Carrier Frequency Synchronization in OFDM-Downlink LTE Systems

Higher the data rates and spectrum efficiency of wireless mobile communications have been significantly improved over the last decade, such as 3GPP Long-Term Evolution (LTE) and terrestrial digital TV broadcasting which are sophisticatedly developed using OFDM. Orthogonal frequency division multiplexing (OFDM) is a modulation technique that achieves high data rates, increased bandwidth efficiency and robustness in multipath environments. However, OFDM has some disadvantages, such as sensitivity to channel fading, large peak to average ratio and sensitivity to frequency offset. The latter causes inter carrier interference (ICI) and a reduction in the amplitude of the desired subcarrier which results in loss of orthogonality. In this paper, the effects of frequency offset are studied in terms of loss of orthogonality. The main goals of this paper is to understand the effects of frequency offset on OFDM systems and to present frequency offset estimation techniques so that we can correct for their effects. The performance of each technique is compared under various conditions. The performance of the estimators is presented in terms of the mean square error (MSE) and Signals to noise ratio (SNR). In this paper, we investigate carrier frequency synchronization in the downlink of 3GPP Long Term Evolution (LTE). A complete carrier frequency offset estimation and compensation scheme based on standardized synchronization signals and reference symbols is presented. The estimation performance in terms of mean square error is derived analytically and compared to simulation results.