# A Visitor Assistance System Based on LoRa for Nature Forest Parks
## 3 Related Work
Then, the RSSI values of signals sent by transmitters installed in the animals are compared by the fixed points, locating them inside the cells where the intersection occurs. Nevertheless, this approach is inefficient in the forest environment, since RSSI presents intense variability. The forest environment is very challenging due to the difficulties of propagating the electromagnetic wave. This difficulty becomes even more pronounced in humid tropical forests, such as the Brazilian Atlantic Forest. Two works are very relevant for our purpose. They focus on locating visitors in natural parks, but none of them consider physical layer aspects. In the works described in [7; 15], the authors introduce the concept of sighting registration as a way to subsidize the location of a sensor on a network with intermittent connection and its joint use with GPS, if available. The sighting record consists of storing the location data of the sensor when it contacts another sensor, together with the remote sensor identification. Both works only use one type of message, the sighting record. There is no handshake and, therefore, no metadata is produced to allow the filtering of records before transmitting them. If sensor memory is full, excess data received is discarded. CenWits [7] is a search and rescue system in the wild, which uses RF transceivers carried by visitors, operating in the 900 MHz range. Each sensor receives its coordinates from location points, or a GPS, if available, and passes it on to other nodes during subsequent encounters. This information is uploaded at access points, distributed in several locations. This data, which consists of location history, can be used to estimate the location of a lost visitor. The system is designed for a network that provides only occasional connectivity. A prototype of CenWits has been implemented using Berkeley Mica2 motes, but the authors do not detail the type of location where the tests were performed, urban or natural. The SenSearch project [15] is an outdoor GPS assisted personnel tracking system. SenSearch is based on CenWits [7] and works in much the same way, but with the exclusive use of GPS for determining the location, increasing the accuracy of the system. A study of the duty cycle is also made, reducing the periods of activation of the GPS and the transceivers to improve the use of the battery. The duty cycling may lead to a decrease in the localization accuracy of the system. This is discussed in the performance evaluation, using analytical, simulation, and experimental results. The experiments are held in urban areas, at the University of California-Merced campus and the University of Colorado-Boulder campus. YushanNet [16] is another system for tracking walkers and the collected hiking traces can provide more precise information to rescue teams if there are hikers lost in the mountains. A demonstration is implemented in Yushan National Park, Taiwan. The park is a subtropical high mountain national park. The central ideas are based on [7; 15], which apply a DTN technique and make use of opportunistic, ad hoc, and short-range wireless communications to disseminate data in a network. Hikers carry a matchbox-sized device, which consists of a ZigBee-based mote and a GPS receiver, and the device records its hiking trace, along with encounter information with other devices. In addition to supplying information about hikers' whereabouts to park administrators and rescue services, the system allows family members to log on to a website and check that hikers have reached their planned destinations. The system design is demonstrated using a small-scale network scenario. Also focused on natural environments, the WebPark [17; 18] was a research and development project funded by the European Community, through the IST (Information Societies Technology) program, between October 2001 and September 2004.