Carrier-frequency estimation for transmissions over selectivechannels

This paper deals with carrier-frequency estimation for burst transmissions over frequency-selective channels. Three estimation schemes are proposed, all based on the use of known training sequences. The first scheme employs an arbitrary sequence and provides joint maximum-likelihood (ML) estimates of the carrier frequency and the channel response. Its implementation complexity is relatively high but its accuracy achieves the Cramer-Rao bound. The second scheme is still based on the ML criterion, but the training sequence is periodic, which helps to reduce the computational load. The third scheme also employs periodic sequences, but its structure comes from heuristic reasoning. Theoretical analysis and simulations are employed to assess the performance of the three schemes     

Rate‐based proportional–integral control scheme for active queue management

Most high‐speed links do not have adequate buffering and as a result Active Queue Management (AQM) schemes that utilize queue size information for congestion control cannot be effectively applied on these links. A high‐speed link will, typically, have small buffers in relation to the bandwidth‐delay product of the link. In this paper we argue that rate‐based AQM schemes be used for such links. The goal here is to match the aggregate rate of the active TCP connections to the available capacity while maintaining minimal queue size and high link utilization. The AQM scheme described here employs a Proportional–Integral (PI) control strategy and explicitly takes into account the time delay in the control process. Copyright © 2006 John Wiley & Sons, Ltd.     

Highly scalable JPEG image transmission with unequal error protection and optimal feedback

This paper investigates the performance of three different Unequal Error Protection (UEP) schemes for progressive JPEG image transmission using delay-constrained hybrid ARQ, with iterative bit and symbol combining. The first UEP scheme considers only the optimization of channel code-rates and keeps the number of retransmissions fixed for all the subbands of the image. The second one optimizes both the channel code-rates and retransmissions, while the third only considers the optimal allocation of retransmission requests. The UEP schemes are designed with two different coding techniques. The first one employs Rate Compatible Punctured Turbo Codes (RCPT) with iterative bit combining and, is suitable for applications requiring high power efficiency. For the second one we propose a new coding strategy, Rate Compatible Punctured Turbo Trellis Coded Modulation (RCPTTCM) with iterative symbol combining, which provides high scalability and bandwidth efficiency. Gains of over 9 dB in Peak-Signal-to-Noise-Ratio are obtained with the UEP schemes as compared to their corresponding Equal Error Protection (EEP) schemes.     

有限秘密下指派秘密共享方案的构造

针对有限个秘密要分享的情况，提出了一种具有指派功能秘密共享方案的新实现方法。为了说明这一方法，给出了两个实现方案：第一个方案通过引入碎片向量的概念来实现；第二个方案通过引入秘密偏移量的概念来对第一个方案进行优化，能够达到对分享着资源的充分利用。和以往的方案相比．这些方案要求更低的通讯和计算成本；且更加合理和容易实施。     

Polarization-independent optical spectral inversion without frequency shift using a single semiconductor optical amplifier

Two schemes for polarization-independent spectral inversion without frequency shift have been experimentally demonstrated. Both schemes use two pump beams and a polarization-insensitive semiconductor amplifier. Polarization-independent optical spectral inversion without frequency shift was obtained for lower wavelength detuning between the two pump beams in the first scheme and for large wavelength detuning in the second scheme. Combining these two schemes allows polarization-independent spectral inversion without frequency shift to be obtained over a quite wide frequency range. The results are in good qualitative agreement with theoretical predictions.     

Low-cost sensorless control of brushless DC motors using afrequency-independent phase shifter

This paper describes a sensorless control scheme for brushless DC motors (BLDCMs) using a phase shifter (FlPS) which can shift the zero-crossing point of the input signal with a specified amount of phase. The detection performance of the proposed FIPS is independent of the frequency of the input signal and quite robust with respect to the measurement noise. It is shown that the proposed sensorless control scheme using the FIPS is more effective in the respects of noise-robustness and cost than the previously known schemes. Moreover, a flux-weakening control scheme can be easily incorporated into the proposed sensorless control scheme. The generality and practicality of the proposed sensorless control scheme is demonstrated through performance analysis and experiments under various operating conditions     

Constraint-Based Control of Boiler Efficiency: A Data-Mining Approach

In this paper, a data-mining approach is used to develop a model for optimizing the efficiency of an electric-utility boiler subject to operating constraints. Selection of process variables to optimize combustion efficiency is discussed. The selected variables are critical for control of combustion efficiency of a coal-fired boiler in the presence of operating constraints. Two schemes of generating control settings and updating control variables are evaluated. One scheme is based on the controllable and noncontrollable variables. The second one incorporates response variables into the clustering process. The process control scheme based on the response variables produces the smallest variance of the target variable due to reduced coupling among the process variables. An industrial case study and its implementation illustrate the control approach developed in this paper     

