A novel joint ML technique for estimation of timing, CFO and channel in OFDMA uplink

In this paper, we propose a joint maximum-likelihood (ML) estimation method for determining the carrier frequency offset (CFO), timing offset and channel response for all active users in an OFDMA uplink. The method is pilot preamble-based and it makes use of the concept of signal decomposition. The problem, due to its multidimensional and multiparameter nature is computationally complex. One approach to reduce the computational complexity of this joint estimation problem is to break it into a series of one-dimensional searches. However, the computational complexity involved with such methods is also very high. In this work, we develop a new signal decomposition method denoted as MRD and propose a computationally efficient technique for the joint estimation of all required parameters at the base station of an OFDMA link. It achieves very good performance with significantly lesser computational load as compared to state-of-the-art techniques reported in the literature. Also, it offers flexibility of application to all subcarrier assignment schemes used in OFDMA systems. Performance advantages of the proposed estimation method are corroborated by means of extensive computer simulation studies.