Robust uplink carrier frequency offset estimation with interference mitigation in OFDMA systems

In orthogonal frequency-division multiplexing access (OFDMA) systems, multiple-user-interference (MUI) between different subscribers due to their non-zero carrier frequency offsets may deteriorate their BER performance greatly. Instantaneously large carrier frequency offset of one subscriber will contribute a heavy interference to its frequency-domain neighbors. MUI not only reduces the effective signal-to-interference-plus-noise ratio (SINR), but sometimes introduces a bias to carrier frequency offset estimators of each subscriber. In this paper, uplink carrier frequency offset estimation in OFDMA systems is discussed. The estimation accuracy of one estimator benefits from an effective MUI elimination/reduction. In the following sections, after analyzing the negative effect of MUI on uplink carrier frequency offset estimation, we will give out some interference reduction/elimination methods in OFDMA systems. Cramer-Rao lower bound (CRLB) for an unbiased carrier frequency offset estimator in a Multi-Access (MA) system is derived in this paper. A new training sequence group named round-robin training sequence group (RRTSG), is also proposed to perform uplink synchronization. It outperforms conventional training sequences with respect to higher interference mitigation/reduction capability