195 research outputs found
Adaptive Segregation-Based MAC Protocol for Real-Time Multimedia Traffic in WLANs
Wireless local area networks (WLANs) have become very popular both in private and public sectors. Despite the fast expansion of WLANs in various environments, quality of service (QoS) issues for multimedia applications in WLANs are not yet resolved. Multimedia applications contain traffic that are sensitive to delay and jitter and therefore a best-effort protocol such as the legacy IEEE 802.11 is not suitable. The 802.11e protocol provides prioritization and classification of traffic to offer better QoS for real-time services. However, it leaves the design and implementation of many important optimization features to vendors. In this paper we introduce a mechanism to improve the delay and jitter of real-time traffic in WLAN nodes supporting multimedia applications. In our proposed mechanism, we segregate voice and video traffic from the best-effort traffic. We create a scheduler that schedules the access of real-time traffic and non real-time traffic to the medium with centralized polling and distributed contention respectively. We show that our proposed protocol performs better in terms of delay and jitter than the legacy 802.11 and 802.11e in a scenario where all wireless nodes carry multimedia traffic simultaneously
Optimization of the interoperability and dynamic spectrum management in mobile communications systems beyond 3G
The future wireless ecosystem will heterogeneously integrate a number of overlapped Radio
Access Technologies (RATs) through a common platform. A major challenge arising from the
heterogeneous network is the Radio Resource Management (RRM) strategy. A Common RRM
(CRRM) module is needed in order to provide a step toward network convergence. This work
aims at implementing HSDPA and IEEE 802.11e CRRM evaluation tools.
Innovative enhancements to IEEE 802.11e have been pursued on the application of cross-layer
signaling to improve Quality of Service (QoS) delivery, and provide more efficient usage of
radio resources by adapting such parameters as arbitrary interframe spacing, a differentiated
backoff procedure and transmission opportunities, as well as acknowledgment policies (where
the most advised block size was found to be 12). Besides, the proposed cross-layer algorithm
dynamically changes the size of the Arbitration Interframe Space (AIFS) and the Contention
Window (CW) duration according to a periodically obtained fairness measure based on the Signal
to Interference-plus-Noise Ratio (SINR) and transmission time, a delay constraint and the
collision rate of a given machine. The throughput was increased in 2 Mb/s for all the values of
the load that have been tested whilst satisfying more users than with the original standard. For
the ad hoc mode an analytical model was proposed that allows for investigating collision free
communications in a distributed environment.
The addition of extra frequency spectrum bands and an integrated CRRM that enables spectrum
aggregation was also addressed. RAT selection algorithms allow for determining the gains obtained
by using WiFi as a backup network for HSDPA. The proposed RAT selection algorithm
is based on the load of each system, without the need for a complex management system. Simulation
results show that, in such scenario, for high system loads, exploiting localization while
applying load suitability optimization based algorithm, can provide a marginal gain of up to
450 kb/s in the goodput. HSDPA was also studied in the context of cognitive radio, by considering
two co-located BSs operating at different frequencies (in the 2 and 5 GHz bands) in the
same cell. The system automatically chooses the frequency to serve each user with an optimal
General Multi-Band Scheduling (GMBS) algorithm. It was shown that enabling the access to
a secondary band, by using the proposed Integrated CRRM (iCRRM), an almost constant gain
near 30 % was obtained in the throughput with the proposed optimal solution, compared to a
system where users are first allocated in one of the two bands and later not able to handover
between the bands. In this context, future cognitive radio scenarios where IEEE 802.11e ad hoc
modes will be essential for giving access to the mobile users have been proposed
An improved medium access control protocol for real-time applications in WLANs and its firmware development
