@conference {
	title = {Performance Evaluation of Hybrid SAMA VSAT with FMCSA and Reservations},
	author = {Perumal, Senni., Baras, John S.},
	year = {2012},
	month = {09/2012},
	abstract = {In this paper, we describe our work on developing and evaluating detailed OPNET simulation models of an enhanced Very Small Aperture Terminal (VSAT) satellite Internet gateway and an enhanced satellite hub based on Cerona SkySPAN technology with capacity and latency optimizations in a hybrid random access and reservation based return channel so as to allow significantly higher number of users and a better user experience. The Cerona SkySPAN technology uses Digital Video Broadcast via Satellite 2nd standard (DVB-S2) in the forward channel and Spread Aloha Multiple Access (SAMA) protocol in the return channel. We augment the SAMA return channel protocol with a hybrid random access and reservation based Dynamic Channel Allocation (DCA) scheme. The overall goal of the DCA algorithm is to make the system behave like a random access system at low loads for small messages so as to provide low message delay and to behave like a MF-TDMA reservation based system at high loads as well as for real time traffic so as to provide high maximum throughput and a better user experience. The random access protocol used at low loads is SAMA enhanced with Fast Multi-channel Slotted Aloha (FMCSA) protocol. FMCSA combines Multi-Channel Slotted Aloha (MCSA) with packet level forward error correction for new messages and scheduled retransmissions for partially received messages. This protocol increases the maximum possible throughput of SAMA and reduces the delay of multi-slot short messages while providing more robust delay performance with respect to load fluctuations, thus resulting in a much better user experience at low loads. The system transitions into a reservation based system at higher loads and for real time traffic so to support higher maximum throughput and achieve good QoS for real time traffic. The satellite return channel is divided into multi-frequency periodic frames. Each frame has mini-slots used for sending reservation requests in contention mode and larger data-slots used for sending data in either contention mode (FMCSA) or reservation mode (where the HUB allocates data-slots based on requests). We show via OPNET simulations that the enhanced SAMA VSAT with the hybrid DCA algorithm improves the throughput, latency and robustness of the SkySPAN SAMA system. We also compare, via OPNET simulations, the enhanced system with a DVB-RCS system to show the improvements in user experience both in terms of delay and throughput.},
	address = {Ottawa, Canada},
	booktitle = {18th Ka and Broadband Communications, Navigation and Earth Observation Conference}
}
@conference {
	title = {Performance Evaluation of Single Channel Virtual-Circuit Medium Access Protocols for MANETs},
	author = {Perumal, Senni., Baras, John S.},
	year = {2011},
	month = {11/2011},
	abstract = {In this paper, we develop and evaluate models for estimating various performance metrics for unicast traffic using a single frequency channel virtual-circuit Medium Access Control (MAC) protocol in mobile wireless ad-hoc networks. Time is divided into periodic frames with a portion reserved for control traffic and the rest divided into timeslots for data traffic. In order to avoid interference between neighboring links, the virtualcircuit MAC protocol uses a set of reservation rules to assign timeslots to links. One such virtual-circuit MAC protocol is the hard scheduling mode of the reservation based Unifying Slot Assignment Protocol (USAP) with the number of frequency channels in a frame set to one. USAP uses a set of generic reservation rules to avoid interference between neighboring links. We model the performance of a single frequency channel virtualcircuit MAC protocol using reduced load loss network models that couple the physical, MAC, and routing layers effects. The blocking probability of a call at a particular link is calculated by considering cliques of neighboring interfering links that cannot transmit simultaneously. These neighboring interfering links and the conflict graph are calculated using the virtualcircuit reservation rules. We compare our results with simulation and show good match for large networks across various offered loads.},
	address = {Baltimore, Maryland},
	booktitle = {Milcom 2011},
	pages = {pp. 926-931},
	organization = {Baltimore Convention Center}
}
@conference {
	title = {Return Channel Performance Evaluation of Enhanced SAMA VSAT with FMCSA and ACM Capability},
	author = {Perumal, Senni., Baras, John S., Roy-Chowdhury, Ayan., Petluri, Hemant S., Robinson, Mitch.},
	year = {2011},
	month = {10/2011},
