On the Design of Preamble for Autonomous Communications with Extended Coverage

5G wireless networks are expected to usher in massive Machine Type Communications (mMTC) pertaining to the Internet of Things (IoT). A large fraction of the devices participating in IoT are likely to be low-power devices that generate sporadic traffic. It is anticipated that autonomous grant-free communications would be needed to accommodate these devices and the traffic they generate. Preamble transmission is a key part of such grant-free communications, and system performance including the desired power savings for the devices depends critically on the preamble detection-false alarm characteristics. In this context, low-power devices in extended coverage scenarios present a stiff challenge to system designers. In this study, we show that with narrowband resource allocations, use of preamble acknowledgements and judiciously set power control targets one can achieve the desired performance even for low-power devices in challenging scenarios.