## 4 The WBANs Communication Stack
### Medium Access Control Layer
#### 4.2.3 Existing State-of-the-Art on the MAC Protocols
The TaMAC protocol is supported by a wakeup radio that is used to accommodate emergency and on-demand events in a reliable manner. The wakeup radio uses a separate control channel along with the data channel and therefore it has considerably low power consumption requirements. Same authors also propose another traffic-based wake up mechanism that utilizes the three categories of traffic patterns of the body sensor nodes, namely: normal traffic, on-demand traffic and emergency traffic in [65]. The wakeup patterns of all body sensor nodes are organized into a table called traffic-based wakeup table. The table is maintained and modified by a network coordinator according to the application requirements. Based on the body sensor node's wakeup patterns, the network coordinator can also calculate its own wakeup pattern. During normal traffic, both the body sensor nodes and the network coordinator send data based on the traffic-based wakeup table. The network coordinator sends a wakeup radio signal to body sensor nodes, which wake up in response to these signals, during on-demand traffic period. During emergency traffic period, the body sensor nodes send a wakeup radio signal to the network coordinator, which responds to the wakeup radio signal. The authors in [66] present a traffic aware fuzzy-tuned dynamic delay MAC for WBAN. It exploits a fuzzy logic decision system integrating application traffic diversity to propose a dynamic controlled range for the randomly chosen back-off periods. The dynamically adjusted upper and lower bounds of back-off period introduced on top of the IEEE 802.15.4 medium access control protocol has resulted in the improvement of delivery ratio in comparison with IEEE 802.15.4. The traffic adaptive fuzzy technique has been performed on both the minimum and maximum bounds of the back-off period. The same authors later [67], proposed an improved lightweight history-based MAC Protocol for WBAN with reduced complexity by using new caching technique to consider the maximum bound of the back-off algorithm to be dynamically adjusted. The reduction in the average number of fuzzy engine runs by the proposed caching algorithm shows a significant improvement over data reliability. TAD-MAC [4] is another traffic-aware dynamic MAC protocol for WBAN. It proposes a CSMA/CA based evolutionary and adaptive algorithm, which is based on traffic status register (TSR). Each node contains TSR, whereas the coordinator node contains a bank of TSR to compute an accurate (traffic-dependent) wake-up interval for all the body sensor nodes. The authors claim to achieve between a 3- to 6-fold increase in the lifetime with regards to other preamble sampling-based MAC protocols for various radio transceivers. Since this CSMA/CA-based protocol is able to optimize most of the energy waste such as idle listening, collisions, over hearing and overheads, it can be considered as quite effective for WBANs. _IEEE 802.15.6-based WBAN MAC Protocols:_ A review of Medium Access Mechanisms under IEEE 802.15.6 standard is presented in [68]. In this work, the MAC protocol concepts of IEEE 802.15.6 and a comparison of exiting MAC protocols (such as TMAC and IEEE 802.15.4 MAC protocol using OMNET\(++\) with Castalia as simulating tools) of WBAN are discussed. Similarly [69] presented a brief overview of the new IEEE 802.15.6 standard. Its authors analyzed the bandwidth efficiency of the standard for CSMA/CA procedure. The efficiency results were presented for different frequency bands and data rates. They observed that increase in the payload size improves the bandwidth efficiency. Further, various proposals from different research centers and companies are presented to IEEE 802.15.6 TG6 (WBAN Task Group) in [70]. In [71] a paper on the performance of an IEEE 802.15.6 Wireless Body Area Network (WiserBAN Project) was proposed. They considered CSMA/CA algorithm which is defined in the standard, for transmitting their data via a direct link. Two different channel models for on-body communication were taken into account for comparison.