Research and implementation of the digital intermediate frequency in LTE superheterodyne transmitter

Abstract

Digital IF (Intermediate Frequency) is an indispensable key technology in modern communication, among which digital up converter (DUC) and digital down converter (DDC) are important parts between baseband and IF. In this paper, we give a general method and solution of designing digital IF to meet the demands of practical application. Firstly, we analyze the theories and technologies of digital IF including filter bank and DUC. Secondly, we set about analyzing how to design filter bank in key part and implement a superheterodyne. Finally, we put forward a specific design plan of DUC and develop a digital IF suitable for TDD-LTE (Time Division Long Term Evolution) system. The results of simulation show that our design method of DUC can satisfy the requirements of relevant indicators. It has been implemented on FPGA platform in a practical LTE based transmitter.