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Design and measurement based evaluations of coherent JT CoMP: a study of precoding, user grouping and resource allocation using predicted CSI
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.
2014 (English)In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, 100- p.Article in journal (Other academic) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2014. 100- p.
Keyword [en]
Coordinated Multipoint, channel predictions, user grouping, resource allocation, robust precoding
National Category
Signal Processing
Research subject
Electrical Engineering with specialization in Signal Processing
Identifiers
URN: urn:nbn:se:uu:diva-224254DOI: 10.1186/1687-1499-2014-100ISI: 000347399300001OAI: oai:DiVA.org:uu-224254DiVA: diva2:716017
Available from: 2014-05-07 Created: 2014-05-07 Last updated: 2017-12-05Bibliographically 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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