The channel characteristics of immersed tunnels play a crucial role in the design and optimization of electronic toll collection (ETC) communication systems in such environments. Due to the lack of channel characteristics for all-metal immersed tunnel environments, this paper conducts an in-depth study on channel measurement, channel modeling, and optimization of ETC systems within all-metal immersed tunnels. Using a channel measurement system based on the universal software radio peripheral (USRP), this study extracts multidimensional channel characteristic parameters from the measured data, such as path loss (PL), shadow fading (SF), K-factor (KF), root mean square delay spread (RMS DS), power angular spectrum (PAS), and azimuth angle spread (ASA). The unique characteristics of the all-metal tunnel are analyzed in comparison to tunnels made of other materials. To develop a comprehensive all-metal immersed tunnel channel model meeting the quasi-deterministic radio channel generator (QuaDRiGa) requirements, we employed ray tracing (RT) methods to supplement angle domain parameters. Subsequently, we used this channel model to aid in the design and optimization of ETC systems, addressing transaction failures and erroneous transactions within all-metal immersed tunnels by establishing optimization targets and constraints, resulting in optimal height, tilt angle, transmission power, and beamforming. The findings of this research not only enrich the channel scenarios in QuaDRiGa but also provide practical guidance for improving the performance of ETC systems.

Precise parameter estimation is essential for developing effective channel models. However, jointly estimating the various channel parameters is a challenging problem as these parameters can only be extracted from comprehensive data collected during massive measurement activities. Traditional algorithms suffer from limited estimation accuracy due to high mobility and signal correlation. In this paper, we propose a low-complexity full-dimension parameter extraction algorithm. The method extends the forward-backward spatial smoothing technique to estimate two-dimensional (2-D) angle information in the uniform planar array (UPA), enhancing aperture size and providing higher resolution for coherent signals. Then, we provide a Doppler compensation technique to prevent the deterioration in complex amplitude estimation quality caused by large Doppler frequency in high-speed mobile environments. Moreover, the proposed algorithm is also applied to the fifth-generation new radio (5G-NR) system. To remedy power leakage in the channel impulse response (CIR), we propose an eigenvalue-assisted sampling point selection scheme. This scheme preserves sampling positions abundant in channel information to reduce computational complexity and eliminate most noise. Simulation and field tests show that the proposed algorithm achieves better performance with lower computational complexity compared to the existing algorithm.