Hybrid ARQ schemes employing coded modulation and sequencecombining

In this paper, we propose and analyze two hybrid automatic-repeat-request (ARQ) schemes employing bandwidth efficient coded modulation and coded sequence combining. In the first scheme, a trellis-coded modulation (TCM) is used to control channel noise; while in the second scheme a concatenated coded modulation is employed. The concatenated coded modulation is formed by cascading a Reed-Solomon (RS) outer code and a block coded modulation (BCM) inner code. In both schemes, the coded modulation decoder, by performing sequence combining and soft-decision maximum likelihood decoding, makes full use of the information available in all received sequences corresponding to a given information message. It is shown, by means of analysis as well as computer simulations, that both schemes are capable of providing high throughput efficiencies over a wide range of signal-to-noise ratios. The schemes are suitable for large file transfers over satellite communication links where high throughput and high reliability are required     

Generalized receiver selection combining schemes for alamouti MIMO systems with MPSK

Analytical results for the symbol error rate (SER) of M-ary phase shift keying (MPSK) in a slow, flat Rayleigh fading channel for a multiple-input multiple-output (MIMO) system using an Alamouti transmission scheme and generalized selection combining (GSC) scheme are given. Two new receiver selection schemes, generalized space-time sum-of-squares (GSTSoS) selection diversity and generalized space-time sum-of-magnitudes (GSTSoM) selection diversity are proposed. The first provides the same performance as conventional GSC, and the second provides slightly poorer performance, but neither requires channel state information and both have much simpler implementations. The SER of MPSK in Rayleigh fading using these two selection schemes is studied and compared to that of conventional GSC. The effects of channel estimation errors on each selection scheme are examined.     

Delay and throughput for three transmission schemes in packet radionetworks

The results of a simulation of a fully connect packet communication network are presented. The network employs the slotted ALOHA channel access protocol, and Reed-Solomon coding is used to correct errors and erasures in the received packets. The network has a fixed number of channels available for packet transmissions. In two of the transmission schemes considered, a given packet transmission occurs on a single channel only. One of these employs fixed assignment of terminals to the channels, and the other employs random assignment. A third method permits each transmitter to hop randomly over the set of channels during the transmission of a packet. The terminal transmits on one channel at a time, and it transmits a fixed number of symbols during each dwell interval. Delay and throughput are evaluated for all three transmission methods. The effects of code rate on the performance of the channel-hopping scheme are explored, and the improvement that can be obtained for the channel-hopping scheme by use of incremental-redundancy transmission is examined     

利用cluster态实现任意两粒子纠缠态的概率隐形传态

提出两个概率隐形传态方案,这两个方案都是以一个四粒子cluster非最大纠缠态作为量子信道来实现未知两粒子纠缠态的隐形传态.在第一个方案中传送的是一个特殊的两粒子纠缠态,此纠缠态可以实现一定的概率传输,此概率由cluster态中绝对值较小的两个系数决定.在第二个方案中,传送的是任意两粒子纠缠态,与第一方案相比,Bob除了需要实施幺正变换外,还要实施量子控制相位门才能重建被传送的纠缠态.使用非最大纠缠cluster态作为量子信道可以节约更多的纠缠资源和经典信息.     

Developments in learning control enhancements for nonlinear servomechanisms

Two learning control enhancement schemes applicable to nonlinear dynamical systems of the type commonly encountered in many practical servomechanisms are developed. The key difference between the two schemes lies in the fact that the first scheme utilizes previous cycle errors in the learning strategy while the second utilizes present cycle errors. The uniqueness of these learning controllers is that, in contrast to existing learning methods, they make full use of available a priori information on nominal models of the system and, as a result, overcome the problem of large swings in the control effort during the learning process, which is a major problem with conventional learning controllers. Properties of the schemes are discussed, and it is shown that the strategies developed assure iterative improvement in repetitive operation and asymptotic tracking of the reference signal. The performance and effectiveness of the proposed schemes are then investigated and compared through simulation.     

Low‐Complexity Symbol Timing Offset Estimation Schemes for OFDM Systems

In this paper, we propose three symbol synchronization schemes for Orthogonal Frequency Division Multiplex (OFDM) systems. The cyclic extension preceding OFDM symbols is of decisive importance for these schemes. The first scheme uses the phase‐differential coding of the received OFDM signal. The second and the third schemes use the length of the received OFDM signal. All three schemes make symbol synchronization possible, even though there is a frequency offset in the system. Simulation results show that these schemes can be used to synchronize an OFDM system over AWGN and multi‐path fading channels.     

