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We investigate in this paper uplink 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 first develop an analytical model for the packet loss rate for a contention based multiple transmission scheme where replica positions are assigned randomly and show that it allows to meet the performance requirements of URLLC for small enough user activity rate. We then propose an advanced replication scheme where positions for the different replicas are pre-allocated to users so that users have pairwise-distinct positions. We show that this advanced scheme achieves very high reliability with low resource consumption.

International audience; This work studies the problems of feedback allocation and scheduling for a multichannel downlink cellular network under limited and delayed feedback. We consider a realistic scenario where a fixed and small number ¯ F of link states can be reported to the base-station (BS) per time-slot. We study the trade-off between knowing at the BS a small number of accurate link states (i.e. that can be reported within one time-slot) and a larger but outdated number of link states (i.e. number of link states > ¯ F that requires more than one slot to be reported). We propose an efficient algorithm that selects the link states that should be reported to the base-station. A novelty here is that this feedback allocation algorithm is performed at the users side. We show that this algorithm combined with the Max-Weight scheduling achieves at least a fraction η of the stability region achieved under the ideal system (i.e. with full and perfect feedback at no cost). We then provide numerical results that show the best aforementioned trade-off under various system setups.

This paper considers a MIMO interference system where interference alignment (IA) technique is adopted to manage the problem of interference. We consider a time division duplex (TDD) system where each transmitter estimates its channel state information (CSI) by probing the receivers. In addition, the transmitters share their local CSI estimate between each other using a backhaul links of limited capacity. A quantization over the backhaul is therefore required to reduce the amount of information to exchange. We study in this paper the impact of this quantization on the system performance and determine the optimal number of transmitter-receiver pairs that maximizes the system throughput.