	abstract = {In this paper, we describe our work on developing and evaluating detailed OPNET simulation models of an enhanced Very Small Aperture Terminal (VSAT) satellite Internet gateway and an enhanced satellite hub based on Cerona SkySPAN technology with capacity and latency optimizations in the return channel so as to allow significantly higher number of users and a better user experience. The Cerona SkySPAN technology uses Digital Video Broadcast via Satellite 2nd standard (DVB-S2) in the forward channel and Spread Aloha Multiple Access (SAMA) protocol in the return channel. We augment the SAMA return channel protocol with Fast Multi-Channel Slotted Aloha (FMCSA) protocol and Adaptive Coding and Modulation (ACM). FMCSA combines Multi-Channel Slotted Aloha (MCSA) with packet level forward error correction (FEC) for new messages and scheduled retransmissions for partially received messages. This protocol increases the maximum possible throughput of SAMA, thus supporting higher number of users. FMCSA also reduces the delay of multi-slot short messages (e.g., HTTP requests) while providing more robust delay performance with respect to load fluctuations, thus resulting in a better user experience. We incorporate Adaptive Coding and Modulation in the return channel in order to automatically adapt the coding and modulation to changing channel conditions so as to ensure remote data service irrespective of the channel degradation due to interference, rain fade or other conditions. We show via OPNET simulations that the enhanced SAMA VSAT with FMCSA and ACM improves the throughput, latency and robustness of the SkySPAN SAMA system. We also compare, via OPNET simulations, the enhanced SAMA system (with FMCSA and ACM) with a DVBRCS system to show improvements in user experience.},
	address = {Palermo, Italy},
	booktitle = {17th Ka and Broadband Communications, Navigation and Earth Observation Conference},
	pages = {pp. 417-424}
}
@conference {
	title = {Modeling TDMA-Based USAP in JTRS MDL for Multicast and Unicast Traffic},
	author = {Perumal, Senni., Tabatabaee, Vahid., Baras, John S., Graff, Charles J., Yee, David G.},
	year = {2010},
	month = {10/2010},
	abstract = {In this paper, we develop loss network models for the hard scheduling mode (virtual circuit mode) of the reservation based USAP scheduling protocol as used in the Mobile Data Link (MDL) of the Joint Tactical Radio System (JTRS). These models are used to find performance metric estimates for both multicast and unicast traffic. USAP (Unifying Slot Assignment Protocol) is a dynamic distributed resource allocation protocol for mobile multihop wireless networks where the channel is partitioned in time and frequency. MDL creates a backbone sub-network and routes all traffic through this sub-network. For the backbone sub-network, we consider algorithms that form Connected Dominating Sets. We use loss network models that couple the physical, MAC, and routing layers effects. The effect of the MAC layer is modeled by approximating available capacity at a node. The available capacity to transmit is computed based on the USAP reservation rules and the node{\textquoteright}s 2-hop neighborhood traffic. For a given time varying scenario, we compute the performance metrics of blocking probability and throughput for both multicast and unicast traffic as a function of time. We compare the results of our model against simulation.},
	address = {San Jose, CA},
	booktitle = {2010 Military Communications Conference (MILCOM 2010)},
	pages = {pp. 1464-1469}
}
@conference {
	title = {Modeling and Sensitivity Analysis of Reservation Based USAP Unicast Traffic in MANETs},
	author = {Perumal, Senni., Tabatabaee, Vahid., Baras, John S., Graff, Charles J., Yee, David G.},
	year = {2009},
	month = {10/2009},
	abstract = {In this paper, we develop and evaluate models to estimate and optimize various performance metrics for unicast traffic using the hard scheduling (virtual circuit connection oriented) mode of the reservation-based protocol USAP in mobile ad-hoc wireless networks (MANETs). USAP (Unifying Slot Assignment Protocol) is a dynamic distributed resource allocation protocol for MANETs. We model USAP hard scheduling mode using loss network models along with reduced link capacity that couple physical, MAC and routing layers effects. The key effect of multiuser interference on a link is modeled via reduced link capacity where the effects of transmissions and receptions in the link neighborhood are modeled using USAP reservation rules. We compare our results with simulation and obtain good results using our loss network models but with reduced link capacity distribution obtained by simulation. We also compute the throughput sensitivities with respect to network parameters and use these sensitivities to improve network performance.},
	address = {Boston, Massachusetts},
	booktitle = {MILCOM 2009 "The Challenge of Convergence"},
	pages = {pp.1-7}
}
@conference {
