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

TL;DR

This study experimentally evaluates the latency impact of combining unlicensed LPWAN with cellular IoT, demonstrating that the additional delay is minimal and feasible for smart city applications.

Contribution

It proposes a concatenated LPWAN architecture and provides extensive experimental latency measurements, showing the feasibility of this approach for smart city use cases.

Findings

Excess delay due to concatenation is less than 300 ms on average.

Concatenated LPWAN architecture introduces negligible latency for human-in-the-loop applications.

Experimental data collected from 30,000 latency measurements supports real-world feasibility.

Abstract

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. The proof-of-concept results suggest that the latency for concatenating unlicensed LPWAN with cellular IoT is negligible for smart city use cases where human perception and decision making is in the loop.