Superimposed Pilots Are Superior for Mitigating Pilot Contamination in Massive MIMO

Karthik Upadhya, Sergiy A. Vorobyov, Mikko Vehkaperä

Research output: Contribution to journalArticleScientificpeer-review

33 Citations (Scopus)

Abstract

In this paper, superimposed pilots are introduced as an alternative to time-multiplexed pilot and data symbols for mitigating pilot contamination in massive multiple-input multiple-output (MIMO) systems. We propose a non-iterative scheme for uplink channel estimation based on superimposed pilots and derive an expression for the uplink signal-to-interference-plus-noise ratio (SINR) at the output of a matched filter employing this channel estimate. Based on this expression, we observe that power control is essential when superimposed pilots are employed. Moreover, the quality of the channel estimate can be improved by reducing the interference that results from transmitting data alongside the pilots, and an intuitive iterative data-aided scheme that reduces this component of interference is also proposed. Approximate expressions for the uplink SINR are provided for the iterative data-aided method as well. In addition, we show that a hybrid system with users utilizing both time-multiplexed and superimposed pilots is superior to an optimally designed system that employs only time-multiplexed pilots, even when the non-iterative channel estimate is used to build the detector and precoder. We also describe a simple approach to implement this hybrid system by minimizing the overall inter- and intracell interference. Numerical simulations demonstrating the performance of the proposed channel estimation schemes and the superiority of the hybrid system are also provided.
Original languageEnglish
Article number7865983
Pages (from-to)2917-2932
JournalIEEE Transactions on Signal Processing
Volume65
Issue number11
DOIs
Publication statusPublished - 1 Jun 2017
MoE publication typeA1 Journal article-refereed

Fingerprint

Hybrid systems
Contamination
Channel estimation
Matched filters
Power control
Detectors
Computer simulation

Keywords

  • Massive MIMO
  • pilot contamination
  • superimposed pilots

Cite this

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abstract = "In this paper, superimposed pilots are introduced as an alternative to time-multiplexed pilot and data symbols for mitigating pilot contamination in massive multiple-input multiple-output (MIMO) systems. We propose a non-iterative scheme for uplink channel estimation based on superimposed pilots and derive an expression for the uplink signal-to-interference-plus-noise ratio (SINR) at the output of a matched filter employing this channel estimate. Based on this expression, we observe that power control is essential when superimposed pilots are employed. Moreover, the quality of the channel estimate can be improved by reducing the interference that results from transmitting data alongside the pilots, and an intuitive iterative data-aided scheme that reduces this component of interference is also proposed. Approximate expressions for the uplink SINR are provided for the iterative data-aided method as well. In addition, we show that a hybrid system with users utilizing both time-multiplexed and superimposed pilots is superior to an optimally designed system that employs only time-multiplexed pilots, even when the non-iterative channel estimate is used to build the detector and precoder. We also describe a simple approach to implement this hybrid system by minimizing the overall inter- and intracell interference. Numerical simulations demonstrating the performance of the proposed channel estimation schemes and the superiority of the hybrid system are also provided.",
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Superimposed Pilots Are Superior for Mitigating Pilot Contamination in Massive MIMO. / Upadhya, Karthik; Vorobyov, Sergiy A.; Vehkaperä, Mikko.

In: IEEE Transactions on Signal Processing, Vol. 65, No. 11, 7865983, 01.06.2017, p. 2917-2932.

Research output: Contribution to journalArticleScientificpeer-review

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