Low-complexity predictive trellis-coded quantization of speech line spectral frequencies

Low-complexity block-constrained trellis coded quantization (BC-TCQ) structures are studied, and a predictive BC-TCQ encoding method is developed for quantization of line spectrum frequency (LSF) parameters for speech coding applications. The performance is compared with the linear predictive coding (LPC) vector quantizers used in the AMR-WB (ITU-G.722.2) and IS-641 speech coding standards, demonstrating reduction in spectral distortion (SD) and significant reduction in encoding complexity.     

一种有限误差线谱频率参数暂时分解量化算法

本文对线谱频率参数量化提出了一种有限误差的暂时分解算法.新算法以原有的暂时分解算法为基础,重新定义了误差约束条件下的插入事件产生规则,并引入了事件消除机制.实验表明,在相同的编码速率下与原算法相比,该算法在对线谱频率参数量化过程中能够取得更低的平均谱失真度,从而获得更高的语音质量,更适用于低速率语音编码系统.     

LDPC编码系统符号同步技术

根据低密度校验码(LDPC)译码算法的统计特性,分析了接收端符号同步误差对译码性能的影响。针对 LDPC 编码系统的特点提出了一种新的符号同步误差校正算法,该算法通过 4 倍过采样技术判断同步误差的大小,并通过插值方式对精确同步采样点的信号进行估计。对于信噪比极低的通信系统,当存在较大符号同步误差时,该算法可以保证 LDPC 编码系统的性能接近精确同步情况下的性能。     

Minimum required power for carrier recovery at optical frequencies

The purpose of this study is to evaluate the minimum optical power required to achieve carrier recovery with arms phase error of 10°. This value corresponds to a degradation of about half a decibel for a coherent communication system using BPSK modulation. Two basic carrier recovery configurations were selected for this study. One uses an injection-locked oscillator; the other utilizes a phase-locked loop. The local source for both circuits is a laser providing 4 mW at 1.5 μm and having a full 3-dB linewidth of 20 MHz. The results show that the carrier recovery requirement can be achieved with a phase-locked loop receiving an unmodulated signal of -50 dBm. The minimum required power increases to a least -26 dBm for an injection-locked oscillator. A reduction of the sources linewidth by a given factor will decrease the minimum required power by the same amount.     

Survey of error recovery techniques for IP-based audio-visualmulticast applications

IP-based audio-visual multicast applications are gaining increasing interest since they can be realized using inexpensive network services that offer no guarantees for loss or delay. When using network services that do not guarantee the quality of service (QoS) required by audio-visual applications, recovery from losses due to congestion in the network is a key problem that must be solved. This survey gives an overview of existing transport-layer error control mechanisms and discusses their suitability for use in IP-based networks. Additionally, the impact of IP over ATM on the requirements of error control mechanisms is discussed. Different network scenarios are used to assess the performance of retransmission-based error correction and forward error correction     

Improved bounds for error recovery times of decision feedbackequalization

New upper and lower bounds on the mean recovery time of decision feedback equalization (DFE) are derived. The recovery time is defined as the time it takes the decision feedback equalizer (DFEQ) to reach the error-free state after an error has corrupted an error-free DFEQ. The derivations of the bounds assume a causal channel response, independent data symbols, and independent noise samples. The bounds are found to be tighter, especially at large SNR, than previous bounds in a numerical example     

一种机载红外光谱相机的角位置误差补偿技术

机载红外多光谱扫描仪采用摆扫扫描成像机制,解决了红外光谱相机的光谱分辨率、高空间分辨率和大成像幅宽之间的矛盾,可实现下视和远距离侧视成像。为了实现采集图像无缝拼接的像元级对准,需保证红外光谱仪的角位置信息准确。本文针对机载扫描成像光谱仪的几何定位问题进行分析,指出角位置误差是影响相机几何定位的主要因素,进而采用一种角位置误差的长短周期双重补偿方法,对角位置误差进行补偿。地面测试结果表明,补偿后相机角位置精度提高10倍,且经环境试验验证,角位置误差仍保持稳定。由机载挂飞试验结果表明,后图像相对几何精度优于一个像元（10）,满足图像拼接的几何定位需求。     

GFF的两种谱线设计方法

掺铒光纤放大器(EDFA)的增益平坦化是密集波分复用(DWDM)系统中的关键问题,通过对比、分析增益平坦滤波器(GFF)的模拟和实验两种谱线的设计及修正方法,认为实验的方法是较好的选择。通过试验,大量数据表明用桌面实验测得的Gain Error谱线与模拟的GFF谱叠加,可得到比模拟更好的GFF设计谱线。     

Channels leading to rapid error recovery for decision feedbackequalizers

The authors define the DFE (decision feedback equalizer) system of interest and their finite-error-recovery-time problem. They present their basic result, which establishes that whenever the channel satisfies a simple frequency-domain constraint, the error recovery time of an ideal DFE is always finite. They also include four applications of this theorem, including analysis of a real channel. Convergence rates and explicit bounds, given an exponential overbound on the channel impulse response, are presented. Results of greater practical interest, where the authors relax most of the major idealized assumptions, are also given. The authors present the result for M-ary data and relate the error recovery time bound back to the binary case. A formula for the error probability, given a high signal-to-noise-ratio channel, is provided     

