Low complexity channel estimation in TDD coordinated multi-point transmission systems

Coordinated multi-point transmission (CoMP) is a promising strategy to provide high spectral efficiency for cellular systems. To facilitate multicell precoding, downlink channel is estimated via uplink training in time division duplexing systems by exploiting channel reciprocity. Virtual subcarriers in practical orthogonal frequency division multiplexing (OFDM) systems degrade the channel estimation performance severely when discrete Fourier transform (DFT) based channel estimator is applied. Minimum mean square error (MMSE) channel estimator is able to provide superior performance, but at the cost of high complexity and more a priori information. In this paper, we propose a low complexity channel estimator for CoMP multi-antenna OFDM systems. We employ series expansion to approximate the matrix inversion in MMSE estimator as matrix multiplications. By exploiting the feature of frequency domain training sequences in prevalent systems, we show that the proposed estimator can be implemented by DFT. To reduce the required channel statistical information, we use the average channel gains instead of channel correlation matrix, which leads to minor performance loss in CoMP systems. Simulation results show that the proposed channel estimator performs closely to the MMSE estimator.