地面无线广播电视频谱监测方法

频谱监测是地面无线广播电视信号监测中一项重要内容,本文阐述了地面无线广播电视监测网频谱监测的实现原理,并对进一步的应用进行了探讨。     

面向接入回传一体化的毫米波空地网络建模与分析

无人机(UAV)作为空中基站有望成为传统地面网络的有力补充,以提供灵活覆盖和容量增强的解决方案。然而,大多现有研究忽略空中基站的无线回传这一实际因素对网络性能和用户体验的影响。为此,考虑接入回传一体化的空地毫米波蜂窝网络场景,其中无人机提供热点流量传输服务,地面基站(TBS)提供无人机回传链路并且服务非热点区域用户,以及接入和回传采用正交资源分配方法。针对该场景,提取地面基站、无人机和用户的空间分布特性,以及不同链路信号的传播特性,该文采用随机几何理论建立与之匹配的毫米波空地网络模型,推导了非热点用户的接入链路覆盖率和热点用户的接入回传链路的联合覆盖率。进一步地,基于地面基站和无人机的负载特性分析,推导了两种用户的速率覆盖率以及总体用户性能。基于所提分析框架,该文研究了关键系统参数,如接入链路频谱分配比例、无人机密度和热点用户密度等对用户性能的影响。     

基于边缘频谱效率的家庭基站无线资源分配算法

为了解决日益增长的室内无线资源的需求,近年来人们提出了基于OFDMA系统的家庭基站网络,但是由于OFDMA系统的频谱资源的匮乏,合理使用无线资源改善家庭基站网络的频谱效率成了人们研究的重点。本论文是在基于OFDMA的家庭基站的场景下提出了一种新的基于Q学习的动态信道分配机制,避免了解决复杂的最优化问题。该算法动态地调整各复用系数下的信道数,同时考虑所有家庭基站的频谱效率作为奖赏函数,在尽量保证最低频谱效率的同时提高家庭基站的系统频谱效率。仿真结果表明该算法在满足了家庭基站网络的QoS要求的基础上提高了家庭基站系统的频谱效率。     

浅析地面无线数字电视广播系统建设

地面无线数字电视发展迅速,特别是随着国标的出台,地面无线数字电视的发展将迎来新一轮快速发展的时代.发展地面无线数字电视,是加速推进广播电视“村村通”工程的有效方式.首先概述了地面无线数字电视,然后介绍地面无线数字电视的优势,最后从建设需求、标准选择、系统结构和组成、信号覆盖情况等多方面,阐述新余市广播电视台的地面数字电视广播系统建设情况.     

WIFI多级桥接应急多媒体通信系统研究

聚焦北京地铁交通轨道应急抢险可视化通信与信号传输的应用领域，针对传统的有线通信系统存在的传输距离短、线路铺设灵活性差；无线通信系统中，无线自组网技术存在的收发单元间传输能力与适应性差；卫星与公网结合的通信系统存在的信号源不稳定等缺陷。提出了WIFI多级桥接应急多媒体通信系统架构，研究基于5.8GHz的WIFI多级接桥技术并研制相关设备，在无线自组网技术基础上，在传输能力与适应性方面进行了改进，能够有效适应远距离、遮挡及垂直差异存在的信号传输场景。提出采用广泛应用的公网4G信号构建通信系统，有效避免当车载基站作为信号源造成的不稳定性，当应急救援现场无4G信号覆盖时，结合WIFI多级桥接技术提供的网络传输保障功能，从而使得整体桥接与通信系统可满足所有的地铁抢险环境并实现相应功能要求。      

VHF/UHF广播电视监测信号接收链路改进研究

随着广播电视事业的飞速发展,地面数字电视(DTMB)和移动多媒体广播(CMMB)等新业务的开展,VHF和UHF波段的广播电视业务的监测工作也有所增加,对接收链路提出了更高的要求.目前使用的接收链路存在两副天线接收信号频谱重叠现象、广播电视频段频谱扫描结果不理想等问题,对此本文提出更换接收天线和优化接收链路的监测前端设备接收改进方案.     

