The Design Of WCDMA Transmitter Based On DIF

Transmitter is the indispensable part of the communication system.With ever-accelerated development of the mobile communication,there have been several changes about the transmitter structure coming forth with many classical structures such as Dual Conversion,Single Conversion and Zero-IF which each communication company have been doing research on in recent years.However, following with the development of communication technology, especially the 3G technology, the previous transmitter system structures and design methods don't satisfy the requirements of the modern communication,innovations and changes in design are necessary.The paper proposes a new WCDMA digital IF structure based on software radios concept,Which process the signal with the conversion from radio frequency to digital IF and implement DIF design using FPGA.The designidea is significant to reduce system cost and raise design flexibility with the increase of performance price ratio about FPGA product.Aiming at reducing the peak-to-average ratio because of the use of modulation mode which improve utilization of frequency spectrum,It adopt IF peak clipping and improve signal peak clipping to dual peak clipping which produces better signal quality. In addition,the introduction of DPD structure combining with CRF, to a large extent, relieves the problems such as spectral re-growth and in-band distortion which is caused by nonlinear devices especially high power amplifier. DPD is also beneficial for advancing the system efficiency.The design mainly includes digit and analog RF part as follow:firstly it introduced the background and the characteristic of the 3rd Generation Mobile Communication System.Bring up the development of transmitter structure and the problem facing us according to WCDMA system structure;explain the significance of topic selection.Secondly, it discusses and analyzes the design of digit and analog RF part.In the design of digital IF, introduce the fundamental theory and knowledge of digital IF, CFR and DPD,come up with DIF structure and design every part with simulation correspondingly using Matlab.In the design of analog RF part, gives transmitting chain structure according to the analysis of system parameters,and simulate some important parameters using ADS.The last is hardware implementation and test results which include issues such as impedance matching and electromagnetic compatibility;test four important parameters with main performance index ACLR reaching to-60dBc at 5MHz and EVM reaching to 11.5.The test results proved that the transmitter meets the demand of 3GPP with good stability and performance.