Uppsala universitet

Design Aspects of Coordinated Multipoint Transmission

A study of channel prediction, resource allocation, user grouping and robust linear precoding for coherent joint transmission.

Rikke Apelfröjd

Licentiate Thesis, Signals and Systems, Uppsala University, May 2014.

Publicly examined in room 2002, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, on Friday, August 22, 2014 at 09.15.
Examiner: Adjunct Professor Antti Tölli, University of Oulu.

The thesis summary in Pdf

Paper copies of the complete thesis can be obtained from Ylva Johansson, Signals and Systems Group, Uppsala University, Box 534, SE-75121 Uppsala, Sweden.

Shadowed areas and interference at cell borders pose great challenges for future wireless broadband systems. Coordinated Multipoint (CoMP) coherent joint transmission has shown the potential to overcome these challenges by turning harmful interference into useful signal power. However, there are obstacles to overcome before coherent joint transmission CoMP can be deployed. Some of these are investigated in this thesis.

First, coherent joint transmission requires very accurate Channel State Information (CSI), but unfortunately long system latencies cause outdating of the CSI. This can to some extend be counteracted by channel predictions. Two schemes are here investigated for predicting downlink Frequency Division Duplex (FDD) Orthogonal Frequency Division Multiplexing (OFDM) channels; Kalman filters and “predictor antennas”. The first is well suited for slow moving users, e.g. pedestrians or cyclists, as it does not require any special antenna setup. The second, which utilizes an extra antenna, located in front of the main receive antennas, is well suited for vehicular users, such as buses or trams, as these requires long spatial prediction horizon.

Second, a user grouping and resource allocation scheme is investigated. This scheme forms CoMP groups by local resource allocations and provides multi-user diversity gains very close to the optimal gains, found through an extensive combinatorial search. It has very low complexity, requires less feedback capacity than other schemes and places no demands on backhaul capacity.

Finally, a linear precoder, which is robust to errors in the CSI, is investigated. This precoder takes the covariances of the channel errors into account while optimizing a Mean Squared Error (MSE) criterion. The MSE criterion includes design parameters that can be used as flexible tools for low dimensional searches with respect to an arbitrary optimization criterion, e.g. a weighted sum-rate criterion. The precoder design is also extended to handle backhaul constraints.

Results show that with the combination of these three schemes: channel predictions, the proposed user grouping and resource allocation scheme and the robust linear precoder, then coherent joint transmission will indeed provide large capacity gains.

Publications included in the Thesis:
IEEE ICC 2012: Measurement-based evaluation of robust linear precoding for downlink CoMP. In Pdf

EURASIP JWCN 2014: Design and measurement based evaluation of coherent JT CoMP - A study of precoding, user grouping and resource allocation using predicted CSI. In Pdf

IEEE ISWCS 2014: Robust linear precoder for coordinated multipoint joint transmission under limited backhaul with imperfect CSI. In Pdf

EuCAP 2014: Analysis and measurement of multiple antenna systems for fading channel prediction in moving relays. In Pdf

Technical Report 2014 on Kalman prediction for multipoint OFDM downlink channels. In Pdf

Related work:

PhD Thesis by Rikke Apelfröjd, April 2018.

IEEE Communications Magazine May 2014: The role of small cells, coordinated multi-point and massive MIMO in 5G.

IEEE WCNC 2012: Using "Predictor Antennas" for long-range prediction of fast fading for moving relays. In Pdf

IEEE PIMRC 2012: Performance evaluation of coordinated multi-point transmission schemes with predicted CSI. In Pdf

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

Channel Estimation and Prediction for MIMO OFDM Systems.
PhD Thesis by Danel Aronsson, Uppsala University 2011.

Prediction of Mobile Radio Channels.
PhD Thesis by Torbjörn Ekman, Uppsala University 2002.

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