Low complexity pilot aided frequency synchronization for OFDMA uplink transmission
IEEE Transactions on Wireless Communications
IEEE Transactions on Signal Processing
ML estimation of time and frequency offset in OFDM systems
IEEE Transactions on Signal Processing
IEEE Transactions on Wireless Communications
A time and frequency synchronization scheme for multiuser OFDM
IEEE Journal on Selected Areas in Communications
Channel-independent synchronization of orthogonal frequency division multiple access systems
IEEE Journal on Selected Areas in Communications
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The IEEE 802.16e standard for nomadic wireless metropolitan area networks adopts orthogonal frequency-division multiple-access (OFDMA) as an air interface. In these systems, residual carrier frequency offsets (CFOs) between the uplink signals and the base station local oscillator give rise to interchannel interference (ICI) as well as multiple access interference (MAI). Accurate CFO estimation and compensation is thus necessary to avoid a serious degradation of the error-rate performance. In this work, we address the problem of CFO tracking in the IEEE 802.16e uplink and present a closed-loop solution based on the least-squares (LS) principle. In doing so, we exploit a set of pilot tones that are available in each user's subchannel. The resulting scheme can be implemented with affordable complexity and is able to reliably track the CFOs of all active users. When used in conjunction with a frequency offset compensator, it can effectively mitigate ICI and MAI, thereby allowing channel equalization and data detection to follow directly. Numerical simulations are used to demonstrate the effectiveness of the proposed solution in the presence of residual time-varying frequency offsets.