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Robust linear precoder for coordinated multipoint joint transmission under limited backhaul with imperfect CSI
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
2014 (Engelska)Ingår i: 2014 11TH INTERNATIONAL SYMPOSIUM ON WIRELESS COMMUNICATIONS SYSTEMS (ISWCS), 2014, s. 138-143Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

Coordinated Multipoint (COMP) transmission provides high theoretic gains in spectral efficiency, in particular with coherent linear Joint Transmission (JT) to multiple users. However, this requires high backhaul capacity. If the backhaul requirement cannot be met by the system, then CoNIP gains decrease as the linear precoder matrix must be adjusted to include zeros. To minimize the loss of CoMP gains, all elements in the precoder should be adjusted as zeros are added to the precoder. We here propose a low complexity method for adjusting a precoder matrix when some elements are required to be zero, with respect to a robust MSE criterion. This is done by introducing penalties on specific precoder matrix elements. This generalized MSE criterion can then be used as a low complexity tool for optimizing e.g. with respect to sum-rate. Results show that this does indeed provide a better solution than if zeros are added separately. It is especially beneficial for cell edge users, i.e. for the same users that can gain the most from JT CoNIP.

Ort, förlag, år, upplaga, sidor
2014. s. 138-143
Nationell ämneskategori
Teknik och teknologier
Forskningsämne
Elektroteknik med inriktning mot signalbehandling
Identifikatorer
URN: urn:nbn:se:uu:diva-235007ISI: 000363906500027ISBN: 978-1-4799-5863-4 (tryckt)OAI: oai:DiVA.org:uu-235007DiVA, id: diva2:758708
Konferens
International Symposium on Wireless Communication Systems ISWCS, Barcelona, Spanien, 25-29 Augusti
Tillgänglig från: 2014-10-28 Skapad: 2014-10-28 Senast uppdaterad: 2018-03-07Bibliografiskt granskad
Ingår i avhandling
1. Channel Estimation and Prediction for 5G Applications
Öppna denna publikation i ny flik eller fönster >>Channel Estimation and Prediction for 5G Applications
2018 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Accurate channel state information (CSI) is important for many candidate techniques of future wireless communication systems. However, acquiring CSI can sometimes be difficult, especially if the user equipment is mobile in which case the future channel realisations must be estimated/predicted. In realistic settings the predictability of radio channels is limited due to measurement noise, limited model orders and since the fading statistics must be modelled based on a set of limited and noisy training data.

In this thesis, the limits of predictability for the radio channel are investigated. Results show that the predictability is limited primarily due to limitations in the training data, while the model order provides a second order limitation effect and the measurement noise comes in as a third order effect.

Then, a Kalman-based linear filter is studied for potential 5G technologies:

Coherent coordinated multipoint joint transmission, where channel predictions and the covariance matrix of the prediction error are used to design a robust linear precoder, evaluated in a three base station system. Results show that prediction improves the CSI for the pedestrian users such that system delays of 10 ms are acceptable. The use of the covariance matrix is important for difficult user groups, but of less importance with a simple user grouping system proposed.

Massive multiple-input multiple-output (MIMO) in frequency division duplex (FDD) systems were a reduced, suboptimal, Kalman filter is suggested to estimate channels based on non-orthogonal pilots. By introducing a fixed grid of beams, the system generates sparsity in the channel vectors seen by each user, which then estimates its most relevant channels based on unique pilot codes for each beam. Results show that there is a 5 dB loss compared to orthogonal pilots.

Downlink time division duplex (TDD) channels are estimated based on uplink pilots. By using a predictor antenna, which scouts the channel in advance, the desired downlink channel can be estimated using pilot-based estimates of the channels before and after it (in space). Results indicate that, with the help of Kalman smoothing, predictor antennas can enable accurate CSI for TDD downlinks at vehicular velocities of 80 km/h.

Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2018. s. 116
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1642
Nyckelord
Channel estimation, Channel prediction, Channel smoothing, Linear estimation, Kalman filter, Massive MIMO, Coordinated Multipoint transmission, Robust precoding, Predictor antennas, Limits of predictability, Long range predictions
Nationell ämneskategori
Signalbehandling Telekommunikation
Forskningsämne
Elektroteknik med inriktning mot signalbehandling
Identifikatorer
urn:nbn:se:uu:diva-344270 (URN)978-91-513-0263-8 (ISBN)
Disputation
2018-04-27, Häggsalen, Å10132, Lägerhyddsvägen 1, Uppsala, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2018-04-05 Skapad: 2018-03-07 Senast uppdaterad: 2018-04-24

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Apelfröjd, RikkeSternad, Mikael

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