## 4 Sensor Network Design  
### Monitoring Goals  
Our proposed wireless sensor network will be used to monitor spatial variations in soil moisture as well as detect the presence of rainfall over time. Our experimental Smart Grid testbed is set up in Jordan monitored surface soil moisture and presence of rainfall. Our long term objective is to monitor soil moisture regularly so as to implement targeted irrigation techniques. The data we gather from our system will also be used for managing the irrigation resources throughout Jordan by providing improved guidelines for the Jordan irrigation management model.  
The reactivity of the system should be also very high to detect the occurrence of the event as soon as possible, as in this case, rainfall. When such an event is detected the data or sensor readings should be sent to the base station reliably and quickly and for this reason we need to select the right routes. This data should be sent to the base station at a higher priority than all other data being sent [30].  
Wireless systems are likely to face errors as the environment in which these sensors are deployed are harsh environments which might have severely dry conditions and can affect their performance. Hence we need a very reliable system which ensures that information is correctly and accurately routed to the base station. The sensor network must also ensure heavy data flow in case of rainfall so that no routes or links are overwhelmed with data. We need to manage the information flow and to also reduce redundancy from data to reduce traffic.  
Finally, since there are always energy crises in the case of wireless sensor networks, we need to carefully plan each activity to maximize battery life and also take advantage of the high duration of sunlight available in the Middle East Region. Hence we make use of the solar-powered WSN nodes by which the problem is somewhat lessened. We still need power management as a lot of data will be sent when a wireless node is experiencing rainfall and it needs to send a lot of information and a lot of power will be required at this time. Hence the sensor network needs to strike a perfect balance and trade-off between the power left and the information required to be sent.  
We need an extended WSN lifetime for the soil moisture monitoring system, because we cannot afford to breakdown the data routing operation during a rainfall event when we need to respond quickly to the change in the soil moisture level. We are using ZigBee medium range communication module standard, which is based on the IEEE 802.15.4 [31], which has a lot of advantages such as: consumes less power, also saves power as it has sleep mode, has a large capacity network, is more reliable and has low cost of related components [23; 32]. The authors in [33] have proposed to reduce energy consumption by using a routing algorithm which is a combination of Ad hoc On-Demand Distance Vector Routing Junior and the Cluster-Tree technique. However, there is no practical implementation for all these research initiatives. In our system, power is directly saved by using priority based routing algorithm hence reducing the data at times of raining event when a lot of data is produced. However, even after raining data should be sampled more frequently in order to keep track of the soil moisture.