Research Summary:

We are currently using OPNET for designing medium access control for directional antennas; scheduling protocols for mesh networks; routing protocols for multihop wireless networks; rate adaptation, power control, fairness issues and security in ad hoc and mesh networks. Multihop wireless networks (MWNs) can be categorized into Mobile Ad Hoc networks (MANETs), wireless mesh networks (WMNs) and wireless sensor networks (WSNs). MWNs have gained wide acceptance and increased popularity in the past few years. These networks are still in their development stages, with current research directed towards protocol development, security, capacity enhancements, deployment, and various other aspects. We have adopted a multifaceted approach in dealing with various challenges that arise in these networks.

The first one is designing medium access and routing protocols. IEEE 802.11 specifies Distributed Co-ordination Function (DCF) as the de facto channel arbitration in MANETs. The CSMA/CA mechanism in DCF provides equal channel access opportunity to all the nodes in neighborhood. However this fairness at single hop leads to severe unfairness in multi-hop scenarios. Nodes that have fewer flows passing through them get the same share of channel access when compared to nodes that have larger number of flows passing through them. This leads to unfairness in throughputs of various flows originating at different nodes. We used wireless module of OPNET for developing proportion based transmission rate control algorithm at MAC layer. We found OPNET as a very useful simulation tool that has comprehensive support for networking simulations. We have implemented a geographical grid-routing scheme (GGR) to route packets in a grid-connected ad hoc network where each node has information about its d-hop neighbors. It is observed by extensive simulation using OPNET that the timely update of routing tables increases the bandwidth efficiency. We have also considered node mobility here. Currently we are using OPNET for developing medium access and routing protocols for ad hoc and mesh networks.

The second challenge is of security in these networks. MANETs may be deployed in the hostile environments that are susceptible to malicious traffic analysis which allow the enemy to trace the routing messages and the sensitive data packets, any leakage of this kind of information is often devastating in security-sensitive scenario. Anonymous routing protocols which can thwart possible traffic analysis attacks by enabling anonymous communications between mobile nodes are under investigating recently. Current existing anonymous routing protocols only provide insufficient anonymous against the traffic attacks. We are working on anonymous secure routing protocol to protect both identity information and position information of mobile node. Authenticating with the pair-wise key between adjacent nodes and using the pseudo identities of mobile nodes, our proposed protocol can achieve both anonymity and security.

The other challenge is enhancing capacity of these networks by using smart antenna technologies, transmission rate adaptation and power control. Smart antenna technology is a new focus area of research for capacity improvements in wireless ad hoc networks. Smart antennas come in different flavors varying from switched beam to adaptive beam forming antennas, single beam or multiple beam directional antennas. It is expected that smart antenna techniques will be adopted for future wireless devices for optimum utilization of available resources. We are using OPNET to study the behavior of IEEE 802.11 DCF in a heterogeneous network, where nodes can communicate in omnidirectional or directional mode. Using some toy topologies we have formulated mode selection criteria for heterogeneous networks where nodes exploit different smart antenna technologies for enhancing the network capacity. This forms the basis of developing efficient medium access protocols for such type of networks. We are also working towards transmission rate adaptation and power control to enhance the network capacity.

Another challenge is the deployment of wireless networks. Wireless local area networks (WLANs) are becoming increasingly popular owing to their ease of deployment and low infrastructure cost. However, in various application scenarios, the placement of the Access Points (APs) is either unplanned or there are multiple such APs, possibly owned by different vendors, within interference range of each other. Identifying a suitable channel for communication in a distributed manner is hence important and this choice should reflect the current network conditions. We have developed a dynamic channel selection scheme for wireless local area networks (WLANs) that addresses this problem. We have used OPNET for our simulation. Results show significant improvement in the number of re-transmission attempts and in the measured signal to noise ratio in systems than use our algorithm over the standard 802.11b MAC protocol.

Overall our experience and productivity with OPNET has been very good. We look forward to work more on OPNET and its wireless module. We are also working on flow fairness in MWNs and thus believe that Flow Analysis and Terrain Modeling Modules will help in our simulation. Below is list of published papers and the ones currently under review, which used OPNET as a simulation tool.

Papers Published

• Torsha Banerjee, Demin Wang, and Dharma Agrawal, “Routing in a Grid Connected Ad hoc Network,” in Proceedings of OPNETWORK, Aug 22-26, 2005. (pdf)

• Yi Cheng and Dharma Agrawal, “Distributed Anonymous Secure Routing Protocol in Wireless Mobile Ad Hoc Networks,” in Proceedings of OPNETWORK, Aug 22-26, 2005. (pdf)

• Vivek Jain, Nagesh Nandiraju, and Dharma Agrawal, “Mode Selection Criteria in Mobile Ad hoc Networks using Heterogeneous Antenna Technologies,” in Proceedings of OPNETWORK, Aug 22-26, 2005. (pdf)

• Nagesh Nandiraju, Kaushik Roy Chowdhury, and Dharma Agrawal, “Investigation of MAC and Network layer Fairness for Multihop Wireless Ad-Hoc Networks,” in Proceedings of OPNETWORK, Aug 22-26, 2005. (pdf)

• Kaushik Chowdhury, Nagesh Nandiraju, D. Cavalcanti, and Dharma P. Agrawal, “C-MAC – A Multi-Channel Energy Efficient MAC for Wireless Sensor Networks,” in Proceedings of IEEE Wireless Communications and Networking Conference (WCNC), April 3-7, 2006

• Lakshmi Santhanam, Deepti Nandiraju, Nagesh Nandiraju, and Dharma Agrawal, “Low Cost reliable Traceback Based on MAC Address Identifier in Wireless Mesh Networks,” in Proceedings of OPNETWORK, Aug 24 - Sept 1, 2006.

Paper under Review

• Deepti Nandiraju, Lakshmi Santhanam, Nagesh Nandiraju, and Dharma Agrawal, “Queue-Based Load Balancing for Wireless Mesh Networks,” manuscript submitted.