Adaptive equalization for high speed optical MIMO wireless communications using white LED

Light emitting diode (LED) is one of the most important light sources in the 21st century and has broad prospects in the illumination.Currently,the white LED is used not only for illumination,but also ...     

中等数据率无线通信实用解决方案(上)

引言本文分析中等数据率（５０～１００ｋｂｉｔ／ｓ）无线点到点链路的各种实用解决方案。选择９０２～９２８ＭＨｚＩＳＭ（工业、科技和医学）频段做为一理想的射频媒体实现低成本和非许可（即ＦＣＣＰａｒｔ１５）工作的无线链路。ＦＣＣ细则允许在频段内连续低功率（接近０ｄＢｍ）或较高功率（接近３０ｄＢｍ）扩展频谱传输。为降低成本和复杂性在此只考虑低功率工作。下面将讨论无线数字通信问题，分析链路的数字和ＲＦ部分的一些解决方案。系统链路实现无线点到点链路必须解决的首要问题之一是采用单工（１路）还是双工（２路）结构…     

Generalized layered space-time codes for high data rate wireless communications

We present the architecture of generalized layered space-time codes (GLST) as a combination of Bell Labs layered space-time (BLAST) architecture and space-time coding (STC) in multiple-antenna wireless communication systems. This approach provides both spectral and power efficiency with moderate complexity. The framework is to partition all the available transmit antennas into groups and apply STC on each group as component codes. Based on the mappings from coded symbols to transmit antenna groups, we can construct different GLST systems. Particularly, horizontal mapping and diagonal mapping are introduced and referred to as HGLST and DGLST respectively. The basic decoding of GLST, under quasi-static flat Rayleigh fading environments and assuming perfectly known channel state information (CSI) at the receiver, combines group interference suppression and group interference cancellation techniques. As a result, the individual STC on each group is decoded serially. To improve the overall system performance, we derive the optimal power allocation among all space-time codewords without requiring the knowledge of CSI at the transmitter and suitable for all GLST systems. We also derive the optimal serial decoding order based on the channel realizations at the receiver for HGLST systems without power allocation. Simulation results show that both can provide much improvement. To further enhance the system performance, we propose a low complexity hard-decision iterative decoding method. This method efficiently exploits full receive antenna diversity and, hence, dramatically improves the system performance which is confirmed by simulation.     

无线光通信中的空时编码研究进展(三)

空时编码利用多天线阵列提供的并行信道传输信息,可以在保证通信质量的前提下进一步提高信息传输速率。介绍了笔者在正交空时码、空时网格码、酉空时码、差分空时码、混合空时码等方面的工作。采用类脉冲位置调制定义了负数、共轭、求补等运算,将编码矩阵转化为一个用脉冲位置表示的实数矩阵。分析了不同发射天线/接收天线数目、大气湍流强度与系统误码率之间的关系。讨论了差分空时码、酉空时码在不同大气湍流条件下的误码率特性;将分层空时码和空时分组码相结合,对复用增益和分集增益进行合理的折中,提出了一种适合于IM/DD式光通信的混合空时编码方案。     

无线光通信中的空时编码研究进展(一)

MIMO技术在射频通信领域已被深入研究,使空间成为一种可以用于提高通信性能的资源。无线光通信与射频通信在调制/解调方法、信道特性诸方面有很大的差异。文中评述了国内外有关无线光MIMO技术的研究进展,对无线光MIMO的提出背景进行了详细分析,最后通过实验说明了MIMO对大气湍流的抑制效应。实验结果表明:无线光MIMO不但使空间成为一种资源,提高了无线光通信的信道容量,而且可以抑制大气湍流效应,扩大了无线光通信的应用场合。     

无线光通信中的空时编码研究进展（二）

无线光MIMO技术结合了天线发射分集、接收分集与信道编码分集,可以显著提高信道容量。介绍了笔者在分层空时编码方面的若干研究进展,分析了误码率特性与发射/接收天线数目、检测算法之间的关系,比较了水平分层空时码、螺旋分层空时码、对角分层空时码和垂直分层空时码不同的编码方案,以及不同检测算法对不同的湍流强度的抑制作用。经分析得出:三种分层空时编码性能最好的是对角分层空时编码,其次是螺旋分层空时编码,最后是水平分层空时编码。     

无线光通信中的空时编码研究进展(四)

