Quality of service for multimedia traffic using cross-layer design

Quality-of-service (QoS) guarantees are critical for the transmission of multimedia traffic over mobile wireless networks. Currently, wireless networks provide QoS guarantees using the legacy layered protocol architecture where each layer provides a separate, independent solution, with its own optimised adaptation and protection mechanisms. Cross-layer design has been proposed as a methodology to extend that paradigm in wireless links where there is interdependence between the layers and hence opportunity for information sharing. Recently, cross-layer adaptation mechanisms have been proposed which attempt to solve the QoS provisioning problem. However, most of these mechanisms only use the lower (physical and data link) layers and the possibility of using higher protocol layers remains unexplored. As a result, restrictions are placed on the system which introduces functional and efficiency limitations. Here, one such limitation is highlighted, namely the inability to insert more than one class of traffic in a physical layer frame. A physical and application layer cross-layer adaptation mechanism is then proposed, which overcomes this limitation. The performance results of the scheme show that the cross-layer mechanism can be efficiently applied for the purpose of providing QoS guarantees for multimedia traffic.     

Authentication mechanism over the integrated UMTS network and WLAN platform using the cross-layer bootstrap

The 3G mobile data network provides always-on and ubiquitous connectivity for subscribers. Although the service coverage area in wireless local area network (WLAN) is much smaller than that in a 3G mobile data network, the data transmission rate in WLAN can be from 2 to 54 Mbps, which is much faster than 3G mobile network. Obviously, the relationship between the 3G mobile data network and WLAN is complementary in terms of service coverage and data transmission rate. Therefore integration of 3G mobile network and WLAN can offer subscribers higher speed wireless service in hot spots and ubiquitous connectivity in 3G mobile data network. An authentication mechanism over the loose coupled integration mechanism using a cross-layer bootstrap is proposed. The benefits of the proposed mechanism are (a) integrating Universal Mobile Telecommunication System network and WLAN using the existing protocols denned in 3GPP, IETF and IEEE 802. Hi, (b) the use of the Extension Authentication Protocol authentication method is flexible, (c) reduction of the authentication signalling when a subscriber roams from one access point (AP) to another AP and (d) user identity privacy protection.     

Cross-Layer Design for EH Systems with Finite Buffer Constraints

Energy harvesting (EH) technology in wireless communication is a promising approach to extend the lifetime of future wireless networks. A cross-layer optimal adaptation policy for a point-to-point energy harvesting (EH) wireless communication system with finite buffer constraints over a Rayleigh fading channel based on a Semi-Markov Decision Process (SMDP) is investigated. Most adaptation strategies in the literature are based on channel-dependent adaptation. However, besides considering the channel, the state of the energy capacitor and the data buffer are also involved when proposing a dynamic modulation policy for EH wireless networks. Unlike the channel-dependent policy, which is a physical layer-based optimization, the proposed cross-layer dynamic modulation policy is a guarantee to meet the overflow requirements of the upper layer by maximizing the throughput while optimizing the transmission power and minimizing the dropping packets. Based on the states of the channel conditions, data buffer, and energy capacitor, the scheduler selects a particular action corresponding to the selected modulation constellation. Moreover, the packets are modulated into symbols according to the selected modulation type to be ready for transmission over the Rayleigh fading channel. Simulations are used to test the performance of the proposed cross-layer policy scheme, which shows that it significantly outperforms the physical layer channel-dependent policy scheme in terms of throughput only.     

Cross-layer design for tree-type routing and level-based centralised scheduling in IEEE 802.16 based wireless mesh networks

Infrastructure wireless mesh network, also named as mesh router, is one key topology for the next generation wireless networking. In this work, the performance optimisation for the infrastructure wireless mesh network is presented and the sub-optimum solution mechanism is investigated. A cross-layer design for tree-type routing, level-based centralised scheduling and distributed power control theme is proposed as the sub-optimum solution strategy. The cross-layer design relies on the channel information and the distributed transmission power control in the physical layer, and the wireless scheduling in the medium access control (MAC) layer, as well as the routing selection mechanism in the MAC upper layer. In this work, a modified distributed power control algorithm is proposed first. In addition, a tree-type routing construction algorithm for centralised scheduling is presented to improve the network throughput by jointly considering interference and hop-count to construct the routing tree. Simulation results show that the proposed cross-layer design strategy can effectively improve the network throughput performance, decrease the power consumption and achieve better performances.     

