Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/15862
Title: Synchronization in CDMA systems
Authors: LOKESH BHEEMA THIAGARAJAN
Keywords: CIR, CFO, Subspace, Blind, Estimator, CDMA
Issue Date: 2-Apr-2009
Source: LOKESH BHEEMA THIAGARAJAN (2009-04-02). Synchronization in CDMA systems. ScholarBank@NUS Repository.
Abstract: In this thesis, a subspace-based blind (non-data-aided) joint carrier frequency offset (CFO) and channel impulse response (CIR) estimator is proposed for uplink carrier frequency synchronization and channel estimation in direct-sequence code division multiple access (DS-CDMA), cyclic-prefix CDMA (CP-CDMA) and multi-carrier CDMA (MC-CDMA) systems. The proposed estimator is formulated by exploiting the orthogonality between the signal and noise subspaces.The noise subspace used by the estimator is estimated from the received signal. Using the knowledge of the user's spreading code, the signal subspace for the desired user is obtained as a function of CFO and CIR parameters. Through matrix manipulations, the orthogonality between the signal and the noise subspaces can be expressed as a set of L linear equations equated to zero, where L denotes the length of CIR. In other words, if the CFO variable is equal to the user's true CFO value, then the desired user's CIR lies in the null space of a (L X L) positive semi-definite matrix. This (L X L) matrix is a function of CFO, noise subspace and desired user's spreading code. The determinant of the above (L X L) matrix is zero only when the CFO variable is equal to the desired user's true CFO value. Due to the presence of noise and use of finite precision, the determinant is not exactly zero at the desired user's true CFO value. By performing a one dimensional grid search for the CFO variable, the search point which minimizes the determinant of the above defined matrix is taken as the user's estimated CFO value. The CIR is estimated as the eigenvector associated with the minimum eigenvalue of the (L X L) matrix corresponding to the estimated CFO value.
URI: http://scholarbank.nus.edu.sg/handle/10635/15862
Appears in Collections:Ph.D Theses (Open)

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