## 1 Introduction  
Nodes in a _Wireless Body Area Network_ (WBAN) are required to operate under strict resource constraints. Specifically, power for transmitting data from nodes to the _Access Point_ (AP) must be preserved so that battery life is extended and recharging is as infrequent as possible. The need to implement frequent recharging procedures is one of the main obstacles impeding wide adoption of WBANs as an alternative to traditional practices of monitoring a patient's physiological condition. To reduce the maintenance requirements associated with recharging of batteries, an efficient routing protocol is crucial for extending battery life. Power-efficient routing for _Wireless Sensor Networks_ (WSNs) has received much attention in the past. However, porting routing solutions from WSNs to WBANs is problematic due the different network architectures and operating conditions. In WSNs hundreds to thousands of sensor-nodes cover large areas and offer a considerable degree of redundancy. The task of monitoring the environment does not have to involve all sensor-nodes all the time. This setting brings about routing solutions which rely on dynamic network configurations involving many hops from sensor-node to sink. WBANs cover an area limited to the human body and offer no redundancy. Data must be collected reliably from all nodes placed on the body, while addressing unique signal propagation conditions not present in WSNs such as body shadowing and mobility of sensors. It follows, that efficient routing solutions should be designed specifically for WBANs. Several routing protocols were designed in the past specifically for WBANs--some prominent examples follow. [PERSON] _et al._ developed the CICADA protocol, consisting of a spanning tree architecture with a time-division scheme for transmission scheduling [1]. In CICADA, nodes closer to the root will deplete their energy source faster due to the need to relay messages from children nodes. [PERSON] _et al._ developed a protocol tolerant to network changes [2]. They proposed a store-and-forward method that maximizes the likelihood of a packet reaching its destination. Each packet is stored by multiple nodes and retransmitted, which consumes more power. One solution to this problem was proposed by [PERSON] _et al._[3]. It consists of using dedicated, non-sensing, relay nodes with larger power sources. While this method increases the _Network Lifetime_ (NL), it requires additional dedicated hardware. This method was further improved by [PERSON] _et al._ in [4], where body movement, such as hand motion while walking/running, was utilized to achieve NL improvement. The approach requires additional hardware and a line of sight between various network components, which limits nodes positioning on the body. [PERSON] _et al._ proposed a similar store-and-forward method that integrates _Transmit Power Adaptation_ (TPA) [5]. Nodes keep track of neighbors and utilize power control to consume minimal transmission power while maintaining a preset link quality. A slightly different approach was used by [PERSON] _et al._[6]. It proposes a Minimum Energy Packet Forwarding Protocol which implements the _Transmission Power Control_ (TPC) similar to the method proposed by [PERSON] _et al._ with _Automatic Repeat Request_ (ARR), where a lost packet is retransmitted only when the link quality returns to acceptable level. Other work on relaying signals in WBANs includes the use of creeping waves by [PERSON] _et al._, to maintain reliable on-body communication while reducing power consumption at the nodes [7,8]. Recent work by [PERSON] _et al._ moves in the direction of developing a routing method based on body posture. In [9] they proposed a delay tolerant routing protocol and compared it with various routing schemes. Finally, [PERSON] _et al._ proposed a data-centric multi-objectiveQoS-Aware routing protocol (DMQoS) [10]. It categorizes a data packet into two different classes, namely, delay and reliability domains.