Enhancing Voice over WLAN via Rate

Adaptation and Retry Scheduling

I. INTRODUCTION 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

to 80%.

II. EXISTING SYSTEM

VoWLAN 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 adaptation.

IEEE 802.11 MAC and QoS Provisioning. Retransmission policy and Access category

III.PROPOSED SYSTEM

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

B . Rate Adaptation: Fast Decrease

C . Retransmissions: Retry Scheduling

D . Retry Scheduling Chain (RS Chain)

Repeated delay the sixth transmission until the next VoIP frame arrival.

V. PERFORMANCE EVALUATION: NS-3 SIMULATION

A. Comparing Algorithms

ARF-Based Families FER-Statistics-Based Families Reference Algorithms

B. Static Topology

Fast Decrease and Retry Scheduling

All the schemes are revised by using FD or both FD and RS.

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 VoIP frames.

Retry Scheduling Chain

The gain of the RS diminishes as the number of contenting stations increases.

The VoIP stations donot need to intentionally delay the transmission.

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 randomly deployed.

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 codecs.Observe that the revised Agile ARF w/ RS and RRAA-e10-FD w/ RS achieve the R-score over 80.

F. Hidden terminal environment

VI.PERFORMANCE EVALUATION: MADWIFI IMPLEMENTATION

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

Static environment

By comparing AgileARF with other algorithms performance is different due to highly fluctuating channelHighly stable

Mobile environment with heterogeneous traffic

The R-score of proposed iRTS algorithm is close to case that VoIP stations that use RTS.

VII.CONCLUSION

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.

VIII.FUTURE ENHANCEMENT

Extension of the proposed approaches for real-time video traffic, whose QoS is also very sensitive to its packet loss rate.

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.

IX.REFERENCES

[1] 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.

[2] Wi-Fi Alliance, http://www.wi-fi.org, online link, 2014.[3] Y. Xiao et al., “Protection and Guarantee for Voice and

Video Traffic in IEEE 802.11e Wireless LANs,” Proc. IEEE INFOCOM, Mar. 2004.

[4] S. Shin and H. Schulzrinne, “Call Admission Control in IEEE 802.11 WLANs Using QP-CAT,” Proc. IEEE INFOCOM, Apr. 2008.

[5] 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.