Pairwise error probability of space?time codes for a keyhole channel

A closed-form upper bound is presented for the average pairwise error probabilities (PEP) of space-time codes for a keyhole channel. It is derived from the exact conditional PEP for given fading channel coefficients using a moment generating function-based approach. Simulation results are included for varying numbers of antennas that affirm that the proposed PEP serves as a tight bound for codes in a keyhole channel     

Pulse position modulated space?time trellis coding for ultra-wideband impulse radio multiple-input multiple-output communication systems

The design of pulse position modulated (PPM) space-time trellis codes (STTC) for ultra-wideband impulse radio (UWB-IR) multiple-input multiple-output (MIMO) communication systems over slow and fast fading multipath channels is considered. First, A probability of error analysis is carried out to derive upper bounds on pairwise symbol error probability at high and low signal-to-noise ratios (SNRs). From the upper bounds, A new distance notion is introduced and novel design criteria for optimal (in error rate performance) M-ary PPM STTC are deduced for UWB. An optimal binary-PPM STTC is designed for two transmit antennas. Finally, simulation results of the UWB-IR MIMO system, using the optimal STTC, confirm significant improvement in bit-error-rate performance over the uncoded UWB-IR single-input single-output system and also over previously proposed space-time coding scheme for UWB, at higher SNR.     

基于喷泉码的放大转发协作通信系统的性能

为了实现在发送端未知信道状态信息(CSI)条件下的高效协作通信,研究了基于喷泉码的协作通信系统的性能.研究表明,在放大转发协作中目的端接收到的喷泉码符号的差错率比译码转发协作低.同时为了更充分地利用协作分集增益,提出了将基于喷泉码的放大转发协作通信与自适应解调技术相结合的方案,该方案使协作分集更有效地作用于喷泉码译码,并实现在发送端未知CSI条件下的自适应传输.仿真结果表明,该方案与采用喷泉码的直传通信和译码转发协作通信相比,能够降低误比特率,加快译码速度.     

Space?frequency coded cooperation in OFDM multiple-access wireless networks

A cooperative space-frequency (SF) coded orthogonal frequency division multiplexing system is considered and its performance over quasi-static frequency-selective Rayleigh fading channels is evaluated. An expression for exact outage error probability is derived and its tight closed-form lower bound is presented. The tightness of the lower bound is demonstrated through Monte Carlo simulation. Asymptotic analysis indicates that the proposed protocol achieves full spatial and frequency diversities available in the cooperative communication system. The theoretical analysis of the proposed SF coded cooperation protocol is further confirmed by computer simulation using a previously introduced SF block code that is capable of achieving full spatial and frequency diversities.     

Super-orthogonal space-time-frequency trellis coded OFDM

Super-orthogonal space-time trellis codes (SOSTTCs) given in the literature are full rate and provide full spatial diversity with high coding gain in narrowband quasistatic fading channels. The high number of parallel transitions in their trellis structure restricts their performance in wideband channels where the code performance suffers from multipath. Code design criteria are derived and a computer search based method is proposed to design full-rate optimised SOSTTCs exploiting full spatial and multipath diversity for multiple-input multiple-output orthogonal frequency division multiplexing systems. The proposed codes have codewords defined in space, time, and frequency. We evaluate the codeword error rates of the new 16, 32 and 64-state super-orthogonal space-time-frequency trellis codes for quadrature phase shift keying by computer simulation and show that they provide significant error performance improvement compared to their counterparts with equivalent delay length     

M-PAM space?time trellis codes for ultra-wideband multiple-input multiple-output communications

Multiple-input multiple-output (MIMO) systems with space-time (ST) coding are desirable in ultra- wideband (UWB) communication systems to improve the error-rate performance of the UWB link. The authors have considered the design of optimal (in error-rate performance) M-ary pulse-amplitude modulated (M-PAM) ST trellis codes (STTC) for a pulse-based UWB MIMO communication system. Following the approach by Vucetic et al. for narrowband systems, the authors carry out a probability of error analysis to derive upper bounds on pairwise symbol error probability for a UWB communication system for slow fading and fast fading at both low and high signal-to-noise ratios (SNRs). The authors deduce the design criteria from the upper bounds. Based on these criteria, an optimal four-state binary-PAM STTC, for two transmit antennas, is designed by hand. Finally, simulation results of the optimal binary-PAM STTC in a UWB communication system confirm significant improvement in bit error-rate performance over previously proposed ST coding scheme for UWB, at higher transmit SNR.     

