Synchronization and cell identification schemes in wireless OFDM systems

Abstract

Reliable cell ID acquisition is the most important prerequisite for the realization of higher data rate and lower latency in OFDM-based cellular networks. The cell ID acquisition process is comprised of timing and frequency synchronization followed by cell identification. It is well known that the OFDM system is very sensitive to both timing and frequency offsets, and uncompensated offsets can degrade overall performance of system substantially. In order to achieve accurate timing and frequency synchronization and reliable cell identification, we propose estimation methods for timing and frequency offsets, and detection algorithm for cell ID acquisition.

For timing synchronization, we propose two-step frame timing (FT) estimation algorithms;coarse and fine FT estimations. Both methods exploit unique structural property of transmitted preambles, where the coarse FT estimation uses autocorrelation property while the fine FT estimation utilizes the statistical property of symmetric correlator. Both schemes improve the FT estimation accuracy significantly compared with the conventional approaches. Furthermore, they are invulnerable to a frequency offset, and does not require a prior information such as SNR and channel statistics.

In the context of the frequency offset estimation, we first decompose the frequency offset into a fractional part (FFO) and an integer part (IFO) to improve the estimation accuracy. Based on the same autocorrelation property of the preamble, then, FFO estimator is devised, and the corresponding Cramer-Rao bound is obtained. Since in reality perfect timing synchronization is difficult to achieve especially for very low SNR region, which is common in cellular system, we propose a joint IFO and residual timing offset (RTO) estimation method to achieve accurate IFO estimation in the presence of residual timing offset. The proposed IFO and RTO estimator has a full acquisition range of IFO, while exhibiting robustness against even a large RTO...