Abstract:
Environmental monitoring in real-time has been more important in automation system nowadays. With the implementation of wireless sensor network, much information about the environment such as temperature, sound, soil moisture level and pressure can be monitored immediately. Especially for soil moisture level, many of the current sensors require the use of a data logger that does not allow the sensors to react to changes of the environment at the same time when the information are being extracted. Data loggers also require cabling which can cause more installation cost and maintenance difficulties. Furthermore, some of the data loggers are not designed for distant monitoring and require the information to be obtained manually resulting in a waste of manpower. Many researches and investigations have been done in the past for the wireless network design. This includes the basic network architecture, structure, the protocols and algorithms used for the wireless network in order to improve the performance of wireless communication. The most important factor to be considered in the designing and implementation of a wireless sensor network is the development of a precise, stable and energy efficient network. This thesis attempts to provide a solution for a convenient and efficient soil moisture network that has previously relied on the data logger in obtaining the information. The sensor network is designed and developed based on the Texas Instrument technology. The architecture is defined by IEEE 802.15.4 standard and the communication protocol between the coordinator and the sensor nodes are also clarified. The soil moisture sensor that is to be improved has been studied with the background of the sensor stated. This leads to the elimination of data logger and the integration of the sensor node to the pre-examined wireless network. Problems regarding the efficiency and cost of the network arise and motivate to the designing and implementation of a new sensor node. The overall system is then reviewed with the steps for the calibration and conversion of the sensor output into volumetric water content. A brief introduction to the use of relay channel is also discussed in the aim to reduce power consumption and increases channel capacity. The investigation of the channel capacity theory for cooperative communication system and the derivation for the formulae are also presented.