WLAN smart antenna with Bluetooth interference reduction

Because of the coexistence of wireless local area network (WLAN) and Bluetooth at the same ISM band, WLAN systems cannot eliminate the interference by Bluetooth in the physical layer by carrier sense multiple access/collision avoidance. A novel smart antenna system for the WLAN systems to suppress the Bluetooth interference is proposed. The proposed smart antenna system employs the property of multi-carrier transmission of an orthogonal frequency-division multiplexing (OFDM) system to eliminate the correlation among the multi-path components, and the direction of arrival (DOA) estimation algorithm can estimate the correct DOAs. In the simulation, we apply the proposed smart antenna to the 802.11 system using OFDM. The simulation results demonstrate a superior performance under Bluetooth interference.     

Mobility model for heterogeneous wireless networks and its application in common radio resource management

User distribution and mobility behaviour vary based on environment types and characteristics. Heterogeneous wireless networks (HWNs) are deployed to utilise these characteristics and serve users with better quality. For efficient resource management in HWN environment, an understanding of multi-mode user mobility behaviour is paramount. Here, a multi-mode user mobility model is proposed in the context of wireless local area network (WLAN) coverage in the hotspot, overlaid on a macrocell of wireless wide area network (WWAN). An expression for microcell residence time of multi-mode users in HWNs is derived, based on the cell residence time in the constituting WLAN and WWAN. The boundary-crossing probabilities of moving into microcell, moving out of microcell and moving out of macrocell during a call for different types of hotspot topologies are also derived analytically. The numerical results obtained using the analytical expressions for boundary-crossing probability are validated by simulation results. The significance of the proposed mobility model is demonstrated through its application in common radio resource management (CRRM). Numerical results show that the mobility-based CRRM scheme exhibits a lower rate of unnecessary vertical handoffs than that achieved by the dasiaWLAN' if coveragedasia scheme that does not use mobility information for resource management.     

Adaptive TDD Synchronisation for WIMAX Access Networks

In adaptive time division duplex (ATDD) wireless systems, severe co-channel interference conditions can occur if the movable downlink/uplink (UL) TDD boundary is not synchronised among all frames in base stations. To reduce interference outage and to improve a system's spectral efficiency, a new single frequency cell (SFC) network architecture is proposed, which allows for distributed boundary synchronisation (DBS) via inter-sector signalling. SFC-DBS dynamically synchronises TDD boundaries among neighbouring sectors for each frame, thus avoiding sector-to-sector interference, while preserving the ATDD radio resource assignment efficiency. Analysis shows that SFC-DBS achieves an additional 6-11 dB in the average UL signal-to-interference ratio, compared with existing channel assignment schemes, which corresponds to 25-50 % capacity gain subject to traffic asymmetry in different sectors. More importantly, the proposed SFC scheme does not incur any further cost in the frequency planning, whereas the DBS scheme requires only minor system modifications. Compared with interference cancellation via antenna arrays and beamforming, SFC-DBS achieves similar performance, albeit without the cost for complex radio transceivers and multiple antenna elements.     

A cross-layer adaptive algorithm for multimedia QoS fairness in WLAN environments using neural networks

The authors address the problem of providing fair multimedia quality-of-service (QoS) in IEEE 802.11 distributed co-ordination function-based wireless local area networks in the infrastructure mode where mobile hosts experience heterogeneous channel conditions due to mobility and fading effects. It was observed that unequal link qualities can pose significant unfairness of channel sharing, which may thereby lead to the degradation of multimedia QoS performed in adverse conditions. A cross-layer adaptation scheme that provides fair QoS by online adjusting the multidimensional medium access control layer backoff parameters in accordance with the application-layer QoS requirements as well as the physical-layer channel conditions was proposed. The solution is based on an optimisation approach, which utilises neural networks to learn the cross-layer function. Simulation results demonstrate that the proposed adaptation scheme can tackle heterogeneous channel conditions and random joining (or leaving) of hosts to achieve fair QoS in terms of throughput and packet delay.     

一种融合MAC层拥塞通告的混合网络TCP协议

在研究无线网络媒体接入控制(MAC)层拥塞测度的基础上,提出了一种跨层的显式拥塞通告(ECN)机制,即:当数据包中记录的请求发送(RTS)次数超过给定阈值时,通过ECN向传输控制协议(TCP)源端发送拥塞通告,从而启动TCP拥塞控制.这种跨层设计是对有线网络中基于主动队列管理(AQM)的拥塞控制的有效补充,由此可以得到一种与已有的协议无缝连接的混合网络TCP模型.通过在网络模拟器NS2中构造多流无线局域网和多跳无线/有线混合网络,对所提出的方法进行了仿真,实验结果说明该方法能够提高混合网络的性能,并且具备良好的扩展性.     