The IEEE 802.11 Wireless Local Area Network (WLAN), commonly known as Wi-Fi, has emerged as a popular internet access technology and researchers are continuously working on improvement of the quality of service (QoS) in WLAN by proposing new and efficient schemes. Voice and video over Internet Protocol (VVoIP) applications are becoming very popular in Wi-Fi enabled portable/handheld devices because of recent technological advancements and lower service costs. Different from normal voice and video streaming, these applications demand symmetric throughput for the upstream and downstream. Existing Wi-Fi standards are optimised for generic internet applications and fail to provide symmetric throughput due to traffic bottleneck at access points. Performance analysis and benchmarking is an integral part of WLAN research, and in the majority of the cases, this is done through computer simulation using popular network simulators such as Network Simulator ff 2 (NS-2) or OPNET. While computer simulation is an excellent approach for saving time and money, results generated from computer simulations do not always match practical observations. This is why, for proper assessment of the merits of a proposed system in WLAN, a trial on a practical hardware platform is highly recommended and is often a requirement. In this thesis work, with a view to address the abovementioned challenges for facilitating VoIP and VVoIP services over Wi-Fi, two key contributions are made: i) formulating a suitable medium access control (MAC) protocol to address symmetric traffic scenario and ii) firmware development of this newly devised MAC protocol for real WLAN hardware. The proposed solution shows signifocant improvements over existing standards by supporting higher number of stations with strict QoS criteria. The proposed hardware platform is available off-the-shelf in the market and is a cost effective way of generating and evaluating performance results on a hardware system
Quality Of Service Improvement With 802.11e Edca Scheme Using Enhanced Adaptive Contention Window Algorithm
Currently users of data services is growing exponentially and the content
accessed by the users are browsing, social media, video streaming and VOIP. Real
time and multimedia communications with Quality of Service (QoS) support are
important in wireless networks of any nature due to network limited capacity. This
QoS is to support the growing demand of services like VoIP, streaming and video
conferencing. The most connection commonly used is wireless LAN IEEe 802.11.
Wireless Local Area Networks (WLANs) have emerged as one of the
prevailing technologies for the broadband wireless access. However, there is a
constraint on Wi-Fi network for media sharing method that relies on the CSMA/CA.
There is a mechanism requirement to improve the Quality of Service in a Wi-Fi
network with a certain method that delivering good Wi-Fi service for real-time and
non-real time traffic.
The introduction in the IEEE 802.11e standard of a new contention access
scheme called Enhanced Distributed Channel Access (EDCA) has provided a new
mechanisms for QoS support compared with previous method called Distributed
Coordination Function (DCF) used in the widely deployed 802.11 WLANs. EDCA
scheme provide four traffic type (voice, video, best effor and background task)
which is called Access Category (AC) to define the priority. Real time traffic such
as VoIP requires good throughput and delay so the priority is the highest.
There are three parameters in EDCA to improve Quality of Service i.e
TXOP (Transmission Opportunity), AIFS (Arbitrary Inter Frame Space) and CW
(Contention Windows). Based on the main reference for throughput and delay
improvement, this research will adjust contention window value adaptively.
Adjustment is based on number of station involved in the network and collision
probability. The more number of stations or the lower contention window value will
result higher collision probability. Different Access Category will have different
adjustment to get optimum throughput and delay improvement.
To validate the result of contention window adjustment, simulation using
NS-2 is applied. Simulation is done during low traffic (non-saturated) and high
traffic (saturated) network. The algorithm avoids saturation and protects the
admitted traffics from being degraded, through a continuous monitoring of the
available resources. The proposed algorithm leads the throughput improvement by
2.29% and delay improvement by 3.32% in average for all traffic category. VOIP
traffic gets the highest improvement for all condition of traffic. Best effort traffic
gets very small improvement during low traffic and considered no improvement
during saturated traffic
THE INFLUENCE OF MAC BUFFER ON THE CONTENTION-BASED ACCESS SCHEME WITH BURSTING OPTION FOR IEEE 802.11E WIRELESS NETWORKS
Wireless LANs are increasingly being used for inelastic applications. Currently, there is little support for quality of service in the IEEE 802.11 MAC protocol, and IEEE task group E has defined the 802.11e MAC extension. Enhanced distributed channel access (EDCA) is a contention-based scheme of the 802.11e standard. To allow a station to transmit more than one frame from a single contention, an optional feature known as controlled frame-bursting (CFB) is introduced in the standard. In this paper, we initially performed an average analysis to determine a suitable burst duration limit. Then, a detailed evaluation and comparison of the EDCA protocol with the CFB option is carried out through simulation to quantify its performance gain. The impact of the MAC transmit buffer size is also incorporated. Accordingly, we have proposed a suitable approach to guide the configuration of the burst duration limit. It is demonstrated that an optimized CFB configuration allows the MAC protocol to achieve 30% more capacity than the basic EDCA scheme
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