Set-covering-based algorithm for delay constrained relay node placement in Wireless Sensor Networks

As Wireless Sensor Networks (WSNs) are widely used in time-critical applications, e.g., factory automation and smart grid, the importance of Delay Constrained Relay Node Placement (DCRNP) problem is becoming increasingly noticeable. This paper proposes a Set-Covering-based Approximation (SCA) algorithm to solve the DCRNP problem. The SCA deploys relay nodes by levels from the sink to sensor nodes. To avoid the limitation suffering by existing algorithms and ensure a polynomial time complexity, SCA employs a novel approach to formulate the deployment of relay nodes at each level as the set covering problem subject to delay constraints, and based on the classic greedy-set-covering algorithm, a set of relay nodes are placed to connect the nodes (sensor nodes and relay nodes) that are already connected to the sink. Since delay constraints are met at each level, all the sensor nodes will be connected to the sink via feasible paths fulfilling delay constraints. In addition, the elaborated analysis of the time complexity and the approximation ratio of the SCA algorithm is given out. Extensive simulations show that SCA can significantly save deployed relay nodes in comparison to existing algorithms.