336 research outputs found
Unmanned Aerial Vehicle with Underlaid Device-to-Device Communications: Performance and Tradeoffs
In this paper, the deployment of an unmanned aerial vehicle (UAV) as a flying
base station used to provide on the fly wireless communications to a given
geographical area is analyzed. In particular, the co-existence between the UAV,
that is transmitting data in the downlink, and an underlaid device-todevice
(D2D) communication network is considered. For this model, a tractable
analytical framework for the coverage and rate analysis is derived. Two
scenarios are considered: a static UAV and a mobile UAV. In the first scenario,
the average coverage probability and the system sum-rate for the users in the
area are derived as a function of the UAV altitude and the number of D2D users.
In the second scenario, using the disk covering problem, the minimum number of
stop points that the UAV needs to visit in order to completely cover the area
is computed. Furthermore, considering multiple retransmissions for the UAV and
D2D users, the overall outage probability of the D2D users is derived.
Simulation and analytical results show that, depending on the density of D2D
users, optimal values for the UAV altitude exist for which the system sum-rate
and the coverage probability are maximized. Moreover, our results also show
that, by enabling the UAV to intelligently move over the target area, the total
required transmit power of UAV while covering the entire area, is minimized.
Finally, in order to provide a full coverage for the area of interest, the
tradeoff between the coverage and delay, in terms of the number of stop points,
is discussed.Comment: accepted in the IEEE Transactions on Wireless Communication
A Stochastic Geometric Analysis of Device-to-Device Communications Operating over Generalized Fading Channels
Device-to-device (D2D) communications are now considered as an integral part
of future 5G networks which will enable direct communication between user
equipment (UE) without unnecessary routing via the network infrastructure. This
architecture will result in higher throughputs than conventional cellular
networks, but with the increased potential for co-channel interference induced
by randomly located cellular and D2D UEs. The physical channels which
constitute D2D communications can be expected to be complex in nature,
experiencing both line-of-sight (LOS) and non-LOS (NLOS) 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
multipath contribution, i.e., propagation characteristics which are quite
dissimilar to conventional Rayeligh fading environments. To address these
challenges, we consider two recently proposed generalized fading models, namely
and , to characterize the fading behavior in D2D
communications. Together, these models encompass many of the most widely
encountered and utilized fading models in the literature such as Rayleigh, Rice
(Nakagami-), Nakagami-, Hoyt (Nakagami-) and One-Sided Gaussian. Using
stochastic geometry we evaluate the rate and bit error probability of D2D
networks under generalized fading conditions. Based on the analytical results,
we present new insights into the trade-offs between the reliability, rate, and
mode selection under realistic operating conditions. Our results suggest that
D2D mode achieves higher rates over cellular link at the expense of a higher
bit error probability. Through numerical evaluations, we also investigate the
performance gains of D2D networks and demonstrate their superiority over
traditional cellular networks.Comment: Submitted to IEEE Transactions on Wireless Communication
Spectrum Leasing as an Incentive towards Uplink Macrocell and Femtocell Cooperation
The concept of femtocell access points underlaying existing communication
infrastructure has recently emerged as a key technology that can significantly
improve the coverage and performance of next-generation wireless networks. In
this paper, we propose a framework for macrocell-femtocell cooperation under a
closed access policy, in which a femtocell user may act as a relay for
macrocell users. In return, each cooperative macrocell user grants the
femtocell user a fraction of its superframe. We formulate a coalitional game
with macrocell and femtocell users being the players, which can take individual
and distributed decisions on whether to cooperate or not, while maximizing a
utility function that captures the cooperative gains, in terms of throughput
and delay.We show that the network can selforganize into a partition composed
of disjoint coalitions which constitutes the recursive core of the game
representing a key solution concept for coalition formation games in partition
form. Simulation results show that the proposed coalition formation algorithm
yields significant gains in terms of average rate per macrocell user, reaching
up to 239%, relative to the non-cooperative case. Moreover, the proposed
approach shows an improvement in terms of femtocell users' rate of up to 21%
when compared to the traditional closed access policy.Comment: 29 pages, 11 figures, accepted at the IEEE JSAC on Femtocell Network
Device-to-Device Communications in the Millimeter Wave Band: A Novel Distributed Mechanism
In spite of its potential advantages, the large-scale implementation of the
device-to-device (D2D) communications has yet to be realized, mainly due to
severe interference and lack of enough bandwidth in the microwave (W)
band. Recently, exploiting the millimeter wave (mmW) band for D2D
communications has attracted considerable attention as a potential solution to
these challenges. However, its severe sensitivity to blockage along with its
directional nature make the utilization of the mmW band a challenging task as
it requires line-of-sight (LOS) link detection and careful beam alignment
between the D2D transceivers. In this paper, we propose a novel distributed
mechanism which enables the D2D devices to discover unblocked LOS links for the
mmW band communication. Moreover, as such LOS links are not always available,
the proposed mechanism allows the D2D devices to switch to the W band if
necessary. In addition, the proposed mechanism detects the direction of the LOS
links to perform the beam alignment. We have used tools from stochastic
geometry to evaluate the performance of the proposed mechanism in terms of the
signal-to-interference-plus-noise ratio (SINR) coverage probability. The
performance of the proposed algorithm is then compared to the one of the single
band (i.e., W/mmW) communication. The simulation results show that the
proposed mechanism considerably outperforms the single band communication.Comment: 6 Pages, 6 Figures, Accepted for presentation in Wireless
Telecommunication Symposium (WTS'18
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