康普：小型天线技术是部署更多蜂窝基站的捷径

现今的无线运营商开始在现有的基站上增加越来越多的蜂窝基站和扇区,以此满足来自于消费者日益激增的带宽需求。复杂地进行此类“蜂窝基站密度”的尝试是由于没有足够空间建立新的蜂窝基站,因此运营商不得不从审美要求和信号塔租赁成本这两大方面绞尽脑汁,力求突破。作为全球领先的通信网络基础设施解决方案的专家,康普公司宣布通过采用一种全新的Andrew小型天线技术来简化蜂窝基站密度的操作难度,进而解决此类挑战。     

远距离定向覆盖技术在应急通信中的应用浅谈

为了在发生火灾、爆炸、化工泄漏等安全事故时,应急通信队伍为现场救援提供及时通信的同时,确保现场执行应急通信任务人员的人身安全,应急通信人员需要与事故现场保持一定距离。通过对特殊灾害场景安全距离需求与现有车载应急通信系统技术性能进行对比,从理论上分析了实现远距离定向覆盖的方法和可行性,并制定对策,进行了实地模拟实验。通过实验,验证了通过替换天馈系统、改造基站射频单元、调整无线参数及提高信号强度和天线增益等方式提升远距离覆盖的效果,实现了在特殊场景下对车载CDMA系统的覆盖需求。     

TDD场景下小基站蜂窝网络上下行交叉干扰建模及性能分析

针对小基站网络立体分布特性,提出了一种TDD制式下小基站蜂窝网络三维随机几何模型并进行了性能分析。首先,本文根据3-D PPP模型下小基站的空间分布特性推导了TDD制式下小基站网络上下行覆盖概率的数学表达式。接下来,基于覆盖概率的表达式和网络频谱效率的定义,分别推导了上下行交叉干扰场景下,小基站网络上下行频谱效率的一般表达式。仿真结果在验证了本文模型的合理性的同时还说明,随着下行小区占比和功率控制因子的增大,网络的频谱效率都呈下降趋势。除此之外,室内环境也会对网络的覆盖性能产生影响。      

5G干扰测试仪在广播电视与电信业务干扰排查中的应用

5G基站的大规模建设，在有效提升人们对互联网通信满意度的同时，带来了新的问题。因中国广电、中国移动共建共享的5G频段（700 MHz）与原规划给中央广播电视节目无线数字化覆盖的地面数字电视段频有重叠，在地面数字电视还未完成清频、5G基站大规模建设的时期，5G基站信号对地面数字电视信号产生了干扰。江西省多地广播电视台相继出现了地面数字电视受5G信号干扰的现象，严重威胁到安全播出。如何快速定位5G干扰，成为一个新的课题。基于此，介绍广播电视与电信业务干扰排查流程，阐述5G干扰测试仪在干扰排查中的实际应用。     

UHF propagation prediction for wireless personal communications

Propagation characteristics of radio signals in the UHF band place fundamental limits on the design and performance of wireless personal communications systems, such as cellular mobile radio (CMR), wireless LANs, and personal communication services (PCS). Because the radio link is direct to each subscriber, the prediction of signal characteristics is most important in urban areas where subscriber density is high, and the buildings have a profound influence on the propagation. The paper starts by reviewing the characteristic signal variations observed in CMR systems employing high base station antennas to cover macrocells having radius out to 20 km. Theoretical models incorporating diffraction are shown to explain the observed range dependence and shadow loss statistics. For the low base station antennas envisioned to cover microcells of radius out to 1 km for PCS applications, signal propagation is more strongly dependent on the building environment and on the location of the antennas in relation to the buildings. Various levels of theoretical modeling of this dependence are discussed in conjunction with measurements made in various building environments. Finally, the paper discusses advances in site specific prediction for outdoor and indoor propagation     

新一代应急综合通信系统的构建

从应用和技术角度分析了应急综合通信系统的需求,提出了基于IP技术的综合网络通信平台——应急综合通信系统的构建方法,有效解决了目前城市应急联动系统亟待解决的3个问题:①传统的电话、VHF/UHF/HF无线电、新一代无线数字集群、VSAT卫星、移动电话网GSM/GPRS、计算机网络综合通信与互通互联;②移动(车载)指挥中心的综合通信;③指挥中心(包括固定和移动指挥中心)间的互联互通。     

超短波电台信道模型的仿真研究

无线信道的特性直接关系到为实现优质可靠地超短波电台通信必须采用的技术措施,因此分析研究无线信道模型对于超短波电台通信有着重要的意义。针对平坦开阔地形的超短波无线信道进行了研究,介绍了无线信道的特性以及多径衰落的信道模型和统计特征,描述了超短波无线信道模型的组成框架,结合应用实际进行了信道仿真与性能分析,得到信道模型的时域和频域特性,仿真结果表明该模型满足应用需求,可以应用于超短波电台的算法设计仿真。     

Toward Distributed Robust Power Allocation of Wireless Backhaul Links in Vehicular Small Cells

