## 3 Models
### Network Model  
The network model assumed in this study is adopted from Reference [5]. The network model is a two-dimensional network domain which contains a set of sensor nodes and links. A wireless sensor node is a computing device enabled with a wireless interface, limited set of computational capabilities and has a unique identifier (ID). Three types of sensor nodes and sensor node capabilities exist in the network domain; sink node, source node and normal nodes. The sink node is a designated node for collecting data from the other nodes in the network. It also acts as an intermediate node between the WSN and the external world. The sink node has more capabilities than the other nodes. It has more memory capacity and more computational power. The main task of a source node is to sense an asset and forwarding the sensed data to the sink node by utilizing multi-hop communication. The functions of a normal node include relaying packets from source nodes to the sink node. All the sensor nodes in the network are stationary. Thus, the network topology does not change throughout the network lifetime. Communication from a node is modelled in a circular communication range which is centered at the node. All the sensor nodes are homogeneous and are designed to have the same communication range. The nodes which are in direct communication range with each other through 1-hop communication are assumed to be neighboring nodes and they can exchange data. Network is event-triggered, which means when a source node senses an asset, it can start sending packets to the sink node, periodically. When a node detects an asset within its monitoring area, it continues to sense the asset until the asset moves out of the area. When the asset moves to a new location, it activates another sensor node to become the new source node. When no asset is sensed, the nodes can follow a sleeping schedule. The packets which are transmitted between the sensor nodes are encrypted. Also, the packets contain source node ID but only the sink node can assume the ID as the asset location. The network functions in two phases. The first phase is the network configuration phase where network initialization and configurations are done. The second phase is the operational phase where packets are routed from the source node to the sink node by using the proposed routing protocols. During the network configuration phase, the network uses the network initialization process similar to References [3,8] as a technique for neighbor discovery and hop-count estimation of the nodes with respect to the sink node. The network uses the k-nearest neighbor tracking approach to track the assets. Before the network initialization process, it is assumed that a network planner will have decided on the important network parameters such as the structure, size and configuration of the network regions. During the network initialization process, each sensor node is first loaded with a unique identifier (ID). Subsequently, the sink node acquires its location information through the use of a global positioning system (GPS). The sink node then broadcasts a beacon packet to all sensor nodes in the network and sets its hop counter to zero. The beacon packet contains information such as sink node ID, sink node position coordinates, and hop counter. Each node in the network receives the beacon packet, stores the hop counter value with a sender node ID, increments the hop counter by one, and rebroadcasts the beacon packet to its neighboring nodes. The hop counter number is used to indicate the hop distance between the sensor nodes and the sink node. The broadcasting of the beacon packet ensures each node acquires information and knowledge about its neighboring nodes and its location with regard to the sink node. If a sensor node receives multiple beacon packets, it stores the minimum hop count in its buffer and deletes other hop counter information. After that, each sensor node computes a list of its neighboring nodes. Each node notifies its hop distance to the sink node.