级联编码是一种提高系统纠错能力以逼近香农限的高效编码方式。当信道编码与空时编码结合使用时性能会大大提升,因此级联空时码研究成为空时编码研究的重要方向之一。笔者介绍了RS 码、LDPC 码与空时码的级联方案,以及在不同大气湍流条件下的误码率特性,并对其进行了仿真分析。结果表明:级联空时码可以极大地改善大气激光通信系统的性能,抑制大气湍流效应,有利于获得编码增益,进一步改善系统的误码性能。     

Efficient data retrieval algorithms for multiple requests in MIMO wireless networks

Given a set of multiple channels, a set of multiple requests, where each request contains multiple requested data items and a client equipped with multiple antennae, the multi‐antenna‐based multirequest data retrieval problem (DRMR‐MA) is to find a data retrieval sequence for downloading all data items of the requests allocated to each antenna, such that the maximum access latency of all antennae is minimized. Most existing approaches for the data retrieval problem focus on either single antenna or single request and are hence not directly applicable to DRMR‐MA for retrieving multiple requests. This paper proposes two data retrieval algorithms that adopt two different grouping schemes to solve DRMR‐MA so that the requests can be suitably allocated to each antenna. To find the data retrieval sequence of each request efficiently, we present a data retrieval scheme that converts a wireless data broadcast system to a special tree. Experimental results show that the proposed scheme is more efficient than other existing schemes. Copyright © 2014 John Wiley & Sons, Ltd.     

High data rate radio communications through the ionospheric channel

An innovative system of digital transmission for long range applications in the HF band (3–30 MHz) is presented. The technical challenge is to increase significantly the data transfer rate when compared with standard modems (typically 4.8 kbits/s in a 3 kHz bandwidth). For this purpose, an original array of collocated receiving antennas is developed as support for the implementation of a blind spatio temporal equalization. Consequently, the effective bandwidth is extended up to 12 kHz. An experimental 780 km range radio link is tested with a data transfer rate attaining 40 kbits/s and a BER (bit error rate) remaining moderate. Still images are transmitted with a specific source-channel coding and the good quality of service is confirmed by the fidelity of the restored images.     

PMT阵列在水下MIMO无线光通信中的应用

水下无线光通信具有的高带宽、低时延等特点,已成为水下通信的可行选择。系统发送端光源由6只绿光发光二极管(LED)构成阵列,接收端由3只光电倍增管(PMT)构成阵列,形成了6×3的多输入多输出(MIMO)传输方式。在室内10 m水槽水下信道下,实现了1 Mbps的信息传输速率。通过MATLAB软件对接收平面光功率分布仿真,最大值为?35.8 dBm。此外,测试了PMT阳极输出电压波形,并推导出阴极电流波形。理论计算得出信噪比为19.4 dB,理论误码率约为1.1×10?5。所选PMT模块理论上最小接收功率可低至1.5×10?9 W,体现出极高的探测灵敏度。最后,通过蒙特卡洛(Monte Carlo)数字仿真说明,在信噪比25 dB可达到约35 bit·s-1·Hz-1的信道容量。     

MIMO characterization of indoor wireless optical link using a diffuse-transmission configuration

Performance of a diffuse optical link may potentially be degraded by temporal dispersions resulting from surface reflections. In order to devise techniques to alleviate the adverse effect of dispersion, an accurate channel model is needed. Obtaining the impulse response (IR) for a given receiver location requires consideration not only of the direct path, but also of reflections up to nth order. The IR is only valid for a specific location and specific receiver parameters. If a receiver moves, the IR has to be recalculated. We propose a new approach for characterizing diffuse links that results in a tremendous saving in calculation and also gives more insight into the channel characteristics. The new approach is based on consolidating the dependence of receiver parameters, transmitter parameters, and the indoor environment into independent components. Thus, changing one of the parameters of the link requires recalculation of one of these components. The new model is utilized to obtain an accurate profile of delay spread and received power throughout a room.     

高性能的电机控制器ADMC401

本文介绍了美国模拟器件公司推出的用于电机控制的高档DSP控制器ADMC401,具体分析了其结构及控制外设,并提供了使用方法.     

Generation of CW MMW using optical signal propagating nonlinear materials for wireless communications and ubiquitous communications systems

A continuous-wave (CW) millimetre-wave (MMW) was generated by using optical signal propagating nonlinear materials for MMW wireless communications and ubiquitous communications systems. The generated MMW signals were radiated in a millimetre waveguide and detected by a detector. The spectral linewidth of the MMW signals was less than 1 kHz, and the power fluctuation of the MMW was less than 1.5 dB over a 30-50 GHz range.     

