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Joint transmission with dummy symbols for dynamic TDD in ultra-dense deployments
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.ORCID iD: 0000-0003-2948-1082
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab). KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.ORCID iD: 0000-0001-7642-3067
2017 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Dynamic time-division duplexing (TDD) is considered a promising solution to deal with fast-varying traffic often found in ultra-densely deployed networks. At the same time, it generates more interference which may degrade the performance of some user equipment (UE). When base station (BS) utilization is low, some BSs may not have an UE to serve. Rather than going into sleep mode, the idle BSs can help nearby UEs using joint transmission. To deal with BS-to-BS interference, we propose using joint transmission with dummy symbols where uplink BSs serving uplink UEs participate in the precoding. Since BSs are not aware of the uplink symbols beforehand, any symbols with zero power can be transmitted instead to null the BS-to-BS interference. Numerical results show significant performance gains for uplink and downlink at low and medium utilization. By varying the number of participating uplink BSs in the precoding, we also show that it is possible to successfully trade performance in the two directions.

Place, publisher, year, edition, pages
IEEE, 2017. 1-5 p.
Keyword [en]
cellular radio;precoding;time division multiplexing;BS-to-BS interference;TDD;base station utilization;downlink;dummy symbols;dynamic time-division duplexing;fast-varying traffic;joint transmission;precoding;sleep mode;ultra-densely deployed networks;uplink symbols;user equipment;Bandwidth;Downlink;Interference;Power control;Precoding;Signal to noise ratio;Uplink;Joint transmission;dummy symbols;dynamic TDD;ultra-dense network
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-214772DOI: 10.1109/EuCNC.2017.7980720OAI: oai:DiVA.org:kth-214772DiVA: diva2:1143166
Conference
2017 European Conference on Networks and Communications (EuCNC), Oulu, Finland
Note

QC 20170922

Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2017-09-22Bibliographically approved
In thesis
1. On the Performance of Dynamic TDD in Ultra-Dense Wireless Access Networks
Open this publication in new window or tab >>On the Performance of Dynamic TDD in Ultra-Dense Wireless Access Networks
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The appetite for wireless high-data rate services is expected to continue for many years to come and drive the need for more capacity. Ultra-dense networks (UDNs) represent a paradigm shift where each base station (BS) serves only a few user equipments (UEs). By most accounts, most of the traffic will be generated indoor and operate in time-division duplex (TDD). This thesis considers dynamic TDD which has shown to perform well indoor for fluctuating traffic where the shorter communication range enables similar transmit powers to be used in uplink and downlink, but also generates potentially more harmful same-entity interference. Because of the sheer number of cells in UDN, the interference management needs to be both effective and scalable.

 

In the first part of the thesis, we compare static TDD with non-cooperative dynamic TDD and show that flexible time resource allocation is preferred for indoor UDNs. However, since it only provides a lower bound on performance, additional interference coordination is required. Unfortunately, existing schemes often consider either too few, too many, or simply the wrong interferers. We introduce a scheduling model that relates BS-to-BS interferences measured offline to individual BS activation probability taking into account traffic and propagation environment. Results show that the proposed scheme performs well when interference is high, and optimally when interference is low.

 

In the second part, we introduce cooperation to utilize the otherwise idle BSs and mitigate same- and other entity interference. Zero forcing (ZF) is employed in the downlink where not only downlink UEs but also uplink BSs are included in the precoding. Since downlink BSs do not know the information to be sent by uplink UEs beforehand, dummy symbols with zero power are transmitted. It shown that both uplink and downlink performance improves at low and medium load. Furthermore, it is possible to trade performance in the two directions at high load.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. 44 p.
Series
TRITA-ICT, 2017:22
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
Identifiers
urn:nbn:se:kth:diva-214775 (URN)978-91-7729-522-8 (ISBN)
Presentation
2017-10-26, Ka-Sal C, Electrum, KTH Royal Institute of Technology, Kistagången 16, Kista, 13:00 (English)
Opponent
Supervisors
Note

QC 20170922

Available from: 2017-09-22 Created: 2017-09-20 Last updated: 2017-09-28Bibliographically approved

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Čelik, HarisSung, Ki Won

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