Key Transmission Technology Research In The Lte System

Single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA) have been chosen as major candidate techniques for future mobile communication system and adopted as the uplink and downlink physical layer multiple access techniques respectively in the Long Term Evolution (LTE) of cellular systems because of its high spectrum efficiency and ability to resist frequency selective fading.However, for downlink OFDMA system and uplink SC-FDMA system exploiting localized subcarrier mapping scheme, the transmitted signals are sums of multiple carrier signals and have high peak-to-average power ratio (PAPR), requiring a large linear dynamic range of amplifiers in the transmitter. Secondly, the uplink SC-FDMA belongs to single carrier system and needs to insert cyclic prefix (CP) redundancy in front of each frame when combined with single carrier frequency domain equalization (SC-FDE) system, which reduces the spectrum efficiency. Besides, how to make full use of the spatial and frequency diversities so as to make a better tradeoff between transmission performance and computational complexity is a great issue for the equalizer design over multiple-input multiple-output (MIMO) channel in LTE system. This dissertation works for above-mentioned problems in key transmission techniques of LTE system.Chapter 1 introduces the principles and system models of OFDMA and SC-FDMA techniques and analyzes the merits and demerits, which shows the importance of the researches on PAPR reduction, cyclic prefix (CP) reduction and equalizers over MIMO channel.Chapter 2 studies the PAPR reduction techniques based on peak cancellation in LTE downlink system. The bit error rate (BER) performances for different modulation schemes in peak cancelled OFDM systems are given and evaluated.Chapter 3 investigates the PAPR characteristic and efficiency optimization in LTE uplink system. On one hand, the PAPR characteristic of SC-FDMA signals is analyzed, providing theoretical basis for system optimization. On the other hand, a novel SC-FDE structure is proposed, which reduces the CP in the transmitter, leading to higher spectrum efficiency.Chapter 4 investigates FDEs over MIMO Channel in LTE uplink and downlink systems and presents detailed analysis and simulations of the principles, system models, computational complexity and BER performance for various algorithms, providing the theoretical basis for the selection of proper FDEs.Chapter 5 concludes this dissertation and discusses the possible future research directions of transmission techniques in LTE system.