An analysis of VoIP service using 1/spl times/EV-DO revision a system

While voice-over-Internet protocol (VoIP) on wireline network is maturing, VoIP on wireless mobile network is still in its infancy. This disparity is due to the fact that the wireline bandwidth is abundant and can be traded off for delay performance and overhead, whereas bandwidth in wireless mobile network is still a scarce resource. With the deployment of 1/spl times/EV-DO revision 0 (DOr0) worldwide, the spectrum efficiency has been significantly improved. However, DOr0 still lacks of features essential for VoIP. For this reason, 1/spl times/EV-DO revision A (DOrA) has been standardized in the 3GPP2 with many improvements favorable for VoIP implementation. In this paper, we identify challenges and explore the feasibility of implementing VoIP using DOrA. We develop both analytical and simulation models to evaluate the VoIP capacity and delay performance over the air interface.     

Gbps试验系统中高速串行接口的设计与实现

介绍Gbps无线通信试验系统中高速串行数据接口的设计与实现。按照Gbps无线通信试验系统对高速串行数据的传输要求,数据传输速率超过1 Gb/s,在基于Xilinx IP core技术上对单板上的FPGA进行逻辑设计,实现了符合系统要求的高速串行数据接口。在系统实际调试中,通过ATCA机箱背板进行数据传输,获得了高达Gbps的数据吞吐速率且传输误码率低于10-14。     

LTE/LTE-A技术及标准进展

随着无线数据业务的迅速增长,新空口技术的不断引入,无线扁平化技术的出现与兴起,无线网络架构会发生什么样的变化成为业界关注的焦点。本文对LTE/LTE-A的需求、研究进展、关键技术进行了介绍,浅析了EUTRAN的演进方式。     

An integrated testbed for wireless multimedia computing

A testbed has been constructed to evaluate node architectures that support multimedia applications and services across a wireless network. Using this testbed, a low bitrate subband video compression algorithm has been prototyped in a field programmable gate array (FPGA) and evaluated for video networking across bandwidth-limited RF channels. A radio interface has been prototyped in an FPGA and a common applications programming interface (API) has been developed to allow experimentation with multiple radios. This testbed has been used to evaluate node performance under two different wireless applications: 1) simultaneous video and data networking (VTALK) and 2) TCP/IP utilities such as FTP and telnet. Based on this evaluation, the design of a battery-operated high throughput wireless multimedia node is presented.     

Asymptotic Critical Total Power for $k$ -Connectivity of Wireless Networks

An important issue in wireless ad hoc networks is to reduce the transmission power subject to certain connectivity requirement. In this paper, we study the fundamental scaling law of the minimum total power (termed as critical total power) required to ensure k -connectivity in wireless networks. Contrary to several previous results that assume all nodes use a (minimum) common power, we allow nodes to choose different levels of transmission power. We show that under the assumption that wireless nodes form a homogeneous Poisson point process with density lambda in a unit square region [0, 1]², the critical total power required to maintain k-connectivity is Theta((Gamma(c/2 + k)/(k - 1)!) lambda^1-c/2) with probability approaching one as lambda goes to infinity, where c is the path loss exponent. If k also goes to infinity, the expected critical total power is of the order of k^c/2 lambda^1-c/2. Compared with the results that all nodes use a common critical transmission power for maintaining k-connectivity, we show that the critical total power can be reduced by an order of (log lambda)^c/2 by allowing nodes to optimally choose different levels of transmission power. This result is not subject to any specific power/topology control algorithm, but rather a fundamental property of wireless networks.     

