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Frontiers of Information Technology & Electronic Engineering
ISSN 2095-9184 (print), ISSN 2095-9230 (online)
2021 Vol.22 No.4 P.503-516
Empirical study on directional millimeter-wave propagation in vehicle-to-infrastructure communications between road and roadside
Abstract: With the increased demand for unmanned driving technology and big-data transmission between vehicles, millimeter-wave (mmWave) technology, due to its characteristics of large bandwidth and low latency, is considered to be the key technology in future vehicular communication systems. Different from traditional cellular communication, the vehicular communication environment has the characteristics of long distance and high moving speed. However, the existing communication channel tests mostly select low-speed and small-range communication scenarios for testing. The test results are insufficient to provide good data support for the existing vehicular communication research; therefore, in this paper, we carry out a large number of channel measurements in mmWave vehicle-to-infrastructure (V2I) long-distance communication scenarios in the 41 GHz band. We study the received signal strength (RSS) in detail and find that the vibration features of RSS can be best modeled by the modified two-path model considering road roughness. Based on the obtained RSS, a novel close-in (CI) model considering the effect of the transmitter (TX) and receiver (RX) antenna heights (CI-TRH model) is developed. As for the channel characteristics, the distribution of the root-mean-square (RMS) delay spread is analyzed. We also extend the two-section exponential power delay profile (PDP) model to a more general form so that the distance-dependent features of the mmWave channel can be better modeled. Furthermore, the variation in both RMS delay spread and PDP shape parameters with TX-RX distance is analyzed. Analysis results show that TX and RX antenna heights have an effect on large-scale fading. Our modified two-path model, CI-TRH model, and two-section exponential PDP model are proved to be effective.
Key words: Millimeter-wave, Two-path model, Root-mean-square delay spread, Power delay profile, CI-TRH path-loss model
电子科技大学通信抗干扰技术国家级重点实验室，中国成都市，611731
概要：随着对高速移动通信日渐增长的需求，人们迫切需要高速车载通信系统。毫米波频段由于其较广的带宽和丰富的频率资源而受到越来越多的关注。然而毫米波通信系统的设计高度依赖于各种环境下的无线信道特性；因此，有必要对不同场景下毫米波信道进行研究。现有的对于长距离传输中毫米波的通信信道特性的研究较为缺乏。本文基于信道实测数据研究了在1900米的长传输距离下41 GHz毫米波的车地通信的信道特征，为今后长距离传输下车地毫米波系统设计提供了研究基础。
41 GHz毫米波通信信道收发器数字基带由模数转换器AD6688、数模转换器AD9163、两个XC7VX690T FPGA和ZYNQ7045芯片组成，在接收机的射频前端使用AD8362芯片记录RSSI值。采用高增益10°半功率波束宽度(HPBW)的定向喇叭天线。利用天线增益高的优点，毫米波探测器能够在长距离传播引起的高信号衰减后检测到毫米波信号。采用基于Golay互补序列对的时域信道测量方法完成车地场景下的信道脉冲响应(CIRs)测量。
测量是在四川省成都市的天府大道进行的，接收机天线安装在路边，发射机天线固定在车顶。天线离地高度均为2米。在测量过程中，汽车以50 km/h的恒定速度向接收机天线行驶，没有其他移动的车辆或散射体，也没有明显的遮挡，发射机和接收机始终处于视线(LoS)条件下。
结合所测数据，分析得出该场景可被建模为考虑了地面粗糙度的两径模型，从发射机到接收机有两条路径，包括直接路径和反射路径。然而，考虑到光滑路面情况，所得结果和实际接收信号强度指示(RSSI)不符。对于表面粗糙的介质，部分电磁能量会因粗糙表面的散射而损失。为获得更好结果，采用的处理方法是引入反射系数。从最终得到的结果可以看出，在引入表面粗糙度后，接收信号强度指示的深衰落明显减小，更加符合实测数据。
均方根时延扩展（RMS delay spread）测量的RMS延迟范围为2~35 ns，平均值为6.99 ns。可以发现实测均方根时延扩展数据与对数正态分布Nlog（1.78, 0.582）较为匹配。除了分析均方根时延扩展的总体分布外，还需讨论均方根时延扩展与发射机-接收机距离的关系。研究均方根时延依赖性的一种有效方法是将发射机-接收机路程上的原始数据划分为若干个单元，使每个单元中的CIRs可以看作是平稳的。随着距离的增加，均方根时延扩展值减小，其原因是由于窄波束天线过滤了大量的散射体，使得直射路径的衰减比散射路径慢得多。
提出一种更为通用的功率延迟分布（PDP）模型，称为两段指数模型，将功率延迟分布曲线分为两段。两段指数模型涵盖了一段指数模型的所有适用情况，并且可以解决噪底的问题。
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DOI:
10.1631/FITEE.2000464
CLC number:
TN928
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On-line Access:
2021-04-15
Received:
2020-09-08
Revision Accepted:
2021-02-18
Crosschecked:
2021-03-05