Robust image communication over wireless channels

Typical image compression algorithms produce data streams which require a very reliable communication-they are not designed for transmission in an environment in which data may be lost or delayed, as provided by current and next-generation wireless communication networks. Compression and transmission provisions that avoid catastrophic failure caused by lost, delayed, or errant packets are therefore imperative in order to provide reliable visual communication over such systems. This robustness is obtained by modifying the source coding and/or adding channel coding. This article presents an overview of both lossy and lossless source coding techniques and combined source/channel techniques providing robustness, presenting examples of successful techniques     

室内无线光通信信道分析

文章采用基于定点的迭代模型对非定向信道进行分析,得出了具体的迭代公式.在有家具的房间环境中,给出了可视光的增益公式,通过MATLAB编程实现了反射次数k=0、1、2三种情况下的脉冲响应,给出了仿真图形并加以说明.同时又对空房间的三种情况下的脉冲响应进行了仿真,通过与有家具的环境的比较,得出了随房间高度增加,非可视分量也增加的结论.     

Power efficient multimedia communication over wireless channels

In this work, we introduce an approach for minimizing the total power consumption of a mobile transmitter due to source compression, channel coding and transmission subject to a fixed end-to-end source distortion. We illustrate our approach both on an abstract class of sources and channels and on a realistic H.263 video transmission system through a wireless channel. Performance under different channel environments and implementation schemes are investigated. Our numerical analysis shows that optimized settings can reduce the total power consumption by a significant factor and prolong battery life considerably compared with fixed parameter settings.     

无线移动信道的仿真模型分析

通过对无线移动信道衰落特性的分析，建立了数学模型和计算机仿真模型，并对计算机仿真结果进行了分析，得出了相应结论。     

Initial estimation of communication efficiency of indoor wireless channels

We report theoretical/numerical estimation of ultimate limits of bandwidth efficient delivery of high bit‐rate digital signals indoors. Specifically, we analyze the Crawford Hill Bell Laboratories building. Single omni transmit and receive antennas are assumed. The signals incur attenuation and distortion due to multipath and at high bit‐rates this frequency selectivity causes ISI. Moreover, there is impairment by gaussian noise. Transmit power and bandwidth constraints limit communications efficiency. We illustrate this limiting of efficiency in examples assuming 5.2 GHz carrier, 10 MHz bandwidth and up to 1 W transmitted power. The experimentally based WiSE ray‐tracing tool models the channels from a base on the ceiling to workspaces in various rooms. Movement within a workspace causes channel changes. Computing the probability distribution of capacity shows substantial capacity for the omni‐omni case with 10 MHz bandwidth for 100 mW transmitted. For the most distant offices, for at least 95% of the area in a workspace, we obtain 3.6 bps/Hz. We also examine diversity methods, illustrating substantial gains with nth order optimum combining (OC(n)):OC(2) improves capacity by over 35% in rooms where capacity is the lowest while OC(4) improves it 70%. We put the results in a pragmatic perspective by highlighting the bit‐rates achievable with decision feedback equalization This revised version was published online in July 2006 with corrections to the Cover Date.     

基于无线信道差异的隐蔽通信

本文在背景噪声存在不确定性的无线通信中,研究对于监控方检测最有利条件下的单向隐蔽通信问题.首先,根据接收方检测能力存在极限的事实,利用信道预编码保证在接收方处汇聚的信号功率超过其检测阈值,同时保证在监控方处弥散的信号功率低于检测阈值,进而实现基于信道差异的隐蔽通信.其次,本文推导了平均遍历隐蔽通信速率的闭式解.理论分析...     

Azimuth and elevation computation in high resolution DOA estimation

A number of high-resolution direction finding methods for determining the two-dimensional DOA (directions of arrival) of a number of plane waves impinging on a sensor array are discussed. The array consists of triplets of sensors that are identical, as an extension of the one-dimensional ESPRIT scenario to two dimensions. Algorithms that yield the correct parameter pairs while avoiding an extensive search over the two separate one-dimensional parameter sets are devised     

Pulse shaping for wireless communication over time- or frequency-selective channels

This letter investigates the influence of transmit and receive filtering on the design and associated performance of wireless communication systems. Based on derivations using power-series models of time- or frequency-selective channels, we present pulse-shaping filters which can be matched to the characteristics of the channel. The choice of filter parameters allows some degree of control over the received signal. The peak-to-average-power-ratio (PAPR) requirements in the transmitter are determined. Orthogonal frequency-division multiplexing (OFDM) represents an alternative method of achieving some of the stated objectives of the pulse-shaping methods developed. Consideration is given to PAPR, bandwidth efficiency, receiver complexity, and performance in terms of error probability for the derived pulses and related forms of OFDM.     

