Performance Analysis of WLAN Medium Access Control Protocols in Simulcast Radio-Over-Fiber-Based Distributed Antenna Systems

The performance of three wireless local-area network(WLAN) media access control(MAC) protocols is investigated and compared in the context of simulcast radioover-fiber-based distributed antenna systems(RoF-DASs) where multiple remote antenna units(RAUs) are connected to one access point(AP) with different-length fiber links.The three WLAN MAC protocols under investigation are distributed coordination function(DCF) in basic access mode,DCF in request/clear to send(RTS/CTS) exchange mode,and point coordination function(PCF).In the analysis,the inter-RAU hidden nodes problems and fiber-length difference effect are both taken into account.Results show that adaptive PCF mechanism has better throughput performances than the other two DCF modes,especially when the inserted fiber length is short.

Green Architecture for Dense Home Area Networks Based on Radio-over-Fiber with Data Aggregation Approach

The high-density population leads to crowded cities. The future city is envisaged to encompass a large-scale network with diverse applications and a massive number of interconnected heterogeneous wireless-enabled devices. Hence, green technology elements are crucial to design sustainable and future-proof network architectures. They are the solutions for spectrum scarcity, high latency, interference, energy efficiency, and scalability that occur in dense and heterogeneous wireless networks especially in the home area network （HAN）. Radio-over-fiber （ROF） is a technology candidate to provide a global view of HAN＇s activities that can be leveraged to allocate orthogonal channel communications for enabling wireless-enabled HAN devices transmission, with considering the clustered-frequency-reuse approach. Our proposed network architecture design is mainly focused on enhancing the network throughput and reducing the average network communications latency by proposing a data aggregation unit （DAU）. The performance shows that with the DAU, the average network communications latency reduces significantly while the network throughput is enhanced, compared with the existing ROF architecture without the DAU.

Development of Millimeter-Wave Radio-over-Fiber Technology

Millimeter-wave radio-over-fiber techno- logy demonstrates the potential for providing wireless broad-band service in the next generation wireless communication system.Optical generation of millimeter-wave signal is one of the most important technologies of millimeter-wave radio-over-fiber system.The virtues and shortcomings of some ways of optical generation of millimeter-wave signal are discussed.Then optical millimeter-wave signal transmission perfor- mance is described.Finally,an overview of the millimeter-wave radio-over-fiber system is given.It is suggested that the millimeter-wave radio-over-fiber technology should be paid more attention,especially for modulators for optical generation of millimeter-wave signal and radio-over-fiber system.

Optical QPSK/16QAM modulation based on serial-parallel MZM scheme in radio-over-fiber system

A novel scheme of optical modulation in 40 GHz radio-over fiber （RoF） system is proposed. It generates optical QPSK/16QAM signals in a serial-parallel structure of Mach-Zehnder modulators （MZMs）. The millimeter-wave is obtained with optical frequency multiplication （OFM）. Furthermore, modulation on optical-wave is transferred onto millimeter-wave. It can be used to increase transmission capacity of millimeter-wave RoF systems.

W-band radio-over-fiber transmission system with delta-sigma modulation and direct detection

We experimentally built a W-band photonics-aided millimeter-wave radio-over-fiber transmission system and demonstrated the delivery of up to 8192-ary quadrature amplitude modulation[QAM] signal.Discrete multitone signals are converted into 1-bit data streams through delta-sigma modulation and then modulated onto a 76.2 GHz carrier.An envelope detector is used at the receiver side for direct detection.The results prove that our proposed system can support 2048QAM and 8192QAM transmission while meeting the hard decision forward error correction threshold of 3.8×10^(-3)and the soft decision forward error correction threshold of 4.2×10^(-2),respectively.We believe this cost-effective scheme is a promising candidate for future high-order QAM millimeter-wave downlink transmission.

Effect of optical losses on the transmission performance of a radio-over-fiber distributed antenna system

The effects of optical losses oil a directly-modulated radio-over-fiber （RoF） system used for distributed antenna networks are determined. The results show that with a properly designed bidirectional amplifier, the RoF link can tolerate over 20 and 16 dB of optical losses for down- and up-links, respectively. Simulation results are also consistent with the experimental data. These findings can contribute to tile design of RoF distributed antenna systems with different topologies.

Highly linear transmission and EVM improvement of vector modulation signals for radio-over-fiber applications

The principle of error vector magnitude （EVM） against modulator nonlinearity for vector modulation signal （VMS） transmission in radio-over-fiber （RoF） systems is theoretically and experimentally investigated. A highly linear modulation scheme is proposed and demonstrated using a single-drive dual parallel Mach–Zehnder modulator （MZM）. This method improves EVM performance and enlarges the linear input dynamic range of the VMS transmission. An index of maximum allowable input power difference （MAIPD） that reflects the difference of upper input power limits between these two schemes is measured. An EVM limitation of 5% MAIPD has 5 dB. Both 16and 64-QAM results indicate that the proposed scheme supports VMS transmission better than the MZM one.