Ultra wideband technologies coexistence in Nakagami-m fading channels

The wide spectrum of ultra wideband (UWB) communications makes it inevitable to consider strategies for avoiding and mitigating interference from narrowband wireless systems such as GPS, UMTS, and WLAN, or other UWB wireless technologies. In this paper, we provide a performance analysis of multiband orthogonal frequency division multiplexing (MB-OFDM) UWB in the presence of binary phase-shift keying time-hopping (BPSK-TH) UWB or BPSK-DS UWB interfering transmissions under Nakagami-m fading. In the bit-error rate (BER) analysis, several UWB interferers are considered to affect the MB-OFDM signal. A Gaussian approximation is considered for the UWB interferers and used in the analysis of the BER performance of the MB-OFDM UWB system. The Nakagami-m distribution is applied to characterise the amplitude of the fading channels for both the reference signal and the interference signals. Furthermore, a waveforming technique is considered for mitigating the effect of interference and its efficiency is illustrated in terms of BER improvement. Numerical and simulation results are provided and compared for different coexistence scenarios.     

嵌入式Linux下无线网卡驱动程序设计

本文采用了搭载ARM11处理器的开发平台,无线网络芯片采用Marvell88W8686芯片,内核采用linux2．6．28内核,介绍了WLAN和无线网卡硬件组成,详细分析了无线网卡在嵌入式Linux下的驱动程序的各个模块功能,在此基础上测试无线网络的性能。     

Power-saving mechanisms for mobile devices in wireless communications

In wireless communications, a sleep mode is commonly used to save power for mobile stations (MS). When there is no traffic to transmit, an MS periodically switches to sleep mode. Obviously, the performance of a power-saving mechanism depends on its sleep mode scheduling algorithm and the traffic characteristics of the user. In real systems, the power-saving mechanism of IEEE802.11 WLAN uses a constant sleep interval, and the IEEE802.16e WMAN adopts one with truncated exponentially extending sleep intervals denoted by PS-16, which contains constant sleep intervals as special cases. The two mechanisms are compared, resulting in the, finding that in the case of Poisson traffic, they have the same performance; whereas in the case of non-Poisson traffic PS-16 has better performance. For non-Poisson traffic, the performance of PS-16 lacks a closed form expression, which makes its design challenging. The authors propose to approximate the idle durations of an MS by hyper-exponentials, based on which an online sleep mode scheduling algorithm is developed. Numerical examples are provided to illustrate the efficiency of the proposed algorithm.     

无线接入点WAPI认证机制的研究与实现

随着无线局域网技术的广泛应用，新的无线局域网安全标准被提出以增强无线局域网的安全性能。在分析WAPI(WLAN Authentication and Privacy Infrastructure)标准的技术特征和基本架构的基础上，介绍了无线接入点对WAPI认证机制的实现机理和具体流程，并对WAPI认证机制的性能进行测试分析。     

一种用于Ad Hoc网络的简单跨层流控机制及其性能分析

为了改善Ad Hoc网络中传输层协议的性能,基于跨层设计思想设计了一种简单的流控机制.该机制有效地利用了网络层路由反馈、传输层协议、应用层速率自适应调节之间的关联性和跨层信息交互,应用层可根据网络层反馈的路由信息来调节发送速率,进而将网络负载维持在合理水平以最大化网络吞吐量.通过计算机模拟评价了此跨层流控机制,模拟评价结果表明,该机制能够使上层应用得到更加智能的控制,改善了基于UDP和TCP的业务性能,尤其是在网络负载较低的情况下效果更为明显.     

基于跨层设计的机械振动WSNs同步采集多跳累积误差控制方法

针对机械振动无线传感器网络跨层同步采集精度随网络深度增加而急剧降低的问题,建立同步采集关键同步信息传输模型,分析多跳同步误差累积机理,得出嵌入式软件调度实时性不高、晶振随机抖动及无线链路随机迟滞是多跳误差累积主要原因。由此提出基于跨层设计的机械振动无线传感器网络同步采集多跳累积误差控制方法:提出多路硬件跨层设计消除嵌入式软件调度迟滞影响,提高同步任务实时性;采用高精度有源晶振抑制晶振随机抖动;建立无线链路跨层传输随机迟滞数学模型,采用回归分析方法校准由此导致的同步信息随机抖动及传输时延计算误差,提升同步采集精度。最后组建4跳网络进行同步采集对比试验,实验结果表明多跳累积误差得到有效抑制。     