Matched filter bounds for wireless communication over Rayleighfading dispersive channels

This letter extends the theory of the matched filter bound for fading dispersive channels. We generalize to arbitrary fading, as well as delay, properties of the channel. The channel model is a standard time varying linear filter and the calculation of the matched filter bound is based on a Karhunen-Loeve expansion of the received pulse spectrum when an isolated pulse is transmitted. Results are presented illustrating the various diversity effects. We conclude that in addition to the effect on probability of bit error of implicit delay diversity there is the less well known effect of implicit Doppler diversity in fast fading. The effect on probability of bit error of pulse shaping and explicit diversity is also illustrated     

Block Markov superposition transmission over turbulence channels in outdoor optical wireless communication

Based on the equivalent genie-aided system,the bit-error rate of the block Markov superposition transmission system was analyzed and the union bound of the bit-error rate of the genie-aided system was derived.When the bit-error rate was extremely low at which the Monte Carlo simulation was time-consuming,the union bound could be adopted to evaluate the performance of the block Markov superposition transmission system.Simulations under turbulence conditions from weak to strong are performed which show that,in the low bit-error rate region,performance of the block Markov superposition transmission system matches well with the lower bound.It is also illustrated that the derived union bound matches well with Monte Carlo simulation result.At the BER of 10^-5,block Markov superposition transmission system with transmission memory 2 performs within 1 dB away from the Shannon limit.     

Bluetooth in wireless communication

Bluetooth is a method for data communication that uses short-range radio links to replace cables between computers and their connected units. Industry-wide Bluetooth promises very substantial benefits for wireless network operators, end workers, and content developers of exciting new applications. This article delves into the implementation and architecture of Bluetooth. It also describes the functional overview and applications of Bluetooth, and deals with the development of a model for recording, printing, monitoring, and controlling of eight process variables at the same time, using a distributed control system. We explain industrial automation via Bluetooth using IISS. Industrial automation is one of the major applications of Bluetooth technology. Industrial automation, in terms of controlling or monitoring a factory, office, or industrial process, means to install machines that can do the work instead of human workers. Industrial plants consists of many devices interconnected in different ways ranging from simple data collection units (I/O) to more intelligent devices such as sensors, one-loop controllers, or programmable controllers, and a supervisory system used as a human-machine interface (HMI) for data logging and supervisory control. An IISS is a controlling device that monitors the devices in a company. It basically communicates via the interface card in the PC; the hardware is connected parallel across the device, and it is interfaced with the PC via a transceiver. The device can be accessed both manually via the switches and remotely via the PC. A simulation of connecting a PC with the machines in a company was executed. Also, we wrote a software program using C language; we will show how the remote monitoring takes place between the control room and the PC. These details in the article establish the growing need for Bluetooth technology     

Performance analysis of wireless communication system over nonidentical cascaded generalised gamma fading channels

Multiplicative fading statistics usually encountered in different radio propagation environments. In this context, we evaluate and analyse the performance of a wireless communication system over the nonidentical cascaded generalised Gamma Fading Channels, also known as generalised Bessel‐K fading channel. To this end, the closed‐form expressions for the amount of fading (AOF), the outage probability (OP), the average symbol error probability (SEP), and the channel capacity are derived. In addition approximate expressions for the average SEP with maximal ratio combining (MRC) diversity are also provided. The low‐ and high‐power solutions for the channel capacity are also provided. Furthermore, simplified asymptotic average SEP expressions for MRC and selection combining (SC) are presented to gain the system performance with diversity. The proposed methodologies provide more flexibility to accommodate different radio propagation scenarios. To examine the accuracy of the proposed solutions, numerical and simulation results are compared and shown to fit for variety of fading parameters.     

