Research On Low-Power Widearea Internet Of Things Energy Effective Signal

With the development of communication technology,the Internet of Things(Io T)technology is gradually growing.However,due to the limitations of node volume and battery resources in the Internet of Things,its application is severely restricted.Low-power wide-area Io T technology has appeared to solve the problem of power consumption cost and transmission distance of traditional Io T,such as NB-Io T and LoRa,which has rapidly become a new trend in the Io T technology because of its low power consumption,long distance,multi connection and other characteristics.And LoRa technology is one of research directions in low-power wide-area Io T,where special Chirp signals and linear frequency modulation are used to transmit information.In this thesis,the error performance of LoRa signal is studied in depth.First,in order to establish and verify the physical layer theoretical analysis model of LoRa technology,the physical layer of LoRa is studied.The Chirp signal is analyzed,the signal model of LoRa is introduced,and the expressions of continuous time and discrete time are derived.The physical layer model of LoRa is established,the encoding and decoding,modulation and demodulation process of LoRa are studied,and the BER performance of LoRa in Gaussian white noise is analyzed from theory and simulation.Then,in order to study the performance difference between LoRa and FSK modulation in the same system further,and the influence of the interference problem in the system model on the error performance,the power performance of LoRa system is compared and interference problem is conducted.The BER performance of LoRa signal and MFSK signal coexisting in LoRa system under AWGN channel,frequency selective channel,time selective channel and Rayleigh channel is compared.The excellent performance of LoRa signal in frequency selective channel is verified.What is more,the internal interference of LoRa signal is analyzed.And the theoretical formula of bit error rate under the same spread spectrum factor interference is derived.The interference between LoRa signal and MFSK signal is studied,it is proved that there is little interference.And the frequency offset interference of LoRa signal is analyzed,where a synchronization algorithm is proposed to reduce the interference.Finally,in order to solve the problem of LoRa maximum rate limitation and improve power efficiency,the improved schemes are proposed based on the traditional LoRa.In order to improve the data rate,a scheme that combines LoRa modulation with NPSK modulation and uses the phase information of LoRa signal to carry extra information bits is proposed,which is called LoRa-NPSK modulation.On this basis,a scheme that uses the falling slope LoRa signal to carry an extra bit of information is proposed to overcome the shortcomings of LoRa-NPSK modulation,such as the need to estimate the channel state information,which is called LoRaCD modulation.In addition,from the perspective of improving power efficiency,the traditional LoRa modulation and Turbo coding are combined,and the simulation result shows that the bit error performance of the proposed scheme performs better in different channel environments compared to the traditional LoRa.