## 5 WST Applications
### Physical Aspects of Applying WST in Agriculture and Food Industry  
Radio propagation in real environments is complex due to multipath propagation, shadowing and attenuation. In agriculture, the radio frequency faces challenges due to placement of nodes for wide-area mesh coverage and reliable link quality above crop canopies. WST must be able to operate in a wide range of environments such as bare fields, vineyards, orchards, from flat to complex topography and over a range of weather conditions, all of which affect radio performance [53]. In these situations, the link power budget is dependent on crop growth and terrain in addition to more common factors such as node spacing and antenna height [54]. For applications inside buildings like burns, greenhouses or warehouses, the radio signal has to go through many objects like walls, windows, pallets, machines, etc. which also cause a significant reduction in signal strength. In general, a received signal level of 10 dB to 20 dB above the sensitive limit of the receiver is an accepted value for the link budget [54].  
One important research topic is fault detection and isolation. In a remote sensing application it is essential to detect the erroneous measurements. Wrong information provided by the monitoring system should be identified and skipped. Also the implementation of artificial intelligence in the core of the system can block the transmission of erroneous data. [PERSON] _et al_. found that sensor measurements become erroneous when the battery voltage was low, between 2,159-2,167 mV (full charge was 3,000 mV) temperature rises enormously and both relative humidity and temperature increase in variability [25]. However, this behavior has not been documented by other studies in other fields that use the same motes [55,56]. Thus the possible influence of other factors like the algorithm installed should be taking into account and studied in further experiments.  
Among the different performance parameters, the rate of message lost or Packet Reception Rate (PRR) is very important in a WST implementation, and should be evaluated for any application. Depending on the operating environment, significant signal loss can occur at these frequencies particularly when the radios require line-of-sight for optimal performance, with 2.4 GHz more susceptible than 900 MHz. Results from experimentation in refrigerated chambers with 2.4 GHz ZigBee motes showed low ratio of data lost packets. Being the maximums detected 15.73% at the laboratory and 4.74% at the wholesale store. In opposition, the ratio founded in a semi-trailer, had a maximum of 100% for two of the motes and a minimum of 32.48% [57]. In the case of [PERSON] _et al._, who monitored cows with 433 MHz motes, the base station directly received less than 50% of temperature measurements stored in the mote buffer [56]. [PERSON] _et al._, that also monitored cows with 2.4 GHz motes, showed packet loss rates of about 25% for wireless sensor data from cows in a pasture when the distance to the receiver was less than 12.5 m. In a potato field, after the first year of experimentation with 868/916 MHz, 98% of data packets were lost. However, during the second year the total amount of data gathered was 51%, which represents a clear improvement [58,59]. Looking for better results, a solution could be to display more intermediates motes that allow peer to peer communication to the base station. Another solution could be to do more experiments testing other frequencies like 868 and 916 MHz, which are used for other commercial motes available. Or to develop motes with more RF power, that can achieve longer radio ranges. Also the transmission could be improved by means of optimizing antenna orientation, shape and configuration [57,60].