# Moving Towards Body-to-Body Sensor Networks for Ubiquitous Applications: A Survey
## 3 BBN Design Considerations
### Energy-Efficiency for BBN
Instead, the wireless channel propagation between distant WBANs is discussed in Section 4.1 and a BBN path loss model is reported. In [53], authors presented a low overhead tree-based energy-efficient routing scheme (EERS) with a multi-hop routing and low overhead in WBANs based on the collection tree protocol (CTP), considering adaptive power control to save energy and keep sensor node for a long time. Upon simulations, authors conclude that EERS outperforms CTP with 30% lower delay, 10% lower energy consumption and reaching 0.95 of packet reception rate (PRR). The EERS routing protocol is proposed for intra-WBAN multi-hop communications, it ensures a good balance of QoS (reliability, delay) and energy parameters. It could be extended to a BBN routing protocol, with adding a mobility management/prediction module and more detailed data traffic classification. Further detailed expressions of the WBAN power consumption are provided in other works. For example, authors of [54] formulate the energy consumed by a sensor node as an equation of the different energy components corresponding to each task performed by the sensor in the transmission process. The main advantages of this model are:* Generic: it does not depend on the type of MAC protocol and thus, it could be used in a heterogeneous WBAN network, like a BBN scenario. * Expanded: each energy component appears clearly in the model and could be optimized to minimize the total energy consumed by a sensor node. However, this model did not take into account the topology constraints and the routing task, and their corresponding energy. Our previous work [55] deals with the topology problem and provides an energy-aware topology design for wireless body area networks (EAWD) that minimizes the number of relay nodes and the total energy consumption. Furthermore, the EAWD model explicitly formulates each energy component by displaying both circuitry and amplifier dissipated energy. The transmission process is split into three instances: (i) sensors transmitting to relays, (ii) relays forwarding to relays and (iii) relays forwarding to sinks. The same for the reception process: (i) relays receiving from sensors, (ii) relays receiving from relays and (iii) sinks receiving from relays. Thereby, EAWD provides more accurate transmission and reception energy values in accordance with topology features, together with sensor roles (node, relay or sink). This is a foremost of EAWD that could apply to BBN context. Then, in the BBN energy profile, sinks should indicate the energy consumed for transmission and reception with the other sinks of the network. Also, two further node roles could be specified in a BBN context, namely: sinks forwarding to sinks and sinks receiving from sinks. Nonetheless, EAWD lacks some important components that were considered in [53], namely the retransmission energy, the MAC access energy and the signaling energy. In a more recent study [56], a cross-layer design optimal (CLDO) scheme optimizes the transmission power balance, among the WBAN nodes, through the use of a relay selection algorithm which relies on two interdependent parameters: the residual energy and the size of the transmitted data packet. However most of CLDO simulations were run with a fixed WBAN topology; just slight body movements have been simulated, at the end, to study the transmission reliability in the presence of body disturbances. Therefore, extensive performance evaluation of CLDO scheme, in dynamic scenarios, is needed to conclude about its suitability for use in BBNs. A similar cross-layer protocol, the autocorrelation-based adaptive transmission (AAT), is proposed in [57]. The main advantage of AAT is the use of adaptive power control, which is the current trend in energy-efficiency research. Therefore, the AAT scheme was proved to ensure a good trade-off between transmission reliability, energy consumption and network delay, in terms of which it outperforms CLDO. Indeed, compared to AAT, CLDO introduces additional delay due to the complexity of its energy theoretical analysis.