This paper addresses the problem of joint estimation of carrier frequency offset (CFO) and channel impulse response (CIR) in the uplink transmission of multicarrier code-division multiple-access (MC-CDMA) systems. A subspace-based blind estimator is proposed, which only uses the received signal and the desired user's spreading code to estimate the CFO and CIR. The CFO is estimated using a one-dimensional linear search where the objective of the search is to minimize the determinant of a low dimensional matrix and the CIR is estimated as the unit-norm eigenvector corresponding to the minimum eigenvalue of this matrix. The identifiability of the CFO and CIR estimates is investigated by imposing asymptotic constraints on the spreading codes. Although the cost function used by the proposed estimator is nonlinear and nonconvex, it is locally convex in the neighborhood of the true CFO value. This property is used to formulate a simple two-stage CFO estimator. In the first stage, a coarse search is performed to lock into the local convexity region. Then, an adaptive algorithm is used in the second stage to finetune the CFO estimate. The ldquolinearizedrdquo proposed estimator is shown to be unbiased. The simulation results show that the proposed estimator's performance is close to the Cramer-Rao lower bound (CRLB).
"The frequency offset appears due to the difference in the frequency of the local oscillators in transmitter and receiver and the Doppler shift in frequency due to motion of transmitter and/or receiver. Performance degradation due to the frequency offset has been extensively studied –, different methods have been proposed to estimate this offset – and to mitigate its effects –. In , –,  expressions for bit error rate is calculated and in  BER is found with simulation. "
[Show abstract][Hide abstract] ABSTRACT: Carrier frequency offset destroys the orthogonality between different subcarriers in multicarrier code division multiple access (CDMA) giving rise to inter-carrier interference (ICI). Taking into account accurate statistical models for the ICI, this paper presents new analytical expression for spectral efficiency of mobile multicarrier CDMA communication system. The expression is then used to estimate the spectral efficiency degradation over Rayleigh fading channels.
Communications (ICC), 2011 IEEE International Conference on; 07/2011
"The noise subspace U n contains (N − QT ) eigenvectors in U corresponding to (N − QT ) smallest eigenvalues ofˆR . This selection of spreading codes also ensures that the ACFO and CIR estimates are unique  "
[Show abstract][Hide abstract] ABSTRACT: Cyclic-prefix code division multiple access (CP-CDMA) has been shown to be effective in combating frequency selective fading channels. However, this effectiveness can be leveraged only with accurate channel impulse response (CIR) estimate and proper compensation for the carrier frequency offset (CFO). In this paper, we formulate a subspace-based joint CFO and CIR estimator without using any pilot symbols. The users' spreading codes are selected following the steps in. We show that the selected users' spreading codes must also satisfy an additional requirement in order to have the signal subspace dimension to be independent of users' CFO and CIR. For high signal to noise ratio, we show that the proposed CFO estimator is unbiased and derive the theoretical mean square error for CFO estimate. Computer simulation results show that the proposed estimator's performance is close to Cramer-Rao lower bound.
Wireless Communications and Networking Conference, 2009. WCNC 2009. IEEE; 05/2009
"Thus the users' CIR can be uniquely identified by just placing a simple rank constraint on the users' spreading codes. The above results hold even when each user transmits different number of data symbols in one MC-CDMA symbol duration, i.e., user i transmits Q i data symbols in one MC-CDMA symbol and Q 0 = Q 1 = · · · = Q T −1 . "
[Show abstract][Hide abstract] ABSTRACT: Subspace-based channel impulse response (CIR) estimators have been proposed for multi carrier code division multiple access (MC-CDMA) systems. Channel identifiability conditions have been formulated for blind (non-data-aided) CIR estimators. These identifiability conditions require the channel filtering matrix to satisfy certain rank conditions. In this paper, the generalized uplink MC-CDMA system model is analyzed in detail. It will be shown that each user's signal subspace dimensionality is independent of the user's spreading code and CIR. Furthermore, for any realization of the users' CIR, the channel identifiability is established by only imposing a simple rank condition on the users' spreading codes.
Communications, 2008. ICC '08. IEEE International Conference on; 06/2008
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