Research On Wireless Communication Technology For Power Internet Of Things

The Internet of Things(IoT) can be applied to the power systems to improve its automation,informatization,and intelligentization,which is referred to the power internet of things(PIo T).In PIo T,the reliable data transmission is required at a low signal-to-noise ratio(SNR).Moreover,the number of terminals in PIo T will increase rapidly,therefore a high throughput is also essential for PIo T.IEEE 802.15.4g standard is specially suitable for smart metering which is of the large-scale process control application with the demands of low complexity,and low power consumption.At present,the State Grid is researching the wireless communication techniques for PIo T based on the orthogonal frequency division multiplexing(OFDM).Therefore,this thesis refers the IEEE 802.15.4g standard and then addresses the problems of the wireless communications in PIo T.The main contributions of the thesis are as follows:1.Firstly,a transceiver simulation platform is built based on IEEE 802.15.4g MR-OFDM physical layer.Then,the traditional synchronization scheme is simulated and compared.The synchronization scheme includes the coarse symbol estimation,the coarse fractional frequency offset estimation,the integer frequency offset estimation,the fine symbol estimation,and the fine fractional frequency offset estimation.However,the traditional synchronization scheme has low accuracy of the frequency offset estimation,which results in a high SNR requirement for the reliable transmission.To solve this problem,an improved frame synchronization header and the corresponding synchronization scheme are proposed.Simulation results show that the proposed scheme can improve the synchronization performance and ensure the reliable transmission at low SNR.2.For the IEEE 802.15.4g wireless communication network,the traditional grouping method for the hidden-node problem is explored.To address the issue of the high computational complexity of the grouping method for the hidden-node problem,a low-complexity grouping method is proposed.In this method,the independent guarantee time slots(GTS)are allocated to the nodes with high collision probability in order to reduce the collision probability.A simulation platform is built on NS3 software,and the simulation results show that the proposed method can effectively improve the throughput of the network.3.To further solve the hidden-node problem in the MAC stage,a method is proposed to optimize the backoff exponent(BE)in CSMA/CA protocol based on the priority.At the beginning,the collision probabilities of the nodes are calculated by collecting the hidden relationshipand the physical distance between a node and the coordinator.Then,the priorities of the nodes are assigned according to the collision probability.Finally,the BE is optimized according to the node priority.In this method,the node with high collision probability has high priority to access the network,which can reduce the collision probability and the retransmissions of data frames.Simulation results show that the proposed method improves the network throughput by 21% compared to the original CSMA/CA protocol,and also reduces the time delay of the end-to-end.