## 3 Proposed Framework
### Mobile Embedded Sensor Node  
In most wireless sensor networks, the sensor nodes operate from fixed locations or in constrained environments, but in cattle tracking the sensor nodes should be moving with the animal hence the  
Figure 1: Basic system structural framework.  
challenges of mobility and reliable network connectivity. Tracking mobile objects have been studied by [23; 24; 25]. A mobile embedded sensor does not control its movement as it is attached or placed in the target. In animal management, it is usually tethered on to the animal [14], placed in the animal rumen [13], or inserted under the animal skin [26]. [PERSON] [27] indicates that there are four types of transponders that can be affixed to an animal, including collar mounted transponders, ear tags, injectable transponders, and rumen bolus transponders. The collar mounted transponders and ear tags can easily be removed and left on the ground as the cattle thief moves with the animals. There are also concerns with use of injectable transponders. The injectable transponders have been reported to migrate from the site of application [28]. The desired sensor node for this study should have the capability to hold the identification information of the target as well as collect the data relating to the target geographic location. Therefore, we propose use of a bolus transponder as a passive sensor node to locate the animal.  
Currently, the rumen bolus is an RFID based transponder for animal identification. Some have thermistors to measure the temperature and are activated to transmit acquisitions after insertion into the animal. One key advantage of using RFID is that it does not require clear line of sight for reading as with the GPS based systems. Other advantages of using RFID include low cost, its small size which means that it can be easily mounted in an animal as an implant, and its long life as it lacks the need for a constant energy supply [29]. However, RFID could be unreliable in its readings, especially in cases when animals move too fast or many of them are present near the reader [29]. RFID is also limited in its maximum reading distance which is just a few meters. These RFID limitations make it unreliable for cattle tracking in case of cattle rustling. Use of virtual fencing or geo-fencing such as in [30; 31] is not applicable as herders usually drive animals over long distances during dry season in search of water and grass. We suggest the use of a rumen-based device that could be an improved version of what was used by [32]. Use of a matchbox sized MICA2 433 MHz motes placed inside standard drug release capsules would be the most appropriate device. Even though [32] concentrates on the internal health statistics of the animals, the motes used were able to communicate over 300 m. This is an indication that if the device is supported with an appropriate localization protocol and a distant estimation algorithm, it could be used to get the current position of the animal. A uniform random deployment will be used when selecting the animals to host the motes. The nodes will not have a priori information about their location and this has to be estimated using a wireless sensor network localization algorithm. Each sensor node will normally operate in sleep mode and will be individually localized by passively receiving wireless control unit messages with minimal inter-node communications.