@conference {
	title = {A Distributed Opportunistic Scheduling Protocol for Multi-Channel Wireless Ad-Hoc Networks},
	author = {Chen, Hua., Baras, John S.},
	year = {2012},
	month = {12/2012},
	abstract = {The topic of opportunistic scheduling for wireless ad-hoc networks has been studied for single-channel networks in several recent works. Since now many wireless systems provide multiple channels for data transmission, this problem is of practical interest for networks with multiple channels. In this paper, we study the problem of opportunistic scheduling for one type of ad-hoc networks where the wireless spectrum can be divided into multiple independent sub-channels for better efficiency. We start with a naive multi-channel protocol where the scheduling scheme is working independently from sub-channel to sub-channel.We show that the naive protocol can only marginally improve the system throughput. We then develop a protocol to jointly consider the opportunistic scheduling behavior across multiple sub-channels. We characterize the optimal stopping rule and present several bounds for the system throughput of the multi-channel protocol. We show that by joint optimization of the scheduling scheme across multiple sub-channels, the proposed protocol improves the system throughput considerably in contrast to that of single-channel systems.},
	address = {Anaheim, California},
	booktitle = {IEEE Globecom 2012},
	pages = {pp. 292-297}
}
@conference {
	title = {Distributed Medium Access and Opportunistic Scheduling for Ad-Hoc Networks: An Analysis of the Constant Access Time Problem},
	author = {Chen, Hua., Hovareshti, Pedram., Baras, John S.},
	year = {2011},
	month = {12/2011},
	abstract = {In this paper, we study the problem of medium access and distributed opportunistic scheduling to exploit channel fluctuations for wireless ad-hoc networks. This work focuses on the Constant Access Time (CAT) problem, where the total time duration of channel probing and data transmission is slotted into fixed block length. In particular, we consider the dependence between channel rates at different time instances during the channel probing phase and its impact on the overall system throughput. We first analyze the system performance of the CAT problem under independent channel rate assumption and compare our result to the existing work on the Constant Data Time (CDT) problem. We then propose a protocol to reduce the channel probing costs based on this analysis. We show analytical results of the proposed protocol for systems with a sufficiently large number of users. We compare the system performance of the proposed protocol with that of the original protocol under independent channel rate assumption. We mathematically prove that the proposed protocol improves the system performance.},
	address = {Houston Texas},
	booktitle = {IEEE Globecom 2011},
	pages = {pp. 1-6}
}
@conference {
	title = {Communication Network Challenges for Collaborative Vehicles},
	author = {Chen, Hua., Hovareshti, Pedram., Baras, John S.},
	year = {2011},
	month = {11/2011},
	abstract = {Networked systems of autonomous mobile agents have emerged in a variety of applications such as collaborative robotics, unmanned aerial/ground vehicles, mobile sensor networks and disaster relief operations. These agents utilize wireless communications for distributed computing, control and decision-making. Due to their limitations on energy supply, design and implementation of efficient distributed algorithms are crucial for these systems. This paper reviews different design aspects of networks of collaborative vehicles. We survey existing methods of addressing physical (PHY) and medium access control (MAC) layer, routing, and geometric connectivity issues for such networks and show limitations of these designs that address only single layer issues. We argue that a system engineering framework is needed for the design of such systems.},
	address = {Pacific Grove CA},
	booktitle = {Asilomar Conference on Signals, Systems, and Computers},
	pages = {pp. 1472-1476}
}
@conference {
	title = {Motif-based Topology Design for Effective Performance by Networks of Mobile Autonomous Vehicles},
	author = {Hovareshti, Pedram., Chen, Hua., Baras, John S.},
	year = {2011},
	month = {06/2011},
	abstract = {To design efficient local connectivity patterns, we have used the idea of network motifs, which was first proposed in the context of biological networks. Network motifs are task specific local connectivity patterns, which exist with much higher frequency in real biological networks compared to those in random networks. These are sub-networks of a low number of nodes (usually 3-4) whose persistence in networks performing similar tasks in different contexts, imply their efficiency in the sense that they optimize certain performance metric in a local scale. We use a simulation test bed to find network motifs for local level communication structures in a collaborative vehicles framework. Here, the group mission consists of several tasks that the agents participate in. The tasks include search operation, data gathering/processing, target finding and leader-follower explorations. Each task gives rise to certain motifs that are specific to that task and the partial knowledge of the environment specifications that the agents operate in. In this way, given the subtasks that are necessary for the mission accomplishment, the most efficient task-specific local topologies are extracted. Switching suitable graphs when the mode of operation is changing can be handled by solving the resulting reachability problem using methods for symbolic planning such as graph grammars. Based on such switching, we also address the effects of split/merge operations on the spectral characteristics of the resulting connectivity graphs.},
	address = {Quincy, MA},
	booktitle = {Eighth International Conference on Complex Systems (ICCS 2011),},
	pages = {pp.  571-573}
}
@conference {
	title = {Opportunistic Communications for Networked Controlled Systems of Autonomous Vehicles},
	author = {Chen, Hua., Hovareshti, Pedram., Baras, John S.},
	year = {2010},
	month = {10/2010},
