Two-Tiered Relay Node Placement for WSN-based Home Health Monitoring System
Motivated by the needs of health monitoring at home (or a senior center) using a sensor network system, we study the problem of how to place the relay nodes so that the data collection and localization requirements of the monitoring system can be satisfied. By exploiting the inherent nature of the problem, we model it as finding a minimum connected k-dominating (k greater than or equal to 3) set. Instead of using idealistic disc radio model, we explicitly take into account the obstacles' effect on the radio propagation in an indoor environment. We prove that the problem is NP-hard and propose an efficient greedy algorithm ORPA (Optimal Relay Placement Algorithm) to compute in polynomial time the best locations to place the relays. Results of extensive simulations have shown that by using our proposed algorithm ORPA, the number of relays required can be substantially reduced in comparison to the random placement and two-stage placement strategies. We also study the impact of the transmission power and grid size on the algorithm and system performance. The result and method presented in the paper is useful to today's indoor deployment of practical WSN-based monitoring system and to ensure the network connectivity with minimal relay node placement.