A First Investigation of Congestion Control for LTE-V2X Mode 4

3GPP LTE-V2X is a recent new cellular technology allowing direct communications between vehicles and any other stations. Its Sidelink mode 4 allows the scheduler to be fully distributed and not requiring any support from cellular infrastructures, thus making this mode well fitted for V2X safety-related communications. Based on a Listen-before-Talk (LBT) strategy, the scheduler, however, remains subject to performance degradation under increased channel load, and thus requires wireless congestion control mechanisms. In this work, we focus on the interactions between the strategies used by the LTE-V2X Sidelink mode 4 for autonomous resource allocations - LBT and Semi-persistent scheduling (SPS) - and decentralized congestion control (DCC) mechanisms. Simulations under various scenarios showed counter-productive interactions leading to performance degradations, and strategies to mitigate them are suggested.