基于D2D链路的测量与建模.doc

基于D2D链路的测量与建模 Abstract: Channel measurements and modelling have been long considered as the foundation for effective and efficient wireless communication system designs. Recently, there has been an explosive growth of research work dedicated to the so-called device-to-device (D2D) communications. In the mean time, however, measurements and modelling of D2D channels seem to somewhat fall behind. To promote research on these aspects, in this study, the authors provide a critical overview of the current state of research on D2D channels, and comprehensively discuss future trends and research directions. 摘要：信道测量与建模被长期作为无线通信系统设计实用性和高效性的基础。近年，对于所谓device-to-device（D2D）通信的研究工作呈现出爆发式增长，但同时关于D2D信道的测量与建模看起来没有同步进行。为了加深对于这些方向上的研究，本文中作者对D2D信道的当前研究现状做出客观的综述，并概要地讨论了未来趋势和研究方向。 1.introduction 1.简介 In recent years, device-to-device (D2D) communications have gained much attention to meet the increasing demand of wireless data service in spite of the increasingly scarce frequency spectrum 1. The D2D communications are defined as the information exchange via a direct link between the end users, as opposed to transmitting and receiving signals through the cellular base station (BS). D2D communications behave as an underlay to the cellular network, which can achieve cellular controlled short-range direct data transmission for local area services by reusing the cellular spectrum, leading to both spectral efficiency improvement and cell throughput enhancement 2. In traditional cellular networks, the radio resource in a cell can be allocated to only one cellular user equipment (UE) link. However, in cellular networks with D2D capability, multiple D2D links can share a resource block by spatially reusing the resource block within a cell. As a matter of fact, the D2D concept has been proposed long time ago for ad hoc networks, for example, WLAN and vehicular networks. Recently, the roadside infrastructure controlled D2D concept has been first proposed for vehicular communications 3.近年来，随着频谱资源越来越稀缺，为满足无线数据业务的增长需要，device-to-device（D2D）通信被广泛关注1。D2D通信指的不是通过蜂窝基站（BS）发送和接收信号，从而在终端用户间建立一个直接相连的信息交换信道。D2D通信作为蜂窝网络的底层可以通过复用蜂窝网络频谱资源，实现多小区控制下本地短距离直接数据传输服务，从而提高了频谱效率，增加了小区吞吐量2。在传统的蜂窝网络中，一个小区的频率资源只能分配给一个用户设备（UE）连接，但是，在应用终端直联（D2D）技术的蜂窝网络中，多个D2D连接可以共享一个小区内空间复用的资源块，事实上，终端直联的概念曾在早起的移动自组网（ad hoc）中作为无线局域网（WLAN）和车载网络的例子被提出，近期，由路边基础设施控制下的终端直联概念在车载通信领域被首次提出3。 Not surprisingly, the D2D concept is embraced by various mainstream communication systems long-term evolution (LTE), LTE advanced and beyond, and vehicular ad hoc networks 4, thanks to its potential of boosting system throughput and improving spectral efficiency, both of which consist of the most important system development objectives 5. Although D2D communication technologies are very promising, many research challenges have to be addressed before their wide deployment. This paper will concentrate on one of the most important challenges, namely the characterisation of D2D communication channels. Reliable knowledge of the propagation channel and a corresponding realistic channel model serve as the enabling foundation for flexible and practical design and testing of D2D systems. This underlines the importance of developing physically meaningful yet easy-to-use methods to mimic D2D channels.Therefore much research attention has been attracted to D2Dchannel measurements, for understanding the underlying physical phenomenon in D2D propagation environments; and to D2D channel modelling, for facilitating the analysis and design of D2D communication systems.