A STOCHASTIC GEOMETRIC ANALYSIS OF DEVICE-TO-DEVICE COMMUNICATIONS OPERATING OVER GENERALIZED FADING CHANNELS
ABSTRACT
Device-to-device (D2D) communications are nowconsidered as an integral part of future 5G networks which willenable direct communication between user equipments (UE) andachieve higher throughputs than conventional cellular networks,but with the increased potential for co-channel interference. Thephysical channels which constitute D2D communications can beexpected to be complex in nature, experiencing both line-of-sight(LOS) and non-LOS conditions across closely located D2D pairs.As well as this, given the diverse range of operating environments,they may also be subject to clustering of the scattered multipathcontribution, i.e., propagation characteristics which are quitedissimilar to conventional Rayleigh fading environments. Toaddress these challenges, we consider two recently proposedgeneralized fading models, namely _-_ and _-_, to characterizethe fading behavior in D2D communications. Together, thesemodels encompass many of the most widely utilized fadingmodels in the literature such as Rayleigh, Rice (Nakagamin),Nakagami-m, Hoyt (Nakagami-q) and One-Sided Gaussian.Using stochastic geometry, we evaluate the spectral efficiency andoutage probability of D2D networks under generalized fadingconditions and present new insights into the trade-offs betweenthe reliability, rate, and mode selection. Through numericalevaluations, we also investigate the performance gains of D2Dnetworks and demonstrate their superiority over traditionalcellularnetworks.
EXISTING SYSTEM:
While D2D communications offer many advantages, theyalso come with numerous challenges. These include the difficultiesin accurately modeling the interference induced bycellular and D2D UEs, and consequently optimizing the resourceallocation based on the interference model. Most of theprevious works published in this area have relied on systemlevelsimulations with a large parameter set, meaningthat it is difficult to draw general conclusions. Recently,stochastic geometry has received considerable attention as auseful mathematical tool for interference modeling. Specifically,stochastic geometry treats the locations of the interfereras points distributed according to a spatial point process.Such an approach captures the topological randomness inthe network geometry, offers high analytical flexibility andachieves accurate performance evaluation .Much work has also been done on evaluating the performanceof D2D networks over Rayleigh fading channels. In, the authors have compared two D2D spectrum sharingschemes (overlay and underlay) and evaluated the averageachievable rate for each scheme based on the stochasticgeometric framework. In, the authors extended the workconducted in by considering a D2D link whose lengthdepends on the user density. Flexible mode selections havealso been considered, in a novel strategy is proposedwhich makes use of truncated channel inversion based powercontrol for underlaid D2D networks. Notwithstanding theseadvances, limited work has been conducted to consider D2Dnetworks with general fading channels, for example in,the authors have considered underlaid D2D networks overRician fading channels and evaluated the success probabilityand average achievable rate.
PROPOSED SYSTEM:
The main contributions of this paper may be summarizedas follows.1) We consider generalized fading conditions, namely, (i)_-_ and (ii) _-_ fading, to account for various smallscalefading effects, such as LOS/NLOS conditions,multipath clustering, and power imbalance between thein-phase and quadrature signal components. These twomodels together encompass most of the popular fadingmodels proposed in the literature. We utilize the seriesrepresentation of the _-_/_-_ distributions to improvetractability and achieve closed form expression.2) We analyze the Laplace transform of the interferenceover _-_ and _-_ fading channels and derive a closedform expression for the D2D and cellular links. By usinga channel inversion based power control, we derive theLaplace transform of the interference in a closed formthat does not involve an integral expression.3) We exploit a novel stochastic geometric approach forevaluating the performance of D2D networks over generalizedfading channels. This approach enables us toevaluate the average of an arbitrary function of the SINRas a closed form expression. We invoke the proposedstochastic geometric approach to evaluate the spectralefficiency and outage probability of D2D networks andcompare that to the performance of conventional cellularnetworks. Furthermore, we study the trade-off aa number of performance metrics, which can provideinvaluable insights that may be used to optimize futurenetwork design.
CONCLUSION
In this paper, we have considered a D2D network overlaidon an uplink cellular network, where the locations of themobile UEs as well as the BSs are modeled as PPP. Inparticular, we exploited a novel stochastic geometric approachfor evaluating the D2D network performance under the assumptionof generalized fading conditions described by the __and _-_ fading models. Using these methods, we evaluatedthe spectral efficiency and outage probability of the overlaidD2D network. Specifically, we observed that the D2D linkprovides higher rates than those of the cellular link whenthe spectrum partition factor was appropriately chosen. Underthese circumstances, setting a large mode selection thresholdwill encourage more UEs to use the D2D mode, whichincreases the average rate at the cost of a higher level ofinterference and degraded outage probability. However, forsmaller values of the spectrum partition factor, the D2D linkhas smaller rates than those of the cellular link. In terms ofthe fading parameters, a dominant LOS component (large _)or a large number of scattering clusters (large _) improvethe network performance, i.e., a higher rate and lower outageprobability are achieved. Finally, we also provided numericalresults to demonstrate the performance gains of overlaid D2Dnetworks compared to traditional cellular networks, where thelatter corresponds to _ = 0 case.
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