## 4 Comparison of MAC Protocols  
In this section, we compare and discuss the MAC protocols designed for CRBANs. In Table 1, the MAC protocols reviewed in Section 3 are compared with respect to the collision ratio, channel access parameters, energy consumption, advantages and limitations. \begin{table}
\begin{tabular}{c|c|c|c|c|c} \hline \hline \multirow{2}{*}{**Protocol**} & **Collision ratio** & **Channel access parameter** & **Energy consumption** & **Advantages** & **Limitations** \\ \hline \multirow{6}{*}{CR-MAC [15]} & \multirow{6}{*}{Low} & \multirow{6}{*}{Energy level detection} & \multirow{6}{*}{Low} & \(\bullet\) High throughput. & \(\bullet\) No advantage in \\  & & & & \(\bullet\) According to the urgency level & increasing the number of \\  & & & & of the monitored traffic, nodes & retransmissions in \\  & & & & are assumed to have the & critical nodes after \\  & & & & capability to dynamically tune & saturation point. \\  & & & & their transmitter power. & \\  & & & & \(\bullet\) QoS promising for traffic of & \\  & & & & different priority classes. & \\ \hline \multirow{2}{*}{DCAA-MAC [16]} & \multirow{2}{*}{Low} & \multirow{2}{*}{Energy level detection} & \multirow{2}{*}{Low} & \(\bullet\) PU protection and QoS provision. & \(\bullet\) Energy detection is only & \\  & & & & \(\bullet\) Provision. & optimal for detecting \\  & & & & \(\bullet\) Each node goes to sleep and & unknown signal if the \\  & & & & wakes up periodically and & noise power is known. \\  & & & & independently. & \\ \hline \multirow{6}{*}{C-RICER [17]} & \multirow{6}{*}{Low} & \multirow{6}{*}{RSSI} & \multirow{6}{*}{Low} & \(\bullet\) Use of power adaption before & \(\bullet\) Random delay. \\  & & & & channel adaption is considered. & \(\bullet\) Rescan cycle should be \\  & & & & \(\bullet\) Dynamically adapts both & sufficient to cover the \\  & & & & transmission power and & duration of the \\ \cline{1-1}  & & & & channel according to & interference, but \\ \cline{1-1}  & & & & interference level. & sufficiently short to \\ \cline{1-1}  & & & & \(\bullet\) To reduce the sensing energy, & ensure energy \\ \cline{1-1}  & & & & the coordinator of C-RICER & efficiency. Thus, the \\ \cline{1-1}  & & & & periodically senses interference & rescan cycle should be \\ \cline{1-1}  & & & & only in the working channel. & adaptively calculated. \\ \hline \multirow{6}{*}{MBAN MAC [20]} & \multirow{6}{*}{Low} & \multirow{6}{*}{UWB radio} & \(\bullet\) Adopts the IEEE 802.15.6 for communication in intra-WBAN tiers and ECMA-368 in inter-WBAN tiers. & \(\bullet\) Neither verified nor evaluated in [20]. \\ \cline{1-1}  & & & & inter-WBAN tiers and ECMA-368 MAC provides a distributed reservation-based channel access mechanism, as well as prioritized contention-based channel access. & \(\bullet\) The coordinator \\ \cline{1-1}  & & & & \(\bullet\) Channel estimation is based on both the RSSI measured during the sensing period and the packet collision rate during the WBAN accessing period. & are found (_i.e._, no interference); hence, \\ \cline{1-1}  & & & & packet collision rate during the \\ \cline{1-1}  & & & & WBAN accessing period. & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of MAC protocols designed for CRBANs. DCAA, dynamic channel adjustable asynchronous; PU, primary user; MBAN, medical body area network; UWB, ultra-wideband; ECMA, European Computer Manufacturers Association. In [15], packet transmission for critical nodes was prioritized over that for non-critical nodes by using the concept of cognitive radio. Critical packets were transmitted with higher power, whereas non-critical packets were transmitted with lower power. As a result, the throughput of critical traffic was higher than that of non-critical traffic. The packet collision ratio was low because of the preference accorded to critical traffic over non-critical traffic. According to the performance results of network throughput and the packet rejection rate, CR-MAC [15] provided QoS support for traffic with different priorities.