多频带混合场景下终端直通通信用户最优用户密度与功率分配研究

该文分析了蜂窝与终端直通(Device-to-Device, D2D)混合网络中多频带资源的场景下D2D用户最佳密度和功率分配问题。在混合网络中包含一个或者多个蜂窝网络,D2D用户复用蜂窝系统上行频谱资源。通过采用随机几何理论,上述问题可以建模成一个以最大化D2D网络容量为目标并以蜂窝用户和D2D用户的中断概率为约束条件的优化问题。由于上述优化问题非凸,因此分成两步解决原问题:首先证明当D2D用户密度确定的时候原问题对于功率分配是凸问题,并通过拉格朗日对偶方法得到了最优功率分配方案;随后证明中断约束条件将D2D用户密度的定义域分成有限个子区间,在每个子区间上可以通过求导的方式得到D2D传输容量局部最优解,基于上述两个结论,文中设计了一种子区间最优值搜索算法。通过仿真验证了算法的有效性,并且反映出D2D传输容量主要由中断约束条件和来自蜂窝网络的干扰决定。     

广播网络中基于补丁流的丢包恢复机制研究

现有的数字广播网络由于没有回传通道,发送端无法知悉传输过程中的丢包状况。接收端处在广播网络的不同位置,常常因处于小区边缘或受障碍物遮挡等原因造成信号减弱,从而导致丢包率提高。该文提出了一种基于pFEC (patching Forward Error Correction,补丁FEC)的丢包恢复机制,来解决单向广播网络的丢包问题。该方法利用蜂窝移动网络的双向信道来传输补丁流,提供自适应的FEC来降低丢包率。这种方式可以在广播业务中为不同位置的用户提供不同的丢包恢复能力。理论建模及仿真结果显示,在蜂窝移动网络丢包率不高的情况下,pFEC机制能够有效应对个别用户突发的丢包,从而提高广播业务整体的可靠性和服务质量。     

视频广播、视频点播和视频会议

视频广播、视频点播和视频会议都是视频应用的方式。 视频广播是基于ＩＰ组播技术的一种单向、一对多的广播服务，它带宽耗费小。对于每个节目，由于只发送一个视频数据流，因而理论上能够支持无限用户对节目的收看，比较适合大量观众的视频应用，是一种经济有效的视频应用。视频点播是一种一对一传输、双向、不对称的视频应用。允许用户随时请求收看节目，对每一个节目请求都需要占用一个单独的数据流，而与收看者点播的节目无关，从视频点播服务器向用户端传输的视频数据量远远大于反向的点播请求传输的信息数据量，应用带宽耗费较大。视…     

用1020卡接收卫星IPTV的方法

亚太2R卫星(76.5°E)上新增加了频率12550MHz,符码率13333kS/s,水平极化的数据广播,它由北京星线空间信息技术有限公司提供的IPTV服务。其中PID码的十六进制数为1202,十进制数为4610。笔者使用普通1020卡加斯威克天线进行试收,获得了成功。该数据广播主要用于通过卫星和互联网为广大网吧和有线网用户提供数字多媒体互动的高速宽带网络服务。它通过整合卫星、有线网络和地面宽带网络(也可拨号上网)等资源,实现了IP数字宽带视频高效率、高质量的传输,用户在观看数字娱乐视频的同时,还可以通过互联网体验与宽带视频内容的互动。同时,该系…     

移动中继多播场景下的节能优化

设备间通信(D2D通信)通过复用蜂窝通信的频带资源,可以使近距离的用户直接通信,而无需通过基站进行中继.它的引入可以提升用户的服务质量,降低终端能耗,拓展小区的覆盖范围.特别的,在CDN场景中,可通过移动中继向请求相同业务内容的用户进行D2D广播传输.但是,在上述场景中,需考虑到移动终端(MT)的能耗和与蜂窝用户之间的同频干扰问题.基于此,提出了一种基于粒子群优化(PSO)算法的联合中继节点选择和功率控制机制来最小化移动中继的总能耗并同时保证两类用户的服务质量(QoS)需求得到满足.通过仿真,此方案效果得到了验证.     

基于部分频率复用的多小区协作方案及容量分析

针对无线蜂窝网中的小区间干扰问题,给出一种基于部分频率复用的多小区协作传输方案.该方案将小区用户划分为中心用户和边缘用户,中心用户采用频率复用因子为1的本地基站通信,边缘用户采用频率复用因子为3的多基站协作通信,并通过对多个小区的基站进行功率控制,达到抑制小区间干扰、提高系统容量的目的.数值分析表明,相对于传统多小区蜂窝系统(Traditional Multi-Cell System,TMCS)和广义分布式天线系统(Generalized Distributed Antenna System,GDAS),所提多小区协作蜂窝系统(Multi-Cell Cooperative System,MCCS)可以有效地克服小区间干扰,提高系统容量.     

