Investigation of the baseline wander effect on indoor optical wireless system employing digital pulse interval modulation [optical wireless communications]

In indoor optical wireless communication (OWC) systems, ambient lights in particular fluorescent lamps introduce a periodic interference signal, which has the potential to severely degrade link performance. One of the simplest techniques often used to mitigate the interference from artificial sources of ambient light is electrical high-pass filtering (HPF). However, HPF introduces baseline wander (BLW), which is more severe for modulation techniques that contain a significant amount of power located at DC and low frequencies. In this paper the effects of BLW on systems employing digital pulse interval modulation (DPIM) are extensively investigated. Also investigated are the effects of cut-on frequency of the HPF on the optical power requirement and power penalty for different bit rates, where results are compared with the more established techniques of on-off keying (OOK) with a non-return to zero signalling and pulse position modulation (PPM). The optimum HPF cut-on frequency, which minimises the overall power penalty, is estimated. It is shown that at high data bit rates (100 Mbps), DPIM power requirement is considerably lower (~5 dB) than OOK and similar to that of PPM.     

Power optimization of wireless optical communication with log-square-Ricean fading

It has been important to optimize the transmitter power in wireless optical communication systems. The conventional approach was based on the reciprocal Pareto model. In this paper, the investigation is extended to a more general scenario where the instantaneous signal-to-noise ratio follows the log-square-Ricean distribution. Accordingly, the optimization model is established. The conventional model thus becomes a special case of the new model. It is shown that the new model can be analytically solved. The sample solutions clearly show how the optima of transmitter power change when the log-square-Ricean profile changes. These results would provide useful guidelines to system design.     

Performance of differential pulse-position modulation (DPPM) with concatenated coding over optical wireless communications [optical wireless communications]

The concatenation of marker and Reed-Solomon codes in order to correct insertion/ deletion errors in differential pulse-position modulation (DPPM) over optical wireless communications is presented. The concatenated code decoding algorithms with hard-decision and soft-decision detection are presented. The performance of the hard-decision coded DPPM system is evaluated over both nondispersive and dispersive channels via analysis and simulation. It is shown that the coding gain provided by the concatenated code is approximately 4 dB when the code rate is about 0.7 and the channel is nondispersive. Over a dispersive channel, the coded system performs better than the uncoded system when the ratio of delay spread to bit duration is not high. A soft-decision detector is employed to combat intersymbol interference. The soft- decision decoding algorithm, which has low complexity and can be practically implemented, is described. The performance over nondispersive and dispersive channels is evaluated by analysis and simulation. It is shown that the soft-decision system requires approximately 2 dB less transmit power than the hard-decision system for additive white Gaussian noise and low-dispersive channels. Soft decoding also provides a performance improvement in high-dispersive channels.     

无线光通信类脉冲位置调制技术研究进展

调制解调是提高无线光通信传输效率的关键技术,不同的调制方式其性能也有所不同.类脉冲位置调制是指脉冲位置调制(PPM)、差分脉冲位置调制(DPPM)及其组合以及由此演变而成的各种脉冲位置调制方式.本文总结了国内外类脉冲位置调制的研究进展,同时介绍了西安理工大学在类脉冲位置调制方面所做的工作,主要对开关键控、脉冲位置调制、...     

Investigation of multilevel amplitude modulation for a dual-wavelength free-space optical communications system using realistic channel estimation and minimum mean-squared-error linear equalization

Fog is a highly dispersive medium at optical wavelengths, and the received pulse waveform may suffer significant distortion. Thus it is desirable to have the impulse response of the propagation channel to recover data transmitted through fog. The fog particle density and the particle size distribution both strongly influence the channel impulse response, yet it is difficult to estimate these parameters. We present a method using a dual-wavelength free-space optical system for estimating the average particle diameter and the particle number density and for approximating the particle distribution function. These parameters serve as inputs to estimate the atmospheric channel impulse response using simulation based on the modified vector radiative transfer theory. The estimated channel response is used to design a minimum mean-square-error equalization filter to improve the bit error rate by correcting distortion in the received signal waveform due to intersymbol interference and additive white Gaussian noise.     

水下无线光通信链路构成与性能优化进展

水下无线光通信(UWOC)可为水下平台提供高速灵活的通信选择。本文介绍了UWOC的基本链路构成,并指出UWOC系统的优化方案。吸收、散射和湍流都会影响UWOC的性能,深入研究信道特性可以指导发射器、接收器和相关信号处理技术的设计。UWOC性能还能够通过复用技术、单光子探测技术和对准系统等进行优化。功能全面的测试平台可以为UWOC系统提供必要的测试环境,为海试与工业化应用奠定基础。本文期望能为UWOC相关研究者带来帮助。

     

电力通信光传输网络优化的分析与应用

当前电力通信光传输网络技术的优化对于整个电力系统的建设和发展来讲均有着重大的意义,故应加强对问题的重视,加强对技术的分析。文章针对这一方面的内容展开论述,详细的分析了电力通讯光传输网络技术的发展和现状,同时对相关技术的优化措施和技术的整改路线进行了细致的研究,旨在不断促进相关技术的发展,保证光传输网络技术可以得到不断的创新改良。     

