Dynamic spectrum sharing and coexistence with full-duplex device-to-device communications in 5G networks

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Opportunistic Spectrum Access has recently become the most desirable solution for greatly improving the performance of telecommunication systems. It has proven to be a viable solution to cope with the challenging problem of spectrum scarcity and also it has been widely explored in 5G networks, so that multiple random access technologies can coexist in a cognitive setup. In 5G networks, such secondary technology candidates like Device-to-Device (D2D) communications, and Licensed-Assisted Access are envisioned to opportunistically exploit spectrum opportunities and coexist with primary technologies like LTE or WiFi. Moreover, Full Duplex (FD) technology is envisioned to play a significant role in 5G networks by allowing a user to transmit and receive on the same frequency band. In this thesis, we present a comparative performance analysis of the spectral efficiency in a heterogeneous system where a cellular network allows the FD-Enabled D2D network to use opportunistically its spectrum while ensuring protection for its transmission/reception through guard zones. The main contributions and emphasis of this work are to explore the spectrum opportunities for secondary users by: firstly, deriving their probability of successful transmissions, deciding the feasible mode of operation (half-duplex, full-duplex or silent); and secondly, incorporating the protection zone for primary users. We assess the overall system performance, analyze the impact of different access mechanisms and propose an efficient mode selection for secondary users. Such a systematic analysis of the integrated technologies requires a rigorous and critical evaluation of the performance gains and the costs incurred in terms of increased interference. Also, ultra-dense and random network models are envisioned in future networks especially in the urban scenario, hence, pre-deployment average system performance over various deployment scenarios can in fact be advantageous. In this thesis, we use stochastic geometry to model and analyze different coexistence scenarios and spectrum sharing frameworks in 5G networks for multiple radio access technologies. We also assess different coexistence methodologies for secondary users to fairly and peacefully coexist with primary users while ensuring the interference protection for primary users. In summary, FD enabled heterogeneous networks have not been critically studied in previous literature, and for this reason a comprehensive study on the use of FD to existing systems is needed. This thesis proposes an innovative FD enabled D2D cognitive setup and carefully studies the improvement in system performance while taking into account the cost of these gains in 5G networks, using stochastic geometry tools.
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