毫无疑问，D2D的概念由于其可能增强系统吞吐量和提高频谱利用率而受到众多主流通信系统【长期演进技术版(LTE), 长期演进技术升级版(LTE-A)和超越长期演进技术版(LTE-B)，以及车载无线自组网】的推崇4，这两者被看作为最重要的系统开发目标5。尽管D2D通信技术非常有前途的,但是在研究工作广泛展开前应当克服众多研究面临的挑战。本文将重点关注其中一个最重要的挑战，即对D2D通信信道的描述。可靠的信息传输信道和一个相应的实际信道模型可作为D2D系统灵活实用研究和测试的理论基础。本文强调利用发展中自身意义深远并且易用的理论来模拟D2D信道非常重要。因此大部分研究的关注点放在D2D信道测量，D2D传播环境中底层物理现象的理解，D2D信道建模和D2D通信系统分析和设计的优化。In this paper, we consider the general D2D concept that can involve any D2D communications, for example, human-to-human, vehicle-to-vehicle (V2V), vehicle-to-human, machine-to-machine,as shown in Fig.1.This is because,from the perspective of channel measurements and modelling, different D2D types will result in different communication scenarios, and thus leading to different D2D channel models. In order to give a comprehensive overview of current D2D channel measurements and modelling ,The D2D concept in this paper is a more general one. In this paper,provide the overview and perspective of D2D channel measurements and modelling.本文中，我们认为大体上终端直联的概念可包含任何终端直联通信的过程，例如人与人、车辆与车辆（V2V）、车辆与人、机器与机器，如图1所示。这是因为从信道测量与建模的角度看，不同的D2D类型作用在不同的通信场景将会产生不同的D2D信道模型。为了对当前D2D信道测量和建模作出全面的综述，本文中D2D的概念更为宽泛。文中我们会提出D2D信道测量和建模的综合性观点。The remainder of this paper is outlined as follows. In the next section, we will give an overview of recent advances in D2D channel measurements，We will then review the state-of-the-art D2D models,Some future challenges of D2D channel Measurements and modelling will then be addressed, followed by conclusions in the last section.本文的其余部分介绍如下。在下一节中，我们将概述D2D信道测量的最新进展。然后我们将回顾D2D信道模型当前发展状况，一些D2D信道测量与建模的未来挑战将会被解决，接下来在最后一节中提出结论。2.D2D channel measurements2.D2D信道测量 The complete process of channel measurements and modeling includes the following steps: (i) channel measurements; (ii) raw data post-processing; and (iii) channel modelling and simulations.These steps are intimately interlaced. For example, the last step consisting of channel modelling and simulation may gain useful information in revising measurement campaigns in the first step.For raw data post-processing, spatial alternating generalized expectation-maximisation 6 has been widely adopted as one of the most popular channel estimation algorithms, thanks to its high accuracy, capability of estimating channel parameters and applicability to almost every type of antenna array. In this section,we will summarise and report some recent D2D channel measurements, followed by the overview of D2D channel modelling efforts in the next section.完整的信道测量和建模的过程包括以下步骤:(1)信道测量;(2)原始数据后处理;(3)信道建模和模拟。这些步骤紧密交错。例如,最后一步组成的信道建模与仿真可能获得有用的信息在第一步修改测量活动。对原始数据后处理、空间交替广义expectation-maximisation6被广泛采用为最受欢迎的信道估计算法,由于其精度高,能力估计信道参数和适用于几乎所有类型的天线阵。在本节中,我们将总结和报告最近的一些D2D信道测量,其次是概述D2D信道建模努力在下一节。 To build up proper channel measurement campaigns, the first step is to choose interesting and typical communication scenarios. This is because different communication scenarios will result in different channel statistics and thus different channel models 7, 8. Therefore how to properly choose and partition typical D2D communication scenarios is significant for D2D channel measurements. Firstly,D2D communications are used in dense and crowded scenarios.Secondly, we choose specific application scenarios from modern society, such as indoor office. Thirdly, we classify the scenarios according to the link specifics, such as outdoor-to-outdoor (O2O).Based on current measurement campaigns and our understanding of D2D communications, this paper classifies D2D communication scenarios as the following ten propagation environments: urban macrocell, urban microcell, suburban, rural, indoor office, indoor shopping mall, stadium, open air festival, road traffic and highway,as shown in Table 1. Detailed explanations about the antenna height, the UE velocity, the UE density and the wave propagation on these scenarios are listed as follows.