283 research outputs found
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
A New Phase Transition for Local Delays in MANETs
We consider Mobile Ad-hoc Network (MANET) with transmitters located according
to a Poisson point in the Euclidean plane, slotted Aloha Medium Access (MAC)
protocol and the so-called outage scenario, where a successful transmission
requires a Signal-to-Interference-and-Noise (SINR) larger than some threshold.
We analyze the local delays in such a network, namely the number of times slots
required for nodes to transmit a packet to their prescribed next-hop receivers.
The analysis depends very much on the receiver scenario and on the variability
of the fading. In most cases, each node has finite-mean geometric random delay
and thus a positive next hop throughput. However, the spatial (or large
population) averaging of these individual finite mean-delays leads to infinite
values in several practical cases, including the Rayleigh fading and positive
thermal noise case. In some cases it exhibits an interesting phase transition
phenomenon where the spatial average is finite when certain model parameters
are below a threshold and infinite above. We call this phenomenon, contention
phase transition. We argue that the spatial average of the mean local delays is
infinite primarily because of the outage logic, where one transmits full
packets at time slots when the receiver is covered at the required SINR and
where one wastes all the other time slots. This results in the "RESTART"
mechanism, which in turn explains why we have infinite spatial average.
Adaptive coding offers a nice way of breaking the outage/RESTART logic. We show
examples where the average delays are finite in the adaptive coding case,
whereas they are infinite in the outage case.Comment: accepted for IEEE Infocom 201
A Unifying Framework for Local Throughput in Wireless Networks
With the increased competition for the electromagnetic spectrum, it is
important to characterize the impact of interference in the performance of a
wireless network, which is traditionally measured by its throughput. This paper
presents a unifying framework for characterizing the local throughput in
wireless networks. We first analyze the throughput of a probe link from a
connectivity perspective, in which a packet is successfully received if it does
not collide with other packets from nodes within its reach (called the audible
interferers). We then characterize the throughput from a
signal-to-interference-plus-noise ratio (SINR) perspective, in which a packet
is successfully received if the SINR exceeds some threshold, considering the
interference from all emitting nodes in the network. Our main contribution is
to generalize and unify various results scattered throughout the literature. In
particular, the proposed framework encompasses arbitrary wireless propagation
effects (e.g, Nakagami-m fading, Rician fading, or log-normal shadowing), as
well as arbitrary traffic patterns (e.g., slotted-synchronous,
slotted-asynchronous, or exponential-interarrivals traffic), allowing us to
draw more general conclusions about network performance than previously
available in the literature.Comment: Submitted for journal publicatio
Uncoordinated access schemes for the IoT: approaches, regulations, and performance
Internet of Things (IoT) devices communicate using a variety of protocols,
differing in many aspects, with the channel access method being one of the most
important. Most of the transmission technologies explicitly designed for IoT
and Machine-to-Machine (M2M) communication use either an ALOHA-based channel
access or some type of Listen Before Talk (LBT) strategy, based on carrier
sensing. In this paper, we provide a comparative overview of the uncoordinated
channel access methods for IoT technologies, namely ALOHA-based and LBT
schemes, in relation with the ETSI and FCC regulatory frameworks. Furthermore,
we provide a performance comparison of these access schemes, both in terms of
successful transmissions and energy efficiency, in a typical IoT deployment.
Results show that LBT is effective in reducing inter-node interference even for
long-range transmissions, though the energy efficiency can be lower than that
provided by ALOHA methods. The adoption of rate-adaptation schemes,
furthermore, lowers the energy consumption while improving the fairness among
nodes at different distances from the receiver. Coexistence issues are also
investigated, showing that in massive deployments LBT is severely affected by
the presence of ALOHA devices in the same area
Comparison of the Maximal Spatial Throughput of Aloha and CSMA in Wireless Ad-Hoc Networks
International audienceIn this paper we compare the spatial throughput of Aloha and Carrier Sense Multiple Access (CSMA) in Wireless multihop Ad-Hoc Networks. In other words we evaluate the gain offered by carrier sensing (CSMA) over the pure statiscal collision avoidance which is the basis of Aloha. We use a Signal-to-Interference-and-Noise Ratio (SINR) model where a transmission is assumed to be successful when the SINR is larger than a given threshold. Regarding channel conditions, we consider both standard Rayleigh and negligible fading. For slotted and non-slotted Aloha, we use analytical models as well as simulations to study the density of successful transmissions in the network. As it is very difficult to build precise models for CSMA, we use only simulations to compute the performances of this protocol. We compare the two Aloha versions and CSMA on a fair basis, i.e. when they are optimized to maximize the density of successful transmissions. For slotted Aloha, the key optimization parameter is the medium access probability, for non-slotted Aloha we tune the mean back-off time, whereas for CSMA it is the carrier sense threshold that is adjusted. Our study shows that CSMA always outperforms slotted Aloha, which in turn outperforms its non-slotted version
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
A Comprehensive Survey of Potential Game Approaches to Wireless Networks
Potential games form a class of non-cooperative games where unilateral
improvement dynamics are guaranteed to converge in many practical cases. The
potential game approach has been applied to a wide range of wireless network
problems, particularly to a variety of channel assignment problems. In this
paper, the properties of potential games are introduced, and games in wireless
networks that have been proven to be potential games are comprehensively
discussed.Comment: 44 pages, 6 figures, to appear in IEICE Transactions on
Communications, vol. E98-B, no. 9, Sept. 201
Interference in spatial non-slotted Aloha networks
In this paper we propose two analytically tractable stochastic-geometric models of interference in ad-hoc networks using pure (non-slotted) Aloha as the medium access. In contrast to the slotted model, the interference in pure Aloha may vary during the transmission of a tagged packet. We develop closed form expressions for the Laplace transform of the empirical average of the interference experienced during the transmission of a typical packet. Both models assume a power-law path-loss function with arbitrarily distributed fading and feature configurations of transmitters randomly located in the Euclidean plane according to a Poisson point process. Depending on the model, these configurations vary over time or are static. We apply our analysis of the interference to study the Signal-to-Interference-and-Noise Ratio (SINR) outage probability for a typical transmission in pure Aloha. The results are used to compare the performance of non-slotted Aloha to slotted Aloha, which has almost exclusively been previously studied in the same context of mobile ad-hoc networks
Achieving Non-Zero Information Velocity in Wireless Networks
In wireless networks, where each node transmits independently of other nodes
in the network (the ALOHA protocol), the expected delay experienced by a packet
until it is successfully received at any other node is known to be infinite for
signal-to-interference-plus-noise-ratio (SINR) model with node locations
distributed according to a Poisson point process. Consequently, the information
velocity, defined as the limit of the ratio of the distance to the destination
and the time taken for a packet to successfully reach the destination over
multiple hops, is zero, as the distance tends to infinity. A nearest neighbor
distance based power control policy is proposed to show that the expected delay
required for a packet to be successfully received at the nearest neighbor can
be made finite. Moreover, the information velocity is also shown to be non-zero
with the proposed power control policy. The condition under which these results
hold does not depend on the intensity of the underlying Poisson point process.Comment: to appear in Annals of Applied Probabilit
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