# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 3 BBN Design Considerations
### Energy-Efficiency for BBN
The second advantage of AAT protocol is the channel state estimation, which makes it possible to handle real WBAN scenarios, taking into account the human body movement and the WBAN topology changes. However only two-hop star topology is considered. The off-body link is not in the scope of AAT protocol. Then, despite its good achievement, AAT is restricted to intra-WBAN communications. Another energy key feature is the duty cycle, implemented in [58] for WBANs. The duty cycle minimizes the amount of extra overhead, by removing the need of idle listening for clear channel, using the TDMA MAC protocol in such a way to reduce communication time relatively to power down time, and this is the major benefit of the duty cycle. However, its major limitation is the assumption of WBAN static topology, which leads to a second assumption, i.e., the synchronization can be simplified since the WBAN has almost fixed topology and the same sensor functions. Although the duty cycle mechanism could be beneficial for BBN use, by reducing the traffic overhead while routing sensor data among WBANs, the static topology assumption does not outfit the dynamic nature of BBNs. Table 1 recapitulates the salient features of the aforementioned energy-aware protocols for intra-WBANs communications. \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Protocol** & **Layer** & **Topology** & **Advantages** & **Limitations** \\ \hline EAAODV [49] & Network & Single-hop & On-demand Routing & Results only for ZigBee \\  & & Mobility management & MAC Model. \\ \hline M-ATTEMPTT [50] & Network & Single-hop/ & Mobility management & Disconnection during sensor node mobility \\  & & Multi-hop & Traffic priorities & \\  & & Intra-WBAN routing & & \\ \hline SIMPLE [51] & Network & Multi-hop & Reliability, High throughput & No mechanism to handle mobility \\  & & On-demand intra-WBAN routing & & \\ \hline EERS [53] & Network & Multi-hop & Joint Routing and Adaptive power control. & Only focus on the data transmission energy. Sensing and \\  & & Low overhead. & reception energy are assumed constant. \\  & & Prolog the lifetime of the overall network. & & \\ \hline EAWD [55] & Network & Multi-hop & Topology-aware energy-efficiency. & Absence of retransmission energy, MAC access energy \\  & & & Minimizing the number of relay nodes. & and signaling energy components. \\  & & & Gnerie (separate energy components). & \\ \hline CLDO [56] & MAC & Multi-hop & Transmission reliability & Do not handle topology changes. \\  & PHY & & Energy efficiency with suitable packet size & \\  & & Prolog WBAN lifetime. & & \\ \hline AAT [57] & MAC & Two-hop & Adaptive power control & Handle only two-hop topology relaying. \\  & PHY & & Channel link estimation & \\  & & Transmission reliability & & \\  & & Reduced delay. & & \\ \hline Duty-cycle [58] & MAC & Single-hop & Guard time: no overlaps, data reliability. & Hardware dependent. \\  & & & Reduce idle listening. & \\  & & TDMA synchronization. & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Energy-aware candidate protocols for body-to-body networks (BBNs). © [2019] IEEE. Reprinted and modified, with permission, from [4].