| With the development of information technology,all kinds of emerging real-time interactive services are increasingly demanding communication networks in terms of bandwidth,speed,and access flexibility.Therefore,the communication network is developing in the direction of broadband and wireless.WDM-RoF combines the characteristics of flexible access in wireless communication with that of optical fiber communication in wide bandwidth,high immunity to interference.It has become one of the hot technologies in the field of wireless broadband transmission.WDM-RoF uses optical fiber as a carrier for RF signals,it can provide long-distance wireless signal access for distributed terminals while providing secure and reliable broadband transmission conditions for data.In addition9the terminal base station of WDM-RoF only needs to be responsible for the photoelectric signal conversion and the radiation receiving task of the signal.Therefore,it is simple in structure,small in size,low in cost.It can provide ubiquitous signal coverage for a wide range of terminals.WDM-RoF has great research and application prospects in an environment with wide geographical distribution and poor communication conditions.As a big agricultural country,the rise of the IoT provides opportunities for the modernization of agriculture.Currently,the methods of information transmission in agriculture mainly involve wireless access technologies such as WIFI,ZigBee,Bluetooth,NB-IoT,LoRa and so on.These wireless access technologies face some limitations when used alone.For example,the transmission rate is low,the communication distance is short,the security is low,and the cost of establishing a base station is high.This thesis uses the technology of WDM-RoF to solve the problems of wide distribution of equipment,incomplete signal coverage and large data communication in the Agricultural Internet of Things.The research content of this thesis mainly involves four aspects:First,the thesis studies WDM-RoF from the aspects of working principle,key device selection and performance parameter indicators.The thesis details the gain,noise figure,nonlinear distortion and dynamic range,which affect the performance of the system.The thesis points out the importance of dynamic range in system performance evaluation by analyzing the three nonlinear distortion states in the link.Second,the thesis has completed the hardware design of the optical transceiver module working in the 2.4GHz band by analyzing the working principle of WDM-RoF in the Agricultural IoT and combining with the requirements of parameter indicators.In addition,the thesis conducts experimental tests on parameters such as gain and standing wave ratio of the optical transceiver module by building the test link.Experimental results shows that the optical transceiver module reaches normal use conditions.Third,in this thesis,we build a complete WDM-RoF test link in the form of Bus Network Topology from the perspective of reducing wiring costs and being easy to expand.We have completed testing the parameters of the entire link OIP3,SFDR,EVM,etc.The system shows Spurious Free Dynamic Range is 111.9dB-Hz2/3,which has practical application conditions.Fourth,in order to verify the applicability of WDM-RoF link in Agricultural IoT,this thesis deploys the complete network transmission link to the actual application environment.In the application layer of the IoT,we develop an Android-based terminal monitoring software.The distributed terminals can transmit the data to the control center by using the signal of the 2.4 GHz band.At the same time,the control center can also realize the functions of graphic display and remote control of the terminal.In addition,the good performance of the WDM-RoF was confirmed by testing the signal uplink and downlink throughput. |