Polarization multiplexing based duplex radio-over-fiber link for millimeter wave signal transmission to a ring of multiple radio access units

A radio-over-fiber(RoF) distributed antenna system(DAS) architecture is proposed, where millimeter wave(mm-wave) signals are transmitted to four different radio access units(RAUs) arranged in a ring topology.The proposed architecture transmits duplex data of 128 Mb/s to each RAU in both downlink(DL) and uplink(UL)directions. The radio frequency(RF) signals are transmitted by polarization multiplexing a multi-wavelength source.Millimeter-wave signals at a frequency of 25 GHz are generated at each RAU using remote heterodyne detection.The proposed architecture provides increased coverage while maintaining good bit error rate(BER) results.

Optically injection-locked Fabry-Perot laser diodes based radio-over-fiber system for hybrid fiber-wireless access networks

A new radio-over-fiber system for use in hybrid fiber-wireless access networks is proposed and experimentally demonstrated,which is based on cascaded injection-locked Fabry-Perot laser diodes.It is verified that the proposed technique is able to achieve a good suppression ratio of an optical carrier suppressed(OCS) signal simultaneously through a programmable optical filter and by use of optical injection locking technique.A 60 GHz carrier with downlink baseband data has been generated and down converted to baseband signal in order to be characterized in our laboratory.

面向FTTR的低成本半双工模式收发机方案及关键技术

为了降低光纤到房间系统中光网络单元的数量和成本,提出了半双工模式收发机方案。该方案通过模式切换开关连通不同电路组件,实现通信系统的收发功能。同时,将该收发机与Wi Fi无线收发系统配合使用,形成了“光纤-无线”半双工收发系统架构,实现光信号和射频信号在光纤到房间系统中的传输。测试结果表明,设计的模式切换开关与收发机协同工作顺畅,在数据传输速率为5 Gb/s时,接收端信号眼图清晰,验证了半双工模式收发机方案的可行性。

光纤时间频率同步技术及应用

时间是人类目前测量和复现不确定度指标最高的物理量,代表了人类科技发展的最高水平。光纤时频同步技术经过几十年的发展,目前已广泛应用于量子计量、射电干涉测量、定位导航、现代通信、电力电网、高能物理、大地测量等诸多领域,成为人类社会高效运行的重要支撑。得益于光纤时频同步技术的高可靠性和高稳定度,综合原子时“分布式”和“实时性”这一长期存在的矛盾得到了解决。文章介绍了光纤时频同步技术的发展历史、各技术路径的研究现状,以及基于北京地区光纤时频同步网生成的分布式实时综合原子时。在此基础上,指出光纤时频同步的发展重点正从技术研究转为大规模网络化应用,开展基于光网络的多功能、多应用融合研究,实现一体化通信、感知、计算、测量、控制,将是未来的重要发展趋势。

外调制倍频光生毫米波技术的研究进展

目前,随着光电子芯片技术的高速发展,高频毫米波通信已成为目前宽带接入网络中的重要发展技术;因为采用外调制倍频方案的光生毫米波系统兼具收发毫米波信号的高效性和稳定性,且能充分利用现有电信网络中的光纤资源,因此,在实际中具备潜在应用价值。综述了光生毫米波倍频基本原理、典型倍频仿真或实验方案及其相关测试结果的研究进展;考虑到马赫-曾德尔调制器(Mach-Zehnder Modulator,MZM)作为倍频光生毫米波的关键电光器件,因此,分析了其中的关键工作参数;最后,对光载无线通信(Radio over Fiber,RoF)系统中光生毫米波技术的应用前景进行了展望。

一种新颖的基于偏振调制器的无码元走离效应的倍频毫米波光载无线系统

为了克服基于马赫-曾德尔调制器(MZM)的倍频毫米波光载无线系统(Radio Over Fiber,ROF)中的MZM存在的直流偏置漂移问题和ROF中的码元走离效应,本文提出了一种基于偏振调制器(Polarization Modulator,PolM)的无码元走离效应的倍频ROF系统。在中心站,利用PolM产生±1阶边带信号,利用复合射频(Radio Frequency,RF)信号来驱动PolM,实现将下行数据信号仅调制在+1阶边带上。复合RF驱动信号由两路信号合成,其中一路信号由数据信号通过相位调制器调制RF驱动信号形成,另一路信号是由数据信号经电放大器进行放大形成。在基站,利用光纤光栅(Fiber Bragg Grating,FBG)反射出部分-1阶边带做上行链路的光载波,实现载波重用;利用透过FBG的±1阶边带在光检测器(Photo Detector,PD)中的拍频产生倍频毫米波信号。在误码率为10-9情况下,经20、40和60公里的传输后,下行链路功率代价分别为1dB、1.2dB和1.22dB,上行链路的功率代价分别为0.5 dB、0.8 dB和1 dB。本文设计的方案能有效地克服光纤色散导致的码元走离效应,极大地提高了系统的传输距离,在ROF系统中具有重要的应用前景。

