Project: Hasan Shahid Ferdous

Enhanced IEEE 802.11 by Integrating Multiuser Dynamic OFDMA

In this research, we have identified the fundamental drawbacks that prohibit the network to utilize the available resources efficiently. We have shown that the medium access control protocol overhead and collisions in contention control messages play a significant role in its performance issues, specially when the number of contending devices is fairly high. We have proposed a novel OFDMA based IEEE 802.11 enhancement with a complete distributed coordinated function (DCF). Our DCF can allow multiple concurrent transmissions or receptions to reduce collisions and consequently improve the throughput and delay significantly. We have developed a complete analytical model of our proposed DCF using a discrete time Markov chain and demonstrated the effectiveness and superiority of the proposed DCF for access point based operations of IEEE 802.11. Finally, we have extended our work to support ad hoc operations of WLANs.

Introducing OFDMA for IEEE 802.11

Our new MAC can incorporate multiple concurrent transmissions or receptions in a dynamic manner and can adjust the collision probability based on the traffic load when nodes are endowed with a single half-duplex radio only.

Analytical Modeling of Enhanced Multiuser Dynamic OFDMA based IEEE 802.11 MAC Performance

Here we provided a complete analytical model of our proposed DCF using a discrete time Markov chain model.

Ad Hoc Operations of Enhanced IEEE 802.11 with OFDMA

we discuss the challenges associated with integrating multiuser OFDMA in a single cell IEEE 802.11 based wireless ad hoc network and propose a new, dynamic and robust approach to improve it.

Performance Comparison of Medium Access Control Schemes for IEEE 802.11

we made a detailed study of the performance comparison between various proposed contention resolution schemes - DCF, CONTI, k-EC, and PREMA.

Publications

[Conference Paper] Kabir, A., Alam, M., Ahmed, L., Sabah, S., and Ferdous, H. S. 2012. Performance Comparison of Medium Access Control Schemes for IEEE 802.11. In Proceedings of the 18th Asia-Pacific Conference on Communications (APCC '12), pp. 652-657, IEEE. [pdf]

The distributed coordination function (DCF) of the IEEE 802.11 standard based medium access control has drawn significant interest from the researchers in the past decade. Many proposals of its performance analysis and modifications to remove its limitations are proposed. In this paper we are considering some recent proposals to make a detailed study of the performance comparison between DCF, CONTI, k-EC, and PREMA, which are various contention resolution schemes proposed in various independent researches. The criteria for performance comparison that we use are collision rate, throughput, and average delay between successful transmissions. Also, we consider queuing delay using an exponential on-off based unsaturated model for these protocols whose implementation and performance is consistent with the saturated mode used in the above contention schemes.

[Conference Paper] Ferdous, H.S. and Murshed, M. 2011. Analytical Modeling of Multiuser Dynamic OFDMA based IEEE 802.11 under Saturation Load. In Proceedings of the 17th Asia Pacific Conference on Communications (APCC '11), IEEE. [pdf]

Multiuser dynamic OFDMA based IEEE 802.11 distributed coordination function (DCF) has received significant interest from the researchers in recent time. Though several proposals have been made, to the best of our knowledge, none of these have presented an analytical model for this kind of medium access control protocols for IEEE 802.11. This paper provides a simple, nevertheless, very accurate analytical model to estimate the performance characteristics of IEEE 802.11 DCF with OFDMA under the assumptions of ideal channel conditions and saturation load. Our model accounts for important system parameters like throughput, collision rate, transmission delay, average contention window size, average retry count and average time wasted in backoff. Analytical results are verified through extensive simulations.

[Conference Paper] Ferdous, H.S. and Murshed, M. 2011. Ad Hoc Operation of Enhanced IEEE 802.11 with Multiuser Dynamic OFDMA under Saturation Load. In Proceedings of the 12th IEEE Wireless Communications and Networking Conference (WCNC '11), IEEE. [pdf]

In this paper, we discuss the challenges associated with integrating multiuser OFDMA in a single cell IEEE 802.11 based wireless ad hoc network and propose a new, dynamic and robust approach to improve it. Our new MAC, using OFDMA in the physical layer, can incorporate multiple concurrent transmissions or receptions in a dynamic manner and adjust the collision probability based on the traffic load when nodes are endowed with a single half-duplex radio only. Simulation results show that for moderate number of users, our system improves throughput by up to 20%, decreases collision in control messages by up to 45% and reduces the average delay by up to 18%.

[Conference Paper] Ferdous, H.S. and Murshed, M. 2010. Enhanced IEEE 802.11 by Integrating Multiuser Dynamic OFDMA. In Proceedings of the 9th Annual Wireless Telecommunications Symposium (WTS '10), IEEE. [pdf]

In this paper, we discuss the problems associated with the present contention resolution mechanism of IEEE 802.11 DCF and present a new, dynamic and robust approach to improve it. Our new MAC, using OFDMA in the physical layer, can incorporate multiple concurrent transmissions or receptions in a dynamic manner and can adjust the collision probability based on the traffic load when nodes are endowed with a single half-duplex radio only. Simulation results show that our system improves throughput by up to 40 percent, reduces collision in control messages by up to 80 percent and reduces the average delay for data transmission by up to 20 percent.

Our Team

We are a multidisciplinary team, from different backgrounds and different institutions!

Hasan Shahid Ferdous

Manzur Murshed

Amran Kabir

Lubna Ahmed

Mahjabeen Alam