103 research outputs found
On the Catalyzing Effect of Randomness on the Per-Flow Throughput in Wireless Networks
This paper investigates the throughput capacity of a flow crossing a
multi-hop wireless network, whose geometry is characterized by general
randomness laws including Uniform, Poisson, Heavy-Tailed distributions for both
the nodes' densities and the number of hops. The key contribution is to
demonstrate \textit{how} the \textit{per-flow throughput} depends on the
distribution of 1) the number of nodes inside hops' interference sets, 2)
the number of hops , and 3) the degree of spatial correlations. The
randomness in both 's and is advantageous, i.e., it can yield larger
scalings (as large as ) than in non-random settings. An interesting
consequence is that the per-flow capacity can exhibit the opposite behavior to
the network capacity, which was shown to suffer from a logarithmic decrease in
the presence of randomness. In turn, spatial correlations along the end-to-end
path are detrimental by a logarithmic term
A measurement-based approach to service modeling and bandwidth estimation in IEEE 802.11 wireless networks
[no abstract
Understanding Fairness and its Impact on Quality of Service in IEEE 802.11
The Distributed Coordination Function (DCF) aims at fair and efficient medium
access in IEEE 802.11. In face of its success, it is remarkable that there is
little consensus on the actual degree of fairness achieved, particularly
bearing its impact on quality of service in mind. In this paper we provide an
accurate model for the fairness of the DCF. Given M greedy stations we assume
fairness if a tagged station contributes a share of 1/M to the overall number
of packets transmitted. We derive the probability distribution of fairness
deviations and support our analytical results by an extensive set of
measurements. We find a closed-form expression for the improvement of long-term
over short-term fairness. Regarding the random countdown values we quantify the
significance of their distribution whereas we discover that fairness is largely
insensitive to the distribution parameters. Based on our findings we view the
DCF as emulating an ideal fair queuing system to quantify the deviations from a
fair rate allocation. We deduce a stochastic service curve model for the DCF to
predict packet delays in IEEE 802.11. We show how a station can estimate its
fair bandwidth share from passive measurements of its traffic arrivals and
departures
Scheduling for next generation WLANs: filling the gap between offered and observed data rates
In wireless networks, opportunistic scheduling is used to increase system throughput by exploiting multi-user diversity. Although recent advances have increased physical layer data rates supported in wireless local area networks (WLANs), actual throughput realized are significantly lower due to overhead. Accordingly, the frame aggregation concept is used in next generation WLANs to improve efficiency. However, with frame aggregation, traditional opportunistic schemes are no longer optimal. In this paper, we propose schedulers that take queue and channel conditions into account jointly, to maximize throughput observed at the users for next generation WLANs. We also extend this work to design two schedulers that perform block scheduling for maximizing network throughput over multiple transmission sequences. For these schedulers, which make decisions over long time durations, we model the system using queueing theory and determine users' temporal access proportions according to this model. Through detailed simulations, we show that all our proposed algorithms offer significant throughput improvement, better fairness, and much lower delay compared with traditional opportunistic schedulers, facilitating the practical use of the evolving standard for next generation wireless networks
On the Asymptotic Validity of the Decoupling Assumption for Analyzing 802.11 MAC Protocol
Performance evaluation of the 802.11 MAC protocol is classically based on the
decoupling assumption, which hypothesizes that the backoff processes at
different nodes are independent. This decoupling assumption results from mean
field convergence and is generally true in transient regime in the asymptotic
sense (when the number of wireless nodes tends to infinity), but, contrary to
widespread belief, may not necessarily hold in stationary regime. The issue is
often related with the existence and uniqueness of a solution to a fixed point
equation; however, it was also recently shown that this condition is not
sufficient; in contrast, a sufficient condition is a global stability property
of the associated ordinary differential equation. In this paper, we give a
simple condition that establishes the asymptotic validity of the decoupling
assumption for the homogeneous case. We also discuss the heterogeneous and the
differentiated service cases and formulate a new ordinary differential
equation. We show that the uniqueness of a solution to the associated fixed
point equation is not sufficient; we exhibit one case where the fixed point
equation has a unique solution but the decoupling assumption is not valid in
the asymptotic sense in stationary regime.Comment: 16 pages, 4 figures, accepted for publication in IEEE Transactions on
Information Theor
End-to-End Delay Distribution Analysis for Stochastic Admission Control in Multi-hop Wireless Networks
published_or_final_versio
W-CBS: A Scheduling Algorithm for Supporting QoS in IEEE 802.11e
This paper presents a new scheduling algorithm, the Wireless Constant Bandwidth Server (W-CBS) for the Access Points of an IEEE 802.11e wireless networks to support traffic streams with Quality of Service guarantees, in particular in the case of multimedia applications which present variable bit rate traffic. The performance of W-CBS is compared to that of the reference scheduler defined in 802.11e standard using the ns2 simulator. The results show that the W-CBS outperforms the reference scheduler with VBR traffic, in terms of resource utilization and maximum admitted flows
- …