Improved error performance for generalised spatial modulation with enhanced spectral efficiency

The existing analytical average bit error rate (ABER) expression of conventional generalised spatial modulation (CGSM) does not agree well with the Monte Carlo simulation results in the low signal‐to‐noise ratio (SNR) region. Hence, the first contribution of this paper is to derive a new and easy way to evaluate analytical ABER expression that improves the validation of the simulation results at low SNRs. Secondly, a novel system termed CGSM with enhanced spectral efficiency (CGSM‐ESE) is presented. This system is realised by applying a rotation angle to one of the two active transmit antennas. As a result, the overall spectral efficiency is increased by 1 bit/s/Hz when compared with the equivalent CGSM system. In order to validate the simulation results of CGSM‐ESE, the third contribution is to derive an analytical ABER expression. Finally, to improve the ABER performance of CGSM‐ESE, three link adaptation algorithms are developed. By assuming full knowledge of the channel at the receiver, the proposed algorithms select a subset of channel gain vector (CGV) pairs based on the Euclidean distance between all CGV pairs, CGV splitting, CGV amplitudes, or a combination of these.     

Evaluation of the mean-squared error for optimum line source patterns

An expression for the error, in the least mean-squared sense, between the desired pattern and the optimum line source approximation pattern is derived. It is shown that the previously used method of truncating the infinite series form for the error leads to highly inaccurate results.     

AUTOREC: an automated error recovery system for network management

The system, which was developed and is being used by AT&T to do error detection and recovery on a packet switching network, is described. Some of the major design issues that were addressed in developing AUTOREC are examined. These include system scope, hardware considerations, language selection, the multiple vendor problem, device recovery capability, and expansion. AUTOREC's modular architecture is described, and how an operator would interface with the system is explained. Some of the benefits that have resulted from the project and some of the lessons learned are discussed     

类4传输协议的差错检测与差错恢复方法分析

随着网络的迅猛发展,网络用户数量激增,节点间数据运输时常出现差错,严重时出现死锁。针对这种情况,通过研究类4运输协议中一些关键的定时器,从TPDU的重传、放弃定时器及静止定时器的使用、参照时间的计算,使用CDT进行流量控制方法以及网络连接时间的作用等方面给出了比较可行的差错检测与恢复方法,为新型网络流量控制系统及差错检测与恢复系统的开发提供了重要的依据。     

Method for testing reflector antennas at THz frequencies

The possibilities of applying far-field, near-field, and compact-range techniques to reflector antennas in the THz frequency range are discussed. Other methods, such as defocusing and combining of the mechanical-reflector-surface measurements and the feed-horn-radiation patterns, are also discussed. A recently introduced hologram type of compact range is described. It may be concluded from the analysis of the different methods that the far-field method can be discarded due to atmospheric effects. The near-field method remains a possibility. However, an expensive, high-quality, moving stage is needed, and phase errors caused by flexible cables have to be dealt with. In some cases, a defocusing method, to bring the far field closer, may prove to be practical. Technically, the most-feasible and least-expensive method appears to be the hologram type of compact range. In this method, a planar-amplitude hologram is used to form the required plane wave. The hologram is inexpensive to manufacture, and it is also less sensitive to surface-accuracy errors than a reflector     

A modified spectral conjugate gradient projection method for signal recovery

In this paper, signal recovery problems are first reformulated as a nonlinear monotone system of equations such that the modified spectral conjugate gradient projection method proposed by Wan et al. can be extended to solve the signal recovery problems. In view of the equations’ analytic properties, an improved projection-based derivative-free algorithm (IPBDF) is developed. Compared with the similar algorithms available in the literature, an advantage of IPBDF is that the search direction is always sufficiently descent as well as being close to the quasi-Newton direction, without requirement of computing the Jacobian matrix. Then, IPBDF is applied into solving a number of test problems for reconstruction of sparse signals and blurred images. Numerical results indicate that the proposed method either can recover signals in less CPU time or can reconstruct the images with higher quality than the other similar ones.     

On ternary error correcting line codes

The authors present Markov diagrams and tables with the capacities in bits/symbol for input restricted ternary channels with various restrictions on maximum runlengths, digital sum variation, and transitions between extreme signal levels. They derive Gilbert-type lower bounds on the minimum Hamming and Euclidean distances achievable with ternary line codes of rates lower than the capacity of the corresponding input restricted channel. They present some single-symbol-error-correcting ternary line codes, found by computer search methods     

Simplified expression for the expected error span recovery for variable length codes

An expression in the form of a series expansion for the error span recovery for variable length codes is presented. Numerical results for both the error span recovery and its standard deviation show complete agreement with those obtained via the complex exact functions. The expression is simple and can be applied to any model where the exact expression is prohibitively complicated.     

Wave impedance of power transmission line at PLC frequencies

The wave impedance associated with a single conductor power transmission line is discussed. Computed results show that for power line carrier (PLC) frequencies and within the inductive field the magnitudes and phases of the impedance componentsZ_{r}andZ_{theta}approximate, respectively, average values of 60 and365 Omegaand-84degand0deg.