Utility-based Downlink Pilot Assignment in Cell-Free Massive MIMO

Conference: WSA 2018 - 22nd International ITG Workshop on Smart Antennas
03/14/2018 - 03/16/2018 at Bochum, Deutschland

Proceedings: ITG-Fb. 276: WSA 2018

Pages: 8Language: englishTyp: PDF

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Interdonato, Giovanni; Frenger, Pal (Ericsson Research, 581 12 Linköping, Sweden)
Larsson, Erik G. (Department of Electrical Engineering (ISY), Linköping University, 581 83 Linköping, Sweden)

We propose a strategy for orthogonal downlink pilot assignment in cell-free massive MIMO (multiple-input multipleoutput) that exploits knowledge of the channel state information, the channel hardening degree at each user, and the mobility conditions for the users. These elements, properly combined together, are used to define an user pilot utility metric, which measures the user’s real need of a downlink pilot for efficient data decoding. The proposed strategy consists in assigning orthogonal downlink pilots only to the users having a pilot utility metric exceeding a predetermined threshold. Instead, users that are not assigned with an orthogonal downlink pilot decode the data by using the statistical channel state information. The utility-based approach guarantees higher downlink net sum throughput, better support both for high-speed users and shorter coherent intervals than prior art approaches.