications over a wireless network during a call connection. Due to limited network resources of wireless mobile networks, a call connection may be prematurely disconnected and the ACCT for the call in general may not be the same as the requested call connection time (RCCT). The ACCT depends not only on the RCCT, but also on the network resource allocation scheme and network traffic. We characterize the ACCT and related performance metrics for wireless mobile networks under a newly proposed general channel allocation scheme. This scheme generalizes the nonprioritized scheme, the reserved channel scheme, the queueing priority scheme and the subrating scheme in such a way as to reduce the blocking probability of the handoff calls while keeping the ACCT as long as possible. Explicit formulae for the distribution and the expectation of the ACCT are obtained. The call completion probability, the call drop probability, and the average actual call connection times for both the complete calls and the incomplete calls are derived. The results can form the basis for designing better billing rate schemes by differentiating incomplete calls and complete calls.     

Antenna systems for broadband wireless access

Broadband wireless access along with evolving mobile Internet and multimedia services are driving the surge of research and development activities for future wireless communication systems. We provide an overview of antenna systems for broadband wireless communications and introduce some of the important issues surrounding them. The approach we use is to first provide a general framework of how antenna systems may be utilized in wireless communication systems and then describe the antenna systems themselves. In particular, we consider antenna systems for the base station, mobile station, and then finally multiple-input multiple-output antenna systems where antenna systems are utilized at both the base and mobile stations     

Adaptive Resource Management in Mobile Wireless Networks Using Feedback Control Theory

Emerging mobile wireless networks are characterized by significant uncertainties in mobile user population and system resource state. Such networks require adaptive resource management that continuously monitor the system and dynamically adjust resource allocations for adherence to the desired system performance requirements. We propose adaptive resource management technique based on control theory. The controller dynamically solves resource allocation problem using feedback control laws. In the base algorithm, the number of guard channels is dynamically adjusted by feeding back the current handoff call dropping probability. The base algorithm is then enhanced in two ways: feeding back the instantaneous number of handoff calls and by probabilistically implementing a fractional number of guard channels. We study the effects of parameter choices on the performance of the proposed algorithms using discrete event simulation. Simulation results indicate that the feedback controllers can guarantee the predetermined call dropping probability under a variety of traffic conditions, and so can utilize the scarce wireless resource efficiently by accepting more new calls.     

分层多跳无线网中结合负载均衡的切换管理

该文主要研究分层多跳无线网络中的切换管理,提出一种新的用户切换管理算法和移动基站路由切换策略.在网络动态变化时,用户切换管理算法可以减少用户的切换次数,使用户负载分布均匀.移动基站路由切换策略则尽可能地从基站本地找出替代路由,可以在较小的开销下达到快速和无缝切换的目的.     

Tracking mobile users in wireless communications networks

Tracking strategies for mobile wireless networks are studied. A cellular architecture in which base stations that are interconnected by a wired network communicate with mobile units via wireless links is assumed. The cost of utilizing the wireless links for the actual tracking of mobile users is considered. A tracking strategy in which a subset of all base stations is selected and designed as reporting centers is proposed. Mobile users transmit update messages only upon entering cells of reporting centers, while every search for a mobile user is restricted to the vicinity of the reporting center to which the user last reported. It is shown that, for an arbitrary topology of the cellular network (represented by the mobility graph), finding an optimal set of reporting centers is an NP-complete problem. Optimal and near-optimal solutions for important special cases of the mobility graph are presented     

Applications of antenna arrays to mobile communications. I.Performance improvement, feasibility, and system considerations

The demand for wireless mobile communications services is growing at an explosive rate, with the anticipation that communication to a mobile device anywhere on the globe at all times will be available in the near future. An array of antennas mounted on vehicles, ships, aircraft, satellites, and base stations is expected to play an important role in fulfilling the increased demand of channel requirement for these services, as well as for the realization of the dream that a portable communications device the size of a wristwatch be available at an affordable cost for such services. This paper is the first of a two-part study. It provides a comprehensive treatment, at a level appropriate to nonspecialists, of the use of an antenna array to enhance the efficiency of mobile communications systems. It presents an overview of mobile communications as well as details of how an array may be used in various mobile communications systems, including land-mobile, indoor-radio, and satellite-based systems. It discusses advantages of an array of antennas in a mobile communications system, highlights improvements that are possible by using multiple antennas compared to a single antenna in a system, and provides details on the feasibility of antenna arrays for mobile communications applications     

An enhanced distributed power control algorithm for mobile femtocells under limited dynamic range and its convergence

This paper presents a distributed power control algorithm for wireless backhaul links of mobile femtocells by using the pilot’s information. Taking into account the limited dynamic range of transmitted powers, the SINR balancing of mobile (vehicular) femto base stations in their home macro base station and the load balancing among the macrocells are achieved by the proposed approach at the cost of exchanging some limited information among both macro and vehicular femto base stations. The algorithm is very beneficial especially in a high load heterogeneous network. Monte Carlo simulation results denote that the mobile femtocells can be uniformly assigned to the macrocells and the SINR balancing is achievable via the proposed scheme.

