Extending Coverage Through Integrating Multiple Low-Power Wide-Area Networks: A Latency Minimizing Approach

Industrial and agricultural Internet of Things (IoT) are emerging in very large-scale and wide-area applications (e.g., oil-field management, smart farming) that may spread over hundreds of square miles (e.g., 45 mi × 12 mi East Texas Oil-field). Although a single Low-Power Wide-Area Network (LPWAN) covers several miles, it faces coverage challenge in such extremely large-area IoT applications, especially in rural or remote areas with no/limited infrastructure, requiring an in-band integration of multiple LPWANs. We consider a seamless integration of multiple SNOW LPWANs. SNOW (Sensor Network Over White spaces) is an LPWAN architecture over the TV white spaces, avoiding overcrowding problems in the limited ISM band and the cost of licensed band and infrastructure. It offers high scalability through concurrent and bi-directional communication between a base station and numerous nodes. Existing integration of multiple SNOW LPWANs does not consider minimizing network latency and is less suitable for delay-sensitive or real-time applications. In this work, we propose the first latency-minimizing scalable in-band integration of multiple SNOWs. Considering the impact of bandwidth on latency and base station power dissipation, low-latency integration of multiple SNOWs as a constrained spectrum allocation problem is formulated. A novel greedy latency- and traffic- aware spectrum allocation to allocate each link's bandwidth is proposed, achieving an integrated network. To enable low-latency integration, we propose two medium access control protocols for multiple SNOWs, RI-TDMA and TDMA, and estimate their latency. We have implemented the proposed integration both on SNOW hardware and in NS-3 simulator. The physical experiments show up to 44% reduction in the maximum network latency under our approach compared to existing approach. The simulation results show at least 62.3% reduction of maximum network latency by the proposed approach with RI-TDMA and 86.7% with TDMA.