Uppsala universitet

Joint Reference Signal Design and Kalman/Wiener Channel Estimation for FDD Massive MIMO

Rikke Apelfröjd , Uppsala University,
Wolfgang Zirwas , Nokia Bell Labs, Munich, Germany, and
Mikael Sternad , Uppsala University.

Extended Report: Technical Report r1701,
Signals and Systems, Uppsala University,
Version 2.0, April 2018.
DOI: 10.13140/RG.2.2.19185.33123

Extended Report, Version 2.0, in Pdf

Corresponding paper in IEEE Transactions on Communications, 2019

Presentation Slides

Massive multiple input multiple output (MIMO) transmission and coordinated multipoint transmission are candidate technologies for increasing data throughput in evolving 5G standards. Frequency division duplex (FDD) is very likely to remain predominant in large parts of the spectrum below 6 GHz for future 5G systems. Therefore,it is important to estimate the downlink FDD channels from a very large number of antennas, while avoiding an excessive downlink reference signal overhead.

We here propose and investigate a three part solution. First, massive MIMO downlinks use a fixed grid of beams. For each user, only a subset of beams will then be relevant, and require estimation. Second, non-orthogonal sets of coded reference signal sequences, with cyclic patterns over time, are used. Third, each terminal estimates its most relevant channels. We here propose and compare a linear mean square estimation and a Kalman estimation. Both utilize frequency and antenna correlation, and the later can also utilize temporal correlation.

In an extensive simulation study, this scheme provides channel estimates that lead to an insignificant beamforming performance degradation as compared to full channel knowledge.

The use of a cyclic pattern of the non-orthogonal coded reference signals is found to be important for reliable channel estimation, withouth having to adjust the reference signals to specific users.

Related publications:

Paper at WSA 2016 Coded CSI reference signals for 5G - Exploiting sparsity of FDD massive MIMO radio channels.

Paper at IEEE PIMRC2017 on how this concept can be used in the effective design of 5G Massive MIMO and CoMP downlinks.

PhD Thesis by Rikke Apelfröjd, April 2018, of which the Extended report version 2.0 constitutes Paper IV.

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