Link Level Simulation Of The LTE-A System And Study On Its Key Technologies

From 2G to 3G, to 3.9G(LTE namely), then to 4G (LTE-A)now, wireless communication technology has experienced great development on the way from theory to practical application, and continues to be mature. In which process, proving and developing the communication technology theoretically by simulation is an integral part. In this paper, the link layer of the LTE-A system is simulated, and its key technologies are studied and improved.Firstly, this paper introduces the process of development of LTE/LTE-Advance, studies the key technology of LTE/LTE-Advance in view of the characteristics of link level simulation, which contain MIMO technology, OFDM technology, design principle of downlink/uplink physical layer. As the simulation using an open loop scheme, this paper studies several common channel models in communication system, compares the different channel characteristics, and gives an appropriate channel model scheme for the simulation.This paper presents an improved algorithm for suppressing the peak to average power ratio of DFT-S-OFDM signals based on STR algorithm. The SC-FDMA technology used in the uplink physical layer makes the single carrier signal have the orthogonality among all subcarriers, just like the multi-carriers signal, which can satisfy the needs of multiple users, and make the uplink and downlink transmission share a lot of common parameters. DFT-S-OFDM technology generate SC-FDMA signal in frequency domain ueing a simple DFT transform, which simplifies implementation complexity of LTE system. However, DFT-S-OFDM technology makes signal peak average power ratio of SC-FDMA signal increased significantly, thereby reducing the power amplifier's efficiency of user equipment. To solve this problem, this paper gives an improved algorithm to inhibit peak to average power ratio of dft-s-ofdm signal and verifies the performance of the improved algorithm through simulation software. Then the improved algorithm is applied to simulate the link level transmission in physical layer. The platform is constructed using software MATLAB and processes signal follows the 3GPP protcols. Using the platform, this paper studies the performance of the optimized DFT-S-OFDM technology in different channel scenarios (including AWGN, EPA) and using different modulation coding mode (MCS).A link level simulation scheme for downlink transmission in TD-LTE system is presented in this paper. FDD-LTE system and TD-LTE system process signal of uplink physical layer in a same way, which is based on the technology of SC-FDMA.But these two systems act differently in downlink, the FDD-LTE system precode downlink signal according to precode book, while the TD-LTE system's downlink precoding scheme is beamforming. Because frame structure embodies the characteristics of TD-LTE system best, this paper studies the frame structure of TD-LTE system and give the appropriate simulation scheme, which simulate TD-LTE system by transmitting uplink and downlink data in a half-duplex manner.This paper uses software MATLAB to build the physical layer transmission simulation platform and study the performance of LTE system's beamforming technology using differrnt MCS in AWGN and EPA channel.This paper reduces the physical layer abstraction technique (L2S interface)'s prediction error of BLER by improving the L2S scheme based on RBIR algorithm. Classical RBIR algorithm calculates the average RBIR and gets the effective signal-to-noise ratio by query SENR-RBIR mapping table, and then predicts the system-level BLER by querying the referential SINR-BLER curves of AWGN channel. In order to reduce interpolation error produced by the query steps, the improved L2S scheme merges the above two-step into one step. By a mass of simulations, the good performance of the improved scheme is verified. Finally, this paper uses the improved L2S method analyzes the link simulation results and verified the validity and correctness of the L2S algorithm, in other words, use the L2S interface technology, system level BLER performance can be predicted by link level simulation.