手持终端设备中基于对象交换协议的红外传输功能的设计与实现

通过红外进行文件传输,在手持终端设备中具有较高的实用意义.在可选的红外协议中,红外对象交换协议(OBEX)具有简单、实用、可移植性强等优点而被广泛应用.本文详细分析了利用对象交换协议进行文件传输的步骤,并给出了基于嵌入式linux系统的具体实现方案,最后介绍了在便携式多媒体中心的应用平台上红外传输功能的实现情况.     

Modelling,Performance Analysis and Design of WPAN Systems

This paper covers the main issues that must be solved in order to design and analyse the performance of Wireless Personal Area Networks (WPANs) with the aid of simulation tools. We review state-of-the-art channel models to account for small- and large-scale propagation conditions in waveform- and system-level simulations. When dealing with waveform simulations, we also look at Montecarlo and importance sampling techniques that allow efficient estimation of error probabilities. Additionally, discrete channel models are introduced to efficiently link both waveform- and system-level approaches and we point out some methods to obtain the model parameters that are suitable for the wireless environment. The discussion of these techniques is complemented with two application examples that show the use of the different simulation levels for system design and performance study. With the paradigm of Bluetooth piconets we illustrate the usefulness of discrete channel models and we consider the design of an OFDM-based WPAN system to exemplify simulation from a waveform-level point of view.     

Performance Analysis of MC-CDMA in the Presence of Carriers Phase Errors

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基于IrDA OBEX协议的移动设备数据传输

随着移动设备的日益普及，红外数据通讯已经进入了黄金发展时期。OBEX对象交换协议具有简单、紧凑、灵活的优点，特别适用于资源受限的移动设备进行快速数据交换。文章在介绍红外通信协议层结构的基础上，分析了OBEX协议的对象模型和会话模型，讨论了OBEX对象交换的传输过程，最后提出了在移动设备上OBEX对象交换的设计与实现。     

Performance of MPEG Codecs in the Presence of Errors

MPEG is emerging as a major international standard for applications in compressed video storage, transmission, and interactive communications. MPEG will be used in applications which involve imperfect channel conditions or storage defects. This work studies the effects of different types of errors on MPEG-encoded bit streams and possible approaches to minimize such effects. The applicability and tradeoff of forward error correction, block interleaving, and error concealment to MPEG-encoded bit streams are also investigated.     

阵列模型误差影响下ESPRIT算法的二阶性能分析

 针对阵列模型误差扰动的影响,该文对ESPRIT算法的方位估计性能进行二阶性能分析(即忽略模型误差扰动量的三次及以上各项).与经典分析方法(即一阶分析方法)相比,文中的性能分析方法能够在模型误差扰动较大的情况下提高性能预测精度.此外,文中的理论推导不仅针对阵列流形失配的情况,还针对阵元噪声模型失配的情形.数值实验表明:在较大模型误差的条件下,文中的二阶性能分析方法能够提高对ESPRIT算法的性能预测精度.     

短距离无线通信技术综述

随着网络及通信技术的飞速发展，人们对无线通信的需求越来越大，也出现了许多的无线通信协议。文章对目前使用较广泛的蓝牙、802．11(Wi—Fi)和IrDA无线协议分别进行了阐述，比较了他们技术上的异同点。讨论了在选择、使用这些技术时应注意的问题，对较具发展潜力的新无线技术标准UWB，zigBee也进行了阐述。对他们的未来应用进行了展望。     

阵列模型误差条件下直接定位性能分析及偏差修正方法

相比于常规的"参数估计+位置解算"两步定位模式，直接定位（DPD）算法具有定位精度高、分辨能力强等诸多优势.但是，DPD算法的性能受到阵列模型误差的影响.本文通过一阶Taylor级数展开，定量推导出模型误差条件下基于多重信号分类直接定位算法（MUSIC-DPD）的定位误差，从定位误差的表达式中可以发现辐射源的真实位置和MUSIC-DPD所得的有偏位置估计之间存在一种非线性关系，但这关系在实际条件下无法精确表示.为此，本文提出一种基于多层感知器（MLP）神经网络的直接定位偏差修正方法，该方法能够直接学习由阵列模型误差引起的定位偏差的规律，有效地修正由阵列模型误差导致的直接定位偏差.     

