Design And Implementation Of Digital Intermediate Frequency In TD-LTE Trunking Communication System

Trunked communication is a wireless mobile communication system that implements a multi-user shared channel in a manner of dynamic channel assignment.With the continuous improvement of the degree of social informatization,the demand for broadband services in trunking communication has further increased,from traditional voice and low-speed data transmission services to the need to provide video transmission,and with requirements of lower network delay in network performance.As 4G and 5G standard,LTE has the advantages of higher spectral efficiency,higher data rate,and lower latency,making LTE-based broadband trunked communication the development direction of broadband trunked communication.Compared with FD-LTE,TD-LTE has a unique advantage for the transmission of asymmetric services.As an important part of software radio,digital intermediate frequency has the characteristics of high flexibility,wide linear dynamic range,lower drift,lower distortion,shorter development cycle and lower cost compared with traditional analog intermediate frequency.FPGA has the advantages of powerful parallel computing power,rich on-chip resources,flexible development methods,etc.It is the mainstream implementation method of digital intermediate frequency.This paper firstly carried out detailed theoretical and simulation analysis of the digital intermediate frequency system.Firstly,according to the 3GPP protocol specifications and project requirements,the design requirements of the digital intermediate frequency are proposed.For the key filter module design,considering the resource consumption,computational complexity and simulation link performance,the advantages and disadvantages of four different filter design schemes are compared and analyzed.The root raised cosine filter and the half-band filter are selected.A cascaded scheme is used to perform sample rate conversion and filtering processing.Secondly,according to the relevant interface protocols,this paper writes an interface module for the SRIO interface,Aurora interface,ADC/DAC interface and SPI interface involved in the system,realizes the interface data transmission,and verifies the interface performance through the respective interface test links;Finally,the modular design of digital intermediate frequency is completed in Vivado,and the performance of the digital intermediate frequency module in the system can be verified by the 16QAM-OFDM link.The DSP,baseband FPGA and intermediate frequency FPGA are used as data processing units and related interfaces.The test link of the TD-LTE trunked communication testing system is formed,and the link performance is verified by the picture service transmission.