	title = {Dynamic Self-Organization and Clustering in Distributed Networked Systems for Performance Improvement},
	author = {Baras, John S., Hovareshti, Pedram., Perumal, Senni.},
	year = {2009},
	month = {09/2009},
	abstract = {We consider two closely related dynamic self-organization problems in networked control systems. Both are forms of the~dynamic clustering of nodes. The structure of networked control systems is often abstracted using graph theory. In this abstraction, the nodes of the graph represent the agents and the edges between them represent the relation(s) or the possibility of communication between the corresponding agents. The topology of the communication network supporting a networked control system has critical consequences for its performance. The first problem we address is the development of a distributed self-organization algorithm, resulting into a dynamic two level hierarchy of leader and regular agents, which substantially improves the convergence speed of distributed algorithms utilized by the networked control system. For the second problem, we consider the collaborative control of a group of autonomous mobile agents (e.g. vehicles, robots) supported by a mobile wireless network, consisting of many grounds and a few aerial nodes. The agents collaborate to achieve a common goal or objective, like to move in a particular area and cover it, while avoiding obstacles and collisions. Building upon our earlier work on deterministic, randomized and hybrid distributed coordination algorithms we consider the communication needs of the agents, and in particular, the connectivity of their communication network as they move. We develop distributed algorithms that automatically select some agents and move them appropriately so as to maintain a~certain degree of desired connectivity among the moving agents. We characterize the trade-off between the gain from maintaining a certain degree of connectivity vs. the combined cost of communications and the associated dynamic re-positioning of agents. We also describe classes of efficient communication topologies and in particular their similarity to dynamic small-world topologies and extensions.},
	address = {Montecello, Illinois},
	booktitle = {Forty-Seventh Annual Allerton Conference on Communication, Control, and Computing (Allerton Conference 2009)},
	pages = {pp. 968-975},
	organization = {University of Illinois at Urbana-Champaign}
}
@conference {
	title = {Event Triggered Distributed Collaborative Control},
	author = {Baras, John S., Hovareshti, Pedram., Perumal, Senni.},
	year = {2009},
	month = {08/2009},
	abstract = {We consider the collaborative control of a group of autonomous mobile agents (e.g. vehicles, robots). The agents collaborate to achieve a common goal or objective, like to move in a particular area and cover it, while avoiding obstacles and collisions. Building upon our earlier work on deterministic, randomized and hybrid distributed coordination algorithms we consider the communication needs of the agents, and in particular, the connectivity of their communication network as they move. We develop algorithms that automatically sense the possibility or inset of loss of connectivity among the agents. We also consider the automatic detection of path disconnection when more than one paths need to be maintained between pairs of agents. Using local probing schemes we formulate such problems as event-triggered control problems. We develop distributed algorithms that automatically select some agents and move them appropriately so as to maintain a~certain degree of desired connectivity among the moving agents. We characterize the trade-off between the gain from maintaining a certain degree of connectivity vs the combined cost of communications and the associated dynamic re-positioning of agents. The results illustrate the efficiency achieved by the~event-triggered control in such problems. We also describe the resulting communication topologies and in particular their similarity to dynamic small-world topologies.},
	address = {Budapest, Hungary},
	booktitle = {European Control Conference 2009 (ECC {\textquoteright}09)},
	pages = {pp.3797-3802}
}
@conference {
	title = {Aerial Platform Placement Algorithm to Satisfy Connectivity and Capacity Constraints in Wireless Ad-hoc Networks},
	author = {Perumal, Senni., Baras, John S.},
	year = {2008},
	month = {11/2008},