基于激光跟踪仪的协作机器人标定算法与实验研究

为了提高机器人末端绝对定位精度,提出了一种基于激光跟踪仪测量的机器人几何参数标定方法,对协作机器人的参数误差进行辨识和补偿.为了避免机械臂相邻两个轴平行时会出现奇异性的情况,采用了MDH参数法建立误差模型;为了把测量数据定义在同一坐标轴上,结合了机器人工具坐标系转换(靶球中心点相对于机器人末端坐标系的平移变换);进而用...     

Performance of binary DS‐SSMA communications through Nakagami fading channel

Abstract

A binary asynchronous direct sequence spread spectrum multiple access system through Nakagami's m‐distributed channel is considered for non‐diversity receptions. Effects of fading and multiple access interferences on the average error probability are investigated. Approximation method to the average error probability is evaluated in two steps based on the moments of multiple access interferences and Nakagami distributions. Gauss quadrature rule is applied to evaluate the conditional probability conditioned on a fixed m‐distributed fading amplitude of the desired signal. Average error probability is then evaluated by the trapezoidal integration which integrates the conditional probability and the m‐distributed probability density function of the desired signal. This method provides a good approximation to the average error probability when the number of simultaneous users is large. Numerical results for the pseudorandom codes of code length 31 and Gold codes of code length 31 and 127 are presented.     

基于Spinal码的编码协作

针对5G的高速率传输需求,研究了基于Spinal码的编码协作。基于Spinal码的无速率性,提出了直接选用不同通道内所有编码符号实现编码协作的CC-SPSC方案。在此方案基础上,考虑基站在设备条件和中心调度方面的优势,引入以基站为控制核心的策略,提出了CC-SPSC-BSC-AL方案和CC-SPSC-BSC-SR方案。仿真结果表明,所提方案在模拟信道和数字信道下均有显著的误码率性能提升,尤其是CC-SPSC和CC-SPSC-BSCSR方案,分别在模拟信道和数字信道下的应用优势突出。     

基于比特可靠性的LDPC码编译码算法

提出了一种基于比特可靠性的低密度奇偶校验(LDPC)码编码算法和一种加权置信传播(BP)译码算法.该编码算法首先利用蒙特卡罗仿真得到LDPC码各个比特节点的出错概率,然后用已知信息替换易出错比特节点进行编码;该译码算法根据比特节点可靠性的差异,在译码时为每个比特节点赋予相应的权值,以调整它们对译码的影响程度.仿真表明,新的编译码算法使得系统性能大大提高,同时加快了译码迭代收敛速度.     

Cyclic optimization algorithms for simultaneous structure and motion recovery in computer vision

With few exceptions, most previous approaches to the structure from motion (SFM) problem in computer vision have been based on a decoupling between motion and depth recovery, usually via the epipolar constraint. This article offers closed-form cyclic optimization algorithms for the simultaneous recovery of motion and depth in the discrete SFM problem. Cyclic coordinate descent (CCD) algorithms in which each stage admits closed-form solutions are developed for two widely used fitting criteria: the geometric error in one image, and the reprojection error criterion. As a by-product, analytic gradients that can be used in descent-based optimization methods are also obtained. The computational efficiency, statistical consistency, noise robustness, and accuracy of the algorithms are assessed via experiments with synthetic image data.     

