Research On Cooperative Transmission For Wireless Sensor Networks

Wireless sensor networks(WSNs) are the wireless self-organizing systems which consist of many small sensor nodes with sensing capabilities. Currently, the main problems of the WSN are the limitation of energy and communication resources of sensor nodes, and the harsh environment of wireless communication with path loss and fading channel. Meanwhile, the increasing demand of quality of service(Qo S) needs a more efficient transmission technology to improve transmission reliability, expand the coverage area of communication, enhance the quality of transmission, decrease the energy consumption, and prolong the lifetime of the network.Cooperative transmission technology is an effective method to improve the performance of data transmission. By using the cooperative node to forward the signal, the cooperative transmission technology can extend the coverage of the communication area, and construct multiple independent links from the transmit node to receive node, which reducing the error rate and improving the quality of the data transmission without increasing the transmission power.By applying the cooperative transmission technology, the WSN can effectively reduce the negative effects on path loss and fading channel in wireless communication environment, and provide an effective solution to enhance the quality of the data transmission and reduce the energy consumption of the sensor nodes. Motivated by this, we study the cooperative transmission schemes for the wireless sensor networks in this paper. The main contributions are summarized as follows:(1) We have investigated a distributed cooperative transmission model in wireless sensor network,(1) We have investigated a distributed cooperative transmission model in wireless sensor network, and proposed a distributed cooperative scheme based on the Qo S criteria. In this scheme, by using the signal-to-noise(SNR) as the Qo S index, we have established the optimization problem for the cooperative transmission, and derived the optimal power weight coefficient of each cooperative node, as well as the approximate power allocation coefficient between the transmit node and the cooperative node. Furthermore, we have derived the approximate expressions of ASER over asymmetric fading channel, and then analyzed the asymptotic ASER at high SNR regime. The simulation results show that the proposed algorithm can significantly improve the efficiency of data transmission between sensor nodes.(2) We have studied a cooperative transmission model for the wireless sensor network, where the base station is used to assist the communications between two sensor nodes, and proposed a cooperative scheme based on the Qo S criteria. We have established an optimization problem based on the Qo S criteria, and derived the optimal solutions in terms of power weight matrix for base station and the power allocation coefficient between the transmit node and the base station. In addition, to quantify the system performance, we have also derived the analytical expressions of outage probability, ergodic capacity and average symbol error rate over asymmetric fading channel. Simulation results show the effectiveness of the proposed scheme.(3) We have analyzed a distributed cooperative transmission model with mutual interference, and proposed an interference suppression scheme for the wireless sensor network via support vector machine(SVM). With limited samples of the channel state information, we have constructed an optimization problem to minimize the transmitted power of the cooperative nodes, while guaranteeing the Qo S of the each user and keeping the mutual interference below an acceptablelevel. Since the optimization problem is non-convex, we have simplified the constraints, and then transformed the optimization problem into the standard SVM regression model. By using the quadratic programming(QP) technique, we have obtained the weight coefficient of interference suppression for cooperative nodes. In addition, considering the high computational complexity of QP with large samples, the iterative reweighted least squares procedure(IRWLS) SVM has also been adopted to solve the optimization problem. The simulation results show that the proposed scheme can effectively suppress the mutual interference, ensuring the quality of the data transmission.(4) We have proposed an interference suppression scheme to suppress the interference of the downlink transmission between multiusers in the wireless sensor network by using least-squares support vector machine(LS-SVM). With limited training samples, we have formulated an optimization problem to minimize the transmitted power at BS, while guaranteeing the SINR of the each user and keeping the mutual interference below an acceptable level. By approximating the constraints, we have transformed the optimization problem into a LS-SVM regression model, and presented a recursive LS-SVM algorithm to tackle the interference suppression problem. The simulation results show that the proposed scheme can effectively suppress the mutual interference between the downlink links, confirming the validity of the proposed scheme.(5) We have presented a cooperative transmission scheme where an unmanned aerial vehicle(UAV) is used as relay between a mobile user and a fixed base station. Based on the criterion of maximizing the output SNR, we have first derived the optimal beamforming weight vectors at the base station and the mobile user, respectively. Then, by using the Dubin model, we have derived the update formula of UAV heading angle to adjust the flight path to maximize the system performance. Finally, the simulation results show that the proposed scheme can obtain the nearly performance comparison with the exhaustive search, indicating the effectiveness of the proposed method.