Maximum likelihood timing and carrier frequency offset estimation for OFDM systems with periodic preambles

Abstract

Timing offset (TO) and carrier frequency offset (CFO) are two common problems observed in OFDM systems. Maximum likelihood (ML) methods have been proposed for CFO estimation. The conventional ML estimates consider a pilot-assisted system, in which two identical preambles are repeatedly transmitted. In some applications, the preambles of an OFDM system are repeated more than two times. A typical example is the preambles of the EEEE802.11a/g wireless local area network (LAN) system. A ML CFO estimation method for the system was proposed recently; however, the method has to solve the roots of the derivative of the likelihood function, and the computational complexity is high. Also, the TO estimation problem is not considered. In this paper, new methods are developed for the TO and CFO estimation problems. Our method is simple and does not rely on the root-finding approach. Simulations show that while the performance of the proposed method is either equal to or better than the existing method, the computational complexity is much lower.