2,286 research outputs found
A Dynamic Multimedia User-Weight Classification Scheme for IEEE_802.11 WLANs
In this paper we expose a dynamic traffic-classification scheme to support
multimedia applications such as voice and broadband video transmissions over
IEEE 802.11 Wireless Local Area Networks (WLANs). Obviously, over a Wi-Fi link
and to better serve these applications - which normally have strict bounded
transmission delay or minimum link rate requirement - a service differentiation
technique can be applied to the media traffic transmitted by the same mobile
node using the well-known 802.11e Enhanced Distributed Channel Access (EDCA)
protocol. However, the given EDCA mode does not offer user differentiation,
which can be viewed as a deficiency in multi-access wireless networks.
Accordingly, we propose a new inter-node priority access scheme for IEEE
802.11e networks which is compatible with the EDCA scheme. The proposed scheme
joins a dynamic user-weight to each mobile station depending on its outgoing
data, and therefore deploys inter-node priority for the channel access to
complement the existing EDCA inter-frame priority. This provides efficient
quality of service control across multiple users within the same coverage area
of an access point. We provide performance evaluations to compare the proposed
access model with the basic EDCA 802.11 MAC protocol mode to elucidate the
quality improvement achieved for multimedia communication over 802.11 WLANs.Comment: 15 pages, 8 figures, 3 tables, International Journal of Computer
Networks & Communications (IJCNC
Supporting Service Differentiation with Enhancements of the IEEE 802.11 MAC Protocol: Models and Analysis
As one of the fastest growing wireless access technologies, Wireless LANs must evolve to support adequate degrees of service differentiation. Unfortunately, current WLAN standards like IEEE 802.11 Distributed Coordination Function (DCF) lack this ability. Work is in progress to define an enhanced version capable of supporting QoS for multimedia traffic at the MAC layer. In this paper, we aim at gaining insight into three mechanisms to differentiate among traffic categories, i.e., differentiating the minimum contention window size, the Inter-Frame Spacing (IFS) and the length of the packet payload according to the priority of different traffic categories. We propose an analysis model to compute the throughput and packet transmission delays. In additions, we derive approximations to get simpler but more meaningful relationships among different parameters. Comparisons with discrete-event simulation results show that a very good accuracy of performance evaluation can be achieved by using the proposed analysis model
On the Throughput Allocation for Proportional Fairness in Multirate IEEE 802.11 DCF
This paper presents a modified proportional fairness (PF) criterion suitable
for mitigating the \textit{rate anomaly} problem of multirate IEEE 802.11
Wireless LANs employing the mandatory Distributed Coordination Function (DCF)
option. Compared to the widely adopted assumption of saturated network, the
proposed criterion can be applied to general networks whereby the contending
stations are characterized by specific packet arrival rates, , and
transmission rates .
The throughput allocation resulting from the proposed algorithm is able to
greatly increase the aggregate throughput of the DCF while ensuring fairness
levels among the stations of the same order of the ones available with the
classical PF criterion. Put simply, each station is allocated a throughput that
depends on a suitable normalization of its packet rate, which, to some extent,
measures the frequency by which the station tries to gain access to the
channel. Simulation results are presented for some sample scenarios, confirming
the effectiveness of the proposed criterion.Comment: Submitted to IEEE CCNC 200
Throughput Analysis of Primary and Secondary Networks in a Shared IEEE 802.11 System
In this paper, we analyze the coexistence of a primary and a secondary
(cognitive) network when both networks use the IEEE 802.11 based distributed
coordination function for medium access control. Specifically, we consider the
problem of channel capture by a secondary network that uses spectrum sensing to
determine the availability of the channel, and its impact on the primary
throughput. We integrate the notion of transmission slots in Bianchi's Markov
model with the physical time slots, to derive the transmission probability of
the secondary network as a function of its scan duration. This is used to
obtain analytical expressions for the throughput achievable by the primary and
secondary networks. Our analysis considers both saturated and unsaturated
networks. By performing a numerical search, the secondary network parameters
are selected to maximize its throughput for a given level of protection of the
primary network throughput. The theoretical expressions are validated using
extensive simulations carried out in the Network Simulator 2. Our results
provide critical insights into the performance and robustness of different
schemes for medium access by the secondary network. In particular, we find that
the channel captures by the secondary network does not significantly impact the
primary throughput, and that simply increasing the secondary contention window
size is only marginally inferior to silent-period based methods in terms of its
throughput performance.Comment: To appear in IEEE Transactions on Wireless Communication
On the Behavior of the Distributed Coordination Function of IEEE 802.11 with Multirate Capability under General Transmission Conditions
The aim of this paper is threefold. First, it presents a multi-dimensional
Markovian state transition model characterizing the behavior of the IEEE 802.11
protocol at the Medium Access Control layer which accounts for packet
transmission failures due to channel errors modeling both saturated and
non-saturated traffic conditions. Second, it provides a throughput analysis of
the IEEE 802.11 protocol at the data link layer in both saturated and
non-saturated traffic conditions taking into account the impact of both the
physical propagation channel and multirate transmission in Rayleigh fading
environment. The general traffic model assumed is M/M/1/K. Finally, it shows
that the behavior of the throughput in non-saturated traffic conditions is a
linear combination of two system parameters; the payload size and the packet
rates, , of each contending station. The validity interval of
the proposed model is also derived.
Simulation results closely match the theoretical derivations, confirming the
effectiveness of the proposed models.Comment: Submitted to IEEE Transactions on Wireless Communications, October
21, 200
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