Partial-response equalization in magneto-optical disk readout: a theoretical investigation

We analyze the application of partial-response equalization and maximum-likelihood sequence estimation in magneto-optical readout. Two filters are proposed, and several aspects of their performance are examined. Filter I has 8 states in its state-transition diagram and is therefore easier to implement than filter II, which has 32 states. We discuss the required signal-to-noise ratio as function of the recorded bit density for these filters. The effects of jitter and bloom on the eye patterns of the output signals are also examined by computer simulation. This analysis indicates that filter II is somewhat superior to filter I, presumably because the output of filter II is more similar to the actual readout signal. We determine the distribution of Euclidean distance between pairs of output sequences and compute upper bounds on the probability of sequence error for both filters. Using two different methods of precoding (i.e., mapping of the user data to the magnetic pattern on the disk), we also compute the probability of bit error for the user data and show that one precoding scheme is slightly better than the other.     

Full-rate full-diversity space-time block codes for any odd number of transmit antennas

The authors propose a new class of space-time block codes (STBCs) achieving full-rate and full spatial diversity for general quadrature amplitude modulation (QAM) when using any odd number of transmit antennas under quasi-static Rayleigh fading channels. These codes are the extended works of the conventional Alamouti-ST constellation-rotating (CR) codes which are designed by serially concatenating CR precoders with the Alamouti scheme for an even number of transmit antennas. From the computer simulation results, it is observed that the best code in this class outperforms the existing ST-CR code and also exhibits error performance within only about 1-dB of the maximal ratio combining receiver. The codes possessing quasi-orthogonal (QO) characteristic are also included in this class, allowing simple maximum likelihood (ML) decoding with almost the same error performance as the best code in this class and the conventional QO-STBCs with full diveristy. These codes have identical or much lowered ML decoding complexity compared with the conventional QO-STBCs.     

Investigation of effectiveness of various methods with differentunknown variables for 3-D eddy current analysis

Computer codes using the A-φ, A-φ-Ω, A*-0Ω-E, T-Ω, and E-Ω methods were developed. The effects of the volume ratio of the conductor region to the whole region, the shape of the conductor, and the ratio of the hole region to the conductor region on the computer storage, the CPU time, and the accuracy of the methods are investigated systematically using a few simple models. The effect of the conductivity of the conductor is also examined. The computer storage, the CPU time, and the error are found to increase with increase of the volume ratio of the conductor region to the whole region. The computer storage and the CPU time are affected by the shape of the conductor in some methods of analysis. The error of the A*-Ω(E-Ω) method is larger than that of the other methods     

Design and performance analysis of code families for multi-dimensional optical CDMA

A code design algorithm for application in multi-dimensional optical code division multiple access (MD-OCDMA) for asynchronous optical fibre communication is proposed. Two-dimensional (2D) wavelength-time or space-time OCDMA and three-dimensional (3D) space-wavelength-time OCDMA are subsets of MD-OCDMA. Some applications and the performance analysis of the algorithm in 2D multipulse per row codes and 3D multipulse per plane codes are shown. In the applications discussed, this design ensures a maximum cross-correlation of '1' between any two codes. The performance metrics studied are the probability of error due to multiple-access interference for different numbers of active users and optimum temporal length for different values of cardinality. The performance analysis shows that the proposed 2D design offers very low probability of error due to multiple-access interference at lower cardinality when compared with other 2D designs using equivalent code dimension. A comparison of the proposed 3D design with an existing 3D design shows better performance at lower cardinality. The 3D designs show better performance when compared with the 2D designs.     

Error probability of direct sequence-code division multiple access systems with adaptive antenna minimum mean-square error multiuser receivers in Rayleigh-lognormal fading

In direct sequence-code division multiple access (DS-CDMA) cellular systems spreading codes, fading and positions of the users can be modelled as independent random variables and the corresponding multiuser interference (MUI) experienced by the base station is non-stationary. Here we evaluate in closed form the bit error probability for space-time linear minimum mean square error (MMSE) multiuser receivers for symbol-synchronous DS-CDMA system (bounds are provided for symbol-asynchronous system) by extending the known asymptotic results for random spreading sequences to non-stationary MUI. The analysis is based on the effective interference at the decision variable that is carried out to account for the non-stationary MUI that results from the multiuser beamforming that adapts each spatial filter to the randomness of the angle of arrivals of all the users. Propagation for each user is Rayleigh-lognormal faded channels as it is fairly general to model the imperfect power-control. The numerical validation proves that a simple geometrical model is accurate to evaluate the error probability for any arbitrary system loading.     

