Profit‐based exclusive‐or coding algorithm for data retransmission in DVB‐H with a recovery network

The digital video broadcasting‐handheld (DVB‐H) standard is developed by European Telecommunications Standards Institute to broadcast digital videos to handheld devices, but data loss is a critical issue due to the broadcast behavior. On the other hand, DVB‐Internet protocol datacasting (DVB‐IPDC) integrates DVB‐H with an Internet protocol‐based wireless network to provide bidirectional communication. We adopt this wireless network to deal with data retransmission and call it a recovery network. The paper argues that network coding can improve retransmission efficiency of the recovery network because DVB‐H packet loss often exhibits high correlation. In addition, DVB‐H packets may be heterogeneous in the sense that they have different importance. According to these two arguments, the paper considers that DVB‐H packets are associated with different profit depending on their importance and proposes an α‐maximum profit network coding problem. It asks the base station in the recovery network to use no more than α coded packets for handheld devices to retrieve the lost DVB‐H packets such that the overall profit is the maximum. An efficient exclusive‐or coding scheme, namely the profit‐based exclusive‐or network coding (PEN) algorithm, is proposed to solve this problem. Extensive simulation results also verify the effectiveness of the PEN algorithm. Copyright © 2014 John Wiley & Sons, Ltd.     

Fast Directional Handoff and lightweight retransmission protocol for enhancing multimedia quality in indoor WLANs

More and more mobile devices such as smartphones are being used with IEEE 802.11 wireless LANs (WLANs or Wi-Fi). However, mobile users are still experiencing poor service quality on the move due to the large handoff delay and packet loss problem. In order to reduce the delay, a new handoff scheme using the geomagnetic sensor embedded in mobile devices is proposed in this paper. The proposed scheme predicts the movement direction of a Mobile Station (MS) from the currently associated Access Point (AP) and performs active scanning with a reduced number of channels. In terms of the packet loss, a lightweight retransmission protocol is also proposed to minimize lost packets on Wi-Fi without producing a lot of acknowledgement packets. The proposed approaches are implemented on Android smartphones, and their performance is evaluated in a real indoor WLAN environment. The evaluation results demonstrate that the proposed schemes maintain seamless quality for real-time video even in an environment with frequent handoffs. Note that the proposed schemes are a client-only solution and do not require modification of the existing APs, which renders them very practical.     

非完全无线报文重传分析研究及其分治策略

网络编码为无线网络报文重传问题WPRTPs(Wireless Packet ReTransmission Problems)提供了有效解决途径.现有关于WPRTP问题的研究主要针对完全无线网络报文重传问题P-WPRTPs(Perfect WPRTPs),而尚未发现对非完全无线网络报文重传问题IP-WPRTPs（ImPe...     

EEFA:高能效的IEEE 802.11N帧聚合调度算法(英文)

Packet size is restricted due to the error-prone wireless channel which drops the network energy utilization.Furthermore,the frequent packet retransmissions also lead to energy waste.In order to improve the energy efficiency of wireless networks and save the energy of wireless devices,EEFA(Energy Efficiency Frame Aggregation),a frame aggregation based energy-efficient scheduling algorithm for IEEE 802.1 In wireless network,is proposed.EEFA changes the size of aggregated frame dynamically according to the frame error rate,so as to ensure the data transmission and retransmissions completed during the TXOP and reduce energy consumption of channel contention.NS2simulation results show that EEFA algorithm achieves better performance than the original frame-aggregation algorithm.     

基于Fourier矩阵的无线广播重传策略

针对随机网络编码重传的缺陷, 将Fourier矩阵和随机网络编码相结合, 提出一种半固定编码系数的广播重传方案FMWBR。利用广播源节点和接收节点双方已知的Fourier矩阵的行向量作为编/解码向量, 保证接收节点接收到的重传包具有完全可解性。理论分析表明, FMWBR增强了无线传输的安全性、提高了网络的鲁棒性、减少了包头开销。仿真测试结果表明, FMWBR跟其他几种重传策略相比, 有效地减少了平均传输次数, 节省了带宽消耗, 提高了网络吞吐量。     

一种应用干扰消除进行冲突消解的分布式无线MAC协议

媒介接入控制(MAC)用以协调无线节点对公共信道的共享,对无线网络性能有至关重要的影响。传统的MAC协议只能抑制冲突,不能根除及处理冲突。提出了一种基于已知干扰消除技术的新型消解冲突方法,并以此为基础设计了一个全新的MAC协议——CR-MAC。在CR-MAC协议中,无线接入点(AP)通过将部分报文传输与已知干扰消除相结合来解码冲突所包含的所有报文。因此发生冲突的报文传输过程能够被充分利用,且所需的报文重传减少了。实验结果表明,在网络吞吐率及预期报文时延指标上,CR-MAC协议较普遍采用的IEEE 802.11DCF协议均有明显优势。     

厦门广电集团6信道高清转播车改造方案

介绍了厦门广电集团6信道高清转播车改造背景,从实用性、经济性的角度出发,介绍了详细的车体改造方案、系统方案和视音频方案等.     

On energy‐efficient aggregation routing and scheduling in IEEE 802.15.4‐based wireless sensor networks

In wireless sensor networks, continued operation of battery‐powered devices plays a crucial role particularly in remote deployment. The lifetime of a wireless sensor is primarily dependent upon battery capacity and energy efficiency. In this paper, reduction of the energy consumption of heterogeneous devices with different power and range characteristics is introduced in the context of duty scheduling, dynamic adjustment of transmission ranges, and the effects of IEEE 802.15.4‐based data aggregation routing. Energy consumption in cluster‐based networks is modeled as a mixed‐integer linear and nonlinear programming problem, an NP‐hard problem. The objective function provides a basis by which total energy consumption is reduced. Heuristics are proposed for cluster construction (Average Energy Consumption and the Maximum Number of Source Nodes) and data aggregation routing (Cluster‐based Data Aggregation Routing) such that total energy consumption is minimized. The simulation results demonstrate the effectiveness of balancing cluster size with dynamic transmission range. The heuristics outperform other modified existing algorithms by an average of 15.65% for cluster head assignment, by an average of 22.1% for duty cycle scheduling, and by up to 18.6% for data aggregation routing heuristics. A comparison of dynamic and fixed transmission ranges for IEEE 802.15.4‐based wireless sensor networks is also provided. Copyright © 2012 John Wiley & Sons, Ltd.     

宽带直升机卫星通信的重发策略研究

针对宽带直升机卫星通信信道的周期性衰落特性建立了周期性删除信道模型,基于此模型研究了重发分集的策略,推导了给定信道删除周期、窗口宽度、突发长度下重发次数、重发间隔的选择方法,讨论了重发模式与参数鲁棒性、系统设计需求的关系,并结合实例讨论了系统设计的设计步骤以及其他考虑因素。分析表明,采用两次重发可在大多数直升机信道条件下实现可靠传输,且具有较好的灵活性、较低的实现复杂度。     

基于TCP的网络拥塞控制机制

本文介绍了网络传输中TCP拥塞控制的基本概念、产生原因、及TCP拥塞控制机制,并初步探讨了TCP拥塞控制机制面临的一些主要问题。