490 research outputs found
Providing Dynamic TXOP for QoS Support of Video Transmission in IEEE 802.11e WLANs
The IEEE 802.11e standard introduced by IEEE 802.11 Task Group E (TGe)
enhances the Quality of Service (QoS) by means of HCF Controlled Channel Access
(HCCA). The scheduler of HCCA allocates Transmission Opportunities (TXOPs) to
QoS-enabled Station (QSTA) based on their TS Specifications (TSPECs) negotiated
at the traffic setup time so that it is only efficient for Constant Bit Rate
(CBR) applications. However, Variable Bit Rate (VBR) traffics are not
efficiently supported as they exhibit nondeterministic profile during the time.
In this paper, we present a dynamic TXOP assignment Scheduling Algorithm for
supporting the video traffics transmission over IEEE 802.11e wireless networks.
This algorithm uses a piggybacked information about the size of the subsequent
video frames of the uplink traffic to assist the Hybrid Coordinator accurately
assign the TXOP according to the fast changes in the VBR profile. The proposed
scheduling algorithm has been evaluated using simulation with different
variability level video streams. The simulation results show that the proposed
algorithm reduces the delay experienced by VBR traffic streams comparable to
HCCA scheduler due to the accurate assignment of the TXOP which preserve the
channel time for transmission.Comment: arXiv admin note: substantial text overlap with arXiv:1602.0369
An admission control scheme for IEEE 802.11e wireless local area networks
Includes bibliographical references (leaves 80-84).Recent times has seen a tremendous increase in the deployment and use of 802.11 Wireless Local Area Networks (WLANs). These networks are easy to deploy and maintain, while providing reasonably high data rates at a low cost. In the paradigm of Next-Generation-Networks (NGNs), WLANs can be seen as an important access network technology to support IP multimedia services. However a traditional WLAN does not provide Quality of Service (QoS) support since it was originally designed for best effort operation. The IEEE 802. 11e standard was introduced to overcome the lack of QoS support for the legacy IEEE 802 .11 WLANs. It enhances the Media Access Control (MAC) layer operations to incorporate service differentiation. However, there is a need to prevent overloading of wireless channels, since the QoS experienced by traffic flows is degraded with heavily loaded channels. An admission control scheme for IEEE 802.11e WLANs would be the best solution to limit the amount of multimedia traffic so that channel overloading can be prevented. Some of the work in the literature proposes admission control solutions to protect the QoS of real-time traffic for IEEE 802.11e Enhanced Distributed Channel Access (EDCA). However, these solutions often under-utilize the resources of the wireless channels. A measurement-aided model-based admission control scheme for IEEE 802.11e EDCA WLANs is proposed to provide reasonable bandwidth guarantees to all existing flows. The admission control scheme makes use of bandwidth estimations that allows the bandwidth guarantees of all the flows that are admitted into the network to be protected. The bandwidth estimations are obtained using a developed analytical model of IEEE 802.11e EDCA channels. The admission control scheme also aims to accept the maximum amount of flows that can be accommodated by the network's resources. Through simulations, the performance of the proposed admission control scheme is evaluated using NS-2. Results show that accurate bandwidth estimations can be obtained when comparing the estimated achievable bandwidth to actual simulated bandwidth. The results also validate that the bandwidth needs of all admitted traffic are always satisfied when the admission control scheme is applied. It was also found that the admission control scheme allows the maximum amount of flows to be admitted into the network, according the network's capacity
Applications of Soft Computing in Mobile and Wireless Communications
Soft computing is a synergistic combination of artificial intelligence methodologies to model and solve real world problems that are either impossible or too difficult to model mathematically. Furthermore, the use of conventional modeling techniques demands rigor, precision and certainty, which carry computational cost. On the other hand, soft computing utilizes computation, reasoning and inference to reduce computational cost by exploiting tolerance for imprecision, uncertainty, partial truth and approximation. In addition to computational cost savings, soft computing is an excellent platform for autonomic computing, owing to its roots in artificial intelligence. Wireless communication networks are associated with much uncertainty and imprecision due to a number of stochastic processes such as escalating number of access points, constantly changing propagation channels, sudden variations in network load and random mobility of users. This reality has fuelled numerous applications of soft computing techniques in mobile and wireless communications. This paper reviews various applications of the core soft computing methodologies in mobile and wireless communications
Quality Of Service Provisioning Scheme For Real-Time Applications in IEEE 802.11 Wireless Local Area Network
This thesis presents a novel quality of service (QoS) provisioning scheme for realtime
applications in IEEE 802.1 1e wireless local area networks (WLAN). The
emerging 802.1 1e standard is tackling the exploding volume of traffic in WLANs
with a long -term solution based on QoS-architectures. QoS delivers predictability
and consistency into existing variability of best-effort delivery system offered in
internet protocol (IP) and IEEE 802.11 wireless networks.
Service differentiation in WLAN networks is achieved by means of assigning
packets (from the network layer) to different access categories (AC), a set of fixed
medium access control (MAC) level parameters that defines the priority echelon for
each AC. Thus real-time applications are assigned higher priority ACs to ensure
better service and to ensure that the delay constraints of these applications are
promptly dealt with.
An algorithm called Slide and Translate (SNT) is proposed for IEEE 802.1 1
WLANs. The SNT adapts contention parameters of individual ACs based on the network load in a basic service set (BSS). SNT is derived from the observations of
the success and failures of previously proposed QoS provisioning schemes. The SNT
adapts the backoff interval, minimum contention window (CW,,,) and contention
offset (CWOffsetto) ensure the QoS constraints for the different ACs are dealt with.
To further understand the SNT, a simple mathematical analysis is presented on the
inter-AC differentiation characteristics; subsequently, through simulation it is shown
that SNT is able to maintain high medium utilisation over a wide range of offered
loads while providing a high degree of isolation (in terms of throughput, delay and
frame loss) to high priority traffic.
Further to this, an extension to the SNT called SNT-AC is proposed in order to
achieve efficient end-to-end resource provisioning. SNT-AC uses an admission
control algorithm to restrict flows in and out of the BSS. The admission controller
resides in the IP layer and makes decision based on the MAC level feedback. The
simulation results indicate that the close coupling QoS coordination can ensure both
bandwidth and latency to admitted flows by controlling the effective offered load
into the BSS. This guarantees high priority ACs protection against overwhelming
traffic in a WLAN.
Finally a brief discussion on future directions of WLANs and hardware
implementation issues conclude the thesis
VoIP Call Admission Control in WLANs in Presence of Elastic Traffic
VoIP service over WLAN networks is a promising alternative to provide mobile voice communications. However, several performance problems appear due to i) heavy protocol overheads, ii) unfairness and asymmetry between the uplink and downlink flows, and iii) the coexistence with other traffic flows. This paper addresses the performance of VoIP communications with simultaneous presence of bidirectional TCP traffic, and shows how the presence of elastic flows drastically reduces the capacity of the system. To solve this limitation a simple solution is proposed using an adaptive Admission and Rate Control algorithm which tunes the BEB (Binary Exponential Backoff) parameters. Analytical results are obtained by using an IEEE 802.11e user centric queuing model based on a bulk service M=G[1;B]=1=K queue, which is able to capture the main dynamics of the EDCA-based traffic differentiation parameters (AIFS, BEB and TXOP). The results show that the improvement achieved by our scheme on the overall VoIP performance is significant
- …