Viterbi decoding and the power spectral densities of some rate one half binary DC free modulation codes

The Hamming distance properties are investigated, and some experimental results obtained with the following R = 1/2 binary dc free modulation codes are presented: the (b, l, C) = (1, 5, 3) Miller²code and codes with (b, l, C), respectively, (1, 4, 3), (0, 3, 3), and (0, 1, 2). A R = 3/6, (b, l, C) = (0, 3, 2) combined error-correcting/ modulation code is also investigated. State systems, power spectral densities, and the bit error rates after computer simulated decoding of these codes on both the binary symmetric channel and a burst erasure channel are presented.     

Modelling and compensation of fixture locators’ error in CNC milling

Fixture errors are one of the error sources in machining operations. The fixture errors consist of positioning inaccuracies and errors due to workpiece and fixture deformations. Fixture locators’ height error causes incorrect positioning of the workpiece in the fixture and inaccuracy in machined surfaces which can be much more than the locators’ height error. For machining precise workpieces, it is necessary to eliminate these errors. This paper presents a method for modelling and compensating the fixture locators’ height error effect on workpiece machined surfaces. In this method, the planes of workpiece actual coordinate system (ACS) are mathematically modelled in the workpiece theoretical coordinate system (TCS). Using the model, required homogenous transformation matrix for coinciding ACS with TCS and modifying machining toolpath for compensating the errors is generated. The presented model is used to develop a post-processing fixture locator error compensation module, which can modify CNC machining codes to eliminate the effect of fixture locators’ height error on the workpiece machined surfaces. For verifying the presented method, machining simulations and cutting experiments have been performed in this work. The results show that the method can eliminate the effect of fixture locators’ height error on the workpiece machined surfaces considerably.     

Packet error rate analysis of decode-and-forward free-space optical cooperative networks in the presence of random link blockage

This paper analyses end-to-end packet error rate (PER) of a free-space optical decode-and-forward cooperative network over a gamma–gamma atmospheric turbulence channel in the presence of temporary random link blockage. Closed-form analytical expressions for PER are derived for the cases with and without transmission links being prone to blockage. Two cooperation protocols (denoted as ‘selfish’ and ‘pilot-adaptive’) are presented and compared, where the latter accounts for the presence of blockage and adapts transmission power. The influence of scintillation, link distance, average transmitted signal power, network topology and probability of an uplink and/or internode link being blocked are discussed when the destination applies equal gain combining. The results show that link blockage caused by obstacles can degrade system performance, causing an unavoidable PER floor. The implementation of the pilot-adaptive protocol improves performance when compared to the selfish protocol, diminishing internode link blockage and lowering the PER floor, especially for larger networks.     

Random optical codes used in optical networks

An analysis of a simple way to design generalised optical orthogonal codes to be used in optical code-division multiple-access systems is presented. They are random optical codes (ROCs). This novel family is especially suitable for optical networks with a large number of channels, low bit rate requirements, energy limitations and packed data. For example, sensor networks need these requirements. An application in an intra-spacecraft telecommand and telemeasurement (TC/TM) optical wireless network is also described. ROCs are selected randomly from all possible rearrangements. However, its probability of error is adequate in many useful parameter ranges. Moreover, ROCs present features not found in other families of codes such as huge cardinality and parameter adaptation to the system necessities. Here, the main contribution is to present a method to optimise the values of the parameters. Furthermore, the optimal weight of the codes is found, given two out of the other set of parameters, that is, the length, the number of users and the probability of error. In addition, a comparison between the length and the power consumption of ROCs and prime codes is also developed.