Performance-based adaptive power optimization for digital optical interconnects

Optical links are traditionally set to transmit maximum power for worst-case loss and consequently to dissipate more power than is required. We describe a technique to minimize power consumption based on the measured bit-error rate (BER) of the link. This technique uses a novel power-negotiation algorithm that optimizes the link power setting to achieve minimum power dissipation for a target BER. A 0.5 microm complementary metal-oxide semiconductor optical transceiver chip was fabricated, and a free-space optical interconnect system was built for validation. The results showed that the algorithm was able to find the optimum power settings for the VCSELs for a target BER and to account for dynamic changes such as variation in the optical loss in the system.     

Development of a miniaturised drug delivery system with wireless power transfer and communication

The development of an implantable system designed to deliver drug doses in a controlled manner over an extended time period is reported. Key performance parameters are the physical size, the power consumption and also the ability to perform wireless communications to enable the system to be externally controlled and interrogated. The system has been designed to facilitate wireless power transfer, which is very important for miniaturisation as it removes the need for a battery.     

航模动力及飞行环境无线实时监测系统设计

介绍一种航模动力及飞行环境无线实时监测系统以及该系统的组成、硬件设计、通信协议、软件设计及系统的应用.测试结果表明,该系统具有测试精度高、可靠性好、操作和维护方便等特点,可用于航模等小型飞行器的生产、科研、试飞及教学过程等.     

Spot diffusing angle diversity MC-CDMA optical wireless system

Multi-carrier code division multiple access (MC-CDMA) combines some of the desirable features of orthogonal frequency-division multiplexing (OFDM) and CDMA in that it offers multi-user capabilities at a reduced channel rate. The authors report the analysis of a MC-CDMA system over the bandlimited optical wireless (OW) channel. Furthermore, the authors evaluate the performance when a line strip multibeam system (LSMS) is used in conjunction with an angle diversity receiver in the OW MC-CDMA system. The results indicate that at a bit error rate of 10^-4 a 7 and 10 dB signal-to-noise ratio (SNR) improvements are obtained through the use of MC-CDMA in a 4-user system when compared to a single-user OW on?off keying system and a 4-user OW CDMA system, respectively. This improvement is obtained by enabling multi-user communication. The performance degrades gradually with increase in the number of users. The use of LSMS and angle diversity offers a more uniform SNR over a given indoor geometry compared to a conventional diffuse OW system (CDS). Results are reported for an angle diversity LSMS MC-CDMA system and are compared to the CDS MC-CDMA system.     

Bit error performance of diffuse indoor optical wireless channel pulse position modulation system employing artificial neural networks for channel equalisation

The bit-error rate (BER) performance of a pulse position modulation (PPM) scheme for non-line-of-sight indoor optical links employing channel equalisation based on the artificial neural network (ANN) is reported. Channel equalisation is achieved by training a multilayer perceptrons ANN. A comparative study of the unequalised dasiasoftdasia decision decoding and the dasiaharddasia decision decoding along with the neural equalised dasiasoftdasia decision decoding is presented for different bit resolutions for optical channels with different delay spread. We show that the unequalised dasiaharddasia decision decoding performs the worst for all values of normalised delayed spread, becoming impractical beyond a normalised delayed spread of 0.6. However, dasiasoftdasia decision decoding with/without equalisation displays relatively improved performance for all values of the delay spread. The study shows that for a highly diffuse channel, the signal-to-noise ratio requirement to achieve a BER of 10^-5 for the ANN-based equaliser is ~10~dB lower compared with the unequalised-soft-decoding for 16-PPM at a data rate of 155 Mbps. Our results indicate that for all range of delay spread, neural network equalisation is an effective tool of mitigating the inter-symbol interference.     

Iterative cancellation of clipping noise in multilevel quadrature amplitude modulation multi-carrier CDMA system

An iterative reconstruction method that was proposed for clipping noise cancellation in orthogonal frequency domain multiplexing (OFDM) systems is applied to multilevel quadrature amplitude modulation-based multi-carrier (MC) code division multiple access signals in downlink. The iterative method uses a known distortion function, maybe a nonlinear one such as a successive clipping and filtering process, in the iterations to give an approximation of inverse of the distortion process and then the iterative method removes distortion under a convergence condition. The authors show that MC signal with properly chosen clipping threshold satisfies convergence conditions of the iterative method. In contrast to some of the other reconstruction-based techniques, this method requires no extra bandwidth and side information and it can be implemented with reasonable complexity. Furthermore, the authors show that the proposed iterative scheme can be enhanced by using an extra frequency bandwidth. Exploiting extra bandwidth improves the performance of the reconstruction-based methods in case of using successive clipping and filtering. Simulation results will be used to demonstrate achievable bit-error-rate improvement by the proposed enhanced iterative scheme.     

