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Cooperative transmissions in ultra-dense networks under a bounded dual-slope path loss model
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).ORCID iD: 0000-0002-7559-8911
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).ORCID iD: 0000-0001-7642-3067
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2017 (English)In: 2017 European Conference on Networks and Communications (EuCNC), Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper, Published paper (Refereed)
Abstract [en]

In an ultra-dense network (UDN) where there are more base stations (BSs) than active users, it is possible that many BSs are instantaneously left idle. Thus, how to utilize these dormant BSs by means of cooperative transmission is an interesting question. In this paper, we investigate the performance of a UDN with two types of cooperation schemes: Non-coherent joint transmission (JT) without channel state information (CSI) and coherent JT with full CSI knowledge. We consider a bounded dual-slope path loss model to describe UDN environments where a user has several BSs in the near-field and the rest in the far-field. Numerical results show that non-coherent JT cannot improve the user spectral efficiency (SE) due to the simultaneous increment in signal and interference powers. For coherent JT, the achievable SE gain depends on the range of near-field, the relative densities of BSs and users, and the CSI accuracy. Finally, we assess the energy efficiency (EE) of cooperation in UDN. Despite costing extra energy consumption, cooperation can still improve EE under certain conditions.

Place, publisher, year, edition, pages
Institute of Electrical and Electronics Engineers (IEEE), 2017.
Keywords [en]
bounded path loss model, cooperative transmissions, multi-slope path loss model, Ultra-dense networks
National Category
Communication Systems
Identifiers
URN: urn:nbn:se:kth:diva-221121DOI: 10.1109/EuCNC.2017.7980732Scopus ID: 2-s2.0-85039946526ISBN: 9781538638736 (print)OAI: oai:DiVA.org:kth-221121DiVA, id: diva2:1174048
Conference
2017 European Conference on Networks and Communications, EuCNC 2017, Oulu, Finland, 12 June 2017 through 15 June 2017
Note

QC 20180115

Available from: 2018-01-15 Created: 2018-01-15 Last updated: 2018-11-20Bibliographically approved
In thesis
1. Ultra-Densification for Future Cellular Networks: Performance Analysis and Design Insights
Open this publication in new window or tab >>Ultra-Densification for Future Cellular Networks: Performance Analysis and Design Insights
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The traffic volume in wireless communication has grown dramatically in the lastdecade. Recent predictions indicate such data storm will be even more violent in theshort run. Potential solutions for accommodating the rapid traffic growth can besummed up into three categories: broadening the available bandwidth, improvingthe spectral efficiency, and densifying the infrastructure. In this thesis, we focuson the densification dimension which has been proven to be the most effectiveone in the past. The current gain of network densification mainly comes from cellsplitting, thereby serving more user equipment (UE) simultaneously. This trendwill decelerate as the base station (BS) density gets closer to or even surpassesthe UE density which forms an ultra-dense network (UDN). Thus, it is crucialto understand the behavior and design operations of ultra-densification in futurenetworks.

An important question for future system design and operating strategy is whichelement is more effective than others. To this end, we start from comparing the effectivenessof densification with spectrum expansion and multi-antenna systems interms of meeting certain traffic demand. Our findings show that deploying more BSsprovides a substantial gain in sparse network but the gain decreases progressively ina UDN. Meanwhile, even with the same area throughput, different combinations ofindividual throughput and UE density lead to different requirements for resources.The diminishing gain appearing in UDNs makes us curious to know if there existsa terminal on the way of densification. Such uncertainty leads to the study onthe asymptotic behavior of densification. By incorporating a sophisticated boundeddual-slope path loss model and practical UE densities in our analysis, we present theasymptotic behavior of ultra-densification: the coverage probability and area spectralefficiency (ASE) have non-zero convergences in asymptotic regions unless theUE density goes to infinity (full load). Our results suggest that network densificationcannot always improve the UE performance or boost the network throughput.

Next, we shift our focus to the operations of UDNs. We first study BS cooperationsin two UDN scenarios: homogeneous and heterogeneous UDNs which aredistinguished by BS types. In both cases, the cooperation rules become more complicatedthan those in traditional networks. Either channel state information (CSI) orextra delay information needs to be acquired in order to obtain cooperation gains.At last, we investigate the feasibility of applying random beamforming to initialaccess in millimeter-wave (mmWave) UDNs. To our surprise, the simple methodcan provide sufficient performance in both control and data plane, comparing withthe existing schemes. Therefore, it may be unnecessary to develop complex algorithmsfor initial access in future dense mmWave networks. The findings indicatethat UDN may complicate network operations while it may also facilitate the use ofsimple schemes. Our work provides insights into the understanding of the networkdensification and thus paves the way for the operational design of future UDNs.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 59
Series
TRITA-EECS-AVL ; 2018:88
National Category
Communication Systems
Research subject
Telecommunication
Identifiers
urn:nbn:se:kth:diva-239175 (URN)978-91-7873-017-9 (ISBN)
Public defence
2018-12-07, Ka-Sal C (Sal Sven-Olof Öhrvik), Electrum, Kungl Tekniska högskolan, Kistagången 16, Kista, Stockholm, 13:00 (English)
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Supervisors
Note

QC 20181119

Available from: 2018-11-19 Created: 2018-11-19 Last updated: 2018-11-19Bibliographically approved

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Yang, YanpengSung, Ki Won

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