Pilot-based joint ML estimation of timing offset, CFO and channel for OFDMA uplink using minimum residue decomposition technique

This paper addresses the challenging issue of joint maximum-likelihood estimation of carrier frequency offset, timing offset and channel response for orthogonal frequency division multiple access (OFDMA) uplink transmissions. A pilot preamble based approach is proposed that makes use of the concept of signal decomposition. Earlier works have demonstrated that it is possible to decompose the multidimensional optimization involved in this joint estimation problem into a series of one-dimensional searches. However, the computational complexity involved with such methods is also very high. In this work, we propose a new signal decomposition method based on a minimum residue criterion. The method with appropriate signal structures provides a computationally-efficient solution for the joint estimation of all required parameters of all users at the base station in an OFDMA link, leading to energy-efficient system design. Another advantage of the proposed technique is that it offers the flexibility of application to OFDMA systems with any subcarrier assignment scheme. Performance advantages of the proposed estimation method are substantiated through extensive computer simulation studies and are compared with that of some important recently-developed algorithms for the problem. Proof of convergence of the new estimation algorithm is also illustrated.