Channel Selection for Spectrum Sharing in Wireless Networks

In this paper, we study a spectrum sharing network (SSN) where a spectrum sharing device (SSD) coexists with multiple wireless communication systems (WCSs) in the same channel. The SSD can operate with either a duty cycle (DC) channel access mechanism or a listen‐before‐talk (LBT) channel access mechanism, whereas WCSs operate with an LBT mechanism. An opportunistic channel selection scheme for the SSD in the SSN is first proposed to minimize the outage probability. The optimal data transmission time for the DC‐based SSD is derived to further improve the outage probability. We also derive the exact and closed‐form outage probability of the proposed channel selection in the SSN by assuming that the number of WCSs operating in each channel is uniformly distributed. The simulation results show that the proposed channel selection scheme outperforms other channel selection schemes. It was also observed that a DC‐based SSD with an optimal data transmission time provides a better outage performance than an LBT‐based SSD. As the number of available channels increases, the channel selection scheme plays an important role in minimizing the outage probability of the SSNs.     

cdma2000 1x的无线接入安全

cdma2000lx无线接入安全基于对称密钥技术，为用户提供匿名服务、基于质询/应答的认证服务、语音保密、控制信令加密和用户数据加密，采用CAVE、专用长码掩码、ORYX和E-CMEA四种安全算法。安全协议依赖于主密钥(A-Key)和移动台的电子序列号(ESN)，A-Key仅对移动台和归属位置寄存器，认证中心是可知的。不直接参与认证和保密，而是用于产生共享秘密数据(SSD)，再由SSD生成子密钥用于语音、信令和用户数据的保密。本研究上述安全机制，分析其安全漏洞。     

Recent advances and evolution of WLAN and WMAN standards [guest editorial]

Standardization of wireless technologies is a continuous process, and even established standards are updated and modified in response to changes in the technology and the marketplace. One such example is the successful IEEE 802.11 standard for wireless local area networks (WLANs), which was originally designed for 1 and 2 Mb/s traffic, and is now being upgraded to support 600 Mb/s in 802.11n and being considered as a high-throughput (up to 1 Gb/s) wireless interface for the nomadic scenarios of the next generation of wireless systems. Similarly, enhancements to the IEEE 802.16 standard for wireless metropolitan area networks (WMANs) are being considered to develop a mobile air interface with support for up to 100 Mb/s in high mobility scenarios. This continuous evolution of the IEEE 802.11 WLAN and 802.16 WMAN standards is made possible with new innovation and contribution from both academia and industry. Given the rapid growth of these technologies, it is important to understand what new application scenarios have triggered the recent developments within WLAN and WMAN standards, how they are evolving, the technological challenges they face, and the opportunities for both the industry and research communities. In this issue, from a large number of submissions, we have selected five key articles for inclusion, which provide the reader with ongoing developments in these standards, technology roadmaps, current research challenges, and comprehensive evolution of these technologies, as well as deployment experience and application requirements.     

基于发布/订阅模型的WSN设计

为降低通信频率对节点能耗的影响同时提高大规模节点下传感器网络的连通率,本文设计了一种以发布/订阅模型作为应用层数据交互方式的无线传感器网络。该网络利用6LoWPAN技术实现组网,并以Contiki操作系统为平台完成了基于发布/订阅模型的MQTT-S应用层协议设计。测试结果表明,该设计能够有效降低节点的通信流量,实现对节点功耗以及网络通信优化,并能与互联网实现无缝连接减少开发成本,对大规模传感器网络的设计与应用具有重要意义。     

On the /spl theta/-coverage and connectivity of large random networks

Wireless planar networks have been used to model wireless networks in a tradition that dates back to 1961 to the work of E. N. Gilbert. Indeed, the study of connected components in wireless networks was the motivation for his pioneering work that spawned the modern field of continuum percolation theory. Given that node locations in wireless networks are not known, random planar modeling can be used to provide preliminary assessments of important quantities such as range, number of neighbors, power consumption, and connectivity, and issues such as spatial reuse and capacity. In this paper, the problem of connectivity based on nearest neighbors is addressed. The exact threshold function for /spl theta/-coverage is found for wireless networks modeled as n points uniformly distributed in a unit square, with every node connecting to its /spl phi//sub n/ nearest neighbors. A network is called /spl theta/-covered if every node, except those near the boundary, can find one of its /spl phi//sub n/ nearest neighbors in any sector of angle /spl theta/. For all /spl theta//spl isin/(0,2/spl pi/), if /spl phi//sub n/=(1+/spl delta/)log/sub 2/spl pi//2/spl pi/-/spl theta//n, it is shown that the probability of /spl theta/-coverage goes to one as n goes to infinity, for any /spl delta/>0; on the other hand, if /spl phi//sub n/=(1-/spl delta/)log/sub 2/spl pi//2/spl pi/-/spl theta//n, the probability of /spl theta/-coverage goes to zero. This sharp characterization of /spl theta/-coverage is used to show, via further geometric arguments, that the network will be connected with probability approaching one if /spl phi//sub n/=(1+/spl delta/)log/sub 2/n. Connections between these results and the performance analysis of wireless networks, especially for routing and topology control algorithms, are discussed.     

