Research On Energy Aware Wireless Transmission Technologies For Wireless Sensor Networks

With the rapid development of chip, communication and sensing technologies, wireless sensor network (WSN) has become the key technology in the new era of sensing technologies. In WSN, the tiny nodes, which consist of sensing, data processing and wireless communication components, are deployed densely and randomly in large numbers. The tiny nodes form the WSN in a self-organization manner. Based on the diverse onboard sensors, the WSN can sense the field and communicate the information to the remote sink in an efficient and timely manner. The sensing performance and reliability have been improved significantly in WSN. So the WSN can be widely used in military sensing, security, environmental monitoring, traffic surveillance, medical treatment, building and structures monitoring, even anti-terrorism, etc. However, since the sensor nodes are battery driven and it is impractical to recharge the battery for so many nodes after deployment, energy efficiency has been a key concern in the research work of WSN. On the other hand, in many WSN applications, the data gathering has the Quality of Services (QoS) requirements in terms of BER performance, end-to-end timeliness and reliability, etc. Therefore, to design the protocols with low energy consumption and flexible QoS provisioning is the guarantee for the efficient information gathering in WSN. According to the analysis of sensor nodes, the main sources of energy consumption are sensing, wireless transmission and data processing. And the energy consumption caused by wireless transmission is much more than sensing and data processing. On the other hand, since most technologies in WSN, such as data routing, distributed information processing, have the requirements for the wireless transmission. Wireless transmission technologies have been identified as the key technologies determining the energy consumption and QoS, which are also the basis for other technologies. Therefore, in this thesis, the author carried out a deep and systematic research work on the energy efficiency and QoS provisioning in WSN by designing the wireless transmission technologies. According to the characteristics of multi-hop transmission, limited energy resource, high density of sensor nodes and the coexistence of multiple applications'requests, the main aspects of wireless transmission technologies in WSN include point-to-point and end-to-end wireless transmission, cooperative wireless transmission among multiple nodes and the wireless transmission in multiple applications scenarios. Therefore, a systematic research work is done in this thesis to design these wireless transmission technologies with focus on energy saving and QoS provisioning. The work has been supported by the National Science Foundation of China "Investigation of Wireless Multimedia Techniques based on Multimedia Transmission Property" (No.60202005). The contributions of this thesis include: (1) Point-to-point wireless communication technology based on adaptive code position modulation This thesis analyzes the requirements of low power consumption and complexity, coexistence and self-adaptation on the design of the point-to-point wireless communication scheme in WSN. The disadvantages of the traditional short-range wireless communication technologies are analyzed. Then, a novel adaptive code position modulation technology is proposed for WSN. The technology has the merit of low power consumption and low complexity. And the communication parameters of the technology can be adjusted adaptively according to the channel condition and QoS requirements, so as to minimize energy consumption and provide QoS gaurantee. (2) End-to-end energy and QoS aware wireless transmission technology This thesis jointly integrates the application's QoS requirements, network routing protocol and the transmission technology into a single framework. The impact of the communication parameters in the framework on the overall energy consumption and QoS performance are investigated and modelled. Based on the results, a centralized offline control policy is designed in the integrated framework to adjust the communication parameters for fixed QoS provisioning. And a distributed online control policy is also designed based on the feedback control theory for dynamic QoS provisioning. (3) Multi-hop cooperative MIMO wireless transmission technologyThis thesis analyzes the phenomena of radio irregularity and multipath fading in some applications of WSN. And a cooperative MIMO technology is designed by forming multiple single antenna nodes as the virtual antenna array. Based on the technology, a cluster based multihop cooperative MIMO protocol is designed, in which the cooperative MIMO technology is incorporated into the transmission between cluster heads. The energy consumption model of the protocol is developed and an adaptive cooperative nodes selection strategy is also designed in the protocol. (4) Energy aware transmission technology in supporting multiple applications' requests This thesis analyzes the coexistence of multiple data gathering applications in WSN. An energy aware wireless transmission technology is developed with focus on the coexistence of multiple applications. The technology has two main components, the optimal transmission policy for each application and the optimal admission control policy for multiple applications. The objective is to maximize the expected overall reward under the residual energy constraint of the network. In designing the optimal transmission policy, a convex optimization model is developed in terms of the transmission scheme and the overall energy consumption of the network. Then the mature optimization technique is employed to solve the model and find the optimal transmission policy. In the design of the optimal admission control policy, the problem is abstracted as a dynamic and stochastic knapsack problem. The related theory is employed to model the problem. Based on the model, the related algorithms are used to design a distributed optimal admission control policy for multiple applications. In this thesis, a systematic research work on the wireless transmission technologies in most possible scenarios has been done with focus on energy efficiency and QoS provisioning. The achievements of the research work can be used to guide the design of the wireless transmission technologies in the real WSN products. And it can also be used in the applications with QoS requirements, such as fire detection and object tracking.