On parameter estimation of MIMO flat-fading channels with frequency offsets
IEEE Transactions on Signal Processing
Zero-forcing methods for downlink spatial multiplexing in multiuser MIMO channels
IEEE Transactions on Signal Processing
Iterative multiuser uplink and downlink beamforming under SINR constraints
IEEE Transactions on Signal Processing
MIMO transmission over a time-varying channel using SVD
IEEE Transactions on Wireless Communications
IEEE Transactions on Wireless Communications
Transmit beamforming and power control for cellular wireless systems
IEEE Journal on Selected Areas in Communications
Improved transmit steering for MIMO-OFDM downlinks with distributed base station antenna arrays
IEEE Journal on Selected Areas in Communications
On the optimality of multiantenna broadcast scheduling using zero-forcing beamforming
IEEE Journal on Selected Areas in Communications
Multiple Frequency Offset Estimation for the Downlink of Coordinated MIMO Systems
IEEE Journal on Selected Areas in Communications
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We consider a coordinated multi-cell (CMC) system and the associated problem of independent carrier frequency offsets (CFOs) at the basestations (BSs). These BS CFOs cause accumulated phase errors that compromise downlink beamforming accuracy, and consequently degrade the spectral efficiency of the CMC system. Since the inherent structure of coordinated downlink beamforming techniques makes it impossible to correct for the BS CFOs at the mobile subscriber (MS), our topic is estimation and correction of the BS CFOs at the BSs. Our method begins with the formation of MS-side estimates of the BS CFOs, which are then fed back to the coordinated BSs. We then derive an optimum maximum likelihood (ML) estimator for the BS CFOs that uses independent MS-side CFO estimates and average channel signal-to-noise ratios. However, it is demonstrated that the CFOs of the MSs themselves introduce a bias to the optimal BS CFO estimator. To compensate for this bias, a joint BS and MS CFO estimator is derived, but shown both to require high computation and have rank deficiency. This motivates an improved technique that removes the rank problem and employs successive estimation to reduce computation. It is demonstrated to overcome the MS CFO bias and efficiently solve the joint BS and MS CFO problem in systems that have low to moderate shadowing. We term the full BS CFO estimation and correction procedure "BS CFO tightening."