Simulation And Implementation Of 3GPP-LTE Downlink

To compete against Mobile Broadband Wireless Access technologies, such as WIMAX, and with the specific aim of'evolving'the 3GPP radio access technology to ensure competitiveness over a 10-year time-frame, the 3GPP organization started the Long Term Evolution (LTE) project of UMTS in 2004. As more and more operators and manufacturers choose LTE system as the future evolution of network, LTE will become the next mainstream wireless communication system technology. The world's first commercial LTE network has started to provide services in the Nordic, and LTE is being deployed by main mobile operators of the world, LTE will be used on a large scale in the future.LTE adopted the OFDM transmission technology, canceled the important element location-Radio Network Controller (RNC), and also included the Evolved Packet System (EPS). LTE defined two modes: TDD and FDD, the former is supported by China Mobile that uses TD-SCDMA and the latter is supported by most telecom operators that use WCDMA or cdma2000. These two modes have their own advantages and complementary, so they could be used together on a single system platform in the future.The topic of this paper comes from National Research Program on Key Basic Research Project (973 Program)-'The fundamental theory and key technologies of cognitive radio networks', Grant No.2009CB320407. The main work is based on the technical specification of 3GPP LTE Release8. In this thesis, we designed the link level simulation platform of LTE downlink, evaluated the platform from functionality and performance verification, and realized the model on TI DSP.This thesis is divided into five parts. In the first part, the thesis summarized the development of mobile communications and the current research situation, introduced the key technology of LTE and Cognitive Radio. In the second part, several kinds of wireless channel characteristics and models are introduced, then the downlink baseband signal process is investigated including CRC calculation, Channel coding, Rate matching, Code block concatenation, Resource mapping. The third part focuses on the OFDM channel estimation which is based on pilot involving LS and MMSE algorithm, and also some interpolation algorithm. In the fourth part of this thesis, two decoding algorithms (SOVA and Log-Map) based on Turbo codes are researched, and the impact of some parameters to the Turbo decoding performance is also researched. At last, considering the simulation conclusion and complexity of hardware implementation, a link level design is implemented on a DSP platform, and the influence of the fixed-point data bit width to the decoding performance under optimal zoom factorλis discussed through the theoretical analysis and simulation.