一种基于跨层设计的UWB无线Ad hoc网络MAC层协议

运用跨层设计思想和方法研究了超宽带（UWB）无线自组织（Ad hoc）网络媒体访问控制（MAC）层协议的设计,提出了一种可利用UWB技术定位性好的优势和实现跨层协作的MAC层协议。该协议通过物理层、MAC层和网络层之间的跨层协作来解决自组织网络单信道无线传输过程中的隐藏终端和暴露终端问题以及网络能量节约问题,以提高网络的性能。仿真实验表明,该协议在平均吞吐量、平均端到端时延以及能量开销等性能指标上,均优于已有的IEEE802．11和MACA—BIMAC协议。该协议的设计思想和方法为下一步的UWB无线Ad hoc网络研究奠定了理论和实验基础。     

Cross-layer queuing analysis on multihop relaying networks with adaptive modulation and coding

Multihop relaying is one of the promising techniques in future generation wireless networks. The adaptive modulation and coding (AMC) mechanisms can be applied in order to increase the spectral efficiency of wireless multihop networks. However, most of these mechanisms concentrate on the physical layer without taking the queuing effects at the data link layer into account, whose performances are overestimated. Therefore the cross-layer analytical framework is presented in analysing the quality-of-service (QoS) performances of the decode-and-forward (DF) relaying wireless networks, where the AMC is employed at the physical layer under the conditions of unsaturated traffic and finite-length queue at the data link layer. Considering the characteristics of DF relaying protocol at the physical layer, the authors first propose modelling a two-hop DF relaying wireless channel with AMC as an equivalent Finite State Markov Chain (FSMC) in queuing analysis. Then, the performances in terms of queuing delay, packet loss rate and average throughput are derived. The numerical results show that the proposed analytical method can be efficiently applied for studying the issues including the relay deployment and the cross-layer design in the multihop relaying networks.     

Switched diversity approach for multireceiving optical wireless systems

A number of existing spatial diversity schemes have been shown to improve the performance of optical wireless communication systems in diversity-rich environments. Among all, switched diversity has low complexity and is simple to implement. In this paper, an innovative spatial diversity scheme based on switched diversity is proposed. The scheme, namely switch-to-dominant combining, contributes to a higher bit error rate (BER) performance when compared to conventional switched diversity schemes, including switch-and-stay and switch-and-examine diversity. The optical multireceiver wireless system operates in a spatially correlated and lognormally distributed fading channel. Analytical analyses are conducted to demonstrate BER and processing load performance offered by the new scheme and compare them to available schemes, i.e., conventional switched combining and selection combining.     

Performance analysis of multipath transmission over 802.11-based multihop ad hoc networks: a cross-layer perspective

Data transmission in ad hoc networks involves interactions between medium access control (MAC)-layer protocols and data forwarding along network-layer paths. These interactions have been shown to have a significant impact on the performance of a system. This impact on multipath data transmission over multihop IEEE 802.11 MAC-based ad hoc networks is assessed; analysis is from a cross-layer perspective. Both MAC layer protocols and network-layer data forwarding are taken into account in the system models. The frame service time at source in a 802.11 MAC-based multipath data transmission system under unsaturated conditions is studied. Analytical models are developed for two packet generation schemes (round robin and batch) with a Poisson frame arrival process. Moreover, an analytical model is developed to investigate the throughput of a multipath transmission system in 802.11-based multihop wireless networks. Two methods are proposed to estimate the impact of cross-layer interactions on the frame service time in such a system. Two bounds of the system throughput are obtained based on these estimation methods. These models are validated by means of simulation under various scenarios.     

一种保证TCP上下行时间公平的新调度算法

针对无线局域网中传输控制协议(TCP)闭环拥塞控制的贪婪性、媒体接入控制(MAC)协议节点接入的公平性和无线信道的异构性导致TCP出现的上下行不公平和时间不公平问题,提出了一种在接入点上实现上下行时间公平的UDTFLAS (Up/Down Time Fair LAS)调度算法.UDTFLAS算法依据信道数据发送速率,给无线信道速率较高的TCP流提供更大的发送概率,以保证上下行各TCP流占用相等的无线信道时间.实验结果表明,UDTFLAS算法可以保护单流的吞吐率,实现上下行流的时间公平,能有效提高网络总吞吐量.