基于NTRIP2.0的北斗地基增强数据播发系统

提出了基于 NTRIP 2.0 地基增强数据播发系统，解决了差分数据在互联网中的传输困难和支持用户数目过少问题。系统包含发送端、播发器、客户端三部分，播发器为系统中的重要组成部分，可以供 200 个发送端和 300 个客户端同时访问。本系统已应用至北斗地基增强系统中，有效提升了差分数据的传输效率，显著提高用户数目，系统性能得到了验证。     

关于发展数据广播的建议

在有线电视中进行数据广播 ,基本做法就是在有线电视前端加入相应的接收、调制、播出设备 ,将图像、声音、图表、文字等多媒体数据信息调制后 ,通过有线电视网络发送给用户 ,用户通过安装在计算机上的信息接收卡或机顶盒解调后收看。采用数据广播技术可以做到先期为用户提供信息服务 ,电视是时分制 ,它的节目都是事先安排好的 ,而利用数据广播技术可以在短短几分钟内 ,把一天的节目先传输给用户 ,用户可以在这个范围内随意点播。1　数据广播适合中国国情(1)许多有线电视网具有 75 0ＭＨｚ传输带宽 ,然而目前在网上基本传输 2 0～ 30套模拟电…     

基于Femtocell网络的时域资源划分

为了满足数据流量增长的需求,在LTE蜂窝系统中引入家庭基站.家庭基站能够分担宏蜂窝的数据流量,与此同时,也给蜂窝系统带来了较大干扰,这些干扰大大影响了用户的通信质量.为解决此问题,提出一种基于家庭基站网络时域资源划分方案(F-MFTR),此方法把时域资源划分与软频率复用技术(SFR)结合起来,边缘用户通过最优化方法寻找最佳的功率段,未参加调度的用户在小区之间形成“隔离带”,在理论上保证了边缘用户与系统中其他用户之间不存在干扰.此外,所有的用户可以在全频段上搜索最佳的资源块,能够提升用户的通信质量.仿真表明,这种方法能大大提升系统的吞吐量.     

多视点立体视频传输系统与错误隐藏算法设计

针对多视点立体视频数据量大、网络带宽受限等问题,提出了一种分组传输多路复用的多视点立体视频实时传输系统。系统将多视点数据通过H.264/AVC压缩编码后,在两个IP链路中进行分组复用,实现了立体视频在带宽受限网络中的实时传输;同时,为了解决IP网络传输中的丢包问题,提出一种联合时域视点间预测的错误隐藏算法。最后通过实验表明,本文错误隐藏算法可以提高多视点立体视频的解码质量。     

A Simulation Analysis of LEDs’ Spatial Distribution for Indoor Visible Light Communication

Visible light communication (VLC) is a promising technology that can jointly be used to accomplish the typical lighting functionalities of the light emitting diodes (LEDs) and data transmission, where light intensity is modulated with the aid of a high rate data that cannot be noticed by the human eye.qu In this paper, a VLC simulation framework to study the effect of LEDs’ distributions on different room dimensions is proposed by considering the performance metrics such as light intensity quality in accordance with the International Organization for Standardization (ISO) recommendation, and data transmission efficiency measured in terms of bit error rate (BER). To achieve that, a VLC communication system is designed that modulates the data, transmits it over the room utilizing the communication channel that is modeled using an accurate ray-tracing algorithm, and receives it. Our work is different from most of the published works, which studied either the data transmission efficiency or lighting quality but not both. In addition, our study investigates the effect of having different rooms dimensions and different number of transmitters on data transmission quality and light illumination. Consequently, this paper can be used as a methodological study to design an efficient VLC system that satisfies the ISO lighting requirement and the VLC application-specific BER requirements. Furthermore, a video transmission use case has been demonstrated, which shows how video quality can be significantly improved when the number of transmitters is increased. However, considering the ISO lighting requirements, one can put a limit on the number of LEDs that can achieve the required application BER and lighting requirements, thus achieving both objectives efficiently.

     

OCDMA and OSTBC based VLC transceiver design using NI cDAQ

Visible light communication (VLC) is a novel technology especially for short-range data communication. IEEE has standardized VLC for 5G systems as a means to short-range wireless communication. In this paper, a complete state-of-the-art VLC software-defined radio is designed using NI cDAQ components tools developed in LabVIEW/MATLAB. The main objectives in designing a VLC transceiver are the suitable envelope for driving LEDs (transmitters) and a high data rate. The current work makes use of optical code division multiple access mainly to achieve the said objectives. It is shown through comparison with existing system that the proposed system is computationally less expensive and provides improved data rate. Finally, simulation programs are also developed and the proposed system is compared with the existing system in terms of bit error rate.     

可见光通信及其关键技术研究

可见光通信系统采用白光发光二极管(LED)作为光源,因而系统具有通信与照明的双重作用,极大地节约了能源.描述了可见光通信的结构与特点,对可见光通信的一些关键技术做了简单的研究,并介绍了可见光通信的发展动态.     

