The emerging road safety and autonomous vehicle applications require timely and reliable data delivery between vehicles and between vehicles and infrastructure. To satisfy this demand, 3GPP develops a 5G Vehicle-to-Everything (V2X) technology. Depending on the served traffic type, 5G V2X specifications propose two channel access methods: (i) Mode 1, according to which a base station allocates resources to users, and (ii) Mode 2, according to which users autonomously select resources for their transmissions. In the paper, we consider a scenario with sporadic traffic, e.g., a vehicle generates a packet at a random time moment when it detects a dangerous situation, which imposes strict requirements on delay and reliability. To satisfy strict delay requirements, vehicles use Mode 2. We analyze the performance of Mode 2 for sporadic traffic and propose several approaches to improve it. Simulation results show that the proposed approaches can increase the system capacity by up to 40% with a low impact on complexity.

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