The Maritime Satellite Communication Channel--Channel Model, Performance of Modulation and Coding

Towards the year 2000, maritime satellite communications using the INMARSAT system will employ a second and third generation of satellites and new ship earth stations (SES). The new SES standards will use very small antennas with gains between 0 and 15 dBi. At the lower end of SES there will be no antenna stabilization. The communication channel for such small stations is described by a model including multipath fading, Doppler shift, and noise. The results of an extensive measurement program were used to determine the parameters of the channel model, which depend on antenna type and elevation angle. Analytical calculations as well as synthetic and stored channel hardware simulations have been used to determine the performance of several modulation schemes. A complete data link using PSK modems with AFC/Costas loop, interleaving, and FEC codecs at 1.2 kbits/s was built up around a hardware maritime channel simulator, to study the performance of data transmission on the small SES maritime channel. Theoretical and measured results are given for interleaved Viterbi decoding with channel state information and Reed-Solomon codes. The measurements show that with interleaved FEC schemes, the requiredE_{b}/N_{o}for a BER 10^-5is in the range of 9-15 dB and the effects of multipath fading are almost compensated for.     

光波分复用在农村广播电视共缆传输中的应用

浙江省海宁市广电网络已发展到光缆到镇、到村、到组的3级光缆传输阶段,在实施广播电视共缆传输中尝试了3种方案,第一种方案为基本配置方案,适用于现有电视网络,第二、第三种方案为网络升级改造方案.第三种方案关键在于光波分复用,技术含量要求较高,为广播电视信号的传输带来诸多优点.     

Probabilistic and Evidential Approaches for Multisource Data Analysis

Two methods for combining the information contents from multiple sources of remote-sensing image data and spatial data in general are described. One is a probabilistic scheme that employs a global membership function (similar to a joint posterior probability) that is derived from all available data sources. The other is an evidential calculus based upon Dempster's orthogonal sum combination rule. A feature of both methods is that uncertainty regarding data analysis can be incorporated into the process. Both schemes are evaluated in terms of their general applicability and certain equivalences are noted. Moreover, both are shown to perform well on mixed multispectral data.     

浅析频率选择性信道中的微分空时编码

本文介绍了两种空-时传输机制,通过在频率选择性衰落信道上使用两根传输天线,来得到全速率和全分集非相干性.第一种机制结合了频域的OFDM微分空-时分组编码;第二种机制采用微分反时空-时分组编码,这样可以保证在不需要当前过采样或多根接收天线的情况下保证盲信道估计.     

Route optimization in mobile ATM networks

This paper presents an algorithm for optimizing the route of a connection that becomes suboptimal due to operations such as handoffs and location-based reroutes, and applies this algorithm to the handoff management problem in mobile ATM (Asynchronous Transfer Mode) networks based on the PNNI (Private Network-to-Network Interface) standard. The route optimization algorithm uses hierarchical route information of the connection and summarized topology and loading information of the network to determine a “crossover node” such that adjusting the connection from that crossover node results in an optimally routed connection. Handoff management schemes that perform local rerouting of connections have been proposed in order to support fast handoffs. These methods result in suboptimally routed connections. In this paper, we demonstrate how this route optimization algorithm can be used to optimize the route of a connection after such a handoff is executed, as the second phase of a two-phase handoff scheme. This route optimization procedure can also be executed as part of the handoff procedure resulting in a one-phase handoff scheme. Applying this route optimization algorithm, we propose two one-phase schemes, the one-phase optimal scheme and the one-phase minimal scheme. A comparative performance analysis of one- and two-phase handoff schemes is presented. Measures of comparison are handoff latency and the amount of network resources used by a connection. Handoff latency in the one-phase optimal scheme is greater than that in the two-phase schemes, and handoff latency in the one-phase minimal scheme is smaller than that in the two-phase schemes. The one-phase methods show a significant increase in efficiency of the connection compared to the two-phase methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

A multicarrier transmission scheme for wireless localcommunications

This paper presents a novel multitone transmission scheme that employs a nonlinear binary code to specify multitone signal constellations. The scheme, which can be viewed as a generalization of M-ary frequency shift keying, is amenable to noncoherent demodulation, and it is therefore useful for communication over fading channels. We determine the performance of this modulation scheme when it is used in conjunction with a Reed-Solomon code for error control. Methods for determining and erasing unreliable multitone constellations are presented and their performance is evaluated when they are used in conjunction with errors-and-erasures decoding. The transmission scheme is evaluated with respect to complexity, bandwidth efficiency, and performance in the presence of Gaussian noise and frequency- and time-selective fading     

Fair e-payment protocol based on blind signature

Electronic transaction through e-payment protocol will grow tremendous in the coming years. In this article, by conversely using blind signature, the authors propose a fair electronic payment scheme for electronic commerce, which can ensure two participants' right simultaneously in electronic transaction process. This scheme is different from other existing schemes and it does not require strong trust relation between customer and merchant. In the scheme, a semi-trusted third party (S-TTP) is involved to provide a fair commerce environment. The S-TTP takes part in the protocol on-line and no secure information about the business is leaked. Moreover, the participants do not need to register to S-TTP. This scheme does not require intervention of a third party in case of dispute, if one user cheats or simply crashes.