     

基于多点协作联合传输的超密集组网性能分析

超密集组网的基站高密度特性会带来严重的小区间干扰,多点协作联合传输应用于超密集组网进行干扰管理是目前的研究热点,该文对多点协作联合传输时基站密度对网络性能的影响进行了分析。首先采用随机几何方法推导了3维空间基站与用户距离的概率密度函数,为选取距离用户最近的多个基站联合传输的协作机制提供了基础;然后结合有界双斜率路径损耗模型,进行用户下行链路的干扰建模,进一步推导出用户下行链路覆盖率和网络区域频谱效率的表达式,并分析了协作基站数、基站密度等参数对网络性能的影响。数值仿真表明:协作基站数为2时就可使下行链路覆盖率增加10%,且实现2到3倍的频谱效率的增益,当协作基站数为3时,费效比更优,同时可得到多点协作下的基站密度极限使区域频谱效率最高。该文工作可为下一代移动通信网络的基站部署提供理论支持。     

Location management strategies for cellular mobile networks

Location management in mobile communication systems is concerned with those network functions necessary to allow the users to be reached wherever they are in the network coverage area. The basic operations for that purpose-paging and location updating-are resource-consuming since both involve signalling over the radio link between the mobile stations and base stations. Future cellular mobile communication networks (wireless personal communication networks (PCN)) will have to support a large number of users, so a significant amount of radio signalling can be expected. This paper describes the conventional location management strategy (the one used in modern cellular systems like the Global System for Mobile communications (GSM)) and reviews, describes and comments on some alternative location management proposals for future high-density PCN environments that aim to reduce this expected high (radio) signalling load     

An efficient heterogeneous key management approach for secure multicast communications in ad hoc networks

In a mobile wireless ad hoc network, mobile nodes cooperate to form a network without using any infrastructure such as access points or base stations. Instead, the mobile nodes forward packets for each other, allowing communication among nodes outside wireless transmission range. As the use of wireless networks increases, security in this domain becomes a very real concern. One fundamental aspect of providing confidentiality and authentication is key distribution. While public-key encryption has provided these properties historically, ad hoc networks are resource constrained and benefit from symmetric key encryption. In this paper, we propose a new key management mechanism to support secure group multicast communications in ad hoc networks. The scheme proposes a dynamic construction of hierarchical clusters based on a novel density function adapted to frequent topology changes. The presented mechanism ensures a fast and efficient key management with respect to the sequential 1 to n multicast service.     

Supporting the WWW in Wireless Communications Through Mobile Agents

Mobile computing is considered of major importance to the computing industry for the forthcoming years due to the progress in wireless mobile communications. We present a proxy-based architecture that manages to accelerate Web browsing in wireless Customer Premises Networks (CPN). We discuss how such an architecture is implemented using the IBM Aglets framework for mobile agents. The suggested architecture relies heavily on proxy caches – maintained in base stations – which are relocated to follow a roaming user in other control areas (clusters of cells). The cache management scheme involves relocation of full caches to the most-likely-to-be visited control areas, but also fractions of the cache to less-likely-to-be-visited neighbours. A movement prediction algorithm, based on a learning automaton, is used to determine the future location of the terminal. The discussed architecture components have been implemented as Aglets to allow for the efficient introduction of the service in a CPN infrastructure.     

Wireless Mesh Architecture for IP-Based Base Stations

Combining the performance advantages of both Wireless Local Area Network (WLAN) and Ad hoc network, Wireless Mesh Network (WMN) is characterized by large capacity, high rate and wide coverage. It has become an effective means for broadband wireless access and can be applied flexibly in various wireless environments. The wired connections between base stations in traditional cellular mobile communications systems can no longer satisfy the requirements for flexible deployment, low cost, high scalability and good reliability. The wireless Mesh architecture for IP-based base stations is thus introduced as an optional solution to support the flat and simplified next generation mobile communications networks. The key technologies used to support self-organization of IP-based base stations involve several aspects, including on-demand self-organization of base stations, joint radio resource scheduling mechanism, routing, security and network management.     

Generalized multiuser orthogonal space-division multiplexing

This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary.     

Adaptive antennas at the mobile and base stations in an OFDM/TDMAsystem

Several smart antenna systems have been proposed and demonstrated at the base station (BS) of wireless communications systems, and these have shown that significant system performance improvement is possible. We consider the use of adaptive antennas at the BS and mobile stations (MS), operating jointly, in combination with orthogonal frequency-division multiplexing. The advantages of the proposed system includes reductions in average error probability and increases in capacity compared to conventional systems. Multiuser access, in space, time, and through subcarriers, is also possible and expressions for the exact joint optimal antenna weights at the BS and MS under cochannel interference conditions for fading channels are derived. To demonstrate the potential of our proposed system, analytical along with Monte Carlo simulation results are provided     

Adjacent-Cell Interference in Direct-Sequence CDMA Forward Traffic Channels

Each transmission from a base station in a mobile cellular direct-sequence CDMA network is a source of interference for the receivers in the mobile handsets that are operating in adjacent cells. This interference can limit the capacity of the forward traffic channels. The effect of adjacent-cell interference on the performance of the handset receivers is evaluated for a mobile cellular CDMA network that employs quadriphase-shift-key spreading, convolutional coding, and soft-decision decoding. It is demonstrated that acceptable performance may not be possible for a fully loaded cellular network. Of particular interest in this paper are cellular networks in which the base stations are mobile and must be interconnected by wireless communication links. Such networks are important for military applications and certain civilian emergency communications services.