D2 d delay aware distributed dynamic adaptation of contention windowin wireless networks

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D2D: DELAY-AWARE DISTRIBUTED DYNAMIC ADAPTATION OF CONTENTION
WINDOWIN WIRELESS NETWORKS
ABSTRACT
The IEEE 802.11e enhanced distributed channel access (EDCA) protocol follows class-
based service differentiation for providing differentiated quality-of-service (QoS). However, its
collision avoidance mechanism using backoff algorithm can be inefficient for providing
improved performance with respect to throughput and channel access delay, especially in a high
network configuration (i.e. number of stations) with imperfect wireless channel. The existing and
emerging works have devoted considerable attention on tuning the backoff parameters for
achieving optimal throughput only. The prior works do not consider the channel access delay and
throughput metrics altogether for performance improvement. Additionally, in most of the cases,
the optimal configuration of backoff parameters is performed by a centralized controller. In this
paper, we propose a delay-aware distributed dynamic adaptation of contention window scheme,
namely D2D, for the cumulative improvement of both the throughput and the channel access
delay at runtime. The D2D scheme requires two ad-hoc, distributed, and easy-to-obtain estimates
– delay deviation ratio and channel busyness ratio – of the present delay level and channel
congestion status of the network, respectively. A key advantage of the D2D scheme is that it is
compliant with the IEEE 802.11 standard, and, thus, can be seamlessly integrable with the
existing wireless card. We show the integrated model of the medium access control protocol,
namely D2DChannel Access (D2DCA), for the IEEE 802.11e networks. We further propose a
two-dimensional Markov chain model of the D2DCA protocol for analyzing its theoretical
performance in saturated networks with imperfect wireless channel. Theoretical comparison with
the benchmark protocols establishes the effectiveness of the D2DCA protocol.
PROPOSED SYSTEM:
We seamlessly integrate the proposed D2D scheme with the QoS version of the IEEE
802.11 medium access control (MAC) protocol. For the integration with the enhanced distributed
channel access (EDCA) protocol, we need to modify only the backoff algorithm used for

Off: 0416-2247353 / 6066663 Mo: +91 9500218218
collision avoidance. We propose a modified version of the EDCA protocol, namely D2D channel
access (D2DCA), for use in IEEE 802.11e WLANs. We propose a Markov chain-based model of
theD2DCA protocol for analyzing its performance theoretically. We compare the results of the
D2DCA protocol with the benchmark protocols for establishing the superiority of the former. We
also investigate the protocol behavior in the presence of hidden terminals and channel error. In
brief, the contributions of this work are as follows: We propose a delay-aware distributed
dynamic adaptation of CW (D2D) scheme for runtime adaptation of CW increase & decrease
depending on the present channel status and experienced delay._ Using the D2D scheme, we
propose a D2D channel access (D2DCA) protocol for use in IEEE 802.11e WLANs._ We design
a Markov chain-based analytical model of the proposed D2DCA protocol for evaluating its
performance theoretically
EXISTING SYSTEM:
The use of feedback-based mechanism for achieving higher performance of a network is
not new in the literature of WLANs. Due to the inefficiency of default values of MAC
parameters with respect to the current network and load conditions the feedback-based schemes
allow the stations to be adaptive with the present conditions. Bononiet al introduced an
additional control on frame transmission for automatic adaptation of CW according to the
present network congestion. Cali et al. developed an analytical model for the p-persistent
IEEE802.11 protocol, and derived the optimal value of p for achieving theoretical throughput
limit. Depending on the optimal p value, the IEEE 802.11+ protocol adjusts the present CW size
for maximizing the protocol capacity. Further, in, the tuning of CW was performed by run time
estimation of the network status and load condition. Denget al., additionally, consider channel
BER in the design of dynamic adjustment of CW scheme. Bononiet al. Proposed a runtime
estimation of slot utilization which could probabilistically control the transmission of a station
for achieving maximum channel utilization. However, none of the above protocols considers the
minimization of channel access delay while optimizing the network throughput. In, the authors
adjust the CW for providing equal QoS opportunity and fairness to all flows belonging to same
traffic class. Few other methods such as and adjust the CW for achieving fairness along with
higher network throughput. Most recently, Hong et al. proposed a solution that dynamically

Off: 0416-2247353 / 6066663 Mo: +91 9500218218
adjusts the CW size for both the saturated and unsaturated traffic condition, while focusing on
achieving optimal throughput. However, these methods do not consider the channel access delay
as well.
SYSTEM REQUIREMENTS:
HARDWARE REQUIREMENTS:
 System : Pentium IV 2.4 GHz.
 Hard Disk : 40 GB.
 Floppy Drive : 1.44 Mb.
 Monitor : 15 VGA Colour.
 Mouse : Logitech.
 Ram : 512 Mb.
SOFTWAREREQUIREMENTS:
 Operating system : Windows XP/7/LINUX/UBUNTU
 Implementation : NS2
 NS2 Version : NS2.2.28
 Front End : OTCL (Object Oriented Tool Command Language)
 Tool : Cygwin (To simulate in Windows OS)

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D2 d delay aware distributed dynamic adaptation of contention windowin wireless networks