Vehicle-to-vehicle (V2V) communication is an important component of the intelligent transportation system (ITS)

and tunnel is an essential application scenario of ITS. Considering the reflection of microwaves by tunnel walls

the diffraction by vehicles

and the dense and complex layout of the tunnel ancillary facilities

it is of great significance to investigate the propagation characteristics of V2V channel in tunnel scenarios. In this study

the V2V channel was measured by means of a broadband channel sounder in the tunnel environment. The carrier frequency and bandwidth were 5.2 GHz and 120 MHz respectively. Regarding to different situations

the measurement was divided into three types: line-of-sight (LOS)

obstructed line-of-sight (OLOS)

and non-line-of-sight (NLOS). Based on the measured data

the path loss models and received signal amplitude fading distributions were established for different scenarios

so as to analyze the channel fading characteristics. Results show that the path loss index and shadow fading in NLOS were larger than those in LOS and OLOS. There were no significant changes in shadow fading between LOS and OLOS. The amplitude fading of the received signal in both LOS and OLOS scenarios followed the Rice distribution

and that in the NLOS scenario followed the Rayleigh distribution. The root-mean-squared delay spread conformed to the log-normal distribution in all the three scenarios. The shadow fading and time-domain dispersion were larger in NLOS. The K factor decreased with increasing distance

indicating that the K factor is dependent on the distance.