Latency of Concatenating Unlicensed LPWAN with Cellular IoT: An Experimental QoE Study

Developing low-power wide-area network (LPWAN) solutions that are efficient to adopt, deploy and maintain are vital for smart cities. The poor quality-of-service of unlicensed LPWAN, and the high service cost of LTE-M/NB-IoT are key disadvantages of these technologies. Concatenating unlicensed with licensed LPWANs can overcome these limitations and harness their benefits. However, a concatenated LPWAN architecture will inevitably result in excess latency which may impact users’ quality-of-experience (QoE). To evaluate the real-life feasibility of this system, we first propose a concatenated LPWAN architecture and experimentally measure the statistics of end-to-end (E2E) latencies. The concatenated delay margin is determined by benchmarking the latencies with different LPWAN architecture schemes, namely with unlicensed IoT (standalone LoRa), cellular IoT (standalone LTE-M), and concatenated IoT (LoRa interfaced with LTE-M). Through extensive experimental measurement campaigns of 30,000 data points of E2E latencies, we show that the excess delay due to LPWAN interfacing introduces on average less than 300 milliseconds. With a users’ QoE satisfaction of 95%, we also found that concatenated LPWAN outperforms unlicensed IoT by roughly 1.5 s. Overall, the result suggests that a concatenated LPWAN is technically feasible and offers an affordable alternative for real-world smart city deployment.