Enhancing Voice over WLAN via RateAdaptation and Retry Scheduling
Enhancing Voice over WLAN via
Adaptation and Retry Scheduling
Investigate the characteristics of VoIP traffic and the
limitations of state-of-the-art rate adaptation algorithms.
Enhance the QoS of voice over WLAN (VoWLAN).
Fast decrease and retry scheduling
NS-3 simulations and MadWiFi implementations.
Proposed schemes improve the R-score performance by up
II. EXISTING SYSTEM
Characteristics of VoIP Traffic are voice codec and mouth-to-ear
delay and performance metric of VoIP(R=Rmax-Idelay-Iloss)
Existing rate adaptation algorithms are ARF and AdaptiveARF,
CARA , RRAA, SampleRate and minstrel ,PHY assisted rate
IEEE 802.11 MAC and QoS Provisioning.
Retransmission policy and Access category
Two novel features for VoWLAN, namely, fast decrease
(FD) and retry scheduling (RS), to improve the QoS.
Evaluate the QoS of the proposed schemes in various
communication environments via network simulator (ns-3)
and MadWiFi implementation results.
IV.ENHANCING QOS OF VOWLAN
A.Limitations of the Existing Rate Adaptation Algorithms
Slow response of ARF based algorithm
PHY assisted algorithm is not feasible
RRAA cannot be fast to trace fast fading channel
D . Retry Scheduling Chain (RS Chain)
Repeated delay the sixth transmission until the next VoIP
V. PERFORMANCE EVALUATION: NS-3
A. Comparing Algorithms
B. Static Topology
Fast Decrease and Retry Scheduling
All the schemes are revised by using FD or both FD and
R-score is enhanced by applying FD while RS enhances
R-score greater than 80.
RS improves the R-score of all rate adaptation algorithm
by removing continuous retransmission failure.
FD and RS algorithm rarely affect mouth to ear delay of
Retry Scheduling Chain
The gain of the RS diminishes as the number of contenting
The VoIP stations donot need to intentionally delay the
Delaying the retransmission is good enough to improve the
QoS of VoWLAN.
C. Random Topology with Heterogeneous Traffic Types
Five static VoIP stations and five static data stations are
Both use same rate adaptation algorithm except RS feature.
Average R-score of scenario with VoIP and data stations are
slightly greater due to random topology.
High chance that VoIP stations get closer to AP.
D. Mobile Topology
Straight-line scenario and Random mobility scenario
E. Effects on Various VoIP Codecs
R-score of ARF, RRAA, and their variants for the four
Observe that the revised Agile ARF w/ RS and RRAA-
e10-FD w/ RS achieve the R-score over 80.
A. Implementation of Adaptive RTS
MAC service data unit (MSDU) is accompanied with
_transmit descriptor generated by MadWiFi.
Multi rate retry control PHY rate.
MRR is specified by vector (R1,C1,R2,C2,R3,C3,R4,C4).
Implementable RTS implemented in MadWiFi driver.
iRTS has two operating parameters, RTSWnd and
RTSCoutner, and one decision parameter x.
B. Implementation of Retry Scheduling
To implement retry scheduling revised MadWiFi is used.
MadWiFi first delivers the original packet to HAL.
MadWiFi removes the copied packet when the
transmission is successful and receives new packet.
Two transmit descriptors for MSDU transmission
Chances to enable/disable CTS/RTS
Group of MPDU transmission
C. Experimental Results
By comparing AgileARF with other algorithms performance
is different due to highly fluctuating channel
Mobile environment with heterogeneous traffic
The R-score of proposed iRTS algorithm is close to case that
VoIP stations that use RTS.
Investigate the characteristics of VoWLAN systems, and
discuss the pros and cons of the existing rate adaptation
algorithms regarding the VoIP traffic.
Fast decrease and Retry scheduling
Extensive ns-3 simulations and MadWiFi measurements
Existing rate adaptation algorithms can dramatically improve
the QoS of VoWLAN.
Extension of the proposed approaches for real-time video
traffic, whose QoS is also very sensitive to its packet loss
Future work on refining the RS design, i.e., jointly
optimizing the delayed transmission and de-jitter buffer size.
Considering silence suppression and high-latency network,
enhance the QoS of VoWLAN.
 B. Kim et al., “Enhancing QoS of Voice over WLANs,”
Proc. IEEE Int’l Symp. a World of Wireless, Mobile and
Multimedia Networks (WoWMoM), June 2012.
 Wi-Fi Alliance, http://www.wi-fi.org, online link, 2014.
 Y. Xiao et al., “Protection and Guarantee for Voice and
Video Traffic in IEEE 802.11e Wireless LANs,” Proc.
IEEE INFOCOM, Mar. 2004.
 S. Shin and H. Schulzrinne, “Call Admission Control in
IEEE 802.11 WLANs Using QP-CAT,” Proc. IEEE
INFOCOM, Apr. 2008.
 J. Yu et al., “Supporting VoIP Services in IEEE 802.11e
WLANs,” Proc. Int’l ICST Conf. Heterogeneous
Networking for Quality, Reliability, Security and
Robustness (QShine), Nov. 2009.