建立适当的信道测量活动,第一步是选择有趣的和典型的沟通场景。这是因为不同的通信场景将导致不同的信道数据,因此不同的信道模型7,8。因此如何正确选择和分区典型D2D通信场景D2D信道测量具有重要意义。首先,D2D通信用于密集和拥挤的场景。其次,我们从现代社会选择特定的应用场景,如室内办公室。第三,我们将根据链接细节的场景,比如outdoor-to-outdoor(O2O)。根据目前的测量活动和我们理解D2D通信,本文将D2D通信场景接下来的十传播环境:城市宏单元,城市微蜂窝,郊区,农村,室内办公,室内购物中心,体育场,露天的节日,道路交通和高速公路,如表1所示。详细解释关于天线高度,速度问题,问题密度和波传播这些场景列出如下。 Urban macro-cell/micro-cell outdoor-to-outdoor(O2O) It is assumed that the UEs are located well below street level (13 m height). The UE velocity is assumed to be in the range of 015 km/h.In the urban macro-cell or micro-cell O2O scenarios, the UE density is higher than that in suburban and rural areas, and the radio wave propagation is mainly affected by the buildings and obstacles in the outdoor 9, 10.城市macro-cell /微蜂窝outdoor-to-outdoor(O2O)假设问题位于远低于街面(1 - 3米高度)。速度问题被认为是在0-15 km / h。城市macro-cell或微蜂窝O2O场景,问题密度高于郊区和农村地区的学生,和无线电波传播主要是在户外建筑的影响和障碍(9、10)。2.1Urban macro-cell outdoor-to-indoor (O2I)2.1城市微蜂窝户外到户内 The urban macro-cell O2I propagation environment is similar to the urban macro-cell O2O scenario. In O2O propagation scenario, UEs are typically located at street level, whereas in the O2I scenario, UEs may be more widely distributed in elevation domain as they may be located on different floors in buildings (1.515 m) 11. The UE velocity is in the same range with the urban macro-cell scenario (015 km/h). The path loss and shadowing model should take different UE heights into account. The penetration loss through the wall depends on the wall thickness and material, and the propagation through the window plays an important role in this scenario 12. Owing to these reasons, the type of buildings should be defined. In old buildings with normal glass windows, the window penetration loss may be remarkably lower than that in modern buildings with thick safety glass or metal-coated windows 13.城市macro-cell O2I传播环境类似于城市macro-cell O2O场景。在O2O传播情况下,问题通常坐落在街道上,而在O2I场景中,问题可能更广泛分布在海拔域可能会在不同的楼层建筑(1.5 -15)11。问题速度与城市在同一个范围macro-cell场景(0-15 km / h)。路径损耗和阴影模型应该考虑不同问题高度。通过墙渗透损失取决于壁厚和材料,透过窗户和传播起着重要的作用在这个场景中12。由于这些原因,建筑物应该被定义的类型。在旧建筑与普通玻璃窗户,窗户穿透损失可能显著低于粗的现代建筑安全玻璃或金属包覆窗户13。2.2Urban micro-cell O2I2.2城市微蜂窝O2I In this scenario, UEs are located below rooftops, typically at 1.515 m depending on the heights of surrounding buildings 14. UEs may be located on different floors of the buildings. The UE velocity in this scenario is about 015 km/h. The radio wave propagation can be divided into outdoor propagation, penetration through the wall and indoor propagation. Since UEs can be located on different floors,the path loss and shadowing model should be determined in the channel model 15.在这种情况下,问题都位于屋顶下面,通常在1.5 -15根据周围建筑物的高度14。问题可能会在不同的楼层的建筑。问题的速度在这个场景中0-15 km / h。无线电波传播可以分为户外传播、渗透穿过墙壁和室内传播。自问题可以在不同的楼层,路径损耗和阴影模型应该确定信道模型15。2.3Suburban/rural O2O2.3城郊/乡村 O2O It is assumed that this scenario represents radio propagation in large areas (radius up to 10 km) with low building density, and the UE antenna height is typically in the range of 13 m, which is similar to the average building height. The UE velocity is assumed to be in the range of 020 km/h. In suburban outdoor scenarios, the UE density is lower than that in the urban scenario, and the wave propagation is affected by the natural environment such as forests and mountains, instead of the high buildings and intensive obstacles 16.