Study And Implementation Of LTE Downlink Shared Channel Based On DSP

LTE shared channel which uses OFDM modulation and Turbo channel compiler can effectively against frequency selective fading channel and has high transmission efficiency. Channel estimation and channel decoding technology are the key technologies of LTE systems. This paper mainly studies PDSCH channel estimation algorithm and Turbo channel decoding implementations.Firstly, the method of the PDSCH data processing is studied, and then complete simulation platform of PDSCH communication link is built according to the protocol of LTE. The performance of PDSCH is simulated under various LTE channel models.Then, a variety of channel estimation methods are studied according to the pilot pattern in PDSCH. In frequency domain, the least-squares (LS) and the minimum mean square error (MMSE) algorithms are analysised and compared. In the transform domain, algorithms based on DFT, DCT and PSE-DFT are focused. Simulation results shows that, the algorithm of PSE-DFT has better estimation performance compared to that of LS, MMSE algorithm, and can eliminate the performance floor phenomenon, with computational complexity.Next, segmented Turbo channel decoding algorithm is studied. It is based on the weighted Max-Log-Map algorithm, and combined with dedicated DSP processing unit. Sliding training window decoder structure is used in the algorithm to improve the decoding parallel processing capability and reduce memory size needed. Simulation results show that segment turbo decoding can reduce decode processing time while maintaining the performance.Finally, the Turbo decoder implemented on the software platform (SB3500) is studied and in detail described. After evaluated performance of different quantization level, the scaling value in Turbo decoding processing is determined. The implementation structure of Turbo encoding and decoding are determined by the characteristics of SB3500 and the performance of Turbo decoding is tested.