Uppsala universitet

Design and Measurement Based Evaluation of Coherent JT CoMP - A Study of Precoding, User Grouping and Resource Allocation Using Predicted CSI.

Rikke Apelfröjd and Mikael Sternad , Uppsala University

EURASIP Journal on Wireless Communications and Networking, June 2014, 2014:100
DOI: 10.1186/1687-1499-2014-100.

Paper In Pdf

Coordinated Multipoint (CoMP) transmission provides high theoretic gains in spectral efficiency with coherent Joint Transmission (JT) to multiple users. However, this requires accurate Channel State Information at the Transmitter (CSIT) and also user groups with spatially compatible users.

The aim of this paper is to use measured channels to investigate if significant CoMP gains can still be obtained with channel estimation errors. This turns out to be the case, but requires the combination of several techniques.

We here focus on coherent downlink JT CoMP to multiple users within a cluster of cooperating base stations. The use of Kalman predictors is investigated to estimate the complex channel gains at the moment of transmission. It is shown that this can provide sufficient CSIT quality for JT CoMP even for long (>20 ms) system delays at 2.66 GHz at pedestrian velocities or, for lower delays, at 500 MHz, at vehicular velocities.

A user grouping and resource allocation scheme that provides appropriate groups for CoMP is also suggested. It provides performance close to that obtained by exhaustive search at very low complexity, low feedback cost and very low backhaul cost. Finally, a robust linear precoder that takes channel uncertainties into account when designing the precoding matrix is considered. We show that, in challenging scenarios, this provides large gains compared with zero-forcing precoding.

Evaluations of these design elements are based on measured channels with realistic noise and intercluster interference assumptions. These show that high JT CoMP gains can be expected, on average over large sets of user positions, when the above techniques are combined - especially in severely intracluster interference limited scenarios.

Related publications:
PhD. Thesis by Rikke Apelfröjd, April 2018
(of which this is the second contribution paper).

ICC 2012, earlier paper on measurement-based evaluation of robust linear precoding for downlink CoMP.

Performance Evaluation of Coordinated Multi-Point Transmission Schemes with Predicted CSI (IEEE PIMRC 2012).

The robust design, generalized to work under feedback constraints and structural backhaul constraints (IEEE ISWCS 2014).

IEEE ISWCS 2014: User-centric pre-selection and scheduling for CoMP.

Report by Rikke Apelfröjd on Kalman prediction for multipoint OFDM downlink channels, May 2014, Revised March 2018.

Channel Estimation and Prediction for MIMO OFDM Systems: Key design and performance aspects of Kalman-based algorithms.
PhD Thesis by Daniel Aronsson, 2012.

Prediction of mobile radio channels, Ph.D. Thesis by Torbjörn Ekman 2002.

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