The vehicular small cell (VSC) is a new paradigm that has been recently proposed to be a potential technology for 5G cellular systems. Briefly, VSC concept lies in using the small cell technology inside vehicles such as buses and private cars to provide better coverage and good internet experience while on the move where the wireless backhaul link is inevitable. However, in order to increase the spectral efficiency, co-channel deployment of VSCs on the wireless backhaul link is preferred. Thus, managing the variable interference on the wireless backhaul and its power allocation requirement seem to be serious challenges in implementing the VSCs. Motivated by the simplicity and practically of the power allocation based on pilot power and received signal strength index (RSSI) information, this paper proposes an evolutionary approach and robust to the interference fluctuations in which, taking the limited dynamic range of transmitted power using linear mapping into account, the signal to interference plus noise ratio (SINR) balancing of the vehicular small base stations in their home macro base station and maximum capacity on the backhaul link are achieved at the cost of exchanging some power level information among both macro and small base stations. Finally, simulation results prove aforementioned potential advantages attained from the presented schemes.     

The wireless last mile

Phone companies losing broadband ground may have to embrace their enemy, wireless metropolitan-area networking itself about to take off now that a new standard, IEEE 802.16, has been adopted. Creating a wireless network is relatively simple. At its heart is a base station, which can be put on top of a building's roof, a cellular tower, or even a water tower. The base station is the bridge between the wired world of the Internet, on one end, and subscribers, with whom it is connected by radio waves, on the other. It largely takes the place of the DSL server in a phone company's central office With each station generally serving a 10- to 15-km radius, base stations can be put up where they're economically justified. The issues involved in the wireless last mile are discussed in this article.     

Immune optimization algorithm for solving vertical handoff decision problem in heterogeneous wireless network

In heterogeneous wireless network environment, wireless local area network (WLAN) is usually deployed within the coverage of a cellular network to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. Vertical handoffs between the WLAN and the cellular network maybe occur frequently. As for the vertical handoff performance, there is a critical requirement for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a mathematical model for vertical handoff decision problem, and propose a multi-objective optimization immune algorithm-based vertical handoff decision scheme. The proposed scheme can enable a wireless access network not only to balance the overall load among all base stations and access points but also maximize the collective battery lifetime of mobile terminals. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed scheme.     

Adjacent-Cell Interference in Direct-Sequence CDMA Forward Traffic Channels

Each transmission from a base station in a mobile cellular direct-sequence CDMA network is a source of interference for the receivers in the mobile handsets that are operating in adjacent cells. This interference can limit the capacity of the forward traffic channels. The effect of adjacent-cell interference on the performance of the handset receivers is evaluated for a mobile cellular CDMA network that employs quadriphase-shift-key spreading, convolutional coding, and soft-decision decoding. It is demonstrated that acceptable performance may not be possible for a fully loaded cellular network. Of particular interest in this paper are cellular networks in which the base stations are mobile and must be interconnected by wireless communication links. Such networks are important for military applications and certain civilian emergency communications services.     

Spectrum considerations for public safety in the United States

Since the inception of mobile radio, public safety agencies have relied on wireless communication systems to coordinate day-to-day and emergency operations. The decentralized and autonomous nature of the various public safety agencies in the United States has led to the deployment of a variety of systems operating in a fragmented spectrum, ranging from lower VHF to upper UHF. Due to the narrowband technologies used in public safety communications systems, public safety agencies have been limited primarily to voice services and low-speed data transfer on their private networks. In contrast, the commercial cellular sector now offers a large portfolio of services that include voice, messaging, email, Web browsing, picture transfer, video streaming, and other wideband services. In this article, some of the factors driving the expansion of spectrum allocated to public safety agencies arc described.     

NOMA-D2D协作无线系统的物理层安全

针对未来海量用户设备接入的物理层安全（physical layer security，PLS）应用需求，提出了一种组合非正交多址接入（non-orthogonal multiple access，NOMA）、终端直通（device-to-device，D2D）与中继协作的NOMA-D2D协作无线系统PLS模型。该模型由采用发射天线选择（transmit antenna selection，TAS）的基站、分别作为基站和D2D发射端的NOMA远端蜂窝用户、D2D接收端以及被动窃听者组成，其中的D2D发射端承担基站的 NOMA 近端用户和解码转发中继两种角色。利用高斯—切比雪夫正交定理推导两种 TAS 方案下NOMA-D2D协作无线系统的安全中断概率、非零安全容量概率以及渐近安全中断概率的近似表达式。数值计算和仿真实验验证了NOMA-D2D协作无线系统PLS性能分析的准确性；在基站总功率恒定时增大分配给远端蜂窝用户的功率能有效提升NOMA-D2D协作无线系统的PLS性能。