Non-Uniform Time Slot Based Modulation for Visible Light Communication System

Recently, visible light communication (VLC) has got increasing attention in the field of indoor wireless communications. VLC has the obligation of lighting besides data communications. The IEEE 802.15.7 task group proposed a VLC modulation format named color shift keying in which data symbols are defined based on the diffused light wavelength. This paper presents a new modulation scheme for indoor wireless visible light communication system named non-uniform time slot modulation (NUTS). The NUTS modulation scheme defines the feeder signals of red, green and blue LEDs as rectangular pulses with appropriate width and their positions. In this method, the time axes of all the three light sources (channels) are slotted to some non-uniform durations that all symbols are spanned over these slots as orthogonal dimensions. The proposed scheme has some advantages with respect to other approaches such as low bit error rate and high bit rate. Furthermore, it provides appropriate synchronization capability. Besides, in the design of NUTS modulation scheme it has been tried to deliberate all practical constraints, as far as possible.     

高速VLC系统中LED直流偏置对系统误码率的影响

研究了高速可见光通信(VLC)系统中荧光型LED光源的直流偏置电流大小与系统响应时间、误码率的关系;搭建了高速可见光通信测试系统,用于验证如何通过设置合适的LED光源的直流偏置电流使可见光通信系统达到更高的通信速率和更低的误码率.实验测试结果表明,在直流偏置电流为60～80 mA,1W的荧光型LED的响应时间较短,系统的误码率较低,此时可见光通信系统可达到最大传输速率.     

An inter-lighting interference cancellation scheme for MISO-VLC systems

In this paper, we propose an inter-lighting interference cancellation (ILIC) scheme to reduce the interference between adjacent light-emitting diodes (LEDs) and enhance the transmission capacity of multiple-input–single-output (MISO)-visible light communication (VLC) systems. In indoor environments, multiple LEDs have normally been used as lighting sources, allowing the design of MISO-VLC systems. To enhance the transmission capacity, different data should be simultaneously transmitted from each LED; however, that can lead to interference between adjacent LEDs. In that case, relatively low-received power signals are subjected to large interference because wireless optical systems generally use intensity modulation and direct detection. Thus, only the signal with the highest received power can be detected, while the other received signals cannot be detected. To solve this problem, we propose the ILIC scheme for MISO-VLC systems. The proposed scheme preferentially detects the highest received power signal, and this signal is referred as interference signal by an interference component generator. Then, relatively low-received power signal can be detected by cancelling the interference signal from the total received signals. Therefore, the performance of the proposed scheme can improve the total average bit error rate and throughput of a MISO-VLC system.     

Advances and prospects in visible light communications

Visible light communication (VLC) is an emerging technology in optical wireless communication (OWC) that has attracted worldwide research in recent years. VLC can combine communication and illumination together, which could be applied in many application scenarios such as visible light communication local area networks (VLANs), indoor localization, and intelligent lighting. In recent years, pioneering and significant work have been made in the field of VLC. In this paper, an overview of the recent progress in VLC is presented. We also demonstrate our recent experiment results including bidirectional 100 Mbit/s VLAN or Li-Fi system based on OOK modulation without blue filter. The VLC systems that we proposed are good solutions for high-speed VLC application systems with low-cost and low-complexity. VLC technology shows a bright future due to its inherent advantages, shortage of RF spectra and ever increasing popularity of white LEDs.     

Analysis of the effects of LED direction on the performance of visible light communication system

Visible light communication (VLC) is expected to be the next generation of indoor wireless communication. A VLC system uses many LED chips, and its performance is greatly affected by the direction of light-emitting diodes (LEDs). Normally, the LEDs are directed vertically downward to the floor. In this paper, we introduce an LED layout scheme in which the LEDs tilt toward the room corners. The effects of changing LED direction on system performance, including illuminance, received power, and SNR, are analyzed. The analysis is then verified by the simulations.     

基于多色LED的可见光通信联合调制技术

提出了一种针对广义色移键控(CSK)调制RGB 3色发光二极管(LED)的可见光通信(VLC)星座图设计方法。为了实现通信与照明的结合,考虑了一些照明条件的约束:首先,LED产生的颜色和强度被限制以达到照明要求;其次,为了减小非线性效应的影响,每盏LED灯的功率被限制在线性范围;最后,利用奇异值分解(SVD)的预均衡来消除多径效应的影响和颜色间的干扰。仿真结果表明,相比较于每路LED分别采用开关键控(OOK)调制的误码率,优化的星座图性能更优。     

DFT-spread combined with clipping method to reduce the PAPR in VLC-OFDM system

Orthogonal frequency division multiplexing (OFDM) is an attractive technique to realize high data rate in light emitting diodes (LEDs)-based visible light communication (VLC). However, high peak-to-average power ratio (PAPR) of OFDM makes VLC-OFDM very sensitive to the nonlinearity of LEDs. In this paper, the discrete Fourier transform-spread (DFT-spread) combined with clipping method is proposed to reduce the PAPR of OFDM signal in VLC system. Combining simulation with experiment, a performance comparison is made among conventional OFDM, DFT-spread-OFDM, and clipped DFT-spread-OFDM with different clipping ratios (CRs) in a single LED-based VLC system. The experimental results show that the proposed clipped DFT-spread-OFDM method can effectively improve the system performance compared with the other two methods. At the optimum signal peak-to-peak (PTP) value, by using the clipped DFT-spread-OFDM scheme with CR at 8 dB, the bit error rate (BER) of the system can be reduced from 0.003 7 to 0.000 287. E-mail:dengrui189@126.com