# Efficient Health Data Transmission Method in a Wireless Body Area Network for Rural Elderly
## 2 Related Works  
To accommodate dynamic link change and signal attenuation, many methods used multi-hop to transmit data. [PERSON] et al. established a signal loss model when the medium is the human body under five bandwidths [9]. In ref. [10], the finite difference time domain method was used to model the WBAN channel, and the statistical parameters of path loss in relation to seven different movements were obtained. [PERSON] et al. defined the minimum energy consumption path in the WBAN by considering factors such as residual energy, node importance and energy difference and designed an optimal WBAN energy consumption routing protocol based on an artificial bee colony [11]. [PERSON] et al. proposed an energy-aware efficient routing method for WBAN links [12]. Taking the energy efficiency as the core, the calculation model of the transmission cost was derived. Based on the energy-aware routing mechanism, the next hop routing model was established. A path cost function considering the residual energy was constructed in ref. [13], considering the number of hops and the transmission distance to select the next hop in the WBAN. In ref. [14], the roles of relay node and sensing node can be interchanged, so that all sensors have the opportunity to become relay nodes. This method reduced the energy consumption, prolonged the network lifetime and improved the WBAN reliability. [PERSON] et al. proposed an energy-aware routing protocol to minimize energy utilization and select a next hop by evaluating the link quality [15]. This protocol evaluated energy levels, link quality, and residual energy to balance loads, minimized energy utilization, and enhanced data transmission. [PERSON] et al. built an objective model to select efficient paths with stable links, and a fuzzy logic system was used to determine the link stability [16].  
[PERSON] et al. studied an Optimum Path Optimum Temperature (OPOT) Routing Protocol [17] that allows sending critical data first when the sensed temperature exceeds the threshold. Some studies also introduced a delay-tolerant network (DTN) into the WBAN to improve the network reliability based on link connection information [18; 19; 20; 21]. Behavior-aware probabilistic routing used probability to measure the historical connection between nodes. An inertial sensor was used to quantify the instantaneous connection status of the sensors. When the node was in violent motion, the next hop judged by the instantaneous sensor node accounted for a more significant proportion. When the node was in stable motion, the proportion of the next hop judged by historical link connection status was larger [21]. [PERSON] et al. regarded the routes in the WBAN as chromosomes, the nodes as genes, and the adaptive values as the availability values of links [22]. After several crossovers and mutations, the path with relatively high reliability can be found. However, the time complexity of the genetic algorithm is relatively high, causing a large consumption of energy. In ref. [23], body posture's influence on various multi-hop transmission methods was analyzed, and a delay-tolerant network was used to design a WBAN transmission strategy. The authors proposed a new improved method for delay-tolerant networks, with better reliability than previous similar data transmission methods.  
Because the opportunistic routing protocol is effective in ensuring a stable transmission, [PERSON] et al. constructed an opportunistic transmission model for the WBAN based on Bayesian probability [24]. In addition, the latest opportunistic transmission method based on maximum/minimum range is discussed in ref. [25]. However, the design of an opportunistic transmission protocol for a delay-tolerant WBAN was rarely considered in the published studies. Based on the link history, data importance and characteristics of delay-tolerant networks, a transmission protocol for the elderly's WBAN was designed. This new protocol provides a scheme for realizing the hierarchical transmission of health data and improving the network reliability.