ZigBee Based Wireless Sensor Network
The problem of online monitoring of cows’ presence and pasture time in an extended area covered by a strip of new grass using wireless sensor networks has been addressed. The total pasture time in the extended area was estimated by measuring the pasture time in a specific part of that area called the gateway connectivity area where sensor nodes mounted on the cows could communicate directly with a gateway. Packet loss causes a node that was present in the connectivity range of the gateway frequently to be classified as an absent node. Therefore, a moving average window with optimal window length and threshold was designed to minimize the misclassification. As the measured pasture time in the gateway connectivity area was an underestimation of the total pasture time in the extended area, an area-based correction factor, same for all individual animals was applied.
As only 23% of the animals in a herd were equipped to be monitored by sensor nodes, investigations to evaluate if the monitored number of animals could represent the whole herd were of great importance. To accomplish the investigations, the number of monitored cows by sensor nodes and the total number of cows (with and without sensor nodes) in the extended area were counted manually each minute over a period of 3 h during 3 days. Pearson chi-square test of goodness of fit showed that the number of cows in the extended area was normally distributed. Furthermore, a statistical test showed that the mean number of monitored cows in the extended area and the mean of total number of cows in the extended area corresponded with the percentage of monitored cows by sensor nodes in the herd (23%).