## 3 Related Work  
In this section, we highlight some state-of-the-art related work that tackled the problem of improving the standard BEB in 802.15.4 MAC to enhance its performance and serve the applications of WBAN. In [14], the authors proposed the genetic fuzzy logic channel optimization (GFCO) approach for IEEE-802.15.4-based low-rate wireless personal area networks. GFCO employs a genetic algorithm to modify a fuzzy logic controller optimally. The main target is to adjust the contention window size to improve the probability of medium access. Through this optimization, the performance is improved in terms of throughput, packet delivery ratio, packet loss ratio, and packet delay. In evaluating their proposed technique, the authors use extensive simulations, considering two WBAN scenarios: in one scenario, a WBAN with 10 sensors was mounted on the body of a single person; while in the other scenario, 10 to 50 persons were considered to be present in a hospital ward. The authors report results that show the ability of GFCO to outperform the standard BEB in terms of the aforementioned metrics. The authors of [15] focused mainly on improving the reliability of the 802.15.4 MAC protocol to better support data transmission in WBANs. After studying a simple two-dimensional Markov chain that models the CSMA-CA algorithm, the authors proved mathematically that the parameter macMaxCSMABackoffs is directly related to the relia  
Figure 1: Slotted CSMA-CA mechanism. bility of packet transmission. Therefore, by properly tuning this parameter, transmission reliability can be improved. With this observation in mind, the value of macMaxCSMABackoffs will be set depending on the severity of the sensed physiological data (termed as the criticality index (CI); the CI lies between 0 and 1). The range of the CI is divided into five sub-ranges, each of which is assigned a different value of macMaxCSMABackoffs. A local processing unit assigns sensor nodes their CIs. Whenever a sensor node has critical packets to transmit, it sets its macMaxCSMABackoffs based on its CI. The reliability was finally studied as a function of the probability of collision, failure during CCA1, and CI. The reported results show promising improvements in transmission reliability when the macMaxCSMABackoffs parameter is properly tuned. In [16], the authors studied the lack of support of data prioritization in 802.15.4 standard and how BEB does not recognize the levels of urgency or importance among different nodes traffics. The authors introduced the class of service traffic priority MAC (CSTP-MAC) scheme to cover that gap. In the CSTP-MAC, nodes are classified based on the different priorities of the data they are carrying. Backoff periods are computed using a set of unique backoff expressions peculiar to the data priorities. The idea behind the unique expressions is to grant nodes a non-conflicting range of backoff periods, which resolves the contention among the nodes to access the shared medium of communication. In [17], the authors proposed the retransmission adaptive intelligent MAC (RAI-MAC) protocol to achieve fair retransmissions in WBANs. In the RAI-MAC, a coordinator node tracks the number of failed transmission attempts by each sensor node in its cluster. By learning about the number of failed transmissions, the coordinator classifies the nodes in the WBAN into priority classes. These priority classes help control the next backoff interval of all current transmitting sensors in a WBAN, which affects the retransmission priority of each node. This approach results in an adaptive adjustment of backoff intervals, which helps RAI-MAC reduce the probability of collisions and delay. The authors in [18] studied the improvement of the backoff and CCA mechanisms in the 802.15.4 MAC protocol to better support WBAN applications. The authors pointed out that the standard specifies that the BE is confined to the interval [0, (macMinBE, macMaxBE)]; macMinBE = 2; macMaxBE = 5.