Adaptive Channel Status Based Access Class Barring Scheme in C-V2X Networks

In high-density C-V2X networks, an effective massive access method for group communications is the basis to assure the performance index for different services and to enhance the spectrum efficiency under limited spectrum resource. In the paper, an improved ACB scheme is proposed using channel status information based on computing ability. Firstly, the gNodeB can estimate the traffic density in single cell and generate the ACB factor. Then the gNodeB broadcasts ACB factor under cellular coverage. According to SINR and ACB factor of the received signal, the terminal on board will compute the access probability, and compare with ACB factor. When the access probability is more than ACB factor, the terminal selects a preamble randomly from unused preamble pool with the access probability or 1. The terminal transmits the selected preamble to the gNodeB for finishing the access procedure. The analysis results show that the access collision probability is a function of channel status with the traffic density as the negative component. The simulation results show that the average access collision probability is deceased about 5% - 20% compared with S-Aloha and M2M-OSA schemes in high-density scenarios, and effectively reduces the average access delay.