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Joint frequency offset and channel estimation in the OFDMA uplink: Cramer-Rao bounds and training sequence design

In this paper, we address the data-aided joint estimation of frequency offsets and channel coefficients in the uplink of an OFDMA scheme. For large training sequence sizes, a compact and informative expression of the Cramer-Rao bound (CRB) is derived. In particular, we show that asymptotic performance bounds for the parameters of a given user do not depend on the number of users. Moreover, it is shown that orthogonal and non-orthogonal carrier assignment schemes (CAS) both lead to the same asymptotic CRB. Finally, we bring to the fore the training sequences that are likely to lead to accurate estimates. Due to the above results, the design of the training sequence of a given user can be achieved independently from other users. Simulation results sustain our claims.