This paper addresses problems related to time and frequency synchronization as well as blind CP (cyclic prefix) type identification in 3GPP LTE system. We start with a general framework based on maximum likelihood (ML) parameter estimation. Then, simplified practical algorithms for estimating time and frequency offset as well as blind CP length are described. Finally, a robust hierarchical scheme is proposed. Specifically, the CP based lagged auto-correlation is first employed to identify the CP type, estimate the carrier frequency offset (CFO), and grossly determine the symbol timing, and then the pilot (i.e. the LTE primary synchronization signal) based cross-correlation is used to more accurately determine the symbol and frame timing. A solution is given to the problem with unequal-length symbols, such as the symbols with the normal CP specified in the LTE. The proposed hierarchical scheme has both low complexity and high accuracy and can be realized without hardware support.
