Resource Re-Selection with Adaptive Modulation and Collision Detection in LTE V2X Mode 4

This paper describes the results of investigations of autonomous resource re-selection for the Cellular-Vehicle-to-Everything (C-V2X) Mode 4 applied in LTE. We have investigated the system-level performance of the Sensing-based Semi-Persistent Scheduling (S-SPS) algorithm that 3GPP has standardized as a resource allocation scheduler. The S-SPS with Adaptive Modulation (AM) and Adaptive Modulation and Collision Detection (AMCD) resource re-selection algorithms are the algorithms newly proposed in this paper to improve the Packet Reception Ratio (PRR) and resource Collision Ratio (CR). It is known that S-SPS faces failures in resource re-selection and causes collision problems when multiple transmitters re-select the same resource at the same time or when channel load is increased for the same transmission range. In the literature, adaptive modulation has been previously introduced to solve this collision problem in IEEE 802.11p by managing the Distributed Congestion Control (DCC). This paper proposes AM and AMCD algorithms in C-V2X Mode 4, depending on the Channel Busy Ratio (CBR) and the probability of resource re-selection P to solve the channel load collision and resource collision problems by broadcasting the collided resource locations to announce the source of these collisions. We show that AMCD is a promising method of maintaining efficient and reliable vehicular communications by re-selecting resources with proper modulation when the Re-selection Counter (RC) applied in the MAC layer reaches zero, and when the current resource is assigned as a collided resource by surrounding vehicles. The AMCD algorithm has shown better performance than the AM algorithm in resource re-selection, and it is more reliable in broadcasting awareness messages.