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Feasibility and Performance of Dynamic TDD in Dense and Ultra-Dense Wireless Access Networks
KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Meeting the seemingly never-ending increase in traffic over wireless networks presents a major challenge for future mobile network design. Given that much of the traffic is expected to be more time-varying and unpredictable, time division duplexing (TDD) is gaining increasing favorability in part thanks to its ability to better accommodate network-wide traffic variations. In order to account for traffic variations in individual cells on much shorter time scales, a more flexible variant called dynamic TDD has resurfaced as a promising technique to further improve resource utilization and performance. In dynamic TDD the traffic in each cell can be served immediately in either direction, but generates same-entity interference which is potentially more harmful. To avoid the much stronger downlink from saturating the uplink, this thesis considers dynamic TDD for dense and ultra-dense networks where transmission powers in the two directions are of comparable strength. Still, inter-cell interference remains an issue given the close proximity of some links. Because of the large number of cells comprising dense and ultra-dense networks, it is imperative that the interference management be both effective and scalable, which is the main focus of this thesis.

In the first part we focus on scalable radio resource management (RRM). We show that non-cooperative dynamic TDD is feasible for indoor ultra-dense deployment and highlight the benefit of employing beamsteering at both the base station (BS) and user equipment (UE) to mitigate interference distributively, especially at high load. Recognizing that beamsteering is better suited for higher frequencies and high data rate applications, we proceed to investigate the efficacy of receive-side interference management in the form of successive interference cancellation (SIC). Being that the interference distribution is different in dynamic TDD, we show that it suffices to cancel only strongest interferer at the UE side and the two strongest interferers at the BS. The combined benefit of SIC and dynamic TDD in reducing delay for low-rate traffic is also displayed. Next, we introduce limited inter-cell information exchange in order to leverage the resource allocation in the medium access control (MAC). To minimize the amount of information exchange and preserve scalability, a scheduling framework is proposed that relates real-time traffic to inter-BS interferences measured offline and mapped to the individual activation probability of each BS. The proposed scheme is shown to perform well with respect to comparable scalable schedulers when interference is high, and optimally when interference is low.

In ultra-dense networks it is expected that some BSs might not have a UE to serve. In the second part, we therefore introduce cooperation to utilize the otherwise idle BSs to improve network performance. To mitigate both same- and other-entity interference, zero forcing (ZF) precoding is employed where not only downlink UEs but also uplink BSs are included in the beamforming. Results show that both uplink and downlink performance improves at low and medium load, and that it is possible to trade performance in the two directions at high load.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. , p. 49
Series
TRITA-EECS-AVL ; 2019:10
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
Identifiers
URN: urn:nbn:se:kth:diva-241134ISBN: 978-91-7873-078-0 (print)OAI: oai:DiVA.org:kth-241134DiVA, id: diva2:1278123
Public defence
2019-02-13, Ka-Sal C, Electrum, KTH Royal Institute of Technology, Kistagången 16, Kista, 13:00 (English)
Opponent
Supervisors
Note

QC 20190114

Available from: 2019-01-14 Created: 2019-01-11 Last updated: 2019-01-17Bibliographically approved
List of papers
1. On the feasibility of blind dynamic TDD in ultra-dense wireless networks
Open this publication in new window or tab >>On the feasibility of blind dynamic TDD in ultra-dense wireless networks
2015 (English)In: IEEE Vehicular Technology Conference, IEEE , 2015Conference paper, Published paper (Refereed)
Abstract [en]

Abstract-Dynamic configuring of uplink and downlink switching point in time division duplex (TDD) systems is considered a promising solution to cope with the traffic variations caused by the burstiness of mobile broadband data. However, such dynamic TDD (D-TDD) requires fast inter-cell coordination which may be difficult to implement in ultra-densely deployed networks (UDNs). In order to explore the possibility of designing simplified UDN, we investigate the feasibility of uncoordinated and greedy TDD operation, namely blind D-TDD. It exploits the characteristics of UDN such as low average network utilization and similar transmit power for base stations (BS) and user equipment (UE). To reduce the impact of co- channel interference (CCI), the effect of beamsteering is also evaluated. Our results indicate that blind D-TDD outperforms traditional static TDD (S-TDD) when instantaneous traffic demands for uplink and downlink are highly asymmetric. Also, beamsteering exerts a significant influence on the feasibility of blind D-TDD.