	abstract = {Situational awareness requires maintaining a reasonable level of communication connectivity in networks of autonomous vehicles. It is difficult to overcome deep fading from time-varying wireless channels in a dynamic and resource constrained environment. Moreover, other system constraints such as the energy consumption and total operation time make the design of communication protocols for such systems more challenging. In this paper, we consider the problem of efficient communications between a group of autonomous vehicles with energy consumption and total operation time constraints in an adversarial environment. We show that the policy of continuously attempting to communicate reliably over the course of the mission may lead to considerable system degradation. We propose an adaptive algorithm to make communication attempts opportunistically, based on the qualities of the wireless channels as the vehicles move throughout the terrain. We compare the proposed algorithm with a non-opportunistic algorithm in which the vehicles blindly attempt to communicate regularly throughout the course of the mission. We show that the proposed algorithm significantly improves the system performance, both in terms of operation time when the agents transmit only situational information and data throughput when additional data transmission is necessary.},
	address = {San Jose, CA},
	booktitle = {2010 Military Communications Conference (MILCOM 2010)},
	pages = {pp. 1306-1311}
}
@conference {
	title = {Distributed Collaborative Controlled Autonomous Vehicle Systems over Wireless Networks},
	author = {Chen, Hua., Hovareshti, Pedram., Baras, John S.},
	year = {2010},
	month = {06/2010},
	abstract = {Inspired by military tactical, civil help-and-rescue applications, it is desirable yet challenging to develop networked systems of autonomous vehicles and sensors in dynamic, resource-constrained and adversarial environments. An essential aspect of designing such collaborative systems is to address the communication needs of the vehicles in order to perform a given mission. The vehicles{\textquoteright} communication network should maintain a connectivity pattern based on the requirements of the mission. In this paper, we consider both the control and communication aspects for coordinated path planning of a group of autonomous vehicles in an adversarial environment. We propose distributed algorithms to control the vehicles{\textquoteright} trajectories over a wireless vehicle-to-vehicle network. Distributed control algorithms both with and without collaboration between the vehicles are presented. We study the performance of the wireless network over the distributed controlled autonomous vehicles. Simulation results show that collaboration between vehicles results in better performance for path planning and wireless inter-vehicle communications. However, contention based communication protocols are likely to fail due to severe channel conditions.},
	address = {Marrakech, Morocco},
	booktitle = {18th Mediterranean Conference onControl and Automation (MED 2010)},
	pages = {pp. 1695-1700}
}
@techreport {
	title = {Distributed Opportunistic Scheduling for Wireless Ad-Hoc Networks with Block-Fading Model},
	author = {Chen, Hua., Baras, John S.},
	year = {2017},
	month = {10/2017},
	abstract = {In this paper, we study a distributed opportunistic scheduling problem to exploit the channel fluctuations in wireless ad-hoc networks. In this problem, channel probing is followed by a transmission scheduling procedure executed independently within each link in the network. We study this problem for the popular block-fading channel model, where channel dependencies are inevitable between different time instances during the channel probing phase. Different from existing works, we explicitly consider this type of channel dependencies and its impact on the transmission scheduling and hence the system performance. We use optimal stopping theory to formulate this problem, but at carefully chosen time instances at which effective decisions are made. The problem can then be solved by a new stopping rule problem where the observations are independent between different time instances. Since the stopping rule problem has an implicit horizon determined by the network size, we first characterize the system performance using backward induction. We develop one recursive approach to solve the problem and show that the computational complexity is linear with respect to network size. Due to its computational complexity, we present an approximated approach for performance analysis and develop a metric to check how good the approximation is. We characterize the achievable system performance if we ignore the finite horizon constraint and design stopping rules based on the infinite horizon analysis nevertheless. We present an improved protocol to reduce the probing costs which requires no additional cost}
}
@article {
	title = {Distributed Opportunistic Scheduling for Wireless Ad-Hoc Networks with Block-Fading Model},
	author = {Chen, Hua., Baras, John S.},
	year = {2013},
	month = {11/2013},
	abstract = {In this paper, we study a distributed opportunistic scheduling problem to exploit the channel fluctuations in wireless ad-hoc networks. In this problem, channel probing is followed by a transmission scheduling procedure that is executed independently within each link in the network. We study this problem for the popular block-fading channel model, where channel dependencies are inevitable between different time instances during the channel probing phase. Different from existing works, we explicitly consider this type of channel dependencies and its impact on the transmission scheduling and hence the system performance. We use optimal stopping theory to formulate this problem, but at carefully chosen time instances at which effective decisions are made. The problem can then be solved by a new stopping rule problem where the observations are independent between different time instances. Since the stopping rule problem has an implicit horizon determined by the network size, we first characterize the system performance using backward induction. We develop one recursive approach to solve the problem and show that the computational complexity is linear with respect to the network size. Due to its computational complexity, we present an approximation for performance analysis and develop a metric to check how good the approximation is. We characterize the achievable system performance if we ignore the finite horizon constraint and apply the stopping rules based on the infinite horizon analysis nevertheless. We present an improved protocol to reduce the probing costs which require no additional cost. We characterize the performance improvement and the energy savings in terms of the probing signals. We show numerical results based on our mathematical analysis with various settings of parameters.},
	pages = {pp. 2324-2337},
	volume = {Vol. 31},
	number = {No. 11},
	journal = {IEEE Journal on Selected Areas in Communications}
}
