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.