	abstract = {In this paper, we address the problem of establishing full connectivity and satisfying required traffic capacity between disconnected clusters in large wireless ad-hoc ground networks by placing a minimum number of advantaged high flying Aerial Platforms (APs) as relay nodes at appropriate places. We formulate the problem of providing both connectivity and required capacity between disconnected ground clusters as a constrained clustering problem with complexity costs. The basic requirement for connectivity between the ground clusters and APs is converted into a summation form distortion function. The additional requirement for connectivity between the various APs is encoded by adding a new (summation form) constraint to the distortion function. In order to satisfy the required capacity out of each cluster to all other clusters, we add a cost function that depends on the assignment probabilities of the APs and relate~the source (prior) probabilities of each cluster to the required capacity out of this cluster. The cost function produces solutions which are load balanced, i.e., the capacities supported through each AP are nearly equal. We solve the resultant clustering problem using Deterministic Annealing in order to find (near) globally optimal solutions for the minimum number and locations of the APs to establish full connectivity and provide required traffic capacity between disconnected clusters. We establish the validity of our algorithm by comparing it with optimal exhaustive search algorithms and show that our algorithm is near-optimal for the problem of establishing connectivity and satisfying capacity requirements between disconnected clusters.},
	address = {New Orleans, LA},
	booktitle = {IEEE Global Communications Conference (IEEE Globecom 2008)},
	pages = {pp. 1-5}
}
@conference {
	title = {Loss Network Models and Multiple Metric Performance Sensitivity Analysis for Mobile Wireless Multi-Hop Networks},
	author = {Baras, John S., Perumal, Senni., Tabatabaee, Vahid., Somasundaram, Kiran K., Purkayastha, Punyaslok.},
	year = {2008},
	month = {11/2008},
	abstract = {We develop and evaluate a new method for estimating and optimizing various performance metrics of mobile wireless multi-hop networks, including MANETs. The method utilizes approximate (throughput) loss model that couples the physical, MAC and routing layers effects. The model provides quantitative statistical relations between the loss parameters that are used to characterize multiuser interference and physical path conditions on the one hand and the traffic rates between origin-destination pairs on the other. The model considers effects of the hidden nodes, node scheduling algorithms, MAC and PHY layer failures and unsuccessful packet transmission attempts at the MAC layer in~arbitrary time-varying network topologies where multiple paths share nodes. The method then applies Automatic Di{\textregistered}erentiation (AD) to these implicit performance models, to compute sensitivities of various performance metrics with respect to net- work parameters. We demonstrate the method by applying it to time-varying mobile network topologies, including reduced connectivity instances, with both random access MAC (contention mode of the 802.11) as well as reservation-based MAC (USAP TDMA based protocol). We analyze throughput, delay and packet loss as metrics and investigate metric optimization and tradeoff analysis. Finally, we provide numerical results for realistic mobile networks with time-varying topologies.},
	address = {Maui, Hawaii},
	booktitle = {Fourth International Wireless Internet Conference (WICON 2008)}
}
@conference {
	title = {Aerial Platform Placement Algorithms to Satisfy Connectivity, Capacity and Survivability Constraints in Wireless Ad-hoc Networks},
	author = {Perumal, Senni., Baras, John S., Graff, Charles J., Yee, David G.},
	year = {2008},
	month = {11/2008},
	abstract = {In this paper, we address the problem of establishing full connectivity and satisfying required traffic capacity between disconnected clusters in large wireless ad-hoc ground networks by placing a minimum number of advantaged high flying Aerial Platforms (APs) as relay nodes at appropriate places. We also extend the connectivity solution in order to make the network survivable to a single AP failure. The problem of providing both connectivity and required capacity between disconnected ground clusters is formulated as a summation-form clustering problem with inter-AP distance constraints that make the AP network fully connected and with complexity costs that take care of cluster to AP capacity constraints. The resultant clustering problem is solved using Deterministic Annealing to find (near) globally optimal solutions for the minimum number and locations of the APs to establish full connectivity and provide required traffic capacity between disconnected clusters. In order to make the network single AP survivable, the connectivity solution is extended so that each AP connects to at least two neighboring APs and each ground cluster connects to at least two APs. We establish the validity of our algorithms by comparing it with optimal exhaustive search algorithms and show that our algorithms are near-optimal for the problem of establishing connectivity between disconnected clusters.},
	address = {San Diego, CA},
	booktitle = {Milcom: 08 Assuring Mission Success},
	pages = {pp. 1-7}
}
