Estimation of Multiuser CFOs in OFDMA Systems

Autor: Shih-Sheng Li, 李世聖
Rok vydání: 2018
Druh dokumentu: 學位論文 ; thesis
Popis: 106
Recently, orthogonal frequency-division multiple access (OFDMA) has been widely adopted in many wireless communication standards. However, the OFDMA-based systems are sensitive to the frequency synchronization error, i.e. carrier frequency offset (CFO), which destroys the orthogonality among the subcarriers. In the uplink OFDMA systems, the received signal at the base station (BS) is composed of all active users with individual CFO. This frequency synchronization error is normally partitioned into an acquisition stage followed by a tracking stage at the BS. CFO induces both intercarrier interference (ICI) and multiple-access interference (MAI), which degrade the performance of systems significantly. Therefore, the estimation and the correction of the frequency synchronization error is a crucial and challenging topic in uplink OFDMA systems. Most existing CFO estimation methods are derived under the certain carrier assignment scheme (CAS). In the thesis, we introduce several new estimation methods that can be applied to generalized-CAS (GCAS). Both blind and pilot-aided methods are considered. In the first part, we first review on estimator using the constant-modulus (CM) constellation and then propose several blind estimations of multiple CFOs, such as virtual carrier based (VC-based), VC-CM based and kurtosis-based (KT-based) estimators. In addition, we develop a closed form solution for CFO tracking and obtain a 2-stage algorithm for the VC-based estimator. The complexity of these closed form solutions are very low. In the second part, for pilot-aided scheme, we propose a new algorithm for the joint estimation of CFO and channel response. We also incorporate the VC in the CFO estimation to further the estimation accuracy. Low complexity closed form solutions are also derived. Moreover, numerical simulations are provided to show the effectiveness of the proposed methods and to compare the performances with other existing methods.
Databáze: Networked Digital Library of Theses & Dissertations
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