On The TDD-LTE Downlink Signal Generator And Synchronization Techniques

Because of its capability in supporting high rate of data transmission, high bandwidth efficiency and resistance to multipath fading, Orthogonal Frequency Division Multiplexing (OFDM) plays a critical role in the LTE system, However, OFDM technique is sensitive to timing and frequency offset. Incorrect timing synchronization between transmitter and receiver, which means an wrong frame starting position, will cause Inter-Symbol Interference (ISI);While incomplete frequency offset compensation will give rise to Inter-Carrier Interference owing to the destroy in the orthogonality among subcarriers, which will degrade the transmission reliability. So how to reduce or even completely eliminate the timing and the frequency offset will be critical for us to exploit the full advantages of the OFDM technology.Based on the36.211and36.212technical specifications, TDD-LTE downlink baseband signal generator was built up by using C++and C#. to realize the signal generated by the Physical Downlink Shared Channel (PDSCH), Physical Broadcast Channel (PBCH), Physical Multicast Channel (PMCH), Physical Control Format Indicator Channel (PCFICH). Physical Downlink Control Channel (PDCCH), as well as the Physical Hybrid ARQ Indicator Channel (PHICH). For each physical channel, the complete processing steps, such as the scrambling, modulation, layer mapping, precoding, antenna port mapping, and the OFDM modulation are included to provide the platform and basis for the the key enabling technologies in TDD-LTE system, especially the downlink OFDM time synchronization and frequency synchronization, which is another focus of this thesis.After a brief introduction of the existing timing synchronization and frequency synchronization algorithms for OFDM system, simulations are performed to validate the achieved synchronization performance, thus to highlight their advantages and disadvantages. After that, the thesis proposed a modified Primary Synchronization Sequence(PSS) design to exploit the inherent symmetric properties in the original PSS sequence. Simulations are presented to corroborate that, the sliding window correlation based timing synchronization by employing the modified PSS provides an effective timing synchronization and frequency choice for TDD-LTE system with minor revision and low implementation complexity.Moreover, previous synchronization research on the synchronization problem for OFDM system seldom consider the joint timing synchronization and frequency synchronization implementation of OFDM system in TDD-LTE system. This thesis analyzed the achieved joint timing synchronization and frequency synchronization performance through simulations. It is shown that the joint timing and frequency synchronization by using the proposed modified PSS provides a reasonable joint synchronization implementation with lower computational complexity, while maintaining the integrity of the frame structure of the original TDD-LTE system.