Uplink Contention-based Transmission Schemes for URLLC Services

We investigate in this paper uplink multiple transmission schemes for 5G Ultra-Reliable Low Latency Communications (URLLC) traffic. The URLLC class of services has been defined for applications requiring extremely stringent latency and reliability. We show that, in systems with episodic traffic and many users compared with the number of transmission resources, randomly transmitting multiple copies of a packet allows to meet the URLLC requirements. We develop analytical models for the packet loss rate for two contention based multiple transmission schemes and show that one dominates the other in the parameter range for which the URLLC requirements are met. We then show on a possible radio setting for 5G, an example of radio resource dimensioning for different user traffic levels and we illustrate how the latency constraint may limit the allowable traffic for a given radio bandwidth.