## 3 Related Work
In the case of recurring collisions, and since macMaxCSMABackoffs = 4, the backoff exponent will be selected from the intervals 0-7, 0-15, 0-31, 0-31, and 0-31. Therefore, in the case of frequent collisions over the wireless medium, there will be several sensor nodes selecting their BE from the interval 0-31, and they may end up selecting the same BE, which leads to more collisions. To mitigate such situations, the authors propose using distinct intervals for each backoff period and reducing the number of backoff periods to 3. As for the CCA mechanism, the authors note that waiting for two idle CCAs may lead to unnecessary delays in communications. Therefore, they propose to allow a sensor node to send its data as soon as it finds the CCA idle. The modifications of the backoff and CCA mechanisms have been modeled mathematically using Markov chains and evaluated through simulations. The targeted performance parameters were energy conservation, packet delivery ratio, throughput, and delay. The reported results show superior performance compared to the standard 802.15.4 MAC protocol. The authors in [19] focused on the requirements of adaptive data traffic and QoS guarantees in several wireless applications like WBANs. As such, they introduced the enhanced superframe offering adaptive duty cycle (ESAD), a new superframe structure for the 802.15.4 standard to support adaptive traffic. ESAD aims at offering better throughput, reduced network delay, and the accommodation of more nodes to transmit data within a time frame. Specifically, the ESAD proposes that the active period of the standard superframe becomes adapted to the traffic requirements, which improves the utilization of the GTSs. Moreover, the slot size of each GTS is reduced in an attempt to double the total number of GTSs. Finally, the allocation of the GTSs by the personal area network coordinator is achieved based on the shortest-job-first algorithm instead of the first-come-first-served algorithm. The performance of the ESAD has been evaluated through simulations. The targeted performance parameters were as follows: delay; data transmission; GTS utilization; and the number of GTS requesting nodes. The generated results show that the ESAD is superior to the conventional 802.15.4 MAC protocol in terms of these parameters. The authors in [20] pointed out that based on the specifications of the standard 802.15.4 MAC protocol, whenever a node detects a busy wireless medium, it increases its BE by 1 (up to macMaxBE). The next backoff period for this node will expand while the node that has attained access to the medium will have a better chance of accessing the medium in the future as its backoff period will be shorter. To fix this unfairness for WBANs, the authors proposed using a fixed value of BE during the execution of all BEB steps. This way, all nodes experience the same backoff periods in their transmission attempts, leading to equal opportunities for medium access. This proposal has been evaluated using simulations focusing on packet reception rate, average delay, and throughput. The simulations considered the typical traffics generated by five biomedical sensors in a patient monitoring system. The reported results indicate that using a fixed BE among different nodes leads to significant improvements in the performance in terms of the parameters mentioned above. In [21], the authors introduced the traffic class prioritization-based CSMA/CA (TCP-CSMA/CA) scheme to support medium access priorities among heterogenous-natured biomedical sensor nodes (BMSNs) in intra-WBANs. The TCP-CSMA/CA provides prioritized medium access to nodes of different traffic classes to improve performance parameters like packet delivery delay, packet loss, energy consumption, throughput, and packet delivery ratio (PDR). Patients' data are classified based on four traffic classes. Prioritizing access to the medium is made possible by allocating a distinct, minimized, and prioritized backoff period range to each traffic class in every backoff during contention.