# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 3 BBN Design Considerations
### Energy-Efficiency for BBN  
WBAN energy constraints have been long discussed in the literature. Naturally, if WBANs are energy-constrained, BBNs are more so. Indeed, the communication and sharing of sensor data among coexisting WBANs, will give rise to further energy consumption. Authors of [49] presented a comparative study of existing WBAN routing protocols for healthcare. The studied scenario consists of a ZigBee network having static IEEE 802.15.4 star topology, taking into account the energy consumption as well as the following QoS metrics: the average end-to-end delay, the throughput, the jitter and the packet delivery rate. The simulation of the ad hoc on demand distance vector (AODV) protocol testifies higher throughput, minimum jitter and reduced delay, in both mobile and stationary situations of WBANs. AODV is then enhanced to an energy-aware  
Figure 3: Application area extension from WBAN to body-to-body networks (BBN). AODV protocol (EAAODV), that builds routes on-demand by flooding route request (RREQ) packets. EEAODV routing relies on mobility metrics and the remaining energy to select the next WBAN as forwarder of the RREQ. In fact, each sensor node defines energy and mobility thresholds and selects the next hop sensor with maximum residual energy and minimum mobility. EAAODV outperforms AODV in terms of energy consumption, and then could provide an appropriate routing for the energy-constrained network of multiple WBANs. Thus, EAAODV is a candidate routing protocol for BBNs. Authors of [50] propose a mobility-supporting adaptive threshold-based thermal-aware energy-efficient multi-hop protocol (M-ATTEMPT) for WBANs, with a prototype using heterogeneous sensors on a single WBAN. An M-ATTEMPT protocol enables a direct link between the sensors and the sink for both real-time and on-demand data, and a multi-hop transmission for normal data. Multi-hop strategy preserves energy consumption, since less energy is required for routing through short distances. The thermal-aware algorithm includes mobility support and energy management. Indeed, it detects link hotspots of implanted sensors and avoids them while transmitting to help them save energy. In addition, the algorithm detects patient mobility and deals efficiently with links disconnections. For normal data, M-ATTEMPT protocol implements a TDMA schedule so that the sensor nodes could transmit data to the sink during the allocated time slots. In case of WBAN mobility, extra energy is used by sensors to maintain the connectivity. The M-ATTEMPT protocol performs for intra-WBAN communication to ensure energy and QoS-aware routing. In BBN context, M-ATTEMPT could be adapted to transmit data between sinks, provided that the traffic data classes and the scheduling scheme would be customized for BBN use. Furthermore, M-ATTEMPT should implement a mobility management process to support inter-WBANs communications in dynamic scenarios. Indeed, the major limitation of this protocol consists of the disconnections caused by sensors mobility that requires restructuring of the WBAN tree topology. A stable increased-throughput multi-hop protocol for link efficiency (SIMPLE) routing protocol was proposed in [51] for intra-WBAN communications. It optimizes the energy-consumption, reliability and throughput of multi-hop communications between sensor nodes and the sink, in comparison to M-ATTEMPT. This protocol provides better stability of the intra-WBAN communications for a long time and under a high speed of the WBAN. It could be extended to apply to BBN communications with further QoS considerations, where each WBAN sink would represent either the parent or the forwarder for the inter-WBANs routing. Nevertheless, for the transmission and reception, the authors have chosen the radio model of Heinzelman [52], where \(d\) is the separation between the transmitter and the receiver, and \(d^{2}\) models the energy waste due to the transmission channel, corresponding to the free space path loss, which is actually very specific and not suitable for WBANs/BBNs.