基于虚拟仪器的任意m序列设计

论述了伪随机m序列的产生原理、特性以及构成方法,利用LabWindows/CVI为开发平台,设计了一种2~22级m序列发生器。仿真结果表明,该系统具有远程通信、界面友好、易于集成和扩展等优点,可实现无线激光通信系统误码率的自动化测试。     

HIPERLAN/1 MAC protocol: stability and performance analysis

HIPERLAN Type 1 is a standard for high-speed wireless local area networks, developed by the European Telecommunications Standards Institute (ETSI). It supports directed point-to-point communication based on ad hoc network topology at a data transfer rate on the air interface of 23.5 Mbit/s. The paper deals with an analytical and simulation analysis of the HIPERLAN/1 MAC protocol. General closed formulas are derived for the major channel access performance indexes, which are used both to prove the operational stability of the MAC protocol, and to derive a figure for the maximum channel utilization achievable. A simulation analysis is then carried out, focusing both on the influence of traffic burstiness on protocol performance, and on the capability to manage traffic classes with different quality of service (QoS) requirements. Simulation results show that HIPERLAN/1 is well suited for managing the bursty traffic that is expected to be generated by wireless LAN applications. Furthermore, HIPERLAN/1 provides a good isolation of the delay-sensitive traffic from the best effort traffic     

IEEE standard 802.16: a technical overview of theWirelessMANTM air interface for broadband wirelessaccess

The broadband wireless access industry, which provides high-rate network connections to stationary sites, has matured to the point at which it now has a standard for second-generation wireless metropolitan area networks. The IEEE standard 802.16, with its WirelessMAN^TM air interface, sets the stage for widespread and effective deployments worldwide. This article overviews the technical medium access control and physical layer features of this new standard     

On the$theta$-Coverage and Connectivity of Large Random Networks

Wireless planar networks have been used to model wireless networks in a tradition that dates back to 1961 to the work of E. N. Gilbert. Indeed the study of connected components in wireless networks was the motivation for his pioneering work that spawned the modern field of continuum percolation theory. Given that node locations in wireless networks are not known, random planar modeling can be used to provide preliminary assessments of important quantities such as range, number of neighbors, power consumption, and connectivity, and issues such as spatial reuse and capacity. In this paper, the problem of connectivity based on nearest neighbors is addressed. The exact threshold function for$theta $-coverage is found for wireless networks modeled as$n$points uniformly distributed in a unit square, with every node connecting to its$phi _n$nearest neighbors. A network is called$theta $-covered if every node, except those near the boundary, can find one of its$phi _n$nearest neighbors in any sector of angle$theta $. For all$theta in (0, 2 pi )$, if$phi _n =(1+delta ) log _ 2pi over 2pi -theta n$, it is shown that the probability of$theta $-coverage goes to one as$n$goes to infinity, for any$delta ≫0$; on the other hand, if$phi _n=(1-delta ) log _ 2pi over 2pi -theta n$, the probability of$theta $-coverage goes to zero. This sharp characterization of$theta $-coverage is used to show, via further geometric arguments, that the network will be connected with probability approaching one if$phi _n=(1+delta ) log _2 n$. Connections between these results and the performance analysis of wireless networks, especially for routing and topology control algorithms, are discussed. Digital Object Identifier 10.1109/TIT.2006.874384     

A broadband wireless packet technique based on coding, diversity,and equalization

The choice of an air interface technique to enable broadband wireless communications has been the subject of extensive research. This article describes an air interface for 2 Mb/s wireless mobile packet data services. The key enabling technique is a reduced-complexity broadband equalizer which provides a delay spread tolerance of up to 50 μs. The proposed air interface emphasizes high packet throughput, robust performance, low packet overhead, and low-cost low-power VLSI implementation     

