Abstract
Very large multiple-input multiple-output (MIMO) technology has a potential of significantly improving the system performance of multi-cell time-division duplexing (TDD) networks, but in practice it is limited by pilot contamination. Different from the traditional channel estimation mean square error (MSE) expressions, the expressions that we derived have algebraic form, which no longer need hard matrix inversion as M, the number of the base station (BS) antennas, increasing. From them, we also found that the average transmitted power and length of training sequence almost does not help in enhancing the performance of MSE as \(M\rightarrow \infty \). Based on this, two pilot contamination reduction methods for the very large MIMO multi-cell TDD system were proposed. One is realized by grouping all the cells into two categories, using orthogonal pilots between these two types of cells or aligning the uplink pilot time slot of the cells in one category with the downlink data time slot of those cells in the neighboring categories. The other is to find the optimal division of pilot sequence length and the set of all users’s pilot transmission slots allocation through BSs’s coordination. The effectiveness of our proposed methods are verified via both theoretical analysis and numerical results.











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Notes
If \(L=3\), \(K=2\), this system needs only 6 orthogonal pilot sequences. Here, limited by the simulation complexity, we can only select smaller L and K, which just for verification.
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Acknowledgements
This work was supported by the National High Technology Research and Development Program of China (863 Program) (2014AA01A705), the National Natural Science Foundation of China under Grants 61071113, 61201172 and 61201176, The Project of Nanjing University of Posts and Telecommunications (NY213072).
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Part of this work was presented at the 2015 IEEE International Conference on Wireless Communications and Signal Processing (WCSP) [1]. This work was supported by the National High Technology Research and Development Program of China (863 Program) (2014AA01A705), the National Natural Science Foundation of China under Grants 61671251, Natural Science Foundation of Jiangsu Province of China under Grants BK20130874, BK20140881, The Project of Nanjing University of Posts and Telecommunications (NY213072).
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Wang, H., Huang, Y., Jin, S. et al. Pilot Contamination Reduction in Multi-cell TDD Systems with Very Large MIMO Arrays. Wireless Pers Commun 96, 5785–5808 (2017). https://doi.org/10.1007/s11277-017-4447-1
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DOI: https://doi.org/10.1007/s11277-017-4447-1