Automatic segmentation system for liver tumors based on the multilevel thresholding and electromagnetism optimization algorithm

In this article, we propose an automated segmentation system for liver tumors using magnetic resonance imaging and computed tomography. The proposed system is based on the algorithm of multilevel thresholding with electromagnetism optimization (EMO). The system starts with visualizing a patient's digital communication in medicine (DICOM) abdominal data set in three views. Two-stage active contour segmentation methods that integrate region-based local and global techniques using the active geodesic contour technique are proposed to segment the liver. To increase the accuracy and speed of segmentation for liver images, we identify the optimal threshold of the image segmentation method based on EMO with Otsu and Kapur algorithms. EMO offers interesting search capabilities while keeping a low computational cost. The proposed system was tested using a set of five DICOM data sets. All images were of the same size and stored in JPEG format (512 × 512 pixels). Experimental results illustrate that the proposed system outperforms state-of-the-art methods such as the watershed algorithm. The average sensitivity, specificity, and accuracy of the segmented liver using the active contour model were 97.05%, 99.88%, and 98.47%, respectively. Moreover, the average sensitivity, specificity, and accuracy of the segmented liver tumor results were 94.15%, 99.57%, and 96.86%, respectively.     

A low power wireless load monitoring system for the treatment of scoliosis

The efficacy of brace treatment for children with abnormal spinal curvature has been hampered by the lack of comprehensive information about wear characteristics. A battery-powered microcomputer system was developed to monitor loads exerted by braces used to treat children with spinal deformities. The system can be used by patients to ensure that the brace is being worn as prescribed, by clinicians to provide a record of how well the brace has been used, and by researchers to investigate brace mechanics. Data acquisition is controlled by a microcontroller and can be sampled with intervals ranging from 1 s to 1 h. In a preliminary study, a subject volunteered to test the system for 1 day. The load level was recorded as 1.20/spl plusmn/0.01 N when the subject was standing normally. The average force for the test day was 1.52/spl plusmn/0.75 N. This study demonstrates the feasibility of the approach, helps patients better wear their braces and increases our understanding of brace mechanics.     

Analysis of the performance of a wireless optical multi-input to multi-output communication system

We investigate robust optical wireless communication in a highly scattering propagation medium using multielement optical detector arrays. The communication setup consists of synchronized multiple transmitters that send information to a receiver array and an atmospheric propagation channel. The mathematical model that best describes this scenario is multi-input to multi-output communication through stochastic slow changing channels. In this model, signals from m transmitters are received by n receiver-detectors. The channel transfer function matrix is G, and its size is n x m. G(i,j) is the transfer function from transmitter i to detector j, and m > or = n. We adopt a quasi-stationary approach in which the channel time variation has a negligible effect on communication performance over a burst. The G matrix is calculated on the basis of the optical transfer function of the atmospheric channel (composed of aerosol and turbulence elements) and the receiver's optics. In this work we derive a performance model using environmental data, such as documented turbulence and aerosol models and noise statistics. We also present the results of simulations conducted for the proposed detection algorithm.     

Low-complexity iterative equalisation and decoding for wireless optical communications [optical wireless communications]

A low-complexity scheme of iterative equalisation and decoding by combining a recursive systematic convolutional code and a pulse-position modulation is proposed here. A graph- based equalisation for intersymbol interference (ISI) known at both transmitter and receiver is considered. By representing the memory channel with ISI as the factor graph and applying sum-product (SP) algorithm to this graph, a posteriori probability (APP) of the desired symbol necessary to implement iterative equalisation and decoding is derived. A partial response precoding is used to reduce the span of ISI from a possible infinite number of two baud periods. This precoding scheme makes the factor graph of memory channel cycle-free, and SP algorithm for combating ISI converges to an optimum detection. Numerical results show that the proposed low-complexity strategy has almost the same performance as the optimum turbo equalisation.     

Design and evaluation of a high data rate optical wireless system for the diffuse indoor channel using barker spreading codes and RAKE reception [optical wireless communications]

The performance of a high data rate optical wireless system (OWS) over the diffuse indoor infrared channel based on direct sequence spread spectrum (DSSS) techniques is highly sensitive to the properties of the aperiodic autocorrelation function and the spreading factor of the spreading sequence used. Ideally, the aperiodic autocorrelation function should have zero sidelobes in order to eliminate intersymbol interference caused by multipath propagation. In practice, such an ideal sequence does not exist in the binary field when data modulation is applied. For high data rates, a small spreading factor is desired in order to avoid an excessive system bandwidth. The family of Barker sequences is investigated in a DSSS-OWS. The Barker sequences are binary spreading sequences which exhibit small aperiodic autocorrelation values and short spreading factors. The system bit error rate (BER) performance is characterized on the diffuse indoor infrared channel when using RAKE reception. Results of BER against Eh/NQ are presented with data rate and spreading factor as parameters. The results demonstrate that of the seven Barker sequences existing, the length three Barker sequence {0 0 1} provides the best system design trade-off in respect of good BER performance and low implementation complexity.