Research On And Implementation Of Transmission Scheme For Backscatter Communications With Multiple Wireless Network Interface Cards

The Internet of Things(Io Ts)technology can bring great convenience to people's lives,but its deployment in practice needs to consider the low-power consumption requirements of nodes and the effective concurrent transmission of multiple nodes.The ambient backscatter communication technology is a potential technology to satisfy the low-power consumption demand of the Io Ts.Through ambient backscattering technology,the nodes can use radio frequency signals in the surrounding environment,such as Wi-Fi signals,cellular network signals,TV tower signals,etc.,to carry their own data information.During the transmission,the nodes do not need to send radio frequency signals,thus greatly saving the energy consumption of the node.In order to further support multi-node concurrent transmission to promote the development of Io Ts,an effective concurrent data transmission scheme must be designed.Considering the universality of Wi-Fi system,this thesis develops a data transmission scheme based on the backscattering communication of multiple wireless network interface cards(NICs).By integrating multiple devices with wireless NICs as nodes,the data of these devices are loaded onto the Wi-Fi signal in the surrounding environment through the backscattering of wireless network cards.These devices do not need to be connected to a network in the process.The main contribution of this thesis is as follows:(1)To facilitate data decoding for multiple nodes at the receiver,a concurrent data transmitting scheme for the backscatter communication system with multiple NIC nodes is developed.Firstly,by analyzing the variation of channel state information(CSI)when the node data is loaded on the Wi-Fi signal in the environment,a packet preamble structure is designed for packet detection and multi-node identification.Secondly,orthogonal coding is employed to encode the payload data sent by each node to assist the transmission of multi-node data.(2)Based on the transmitting scheme designed in this thesis,a corresponding receiving scheme is proposed.Firstly,the Wi-Fi CSI information is pre-processed to facilitate data decoding.Secondly,the receiving scheme detects the start time of the node data through the cross-correlation method and then detects the number and identification information of the nodes who send the data.Finally,orthogonal decoding is exploited to decode the payload sent by each node.(3)A backscatter communication system for multiple devices with NIC isimplemented based on the commercial equipment.The performance of the transmission and reception scheme proposed is then evaluated based on the system.During the evaluation,the impact of the environment condition on the system performance is first analyzed;then commercial equipment and dedicated equipment is utilized separately to test the performance of the system from the aspects of transmission rate and transmission distance;finally the performance analysis of the system under the condition of non-line-of-sight transmission and the existence of human interference is performed.