## 1 Introduction
Depending on the data type, a different routing scheme is applied to that specific packet. While this approach improves the delay and bit error rate statistics, energy consumption increases significantly, in turn decreasing the overall NL. Global routing algorithms are usually avoided in _Wireless Sensor Networks_ (WSNs) where the network comprises hundreds to thousands of nodes and great distances are covered. The exponentially increasing complexity with the number of nodes and the need to exchange large volumes of link-state information make such algorithms prohibitive. Unlike WSNs, a common network architecture used in WBANs is a star-topology, where an AP is placed on the body and the nodes are distributed up to 1.5 meters from the AP. The AP collects data from the nodes and acts as a gateway for remote access. The AP is typically a PDA-like device equipped with substantial computation power, energy source and memory space compared to the simpler distributed nodes. This asymmetry between AP and nodes extends to their functionality as well: the AP is typically the coordinator of all network activities (master node), and the nodes' functionality is kept as simple as possible to preserve resources (slave nodes). The asymmetric star-topology architecture coupled with the low number of nodes (typically on the order of 10) makes global routing protocols a viable option for collecting data at the AP. Implementing a global routing algorithm would require periodically gathering link-state information from nodes to AP, optimizing all the routing paths at the AP and sending routing instructions from AP to all nodes. Alternative network architectures for WBANs make use of an off-body AP with a single or multiple antennas. Such architectures can be efficiently employed in indoor environments with supporting infrastructure. Examples include healthcare facilities and protected-living environments, where the off-body AP can be easily integrated with other information services and hardware. An off-body AP relieves the need to maintain the on-body APs of multiple patients (recharging schedules, _etc._) and reduces the need for patient compliance. In this contribution, we propose a global routing protocol based on [PERSON]'s algorithm [11] with a novel link cost function specialized for balancing energy consumption and increasing NL in WBANs. NL is defined as the time it takes a single component of the network to deplete its power source from network startup. Given the asymmetric WBAN topology, we consider the time it takes a single node to deplete its battery, assuming the AP has abundant energy compared to the more compact nodes on the body. We view the nodes' batteries as a distributed network resource. It follows that no single node should deplete its battery while there are other nodes with available energy. Thus, our proposed link cost function is designed to ensure that all nodes deplete their battery at the same time. We presented preliminary results of the proposed approach in [12], where the link cost function was implemented for a single network architecture with on-body AP. In [12] the NL was evaluated for a single run and an arbitrary value of the protocol parameters. In this contribution, we present more comprehensive results for the on-body AP network architecture, including evaluation of _Energy per Bit_ (EpB), finding optimal value for protocol parameters and insights on the workings of the protocol. In addition, we extend the work to include network architectures comprising an off-body AP with multiple antennas and analysis of network connectivity. We focus on NL and EpB as the performance parameters of interest. EpB is defined as the average energy spent globally to deliver a single bit to the AP [13, 14]. It is a good indication of the overall energy efficiency of the system--lower EpB corresponds to less battery weight and less heat dissipation which in turn increase wearability of the WBAN. For the scope of this work, we do not consider latency as a performance parameter.