Portable video-on-demand in wireless communication

Our present ability to work with video has been confined to a wired environment, requiring both the video encoder and decoder to be physically connected to a power supply and a wired communication link. This paper describes an integrated approach to the design of a portable video-on-demand system capable of delivering high-quality image and video data in a wireless communication environment. The discussion will focus on both the algorithm and circuit design techniques developed for implementing a low-power video compression/decompression system at power levels that are two orders of magnitude below existing solutions. This low-power video compression system not only provides a compression efficiency similar to industry standards, but also maintains a high degree of error tolerance to guard against transmission errors often encountered in wireless communication. The required power reduction can best be attained through reformulating compression algorithms for energy conservation. We developed an intra-frame compression algorithm that requires minimal computation energy in its hardware implementations     

Cooperative communication in wireless networks

Transmit diversity generally requires more than one antenna at the transmitter. However, many wireless devices are limited by size or hardware complexity to one antenna. Recently, a new class of methods called cooperative communication has been proposed that enables single-antenna mobiles in a multi-user environment to share their antennas and generate a virtual multiple-antenna transmitter that allows them to achieve transmit diversity. This article presents an overview of the developments in this burgeoning field.     

Performance of MDPSK, MPSK, and noncoherent MFSK in wireless Ricianfading channels

Closed-form solutions for the average error rate of MDPSK, coherent MPSK, and noncoherent MFSK over slow, flat, Rician fading are derived. The solutions are sufficiently simple so that no approximations are needed for the numerical computations and general enough so that it includes AWGN and Rayleigh fading as special cases. Error probabilities are graphically displayed for various values of M. The dependence of error rate on the channel specular-to-scatter ratio are plotted and examined. Performance comparisons for a range of values of the Rician parameter K, corresponding to the measured statistics of mobile and indoor wireless channels, are made for the different digital modulation schemes. The analytical results presented in this paper are expected to provide information that is important for radio systems design and the evaluation of performance over a fading channel     

A model for teletraffic performance and channel holding timecharacterization in wireless cellular communication with general sessionand dwell time distributions

Channel holding times and user mobility are important topics in the study of wireless cellular communications. We present an approach to modeling user mobility and session time which enables both the calculation of teletraffic performance characteristics and a characterization of holding time which agrees with published reports. The model allows both the dwell time and unencumbered session time to have general distributions. A derivation of the channel holding time distribution is given. We then show how the model's parameters can be chosen to fit empirical data including observations of channel holding time     

关于配网通信中无线通信技术的探讨研究

本文介绍了配网自动化的信息,还解析了现阶段使用的配网通信技术的优点以及缺点等一系列问题,并根据实际需要进行了比较,最终还将配网通信中的无线通信技术进行细致地讨论.     

Appropriateness and effectiveness of communication channels in competent interpersonal communication

We examined perceived appropriateness and effectiveness of six communication channels (face-to-face, telephone, voice mail, electronic mail, letter, fax) used in relation to interpersonal communication motives (inclusion, affection, control relaxation, escape, pleasure) in other-directed and self-directed need-fulfillment situations. In Study 1, respondents selected the channel they thought would best communicate standard messages and rated it on effectiveness and appropriateness. In Study 2, respondents rated the effectiveness and appropriateness of all six communication channels by considering scenarios that reflected the two need-fulfillment directions of all six motives. Analyses revealed significant main effects for direction, channel, and motive, and significant interaction effects.     

Analysis of ML and WSF in wireless channels

The performances of the WSF and deterministic ML methods are studied and compared when used without minimising techniques to super-resolve the coherent multipath components in simulated and experimental multipath channels. Studies have shown that, when all the sources are coherent, the WSF and the deterministic ML methods achieve the same results     

Multimedia communication in wireless sensor networks

The technological advances in Micro ElectroMechanical Systems (Mems) and wireless communications have enabled the realization of wireless sensor networks (Wsn) comprised of large number of low-cost, low-power, multifunctional sensor nodes. These tiny sensor nodes communicate in short distances and collaboratively work toward fulfilling the application specific objectives ofWsn. However, realization of wide range of envisionedWsn applications necessitates effective communication protocols which can address the unique challenges posed by theWsn paradigm. Since many of these envisioned applications may also involve in collecting information in the form of multimedia such as audio, image, and video; additional challenges due to the unique requirements of multimedia delivery overWsn, e.g., diverse reliability requirements, time constraints, high bandwidth demands, must be addressed as well. Thus far, vast majority of the research efforts has been focused on addressing the problems of conventional data communication inWsn. Therefore, there exists an urgent need for research on the problems of multimedia communication inWsn. In this paper, a survey of the research challenges and the current status of the literature on the multimedia communication inWsn is presented. More specifically, the multimediaWsn applications, factors influencing multimedia delivery overWsn, currently proposed solutions in application, transport, and network layers, are pointed out along with their shortcomings and open research issues.