Wireless body area networks (WBANs) have emerged as a key technology to provide real-time health monitoring and entertainment services. In high dense WBAN environment like hospital and senior center, however, there occurs coexistence problem which is caused by interference. Especially, contention free period of each WBAN may not be provided transmission opportunity due to channel interferences. In this paper, we focus on the coexistence problem when geographically co-located WBANs share the contention free period in the overlapped WBAN environment. In addition, we address the problem by introducing cooperative game theory based on the Cournot competition. An approach to model such a competition scenario is the static and strategic game model in which players try to maximize their benefits. We define the utility function for QoS support in overlapped WBAN environment and analyze player's utility related with QoS parameters (i.e., throughput, delay, and priority). We verify that the player's utility increases with increasing throughput and decreasing delay through a mathematical method by using the Cournot competition model. Finally, we observe the change of resulting utilities according to demanded throughput and traffic priority in overlapped WBAN environment.

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