假设这个场景代表了无线电传播大面积(半径10公里)建筑密度较低,和问题天线高度一般在1 - 3米的范围,这是类似于普通建筑高度。速度问题被认为是在0-20 km / h。在郊区的户外场景中,问题密度低于在城市场景中,波传播是受自然环境影响,如森林和山脉,而不是高的建筑物和密集的障碍16。Suburban/rural O2I城郊/乡村 O2I In this scenario, the UE antenna height is in the range of 1.510 m,which depends on the average height of buildings in suburban or rural environments. The UE velocity is about 020 km/h that is higher than urban scenarios. Line-of-sight (LoS) probability from UEs to building walls is high because of wide open areas and low building heights 17. However, depending on geographical location, there might be heavy vegetation (forest) and/or hilly terrain resulting in low probability of LoS. The penetration loss through the wall is assumed to be several tens of decibels owing to collapsed buildings 18.在这个场景中,问题天线高度是1.5 -10米的范围内,这取决于建筑物的平均高度在郊区或农村环境。问题的速度大约是0-20 km / h,高于城市场景。视距(LoS)概率问题建筑墙很高,因为开放地区和低建筑高度17。然而,根据地理位置不同,可能会有沉重的植被(森林)和/或丘陵地形导致低概率的洛杉矶。渗透损失通过墙被认为是几十分贝的由于倒塌的建筑18。 Indoor office indoor-to-indoor (I2I) 室内办公室户内到户内 (I2I) It is assumed that the UE antennas are located from 0.5 to 3 m up to the ceiling level. The UE velocity is assumed to be in the range of 010 km/h. The UEs may be distributed over the same floor in a single building or different floors in a single building and/or in different buildings, which results in different wave propagations. If the UEs are on the same floor, the propagation depends on the walls and obstacles around; if the UEs are on the different floors in a single building, the propagation should consider the penetration caused by the ceilings between different floors; if the UEs are in different buildings, the propagation is divided into outdoor propagation,penetration through the wall and indoor propagation.假设问题天线位于从0.5到3米的上限水平。速度问题被认为是清廉的km / h。问题可能分布在同一层在一个建筑或不同的层在一个单一的建筑和/或在不同的建筑物,导致不同的波传播。如果问题是在同一层,传播取决于周围的墙壁和障碍物;如果问题在不同的楼层在一个大楼,传播应该考虑不同层之间的渗透造成的天花板,如果问题在不同的建筑物,传播分为户外传播、渗透穿过墙壁和室内传播。Indoor shopping mall I2I户内购物中心I2I The shopping mall propagation scenario consists of an open space,which is surrounded by smaller rooms, for example shops. The open space usually contains some obstructions, such as catering areas and escalators. Additionally, there may be multiple floors with shops located on different floors. The indoor UE height is assumed to be in the range of 0.53 m on each floor, 0.515 m on different floors and the distance between UEs is 130 m or longer depending on the mall size. In open space, it is assumed that there are reflected multi-paths with rather long delays compared to indoor closed space. The movement of UEs is quite slow and the speed varies from 0 km/h (catering area and inside shops) to 10 km/h (walking space and gallery). Additional loss caused by human body shadowing may need to be considered when the shopping centre is crowded. Body effects are, however, missing in the initial channel models. The penetration and diffraction loss through concrete walls as well as glass windows/doors may need to be considered, when interference between indoor and outdoor users has to be taken into account.购物中心传播场景包括一个开放的空间,周围的小房间,例如商店。开放空间通常包含了一些障碍,比如餐饮领域,自动扶梯。此外,可能会有多个层商店在不同的楼层。室内问题高度的范围被认为是0.5每层3米,0.5 -15在不同的楼层和之间的距离问题外墙面米或更长时间根据商场的大小。在开放空间,它假定有反映归纳相当长的延迟相比,室内封闭的空间。问题的运动比较缓慢,从0公里/小时的速度变化(餐饮面积和内部店)到10公里/小时(步行空间和画廊)。额外的损失造成的人体跟踪时可能需要考虑拥挤的购物中心。身体影响,然而,失踪在最初的信道模型。通过混凝土墙渗透和衍射损失以及玻璃窗户/门可能需要考虑,当室内和室外之间的干扰用户必须考虑。