The Research On Cooperative Protocol In Wireless Sensor Network

As the development of the Internet of Things, wireless sensor network (WSN) has drawn more and more attention. But, due to the limitation of the low-power and fading, it is difficulty to improve the communication quality in wireless sensor network. Multiple-input and multiple-output (MIMO) technology presents a new vision. Unfortunately, to form the MIMO channel, multiple antennas should be located at the transmitter and receiver, which is hard to accomplish. In virtual MIMO and cooperative technology, the adjacent sensors cooperate with each other to form a virtual antenna array. So, diversity gain can be achieved. With the help of cooperative technology, data transmission rate is increased and transmitting quality is improved in wireless sensor network.As a sub-project of the project supported by National Science Foundation of China (No. 50275017), the major efforts of this thesis are focused on the relay forward protocol. Firstly, the model of Rayleigh fading and additive white Gaussian noise channel is introduced. Then, the diversity technology which is used to resist fading is presented. At the same time, the channel model and capacity of MIMO system are analyzed emphatically. Next, cooperative communication is indicted in depth, in which the chief efforts have been made to introduce the slot allocation schemes and relay forward protocols. Meanwhile, under orthogonal slot allocation, the outage probability and diversity order of two basic relay forward protocols, amplify-and-forward (AF) and decode-and-forward (DF) are analyzed. Then, a new relay forward protocol, which is called nonlinear amplify-and-forward (NAF), is introduced. In the new protocol, it is given out that a closed-form solution of the optimal signal estimation at the relay by the minimum mean square error (MMSE) criterion. Then, the solution is simplified by set reduction, and the simplification is proved to be a tight approximation. NAF can help the destination to obtain a higher SNR than AF and prevent the case in DF that all power is used to transmit the incorrect signals. Both of the theoretical analysis and simulations are carried out in three-terminal relay system and multi-relay system. The results show that NAF can achieve full spatial diversity, and it outperforms AF and DF.