Minimizing upload latency for critical tasks in cellular-based IoT networks using multiple relays

Most existing or developing IoT communication standards are based on the assumption that IoT services only require low data rate transmission and therefore can be supported by limited resources such as narrow-band channels. This assumption rules out those IoT services with burst traffic, critical tasks, and low latency requirements. In this paper, we propose to utilize idle devices in IoT networks to boost the transmission data rate for critical tasks through multiple concurrent transmissions. This approach virtually expands the existing narrow-band IoT protocols to support channel aggregation in order to realize low latency services for critical tasks in IoT networks. We propose task-balance method (TBM) and first-link descending order (FDO) to determine the relay order and data partition in a given relay set. We theoretically prove that the optimal relay configuration that minimizes the uploading latency can be derived in polynomial time. We then show that relay selection problem is NP-hard and propose a greedy algorithm to approximate the optimal solution within a 1/2 performance lower bound. The simulation results shows that the proposed approach can reduce the latency of critical tasks up to 76% comparing with traditional approaches.