Enabling LPWAN Massive Access: Grant-Free Random Access with Massive MIMO

With the rapid growth of the number of Internet of Things (IoT) devices, the support for massive access is becoming vital for future low power wide area network (LPWAN). Up to now, LoRa (TM) and NB-IoT are the two leading LPWAN technologies that use very distinct random access (RA) schemes, that is, grant-free RA scheme and grant-based RA scheme, respectively. The low-overhead grant-free RA of LoRa makes it suitable for light traffic load, while the grant-based RA scheme of NB-IoT is more suitable for moderate traffic load as it could provide high reliability in data-transmission stage for the active terminals without collisions. However, when facing massive access and high traffic load, both LoRa and NB-IoT are unable to provide high throughput and high success rate with low signaling overhead. To address the challenge of massive access, grant-free RA with massive multiple-input and multiple-output (MGFRA) is being considered as an alternative technique. In this article, we first introduce MGFRA and present simplified analysis and simulations to demonstrate its effectiveness. Then, we envision the future LPWAN requirements on RA and compare the performance of the existing leading LPWAN technologies with MGFRA. Finally, a proof-of-concept prototype of LPWAN based on MGFRA, called as TurMass (TM), is introduced and some experimental results are provided to demonstrate its effectiveness in realistic wireless environments.