Place, publisher, year, edition, pages
IEEE, 2015
Keywords
Blind, Dynamic TDD, Throughput, Ultra-dense network, Interference suppression, Mobile telecommunication systems, Cochannel interference (CCI), Dense network, Dense wireless networks, Inter-cell coordinations, Net work utilization, Switching points, Time-division duplex systems, Cochannel interference
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-175070 (URN)10.1109/VTCSpring.2015.7145967 (DOI)000371404700381 ()2-s2.0-84940434725 (Scopus ID)9781479980888 (ISBN)
Conference
81st IEEE Vehicular Technology Conference, VTC Spring 2015, 11 May 2015 through 14 May 2015
Note

QC 20151210

Available from: 2015-12-10 Created: 2015-10-09 Last updated: 2019-01-11Bibliographically approved
2. Efficacy of Successive Interference Cancellation in Dynamic TDD Cellular Networks
Open this publication in new window or tab >>Efficacy of Successive Interference Cancellation in Dynamic TDD Cellular Networks
(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-241130 (URN)
Note

QC 20190114

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-14Bibliographically approved
3. Success Probability of Successive Interference Cancellation in Random Wireless Networks
Open this publication in new window or tab >>Success Probability of Successive Interference Cancellation in Random Wireless Networks
(English)Manuscript (preprint) (Other academic)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-241131 (URN)
Note

QC 20190114

Available from: 2019-01-11 Created: 2019-01-11 Last updated: 2019-01-14Bibliographically approved
4. Scalable Resource Allocation for Dynamic TDD with Traffic and Propagation Awareness
Open this publication in new window or tab >>Scalable Resource Allocation for Dynamic TDD with Traffic and Propagation Awareness
2018 (English)In: 2018 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE (WCNC), IEEE , 2018Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a scalable scheduler for dynamic TDD systems in ultra-dense indoor deployments applicable to diverse traffic and radio propagation conditions. To minimize signalling for the channel estimation and feedback, the proposed scheduler employs offline BS-to-BS measurements to approximate the real interference for different traffic conditions. Thus, no CSI is required once the network is online. Furthermore, we show that signalling can be further reduced by considering only meaningful interferers above a received power threshold for the traffic information exchange. To perform the scheduling, a function that maps interference into individual BS activation probabilities is also introduced. Results show that the proposed scheme performs reasonably well in high interference situations compared to comparable scalable schedulers, and optimally when interference is low, both in average and 5th percentile sense.

Place, publisher, year, edition, pages
IEEE, 2018
Series
IEEE Wireless Communications and Networking Conference, ISSN 1525-3511
Keywords
Dynamic MD, ultra-dense network, scalability
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-232289 (URN)000435542401101 ()2-s2.0-85049218813 (Scopus ID)978-1-5386-1734-2 (ISBN)
Conference
IEEE Wireless Communications and Networking Conference (WCNC), APR 15-18, 2018, Barcelona, SPAIN
Note

QC 20180718

Available from: 2018-07-18 Created: 2018-07-18 Last updated: 2019-01-11Bibliographically approved
5. Joint transmission with dummy symbols for dynamic TDD in ultra-dense deployments
Open this publication in new window or tab >>Joint transmission with dummy symbols for dynamic TDD in ultra-dense deployments
2017 (English)In: EuCNC 2017 - European Conference on Networks and Communications, IEEE, 2017, article id 7980720Conference 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
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-214772 (URN)10.1109/EuCNC.2017.7980720 (DOI)2-s2.0-85039925551 (Scopus ID)9781538638736 (ISBN)
Conference
2017 European Conference on Networks and Communications, EuCNC 2017, Oulu, Finland, 12 June 2017 through 15 June 2017
Note

QC 20170922

Available from: 2017-09-20 Created: 2017-09-20 Last updated: 2019-01-11Bibliographically approved

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