King's College London

Narrowband-IoT (NB-IoT) has been released by 3GPP to provide extended coverage and low energy consumption for low-cost machine-type devices. Requiring only a reasonably low-cost hardware update to the already deployed Long Term Evolution (LTE) base stations and being compatible with current core network and enhanced core solutions that aim to reduce the battery consumption and minimize the signalling, NB-IoT deployments are quickly increasing, making NB-IoT a dominating technology for low-power wide area (LPWA) networks. To this aim, in this paper we focus on group communications (i.e., multicast) in NB-IoT to efficiently support the transmission of firmware, software, task updates or commands towards a large set of devices. We discuss the architectural and procedural enhancements needed to support the unique features of group communications in machine-type environments, such as customer-driven group formation. We also extend the NB-IoT frame to include a channel for multicast transmissions. Finally, we propose two transmission strategies for multicast content delivery and evaluate their performance considering the impact on the downlink background traffic and the channel occupancy.