Design and Analysis of D2D Communication Mechanisms in 5G Cellular Networks
Abstract
Fifth Generation (5G) cellular networks are expected to cater to booming data demand and immensely high user densities. Device-to-Device (D2D) communication has emerged as a promising enabling technology for 5G to support higher cellular network performance and efficiency. In D2D communication, devices with close proximity establish direct connection among each other with or without network control. Integration of D2D communication into the cellular network can greatly enhance the spectrum utilization as well as creating additional communication opportunities. D2D can be combined with Cognitive Radio (CR) to further enhance spectrum utilization and cellular network performance. Unlike the traditional D2D communication approach which employs only cellular spectrum, cognitive D2D (cD2D) can enable sensing and utilization of non-cellular spectrum opportunistically as well, thus allowing to offload cellular base station traffic to non-cellular spectrum such as WiFi, Bluetooth, or TV white-spaces.
Cognitive D2D users (cDUs) must vacate channel for primary users and hand-off to another secondary channel which renders it quite challenging to meet Quality of Service (QoS) requirements of multi-class cDUs in the presence of higher primary network load. Moreover, mobility of users also causes many problems like blind spots. Blind-spots refer to the areas where wireless signals cannot reach or reach without significant signal strength, they greatly reduce overall system performance in terms of coverage and throughput. Blind-spots often emerge in dynamic environment due to obstacles and mobility of cellular users (CUs).
In first contribution of this work, an enhanced hybrid spectrum access scheme has been developed based on non-switching spectrum hand-off for multi-class DUs, utilizing both interweave and hybrid interweave underlay spectrum access strategies. Further, lower priority cDUs with non-real-time traffic remain in the system and wait for channels to become available, rather than being dropped from the system due to lack of secondary channels. A Continuous-Time Markov Chain (CTMC) has been developed to analyze the performance of the proposed scheme. For comparison, several cases, ranging from the simple cellular network to complex cellular-cognitive-D2D with hybrid-spectrum-access, have been analyzed. The main focus of the analysis is to compare the efficacy of enhanced hybrid spectrum access scheme with individual interweave and hybrid interweave underlay spectrum access strategies in terms of QoS provisioning for multi-class cDUs. The results depict improvement in throughput, spectrum utilization, and extended data delivery time for the proposed scheme and validate the suitability of the proposed scheme to meet QoS requirements for both delay-sensitive and delay-tolerant users of the multi-class cognitive D2D communication system.
In second contribution of this work, a relay-aided cognitive Device to Device (cD2D) communication system underlying 5G cellular network which can help mitigate blind spots and enhance user satisfaction is developed. Cognitive capability helps D2D users (DUs) acquire the spectrum opportunistically for proximity communication and establish a semi-independent network underlying 5G network to offload 5G-New Radio (NR) gNodeB base station and enhance overall system performance. In this work, a relay aided cognitive D2D network is developed which help CUs falling into blind spots to get access to 5G network and increase wireless coverage. However, the selection of a relay among many devices needs mutual consent between relay and the device; further, a suitable incentive mechanism is required to tempt uninterested devices to act as relay involving sharing of their scarce resources. Moreover, it is very critical to match devices to suitable relays by ensuring privacy to guarantee user data integrity. In this work, cD2D enabled relay selection algorithm (cDERSA) is proposed wherein the cognitive D2D users (cDUs), which are CUs within blind spots and cognitive relay users (cDRs) which are relay capable CUs, establish a relayed cD2D link to access 5G-NR gNodeB. All users will first scan their surroundings for possible D2D candidate and based on multi-criteria objective functions build their priority table. A stable marriage problem (SMP) is formulated and solved using a unique stable distributed matching algorithm based on Gale-Shapley matching algorithm (GSMA). A new incentive mechanism is also developed to keep cDRs motivated to act as relays. Simulations have been performed and their results validate the significant improvement in throughput and average DU satisfaction with cDERSA.
The work in this thesis has demonstrated that the performance of 5G cellular networks can significantly be enhanced through integration and combination of various enabling technologies that can help in meeting the demands and expectations that has been placed on 5G systems.
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