Research And Hardware Implementation Of Initial Synchronization System For Dual-mode Internet-of-Things

Internet-of-Things(IoT)is one of the most important extensions of the Internet in the 21st century.As a bridge of terminals to terminals and terminals to servers,IoT wireless communication technology has also flourished in recent years.With the maturity of the market,IoT wireless communication technologies are divided into two categories:low-power personal area networks and low-power wide area networks.A dual-mode IoT communication system that combines the advantages of two types of technical has also been developed and applied.Initial synchronization,as the basis for the establishment of communication links,has always been the focus of scholars'research.The efficient initial synchronization scheme not only shortens the communication link setup time,but also reduces the bit error rate and reduces retransmissions,thus meeting the low-power IoT requirements.This dissertation explores and studies the initial synchronization problem in a dual-mode IoT baseband system based on NarrowBand Internet-of-Things(NB-IoT)and Bluetooth Low Energy(BLE).Based on the technical characteristics of NB-IoT and BLE,this dissertation analyzes the current research status and finds that there are still some technical problems to be solved or improved in the initial synchronization scheme:1)When NB-IoT works under extended coverage,the low signal-to-noise ratio(SNR)results in low synchronization signals utilization rate,and the initial synchronization window accounts for an excessive proportion of the entire communication process,which is not conducive to low power consumption of the system;2)The time domain joint initial synchronization scheme can effectively improve the detection probability and reduce the false alarm probability;3)The initial synchronization scheme applicable to BLE in the current literature lacks considerations for the BLE protocol and application characteristics,so there is room for improvement in the synchronization algorithm and implementation scheme.Based on this,the initial synchronization schemes of NB-IoT and BLE are studied and implemented,and the dual-mode baseband system is improved and simulated.In order to solve the problem that the detection window is too long due to the low utilization rate of NB-IoT synchronization signals,this dissertation proposes a time detection cost function that can eliminate the fractional frequency offset in advance by analyzing the usage limitation of the current schemes in the NB-IoT scenarios.At the same time,noise power estimation is used to reduce the performance degradation of the cost function in low SNR scenarios.In order to further ensure the performance of synchronous detection,this dissertation adopts a double thresholds decision scheme to improve the detection probability and reduce the false alarm probability.The simulation results show that the joint initial synchronization scheme proposed in this dissertation can meet the NB-IoT system requirements in terms of synchronization accuracy,and the number of radio frames required to achieve 95%detection probability is also less than that in the current literature.In order to reduce the power consumption of BLE terminal and extend the battery life,the baseband system and its initial synchronization schemes which are suitable for BLE in the current literature are studied and analyzed.By considering the structure of BLE packet and the characteristics of burst transmission jointly,the start of burst detection,time synchronization and carrier frequency offset synchronization schemes are presented.The main feature is to achieve the purpose of estimating the initial deviation and fast convergence by efficiently multiplexing the preamble,thereby effectively reducing the bit error rate.Besides,a Kalman filter based fine frequency offset estimation and tracking scheme is proposed,and the recovery method combining feedforward and feedback is adopted to reduce the influence of frequency offset on the decision result.The simulation results further demonstrate the effectiveness of the proposed synchronization scheme.The hardware implementation of the initial synchronization system for NB-IoT and BLE is carried out.The implementation scheme is clarified by describing the core functional modules,and the hardware resource consumption is evaluated by the field programmable gate array and its development kit.In order to further verify the validity of the proposed synchronization scheme and provide the basis for the feasibility of the dual-mode baseband system implementation,the complete NB-IoT and BLE transceiver baseband links are simulated at the end of this dissertation.In addition,in order to improve the link performance,a low computational cell identity search scheme and a maximum likelihood based frequency offset tracking scheme are proposed for NB-IoT.A soft decision is proposed for BLE that can effectively suppress the inter-symbol interference introduced by Gaussian filtering.In order to fully explain the performance of the baseband link,by setting multiple sets of simulation scenarios,the degree of influence of various errors and interference factors on performance is visually displayed.