No downlink pilots are needed in Massive MIMO

Hien Quoc Ngo, Erik G. Larsson

Research output: Contribution to journalArticlepeer-review

105 Citations (Scopus)
290 Downloads (Pure)

Abstract

We consider the Massive Multiple-Input Multiple-Output downlink with maximum-ratio and zero-forcing processing and time-division duplex operation. To decode, the users must know their instantaneous effective channel gain. Conventionally, it is assumed that by virtue of channel hardening, this instantaneous gain is close to its average and hence that users can rely on knowledge of that average (also known as statistical channel information). However, in some propagation environments, such as keyhole channels, channel hardening does not hold. We propose a blind algorithm to estimate the effective channel gain at each user, that does not require any downlink pilots. We derive a capacity lower bound of each user for our proposed scheme, applicable to any propagation channel. Compared with the case of no downlink pilots (relying on channel hardening), and compared with training-based estimation using downlink pilots, our blind algorithm performs significantly better. The difference is especially pronounced in environments that do not offer channel hardening.
Original languageEnglish
Pages (from-to)2921-2935
JournalIEEE Transactions on Communications
Volume16
Issue number5
DOIs
Publication statusPublished - 17 Mar 2017

Keywords

  • Blind channel estimation, downlink, keyhole channels, Massive MIMO, maximum-ratio processing, timedivision duplexing, zero-forcing processing

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