Blind repetitions for cellular-IoT: Performance analysis of combination mechanisms

As evident from the increasing number of technical studies on machine type communications, Internet of Things (IoT) has become a hot topic. Among all the initiatives attempting to build end-to-end connectivity solutions, the 3rd Generation Partnership Project (3GPP) is actively working on the integration of IoT features into the existing 2G and 4G network specifications. In the framework of the adaptation of the GSM (Global System for Mobile communication) and EDGE (Enhanced Data rates for GSM Evolution) systems to IoT applications, several solutions have been proposed at the PHY/MAC level, all sharing a common trait: enhancing the coverage using blind repetition mechanisms. The question of how to recombine the repeated symbols at the receiver side has then to be raised. In this work, we analyze the performance of state-of-the-art combination approaches that are carried out at different levels of a classic GSM receiver and we propose a new combination scheme. To mitigate the drawbacks of each individual solution, two hybrid strategies are proposed involving these different levels of combination. Performance comparison is led for the different cases considering constant as well as time variant channels, leading to a discussion about the most efficient strategy to follow, depending on the targeted application. To the best of our knowledge, this is the first work dealing with the comparison of combination mechanisms including hybrid combining solutions.