462 research outputs found
Stochastic analysis of spatial and opportunistic Aloha
International audienceSpatial Aloha is probably the simplest medium access protocol to be used in a large mobile ad hoc network: each station tosses a coin independently of everything else and accesses the channel if it gets heads. In a network where stations are randomly and homogeneously located in the Euclidean plane, there is a way to tune the bias of the coin so as to obtain the best possible compromise between spatial reuse and per transmitter throughput. This paper shows how to address this questions using stochastic geometry and more precisely Poisson shot noise field theory. The theory that is developed is fully computational and leads to new closed form expressions for various kinds of spatial averages (like e.g. outage, throughput or transport). It also allows one to derive general scaling laws that hold for general fading assumptions. We exemplify its flexibility by analyzing a natural variant of Spatial Aloha that we call Opportunistic Aloha and that consists in replacing the coin tossing by an evaluation of the quality of the channel of each station to its receiver and a selection of the stations with good channels (e.g. fading) conditions. We show how to adapt the general machinery to this variant and how to optimize and implement it. We show that when properly tuned, Opportunistic Aloha very significantly outperforms Spatial Aloha, with e.g. a mean throughput per unit area twice higher for Rayleigh fading scenarios with typical parameters
Distributed SIR-Aware Opportunistic Access Control for D2D Underlaid Cellular Networks
In this paper, we propose a distributed interference and channel-aware
opportunistic access control technique for D2D underlaid cellular networks, in
which each potential D2D link is active whenever its estimated
signal-to-interference ratio (SIR) is above a predetermined threshold so as to
maximize the D2D area spectral efficiency. The objective of our SIR-aware
opportunistic access scheme is to provide sufficient coverage probability and
to increase the aggregate rate of D2D links by harnessing interference caused
by dense underlaid D2D users using an adaptive decision activation threshold.
We determine the optimum D2D activation probability and threshold, building on
analytical expressions for the coverage probabilities and area spectral
efficiency of D2D links derived using stochastic geometry. Specifically, we
provide two expressions for the optimal SIR threshold, which can be applied in
a decentralized way on each D2D link, so as to maximize the D2D area spectral
efficiency derived using the unconditional and conditional D2D success
probability respectively. Simulation results in different network settings show
the performance gains of both SIR-aware threshold scheduling methods in terms
of D2D link coverage probability, area spectral efficiency, and average sum
rate compared to existing channel-aware access schemes.Comment: 6 pages, 6 figures, to be presented at IEEE GLOBECOM 201
Stochastic Analysis of Non-slotted Aloha in Wireless Ad-Hoc Networks
In this paper we propose two analytically tractable stochastic models of
non-slotted Aloha for Mobile Ad-hoc NETworks (MANETs): one model assumes a
static pattern of nodes while the other assumes that the pattern of nodes
varies over time. Both models feature transmitters randomly located in the
Euclidean plane, according to a Poisson point process with the receivers
randomly located at a fixed distance from the emitters. We concentrate on the
so-called outage scenario, where a successful transmission requires a
Signal-to-Interference-and-Noise Ratio (SINR) larger than a given threshold.
With Rayleigh fading and the SINR averaged over the duration of the packet
transmission, both models lead to closed form expressions for the probability
of successful transmission. We show an excellent matching of these results with
simulations. Using our models we compare the performances of non-slotted Aloha
to previously studied slotted Aloha. We observe that when the path loss is not
very strong both models, when appropriately optimized, exhibit similar
performance. For stronger path loss non-slotted Aloha performs worse than
slotted Aloha, however when the path loss exponent is equal to 4 its density of
successfully received packets is still 75% of that in the slotted scheme. This
is still much more than the 50% predicted by the well-known analysis where
simultaneous transmissions are never successful. Moreover, in any path loss
scenario, both schemes exhibit the same energy efficiency.Comment: accepted for IEEE Infocom 201
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