Urban road vehicle-to-vehicle (V2V)城市道路车辆到车辆(V2V) In the urban V2 V scenario, the road consists of two to four lanes, the houses are closer to the curb, and the traffic density is higher than the other scenarios. The V2 V distance is usually smaller than 300 m and the vehicle antenna height is in the range of 13 m. In the urban road, the velocity of vehicles is about 060 km/h because of the high traffic density 19. The propagation includes the penetration caused by the cars, buildings and other obstacles along the roadside 20, 21.在城市V2V场景中,道路由两个四车道,房子靠近路边,交通密度高于其他场景。V2 V通常小于300米,距离和车辆天线高度是1 - 3 m的范围。在城市道路,车辆的速度大约是0-60 km / h因为交通密度高19。传播包括渗透造成的汽车,沿着路边建筑物和其他障碍(20、21)。Highway V2V高速公路V2VIn the highway V2 V scenario, there are two to four lanes in each direction with few buildings and cars around, thus the velocity is much higher than that in the urban road. The V2 V distance is normally larger than 1 km or ranges from 300 m to 1 km, and the vehicle antenna height is in the range of 13 m. In the highway,the velocity of vehicles is 60120 km/h, which is higher than the road traffic scenario. The propagation is mainly caused by the natural environment and metal fences on the highway side 22.在高速公路V2 V的场景中,有两到四车道在每个方向上很少有建筑和汽车,因此速度远远高于城市道路。V2 V通常大于1公里距离或范围从300到1公里,和汽车天线高度是1 - 3 m的范围。在高速公路上,车辆的速度是60 - 120公里/小时,这是高于道路交通场景。造成的传播主要是自然环境和金属栅栏在高速公路上22。 Based on the aforementioned scenarios, several D2D channel measurement campaigns have been built up recently. These measurement campaigns only cover parts of the above-defined scenarios and more measurements are needed for better understanding of D2D channels. Compared with the conventional cellular link, the major characteristics of D2D channels can be observed in the following two aspects: (i) both the transmitter and the receiver have low elevation antennas in D2D links, whereas either the transmitter or the receiver is located at higher grounds (above rooftops/ceiling/close to rooftops) in the traditional cellular link; (ii) both the transmitter and the receiver could be moving in D2D links (dual mobility), while at most one is moving in a traditional cellular link. These factors contribute significantly to the specific channel propagation characteristics of D2D channels 23.基于上述场景,几个D2D信道测量运动最近建立了。这些测量运动只覆盖部分上述定义场景和更多的测量需要更好地理解D2D频道。相比与传统的蜂窝连接,D2D渠道的主要特点可以观察到在以下两个方面:(i)发射机和接收机低海拔天线在D2D链接,而发射机或接收机位于更高的理由(上图屋顶天花板/接近屋顶)在传统的蜂窝联系;(2)发射机和接收机可以朝着D2D链接(双移动),而一个正朝着一个传统的蜂窝连接。这些因素显著的特定信道传播特性D2D频道23。 Symmetric and low UE antenna height: D2D path loss should reflect the fact that the nodes have nearly the same low antenna height, thus higher signal attenuation can be expected for the same distance between UEs and the probability of LoS against distance is expected to be lowered. The scattering environment on both sides of transmission link has similar statistical properties, such as the distributions of angle of departure (AoD) and angle of arrival(AoA).对称天线高度和低问题:D2D路径损耗应该反映这一事实节点几乎相同的天线高度较低,因此可以预期更高的信号衰减相同的距离问题和洛杉矶的概率距离预计将降低。散射环境传播双方的链接也有类似的统计特性,如离去角的分布(AoD)和到达角(AoA)。 UE density/proximity: Nearby UEs have high probability of LoS propagation, thus stochastic system level analysis requires the introduction of LoS probability or some break point distance.Interlink dependency is expected to be higher owing to UE proximity. Effect of shadow fading correlation for D2D links and cellular links will be more noticeable.问题密度/距离:附近的议题LoS传播的概率很高,因此随机系统级分析要求引入洛杉矶概率或一些断点的距离。连接依赖有望更高由于问题接近。影响D2D阴影衰落相关性的链接和蜂窝链接会更明显。 Mobility: Terminals and surrounding objects are moving, which results in large Doppler spread compared with cellular links,