High-speed GaAs-(GaAl)As DH LED's with output waveguide structure for optical communications

High-speed GaAs-(GaAl)As DH edge-emitting LED's with an output waveguide structure and a reversed p-n junction for current confinement are described. A cutoff frequency of 115 MHz and a radiance of 1100 W/sr cm²at a diode current of 200 mA have been measured. The output power at the end of a fiber pigtail is about 200 µw with a driving current of 200 mA (core diameter of fiber = 60 µm and numerical aperture NA = 0.2). The coupling efficiency between the diode and a single fiber amounts to 10 percent. Factors affecting both the radiative output and the modulation characteristics are analyzed and discussed.     

Coherent optical MIMO (COMIMO)

We present a multiple-input multiple-output (MIMO) optical link based on coherent optics and its ability to exploit the inherent information capacity of multimode fiber. A coherent implementation differs from previous work in optical MIMO by allowing the system to tolerate smaller modal delay spreads, because of a much larger carrier frequency, and yet maintain the necessary diversity needed for MIMO operation. Furthermore, we demonstrate the use of MIMO adaptive equalization to mitigate intersymbol interference when exceeding the bandwidth-length product of the link. The impact of phase noise is studied with numerical simulation.     

Space–time coding and signal processing for high data rate wireless communications

The information capacity of wireless communication systems can be increased dramatically by employing multiple transmit and receive antennas [Foschini GJ, Gans MJ. On limits of wireless communications in a fading environment when using multiple antennas. Wireless Communications Magazine 1998; 6 311–335. Telatar E. Capacity of Multi‐Antenna Gaussian Channels, Technical Memorandum, AT&T Bell Laboratories, 1995.] An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space–time coding. Space–time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial–temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This paper provides an overview of space–time coding techniques and the associated signal processing framework. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis of wireless optical communications feasibility in presence of clouds using markov chains

Free Space Optical (FSO) communications is a practical solution for creating a three dimensional global broadband communications grid, offering bandwidths far beyond possible in Radio Frequency (RF) range. However, attributes of atmospheric turbulence (scintillation) and obscurants such as clouds impose perennial limitations on availability and reliability of optical links. To design and evaluate optimum transmission techniques that operate under realistic atmospheric conditions, a good understanding of the channel behavior is necessary. In most prior works, Monte-Carlo Ray Tracing (MCRT) algorithm has been used to analyze the channel behavior. This task is quite numerically intensive. The focus of this paper is on investigating the possibility of simplifying this task by a direct extraction of state transition matrices associated with standard Markov modeling from the MCRT computer simulations programs. We show that by tracing a photon?s trajectory in space via a Markov chain model, the angular distribution can be calculated by simple matrix multiplications. We also demonstrate that the new approach produces results that are close to those obtained by MCRT and other known methods. Furthermore, considering the fact that angular, spatial, and temporal distributions of energy are inter-related, mixing time of Monte-Carlo Markov Chain (MCMC) for different types of aerosols is calculated based on eigen-analysis of the state transition matrix and possibility of communications in scattering media is investigated.     

Simplified adaptively modulated optical OFDM modems using subcarrier modulation with added input/output reconfigurability

Three novel designs of adaptively modulated optical orthogonal frequency division multiplexing modems using subcarrier modulation (AMOOFDM-SCM) are proposed,for the first time,each of which requires a ...     

Idle-signal casting multiple access with data slot reservation(ICMA-DR) for packet radio communications

A population of terminals communicating with a central station over a packet-switched multiple access radio channel is investigated with regard to multiple access control schemes. The authors describe the ICMA-DR, which is an advanced idle-signal casting multiple access (ICMA) scheme characterized by data slot reservation. This improved central controlled multiple-access scheme for packet transmission in terrestrial radio communications is evaluated in terms of throughput traffic, throughput delay characteristics, and handling capacity. It is shown that the throughput characteristics of ICMA-DR are superior than those of ICMA or slotted ALOHA when a packet for data slot reservation is relatively short in comparison to that for upward data. Thus, it is shown that ICMA-DR is suitable for the packet radio multiple-access scheme, especially in the case where fading packet error occurs frequently and ordered traffic is heavy. The ICMA-DR scheme has been utilized for the access control channel of NTT's new 800-MHz-band high-capacity land mobile communication system since the Spring of 1988     

Mismatch-induced bit error rate in optical chaos communications using semiconductor lasers with electrooptical feedback

We analyze the influence of parameter mismatch between emitter and receiver systems on the bit error rate of an optical chaos communication scheme. Intensity hyperchaos is generated in the system by semiconductor lasers with electrooptical feedback. We find analytical predictions for the dependence of the bit error rate with the amplitude of the various mismatches and the statistical properties of the hyperchaotic carrier. A good concordance is found with numerical and experimental results.