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Downlink Throughput Driven Channel Access Framework for Cognitive LTE Femto-Cells
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.ORCID iD: 0000-0003-3860-5964
Academy for Natural Science and Built Environment, University of Gävle. (Elektronik)
KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS. KTH, School of Information and Communication Technology (ICT), Centres, Center for Wireless Systems, Wireless@kth.ORCID iD: 0000-0001-9697-9978
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This paper proposes an optimized sensing based channel access framework for the LTE cognitive femto cells with an objective of maximizing femto-cells downlink throughput. Energy detection is used by the LTE cognitive femto cells to locate and thereafter utilize the free channels. Moreover, periodic sensing is adopted to detect any changes of the sensing outcomes. The developed channel access framework is based on an objective of maximization the femto-cell downlink throughput which varies with the macro-cell channel occupancy. Therefore, the LTE macro-cell occupancy statistics are empirically modelled using exponential distributions mixture. The LTE cognitive femto-cell downlink throughput is maximized by compromising the transmission efficiency, the explored spectrum opportunities and the interference from the macro-cell. An analytical solution for the optimal periodic sensing interval that maximizes the throughput is found and verified by simulations. The obtained results show that there is indeed a single periodic sensing interval value that maximizes the LTE cognitive femto-cell downlink throughput which changes with the change of the macro-cell channel occupancy. Yet, at a specific channel occupancy statistical parameters, our framework provides the optimal throughput. At the peak of the macro-cell traffic, our framework increased the femto-cell throughput by $\simeq 15\%$ compared to the senseless case. The impact of the available channels for opportunistic access is studied. The simulation results show that increasing the number of the available channels becomes less significant for more than three channels.

Keyword [en]
Two tier LTE network, Cognitive femto-cell, Channel occupancy, Downlink throughput, Periodic sensing, Energy detection.
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-159565OAI: diva2:785775

QS 2015

Available from: 2015-02-03 Created: 2015-02-03 Last updated: 2015-02-09Bibliographically approved
In thesis
1. On Spectrum Sensing for Secondary Operation in Licensed Spectrum: Blind Sensing, Sensing Optimization and Traffic Modeling
Open this publication in new window or tab >>On Spectrum Sensing for Secondary Operation in Licensed Spectrum: Blind Sensing, Sensing Optimization and Traffic Modeling
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

There has been a recent explosive growth in mobile data consumption. This, in turn, imposes many challenges for mobile services providers and regulators in many aspects. One of these primary challenges is maintaining the radio spectrum to handle the current and upcoming expansion in mobile data traffic. In this regard, a radio spectrum regulatory framework based on secondary spectrum access is proposed as one of the solutions for the next generation wireless networks. In secondary spectrum access framework, secondary (unlicensed) systems coexist with primary (licensed) systems and access the spectrum on an opportunistic base.

In this thesis, aspects related to finding the free of use spectrum portions - called spectrum opportunities - are treated. One way to find these opportunities is spectrum sensing which is considered as an enabler of opportunistic spectrum access. In particular, this thesis investigates some topics in blind spectrum sensing where no priori knowledge about the possible co-existing systems is available.

As a standalone contribution in blind spectrum sensing arena, a new blind sensing technique is developed in this thesis. The technique is based on discriminant analysis statistical framework and called spectrum discriminator (SD). A comparative study between the SD and some existing blind sensing techniques was carried out and showed a reliable performance of the SD.

The thesis also contributes by exploring sensing parameters optimization for two existing techniques, namely, energy detector (ED) and maximum-minimum eigenvalue detector (MME). For ED, the sensing time and periodic sensing interval are optimized to achieve as high detection accuracy as possible. Moreover, a study of sensing parameters optimization in a real-life coexisting scenario, that is, LTE cognitive femto-cells, is carried out with an objective of maximizing cognitive femto-cells throughput. In association with this work, an empirical statistical model for LTE channel occupancy is accomplished. The empirical model fits the channels' active and idle periods distributions to a linear combination of multiple exponential distributions. For the MME, a novel solution for the filtering problem is introduced. This solution is based on frequency domain rectangular filtering. Furthermore, an optimization of the observation bandwidth for MME with respect to the signal bandwidth is analytically performed and verified by simulations.

After optimizing the parameters for both ED and MME, a two-stage fully-blind self-adapted sensing algorithm composed of ED and MME is introduced. The combined detector is found to outperform both detectors individually in terms of detection accuracy with an average complexity lies in between the complexities of the two detectors. The combined detector is tested with measured TV and wireless microphone signals.

The performance evaluation in the different parts of the thesis is done through measurements and/or simulations. Active measurements were performed for sensing performance evaluation. Passive measurements on the other hand were used for LTE downlink channels occupancy modeling and to capture TV and wireless microphone signals.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xv, 75 p.
TRITA-ICT-COS, ISSN 1653-6347 ; 1502
Cognitive Radio, Spectrum Sensing, Sensing Optimization, Blind Sensing, Traffic Modelling, Energy detection, Maximumum-minimum Eigenvalue Detection, Discriminant anlysis
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Information and Communication Technology
urn:nbn:se:kth:diva-159639 (URN)
Public defence
2015-03-13, 99:131, Hus 99, Högskolan i Gävle, Kungsbäcksvägen 47, Gävle, 13:15 (English)

QC 20150209

Available from: 2015-02-09 Created: 2015-02-05 Last updated: 2015-02-10Bibliographically approved

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