Connectivity of wireless sensor networks in greenhouse for plant growth

Wireless sensor networks have been applied in farmland and greenhouse. However, poor connectivity always results in a lot of nodes isolation in the network in a scenario. For this reason, the network connectivity is worth considering to improve its quality, especially when the collected data cannot be sent to the data center because of the obstacles such as the growth of crop plants and weeds. Therefore, how to reduce the effect of crop growth on network connectivity, and enable the reliable transmission of field information, are the key problems to be resolved. To solve these problems, the method which adds long distance routing nodes to the WSN to reduce the deterioration of WSN connectivity during the growth of plants was proposed. To verify this method, the network connectivity of the deployed WSN was represented by the rank of connection matrix based on the graph theory. Consequently, the rank with value of 1 indicates a fully connected network. Moreover, the smaller value of rank means the better connectedness. In addition, the network simulator NS2 simulation results showed that the addition of long-distance backup routing nodes can improve the network connectivity. Furthermore, in experiments, using ZigBee-based wireless sensor network, a remote monitoring system in greenhouse was established, which can obtain environmental information for crops, e.g. temperature, humidity, light intensity and other environmental parameters as well as the wireless link quality especially. Experimental results showed adding of long-distance backup routing nodes can guarantee network connectivity in the region where received signal strength indication (RSSI) was poor, i.e. RSSI value was less than −100 dBm, and the energy was low. In conclusion, this method was essential to improve the connectivity of WSN, and the optimized method still needs further research.