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Conference Proceedings

1. Yogesh R Kondareddy and Prathima Agrawal, "Synchronized MAC Protocol for Multi-Hop Cognitive Radio Network", IEEE International Conference on Communications 2008 , Beijing, China.
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   Abstract-Cognitive networks enable efficient sharing of the radio spectrum. Multi-hop cognitive network is a cooperative network in which cognitive users take help of their neighbors to forward data to the destination. Control signals used to enable cooperation communicate through a common control channel (CCC). Such usage introduces conditions like channel saturation which degrades the overall performance of the network. Thus, exchanging control information is a major challenge in cognitive radio networks. This paper proposes an alternative MAC protocol for multi-hop cognitive radio networks in which the use of a CCC is avoided. The scheme is applicable in heterogeneous environments where channels have different bandwidths and frequencies of operation. It inherently provides a solution to issues like CCC saturation problem, Denial of Service attacks (DoS) and multi-channel hidden problem. The proposed protocol is shown to provide better connectivity and higher throughput than a CCC based protocol, especially when the network is congested.

2. Yogesh R Kondareddy and Prathima Agrawal, "Selective Broadcasting for Multi-Hop Cognitive Radio Networks", IEEE Sarnoff Symposium 2008 , Princeton, NJ.
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   Abstract-Cognitive networks enable efficient sharing of the radio spectrum. Control signals used to setup a communication are broadcast to the neighbors in their respective channels of operation. But since the number of channels in a cognitive network is potentially large, broadcasting control information over all channels will cause a large delay in setting up the communication. Thus, exchanging control information is a critical issue in cognitive radio networks. This paper deals with selective broadcasting in multi-hop cognitive radio networks in which, control information is transmitted over pre-selected set of channels. We introduce the concept of neighbor graphs and minimal neighbor graphs to derive the essential set of channels for transmission. It is shown through simulations that selective broadcasting reduces the delay in disseminating control information and yet assures successful transmission of information to all its neighbors. It is also demonstrated that selective broadcasting reduces redundancy in control information and hence reduces network traffic.

3. Yogesh R Kondareddy and Prathima Agrawal, "Cognitive Radio Network Setup without a Common Control Channel", IEEE Military Communications Conference 2008 , San Diego, CA.
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   Abstract-The concept of cognitive radio networks has introduced a new way of sharing the open spectrum flexibly and efficiently. However, there are several issues that hinder the deployment of such dynamic networks. The common control channel problem is one of such issue. Cognitive radio networks are designed by assuming the availability of a dedicated control channel. In this paper, we identify and discuss the network setup problem as a part of the common control channel problem. Probabilistic and deterministic ways to start the initial communication and setup a cognitive radio network without the need of having a common control channel in both centralized and multi-hop scenarios are suggested. Extensive MATLAB simulations validate the effectiveness of the algorithms.

4. Yogesh R Kondareddy and Prathima Agrawal, "A Graph Based Routing Algorithm for Multi-hop Cognitive Radio Networks", Wireless Internet Conference, ACM International Conference Proceeding Series 2008 , Lahaina, Hawaii.
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   Abstract-Cognitive radio networks that allow dynamic spectrum access are considered spectrally more efficient than networks using fixed spectral allocation. These networks are characterized by dynamically changing channel sets at each node. The graph theoretic approach used in traditional multi-hop networks fails to efficiently model multi-hop cognitive radio networks and capture the required information for optimal routing. Hence, conventional graph-based routing protocols such as DSR or AODV cannot be used directly, for route discovery in such networks. In this paper, a unique multi-edge planar graph model for routing in such type of networks is proposed, which is quite simple and could be used in conjunction with any conventional graph-based routing protocol. The model is validated through simulations and the complexity of the model is shown to be lesser than an earlier layered graph model.

5. Yogesh R Kondareddy and Prathima Agrawal, "On the Capacity of Secondary Users in a Cognitive Radio Network", IEEE Sarnoff Symposium 2009 , Princeton, NJ.
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   Abstract-Cognitive radio networks deal with opportunistic spectrum access leading to greater utilization of the spectrum. The extent of utilization depends on the primary user's traffic and also on the way the spectrum is accessed by the primary and secondary users. In this paper Continuous-time Markov chains are used to model the spectrum access. The proposed threedimensional model represents a more accurate cognitive system than the existing models with increased spectrum utilization and than the random and reservation based spectrum access. A nonrandom access method is proposed to remove the forced termination states. In addition, call dropping and blocking probabilities are reduced. It is further shown that channel utilization is higher than random access and reservation based access.

6. Yogesh R Kondareddy and Prathima Agrawal, "Effect of Dynamic Spectrum access on TCP Performance", IEEE Global Telecommunications Conference 2009 , Honolulu, Hawaii.
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   Abstract-Transmission Control Protocol (TCP) is the most commonly used transport protocol on the Internet. All indications assure that it will be an integral part of the future internetworks. In this paper, we briefly discuss how regular TCP which was designed for wired networks is not suitable for dynamic spectrum access networks. We develop an analytical model to estimate the TCP throughput of Dynamic spectrum access networks. Dynamic spectrum access networks deal with opportunistic spectrum access leading to greater utilization of the spectrum. The extent of utilization depends on the primary user's traffic and also on the way the spectrum is accessed by the primary and secondary users. The proposed model considers primary and secondary user traffic in estimating the TCP throughput by modeling the spectrum access using continuous-time Markov chains, thus providing more insight on effect of dynamic spectrum access on TCP performance than the existing models.

7. Kongara H, Yogesh R Kondareddy and Prathima Agrawal, "Fairness and Gateway Classification Algorithm in Multi-hop Wireless Mesh Networks", 41st IEEE Southeastern Symposium on System Theory 2009 , Tullahoma, Tennessee.
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   Abstract-Wireless Mesh Network (WMN) appears to be a promising alternative for next generation wireless networking. Wireless mesh networks have applications ranging from civilian wireless Internet applications to tactical and emergency response applications. Though wireless mesh networks appear as a viable alternative to the existing wireless infrastructure, there are still many issues which require more investigation. In this paper, we first analyze the fairness issue in WMNs by using simulation. We then propose Gateway Classification Algorithm (GCA) which classifies gateways into high data rate gateways and low data rate gateways. Simulation results show that the proposed GCA can improve the performance significantly.

8. Giovanni D Crescenzo, Yogesh R Kondareddy and Tao Zhang, "Random Graphs in Vehicular Networks and Security Applications", Submitted to Infocom 2010 , Sandiego, California.
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   Abstract-Random graphs have been studied extensively in literature. Dynamic random graphs which are assumed to be a good model of mobile ad-hoc networks such as vehicular networks have been comparatively less explored. But it is often vague to see that, nodes moving on a specific geographical model and a mobility model form a random graph. In this paper, we start by formulating well-studied geographical, mobility, and communication model and show that these result in the spatial distribution of nodes (vehicles) being stationary, which, in turn, is used to prove that vehicles form a random graph G(n,p), where p has a closed-form expression. We then extend this result to quite general geographical, mobility, and communication models, ad still obtain a random graph G(n,p), where p has an algorithmically computable expression. Thus one can measure and analyze properties of mobile ad-hoc or vehicular networks such as connectivity, broadcast time, and related security questions, as a function of basic communication, geographic and mobility parameters. As an application, we show how to investigate security questions how much infrastructure is required to improve the connectivity and malicious user detection in the vehicular network. Simulations are used to visualize and verify the analysis.