光学元件亚表面缺陷表征与检测技术研究现状分析（特邀）

光学元件常用脆性材料作为原材料,脆性材料加工过程中极易引入亚表面缺陷,亚表面缺陷对脆性材料的制造阶段和应用阶段均存在严重的危害。制造方面,亚表面缺陷影响工序的选择与衔接,易产生过加工、欠加工等问题,导致加工效率低下;应用方面,亚表面缺陷影响光学元件的成像质量、稳定性、使用寿命等关键技术参数。为了高效率、高质量地去除亚表面缺陷,全面表征和准确检测光学元件的亚表面缺陷至关重要。文中首先介绍了不同加工方式对应的亚表面缺陷形成机理与亚表面缺陷的表征方法研究现状;其次归纳总结了破坏性与非破坏性的亚表面缺陷检测方法,分别介绍了不同检测方法的原理、适用材料与加工阶段、优点与不足之处;并介绍了基于表面粗糙度、加工参数的亚表面缺陷预测方法;最后,对亚表面缺陷检测技术的发展趋势进行了展望。     

基于MPEG-4编码的近距离无线视频传输系统

为实现近距离无线视频传输,提出了一种基于MPEG-4编码的近距离无线视频传输方案.由CMOS摄像头OV7620采集到的数据,通过专用MPEG-4编码器,ML86410得到速率低于2 Mbit·s-1的MPEG-4数据流,在FPGA控制器的控制下,通过nRF24L01无线发送;接收端利用同系列芯片nRF24LU1接收无线...     

Influence of surface states on the voltage robustness of AlGaN/GaN HFET power devices

In this work we discuss the influence of the donor-like surface state density (SSD) on leakage currents and the breakdown voltages of AlGaN/GaN heterostructure field-effect transistors (HFET) at high temperature reverse bias (HTRB) step stress. A method to extract charges at the surface by high voltage capacitance voltage (HV–CV) profiling of the gate–drain diode of a HFET is presented. Two samples with different surface passivation are compared. The SSD of the first sample is found to be similar to the polarization charge, whereas it is elevated by a factor of three on the second sample. The influence of the SSD on the electric field is investigated with electroluminescence (EL). The elevated SSD of the second sample engenders severe deficiencies in robustness found in the HTRB. The stress data, the simulation model and the images of EL indicate that the catastrophic failure arises in the dielectric underneath the gate field plate (GFP).     

A 195-gb/s 1.2-W inductive inter-chip wireless superconnect with transmit power control scheme for 3-D-stacked system in a package

A wireless interface by inductive coupling achieves aggregated data rate of 195 Gb/s with power dissipation of 1.2W among 4-stacked chips in a package where 195 transceivers with the data rate of 1 Gb/s/channel are arranged in 50-/spl mu/m pitch in 0.25-/spl mu/m CMOS technology. By thinning chip thickness to 10/spl mu/m, the interface communicates at distance of 15 /spl mu/m at minimum and 43 /spl mu/m at maximum. A low-power single-end transmitter achieves 55% power reduction for multiple connections. The transmit power is dynamically controlled in accordance with communication distance to reduce not only power dissipation but also crosstalk.     

一种面向无线音频应用的片上系统平台

提出并实现了一种面向无线音频的高性能、低功耗Calliope SoC架构平台.该平台通过多媒体DSP指令扩展的CK510E处理器、前向纠错编解码ASIC IP和双协议(I2S和S/PDIF)数字音频接口IP,兼容多种音频编解码标准和数字音频传输标准,并可有效提高无线传输信道的容错性.基于Calliope SoC架构平台,给出了音频编解码算法的优化实现方法.实验证明:使用RS(32,24)的FEC使无线数字音频传输系统的丢包率在移动情况下由7.21%降到4.87%,有效提高了系统的准确稳定性.Calliope SoC平台可分别在40 MHz、80 MHz和70 MHz系统工作频率下实现SBC、MP2和FLAC三种不同音频实时编/解码运算.