Performance Analysis of Dual-Hop AF Relay Networks in the Presence of Channel Estimation Errors and Feedback Delay

In this letter, we investigate the performance of multiple-input multiple-output two hop beamforming amplify-and-forward (AF) relay networks under imperfect channel state information (CSI) including channel estimation errors (CEE) and feedback delay (FD). To quantify the effect of imperfect CSI on our considered network, we derive the closed-form expression for the outage probability. To gain more insight, we also present an asymptotic analysis which provides the details of the diversity order and array gain. Through our works, one can see the effect of CEE and FD on the system as well as the benefits of deploying multiple antennas at the terminals. Numerical and simulation results are provided to verify the analysis and compare the performance of the considered network for two different models for channel estimation error.     

Bluetooth与其他无线接入技术

介绍了无线接入的4种技术，总结了他们的特点和典型应用，分析了其他3种技术和蓝牙之间的关系，最后对他们的性能做了比较。     

Performance of Transmit and Receive Antenna Selection in the Presence of Channel Estimation Errors

This letter considers the effect of channel estimation errors on the performance of space-time coded (STC) systems with transmit and receive antenna selection over quasi-static flat fading channels. By performing pairwise error probability analysis and presenting numerical examples, we show that the diversity order achieved with perfect channel state information (CSI) is still achievable with imperfect CSI used both at the antenna selection and the space-time decoding processes. We note that our results apply to general STC systems with both transmit and/or receive antenna selection based on largest received powers which can be estimated by any channel estimator.     

Average- and Median-Based Smoothing Techniques for Improving Digital Speech Quality in the Presence of Transmission Errors

In digital speech communication, transmission errors generally introduce impulsive distortions in the received speech waveform. Smoothing of this waveform results at once in a squelching of the distortion component, and in an undesirable smearing of the speech. However, our experience with practical differential PCM (DPCM) codes (with adaptive quantizers and first-order predictors) has shown that if the error probability is fairly significant (for example, 0.025), the noise attenuation is perceptually desirable in spite of the attendant speech-muffling. Our observations are based on computer simulations and informal listening tests. The smoothing can be performed either on the received DPCM word (prediction error signal) or the reconstructed speech amplitude. (The two signals are identical in nondifferential PCM.) Smoothing algorithms can be either linear (based, for example, on running averages) or nonlinear (based, for example, on running medians). Studies with 3-bit quantizers indicate that with independently occurring transmission errors, smoothing of the prediction error signal is perceptually desirable, although the benefits decrease as a function of the predictor coefficient a, with the maximum advantage showing up fora = 0(PCM). Running averages and running medians seem to work equally well, and suggested block lengths for their computations are three or five samples. Results with clustered transmission errors show a higher advantage due to smoothing and a preference of linear methods and longer block lengths.     

JTIDS数据链在多音干扰下经过莱斯衰落信道的传输性能分析

联合战术信息分发系统(joint tactical information distribution system,JTIDS)采用软扩频、跳频、纠错编码相结合的抗干扰体制,具备很强的抗干扰能力。通过已公开的JTIDS技术体制,分析了JTIDS通信链路的数学模型,在此基础上,研究并得出了采用相干解调方式JTIDS数据链在高斯白噪声干扰和人为多音干扰条件下,经过莱斯衰落信道的符号错误概率(symbol error probability,SEP),根据理论结果进行计算,并由所得计算结果分析了干扰频率点数分布以及干扰频率偏移对于JTIDS传输性能的影响,为评估JTIDS通信网络在干扰环境下的效能提供基础。     

XTND Access Blue SDK蓝牙协议软件的结构、移植与应用

本文以Extended Systems公司的蓝牙协议栈产品XTNDAccess Blue SDK为例介绍了蓝牙协议软件的设计原理、协议栈结构、移植过程及应用的开发方法。     

