Doctoral Defense Carlos Héracles Morais de Lima

Friday, August 23, 2013

Master of Science Carlos Héracles Morais de Lima

Faculty of Technology, Departmen of Communications Engineering

23 August, 2013 at 12
Linnanmaa, OP-sali (L 10)

Opportunistic resource and network management in autonomous packet access systems

Professor Jyri Hämäläinen, Aalto University

Professor Matti Latva-aho



This thesis aims to evaluate networking aspects of autonomous packets access systems when dynamically and adaptively performing resource and network management. In this context, Quality of Service (QoS)-aware solutions for resource sharing and control (e.g., channel access, load control, interference management and routing techniques among others) in large-scale wireless networks are envisaged.

We propose and investigate distributed coordination mechanisms for controlling the co-channel interference generated in multi-tier coexistence scenarios consisting of macrocells underlaid with short-range small cells. The rationale behind employing such mechanism is to opportunistically reuse resources without compromising ongoing transmissions on the overlaid macrocells, while still guaranteeing QoS in both tiers. To mitigate the resulting co-channel interference, the underlaid tiers of small cells use distributed mechanism that relies on minimal signaling exchange, e.g., the Time Division Duplexing (TDD)-underlay approach which is based on regular busy tones.

Herein, stochastic geometry is used to model network deployments, while higherorder statistics through the cumulants concept is utilized to characterize the probability distribution of the aggregate interference at the tagged receiver. To conduct our studies, we consider a shadowed fading channel model incorporating log-normal shadowing and Nakagami-m fading. In addition, various network algorithms, such as power control and frequency (re)allocation, are included in the analytical framework. To evaluate the performance of the proposed solutions, we also derive closed-form expressions for the outage probability and average spectral efficiency with respect to the receiver of interest under various channel conditions and network configurations.

Results show that the analytical framework matches well with numerical results obtained from Monte Carlo simulations, and that the coordination mechanisms substantially improve the performance of overlaid macrocell networks, while also benefiting small cells. In contrast to the uncoordinated Frequency Division Duplexing mode, the coordinated TDD-underlay solution shows a reduction in the outage probability, while the average spectral efficiency increases at high loads. Although more elaborated interference control techniques such as, downlink bitmap and distributed antennas systems become needed, when the density of uncoordinated small cells in the underlaid tier gets high.

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Last updated: 26.8.2013