Optimal relaying nodes selection for IEEE 802.15.6-based two-hop star topology WBAN

Wireless body area networks (WBANs) are a promising communication technology that supports various types of medical and non-medical applications with heterogeneous requirements. Gen-erally, IEEE 802.15.6-based WBAN use one-hop star topology to establish direct communication between the hub and body sensors. The standard also supports two-hop star topology to establish communication where direct transmission between the hub and sensor nodes is not possible due to poor link quality caused by body shadowing. Data transmission reliability and network lifetime are key factors in WBANs. Therefore, we propose an optimal relaying nodes selection mechanism as an alternative to the two-hop star topology extension of IEEE 802.15.6 to enhance the packet delivery ratio, network lifetime, and throughput. In this work, while choosing a relaying node for a disconnected node, we consider the fitness value of all the relaying capable nodes and select the fittest node as relaying node. We calculate the fitness value of all the relaying capable nodes based on their link quality, residual energy, and current traffic load using the multi-criteria decision making method "Technique for Order Preference by Similarity to Ideal Solution (TOPSIS)", which was originally developed by Ching-Lai Hwang and Yoon in 1981. We use the Mamdani fuzzy inference system (FIS) to calculate the link quality index of relaying capable nodes based on various link quality parameters such as Received Signal Strength Indicator (RSSI), Signal-to-Noise Ratio (SNR), and Packet Error Rate (PER). Moreover, we also designed a schedule slot allocation mechanism for all the sensor nodes based on their packet generation rate (PGR). The proposed scheme significantly improved packet delivery ratio, throughput, and network lifetime compared to the IEEE 802.15.6 standard's two-hop extension of star topology and other relay selection mechanisms. The simulation result of the proposed mechanism shows that the packet delivery ratio and network lifetime increase by (5-30)% and 50% respectively, compared to the IEEE 802.15.6 two-hop star topology.