Iterative receiver with joint channel estimation and decoding in LTE downlink

In this paper, an iterative receiver using joint channel estimation and channel decoding is proposed for LTE downlink. In each iterative process, a modified LMMSE estimator is adopted to estimate the channel gain based on pilots as well as signals fed back from Turbo decoder. In contrast to a traditional LMMSE estimator, the modified estimator can make more precise channel estimation because a smaller spacing interpolation is performed with the help of feedback signals. The estimator and the decoder provide each other more accurate information in an iterative way, thus the performance of the receiver is improved. Three distribution patterns of the signals fed back from Turbo decoder with different density is compared, and the one with medium density is demonstrated to be the best by simulation results. To reduce the computational complexity of the receiver, cyclic redundancy check (CRC) is used to early stop the iteration. Simulation is done according to LTE physical layer specifications and the results show that the iterative receiver can provide about 50% accuracy improvement compared with a non-iterative receiver when SNR is 10dB. At the same time, the iterative receiver's computational complexity is in the same order of magnitude as the non-iterative receiver.