面向5G光载通信系统的数字预失真线性化技术应用

随着5G通信技术的迅猛发展,光载无线(Radio-over-Fiber,RoF)通信系统在实现高数据传输率和低延迟方面日益发挥出重要作用。然而,该系统在处理高频宽带5G信号时,常受到射频功率放大器和光电组件非线性特性的影响,导致信号产生失真问题。为解决这一问题,文章深入探讨了数字预失真(Digital Predistortion,DPD)技术在5G RoF通信系统中的应用及其效果。

5G光载无线通信前传系统数字预失真线性化研究

第五代移动通信系统新空口(5G NR)的信号带宽、调制度和峰均比相比4G信号高很多。用于小蜂窝或微蜂窝基站组网的光载无线通信(Radio-over-Fiber,RoF)前传系统的非线性失真也更加严重。为了使5G NR信号线性传输,采用记忆多项式(Memory Polynomial,MP)和广义记忆多项式(Generalized Memory Polynomial,GMP)模型构建数字预失真器,矫正5G RoF前传系统的非线性。在实验中搭建了2 km光纤的RoF前传系统,并采用100 MHz带宽5G NR信号作为测试信号对其进行线性化测试。实验结果表明,采用MP和GMP数字预失真器进行线性化时,5G RoF前传系统的邻信道功率比(Adjacent Channel Power Ratio,ACPR)可分别改善13 dB和17 dB以上。这说明MP和GMP数字预失真器对5G RoF前传系统的非线性具有显著的抑制作用。因此基于MP和GMP两个模型的数字预失真器均可用于5G RoF前传系统的线性化,而且GMP预失真器比MP预失真器对该系统线性化的能力更强。

基于RoF和OTFS调制技术的新型高铁移动通信双层链路结构

为了克服高铁移动通信场景下传输容量和多普勒频移带来的困难,提出一种基于光纤无线电(RoF)和正交时频空间(OTFS)调制技术的新型高铁移动通信双层链路结构。在高铁移动通信场景下,有线部分使用RoF技术作为沿铁路分配高频宽带无线信号的解决方案;无线部分使用OTFS调制,通过将时频域信号转换为相对稳定的时延多普勒域信号来解决多普勒频移(DFS)破坏现行宽带正交频分复用(OFDM)信号子载波间正交性的问题。仿真结果表明:在相同传输条件下,当OFDM调制的误码率降为10-1以下时,OTFS调制的误码率已经降低到10-4量级,因此OTFS调制的传输性能更优。

面向下一代移动通信的前传网络关键技术

下一代宽带移动通信的容量相对5G通信提升百倍至千倍,这对支撑其发展的前传光通信网络的物理基础提出了巨大的挑战。系统回顾和梳理了移动前传网络的需求、技术和实现架构等。以光纤无线融合接入为基础,重点针对数字前传技术、模拟前传技术和数模结合前传技术3类移动前传架构,围绕其网络架构、关键技术和未来发展方向进行了深入的分析和探讨,并对未来前传网络关键技术进行展望。本研究可为未来移动前传网络的研究提供参考。

一种基于DPMZM的16倍频光生毫米波方案

为提高光载无线(RoF)中光生毫米波的倍频系数及降低系统的复杂度,提出了一种基于双平行马赫曾德尔调制器(Dual-Parallel Mach-Zehnder Modulator,DPMZM)和偏振复用技术的抑制载波的16倍频毫米波信号产生方案。推导了理想情况下倍频方案的产生机理。在仿真实验中,分别分析了调制器调制指数、消光比、电移相器相移、偏振器件角度漂移等非理想因素对系统光边带抑制比(OSSR)和射频杂散抑制比(RFSSR)的影响。结果显示,当合理设置各参数的取值范围,其对应的OSSR和RFSSR的饱和值高达29.88 dB和23.9 dB。该方案在一定程度上简化了16倍频的系统模型且生成的毫米波信号性能较为高效、频谱纯度较好,对实际系统设计具有一定的参考价值,为微波光子学的发展提供了新途径。

平衡探测技术在ROF系统获取高质量毫米波上的应用

Radio-over-Fiber系统是基于光纤通信和高频无线电通信的系统,同时具有光纤远距离传输和无线电大带宽传播的优点。本文从当前Radio-over-Fiber系统中存在的几种常用毫米波产生方法的分析入手,指出其存在的不足,提出运用平衡探测技术获取毫米波的方法。该方法可获得高质量的毫米波,为提高系统通讯质量奠定了基础。

采用电光调制器产生光毫米波的全双工通信光纤无线通信系统

实验研究了一种采用单个电光调制器产生光毫米波的方法和相应的全双工无线通信系统。在中心站采用电混频器产生电毫米波,然后再利用电光制器产生双边带信号。利用光交错复用器将中心载波和双频一阶边带信号分离。双频一阶边带用于产生2倍射频信号的光毫米波,而中心光载波用来作为上行链路的光载波。实验显示采用频率为20GHz射频信号产生光毫米波的频率为40GHz,而且将下行链路和上行链路中2.5Gbit/s的数据在单模光纤中传输距离达20km,而功率代价均小于0.5dB。