Performance of Collaborative Spectrum Sensing for Cognitive Radio in the Presence of Gaussian Channel Estimation Errors

The performance of collaborative spectrum sensing for cognitive radio in a lognormal shadowing and Rayleigh fading channel is investigated. Unlike previous works that assume perfect knowledge of the average channel signal-to-noise ratio, this paper considers the realistic case where estimation of the average channel signal-to-noise ratio has error. Furthermore, while previous works have designed and examined estimators based on assuming that the channel samples used in the average signal-to-noise ratio estimators are noiseless, the present work assumes that the channel samples are noisy, as is the case in practical systems. Numerical results show that the probability of missed opportunity decreases as the estimation error decreases, as expected. Perhaps unexpectedly, the results also show that in the presence of noise, there exists a threshold phenomenon for the noise level. Below a particular threshold, the probability of missed opportunity increases as the noise level increases. Yet above this threshold, the probability of missed opportunity decreases as the noise level increases.     

Performance Analysis of the Advanced Infrared (AIr) CSMA/CA MAC Protocol for Wireless LANs

Advanced Infrared (AIr) is a proposed standard of the Infrared Data Association (IrDA) for indoor infrared LANs. AIr Medium Access Control (MAC) employs Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) techniques with Request To Send/Clear To Send (RTS/CTS) frame exchange to address the hidden station problem. A long Collision Avoidance Slot (CAS) duration, that includes the beginning of the CTS frame, is defined to cope with collisions caused from hidden stations. AIr MAC employs linear adjustment of the Contention Window (CW) size to minimize delays emerging from the long CAS duration. This paper provides a simple and accurate analytical model for the linear CW adjustment that calculates AIr throughput assuming a finite number of stations and error free channel transmissions. Validity of the model is verified by comparing analysis with simulation results. By examining the first derivative of the throughput equation, we derive the optimum CW size that maximizes throughput as a function of the network size. In the case of the AIr protocol, where a collision lasts exactly one CAS, different conclusions result for maximum throughput as compared with the corresponding conclusions for the similar IEEE 802.11 protocol. Using the proposed model, we present an extensive AIr throughput performance evaluation. The effectiveness of physical and link layer parameters on throughput performance is explored. The proposed long CAS duration combined with CW linear adjustment are proven quite effective. Linear CW adjustment combined with the long CAS duration offer an efficient collision avoidance scheme that does not suffer from collisions caused from hidden stations.     

SyncML在蓝牙车载信息娱乐设备上构设计与实现

通过把SyncML绑定在蓝牙的OBEX协议上,笔者在一款蓝牙车载信息娱乐设备中开发了SyncML服务器,实现了蓝牙手机和车载信息娱乐设备间的电话薄同步应用.本文首先介绍蓝牙协议栈结构,然后分析SyncML OBEX绑定协议实现的关键点,并结合vCard规范详细介绍电话薄同步应用的具体实现.     

Simulation of MC-CDMA in the Presence of Timing Errors

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存在非线性失真和相位噪声影响的CP-OFDM与 TDS-OFDM数字电视地面广播传输系统的性能分析

本文概述了数字电视地面广播传输系统中存在的非线性失真和相位噪声影响因素;用模型统一表达了CP-OFDM和TDS-OFDM的OFDM复包络信号;从理论上分析了循环前缀和不断插入的导频训练序列会导致基于CP-OFDM的数字电视地面广播传输系统比在同等的外界条件下的基于TDS-OFDM的数字电视地面广播传输系统具有更低的有效数据符号信噪比水平;详细推导了在非线性失真和相位噪声共同影响下的CP-OFDM系统和TDS-OFDM系统的有效数据符号的统一信噪比表达式;定义并统一表达了在非线性失真和相位噪声共同影响下的CP-OFDM系统和TDS-OFDM系统的性能恶化指标;从理论和计算机仿真两方面比较分析了受到各种不同非线性失真和相位噪声影响的基于CP-OFDM和基于TDS-OFDM的两种不同数字电视地面广播传输系统的性能恶化程度.