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Measurement-based evaluation of robust linear precoding for downlink CoMP
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
2012 (English)In: IEEE International Conference on Communications, ICC, Ottawa, Canada, 2012Conference paper, Published paper (Refereed)
Abstract [en]

We study the design and evaluation of joint processing coordinated multipoint (CoMP) downlink transmission. Precoders will then be designed based on outdated channel state information (CSI), so interference cannot be eliminated completely as by an ideal zero-forcing (ZF) solution. We here strive to design and evaluate realistic linear transmit schemes. Kalman predictors are used for orthogonal frequency-division multiplexing (OFDM) channels. They provide optimal linear predictions and also estimates of their uncertainty. Robust linear precoders are designed based on these uncertainty estimates. We introduce and use robust linear quadratic optimal feedforward control, with the criterion averaged (marginalized) over the CSI uncertainty. This flexible solution performs minimum mean square error (MSE) minimization. It can also iteratively optimize other criteria, such as sum-rate. The prediction- and transmission performance is evaluated using measured data on 20 MHz OFDM downlinks from three base stations, for users at fast pedestrian velocities. Downlink CoMP is here also compared to cellular transmission, that uses orthogonal resources within cells but allows uncontrolled interference between cells.

Place, publisher, year, edition, pages
2012.
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
URN: urn:nbn:se:uu:diva-181051OAI: oai:DiVA.org:uu-181051DiVA: diva2:552791
Conference
IEEE International Conference on Communications, ICC, June 10 - 15, Ottawa, Canada.
Available from: 2012-09-17 Created: 2012-09-17 Last updated: 2014-06-04Bibliographically approved
In thesis
1. Design Aspects of Coordinated Multipoint Transmission: A Study of Channel Predictions, Resource Allocation, User Grouping and Robust Linear Precoding for Coherent Joint Transmission
Open this publication in new window or tab >>Design Aspects of Coordinated Multipoint Transmission: A Study of Channel Predictions, Resource Allocation, User Grouping and Robust Linear Precoding for Coherent Joint Transmission
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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 the 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 require 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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. xiv+39 p.
Keyword
Network MIMO, Centralized CoMP, Robust beamforming with imperfect CSI, Limited backhaul, Linear predictions of OFDM channels, Kalman filters, Predictor antennas, Long term channel prediction, Local resource allocation and user grouping
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
urn:nbn:se:uu:diva-224264 (URN)
Presentation
2014-08-22, 2002, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2014-06-04 Created: 2014-05-08 Last updated: 2014-06-04Bibliographically approved

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