Research Article Channel Measurement for Multiple Frequency Bands in Subway Tunnel Scenario Zhuomin Hu , 1 Wenli Ji, 2 Hengkai Zhao , 1 Xuping Zhai, 1 Asad Saleem , 3 and Guoxin Zheng 1 1 Key Laboratory of Specialty Fiber Optics and Optical Access Networks, Joiny International Research Laboratory of Specialty Fiber Optics and Advanced Communication, Shanghai University, Shanghai 200444, China 2 System Integration Department, Technical Center, Shanghai Shentong Metro Group Co.,Ltd, Shanghai 201103, China 3 Guangdong Engineering Research Center of Base Station Antennas and Propagation, Key Laboratory of Antennas and Propagation, Shenzhen University, Shenzhen 518000, China Correspondence should be addressed to Hengkai Zhao; zhaohk@shu.edu.cn Received 9 March 2021; Accepted 18 May 2021; Published 3 June 2021 Academic Editor: Renato Cicchetti Copyright©2021ZhuominHuetal.isisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In next-generation radio communication systems, the use of higher frequency bands and the massive multiple-input-multiple- output (MIMO) systems has turned into hot research topics because they have the potential to increase network capacity significantlybyexploitingtheavailablenarrowbandandbroadbandspectrums.erefore,thenarrowbandchannelmeasurements are executed at the following five potential frequency bands, including 2.6GHz, 3.5GHz, 5.6GHz, 10GHz, and 28GHz in the Shanghaisubwaytunnelenvironmentinordertofulfillthelateststandardsoffifthgeneration(5G).Moreover,inthebroadband channelmeasurements,thecenterfrequencyis3.5GHzand5.6GHzandthebandwidthisconsideredas160MHz,respectively. Atthetransmitter(Tx)side,auniformrectangularantennaarraycomposedof32elementsisfixedontheplatformnearthetunnel walls.ereceiver(Rx)isequippedwithauniformcylindricalantennaarrayconsistingof64elements,whichissetonatrolley along the track. Based on the acquired massive MIMO channel impulse responses, delay spread, angle spread, eigenvalue and channelcapacityareanalyzed.eresultsrevealthatthemultipathdelayinthetunnelscenarioisquiteshort,thedelayspreadand angle spread drop rapidly as the distance between Tx and Rx increases and the channel matrix gradually becomes serious. is research provides a reference for the deployment of future 5G systems in the subway tunnel. 1. Introduction Inrecentyears,inordertoensurethesafetyandefficiencyof train operations, it is necessary to transmit data such as ultra-high-definition video stream monitoring, train oper- ation control, and on-board sensing at a high rate and high reliability between train and ground, which has created an urgent need for the application and deployment of 5G in subway communications. e characteristics of the wireless propagationchanneldeterminethefinalperformanceofthe wireless communication system. erefore, it is very im- portant to detect the actual performance of wireless prop- agationchannelsinarealtunnelenvironment.Sofar,alarge number of channel measurements [1–14] have been carried out in different subway tunnel environments. e pio- neering paper [1] shows that multiple reflections on the tunnel wall and changes in tunnel cross-section result in a relatively high diversity of MIMO channels in the tunnel environment.Accordingtothemodaltheory[2],thetunnel can be regarded as a lossy waveguide, and the number of active modes decreases rapidly as the Tx-Rx distance in- creases, which limits the degree of freedom of the MIMO channel matrix. However, compared with single-input- single-output (SISO) channel, the improvement in channel capacityissignificant.Onthebasisofchannelmeasurements in a subway tunnel, the influence of polarization diversity, Hindawi International Journal of Antennas and Propagation Volume 2021, Article ID 9991758, 13 pages https://doi.org/10.1155/2021/9991758