Fundamentals of statistical signal processing: estimation theory
Fundamentals of statistical signal processing: estimation theory
Maximum Likelihood Estimation of Compound-Gaussian Clutter and Target Parameters
IEEE Transactions on Signal Processing
A robust timing and frequency synchronization for OFDM systems
IEEE Transactions on Wireless Communications
Time and Frequency Synchronization for OFDMA Uplink System using the SAGE Algorithm
IEEE Transactions on Wireless Communications
Robust frequency synchronization for OFDM-based cognitive radio systems
IEEE Transactions on Wireless Communications - Part 2
WiMAX femtocells: a perspective on network architecture, capacity, and coverage
IEEE Communications Magazine
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
IEEE Journal on Selected Areas in Communications
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Spectrum sharing employs dynamic allocation of frequency resources for a more efficient use of the radio spectrum. Despite its appealing features, this technology inevitably complicates the synchronization task, which must be accomplished in an environment that may involve interference. This paper considers the uplink of an orthogonal frequency-division multiple-access (OFDMA)-based spectrum sharing system and provides solutions for estimating the frequency and timing errors of multiple unsynchronized users. In doing so, we exploit suitably designed training blocks and apply maximum likelihood methods after modeling the interference power on each subcarrier as a random variable with an inverse gamma distribution. The resulting frequency estimator turns out to be the extension to a multiuser scenario of a scheme that has previously been proposed for single-user spectrum-sharing systems. Timing recovery is more challenging and leads to a complete search over a multidimensional domain. To overcome such a difficulty, two alternative approaches are proposed. The first one relies on a simplifying assumption about the interference distribution in the frequency domain, while the second scheme operates in an iterative fashion according to the expectation-maximization algorithm.