@conference {
	title = {Rate-Control System with Heterogeneous Time-varying Delays in Broadband Satellite Networks},
	author = {Zeng, Hui., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2009},
	month = {09/2009},
	abstract = {In a broadband satellite communications network, the propagation delays are not only significant, but also variable among users due to their different geographical locations and the problem becomes more severe with increasing data rates. We consider rate control algorithms with user feedback in the form of single bits and formulate analytic fluid flow models composed of first-order delay differential equations. Both single-flow and multi-flow system models are analyzed, with special attention paid to the Mitra-Seery algorithm. The stationary solutions are investigated first. For the fluctuating solutions, their dynamic behavior is analyzed, in terms of amplitude, transient behavior, fairness, and adaptability, etc., analytically and numerically. Especially the effects of heterogeneous time-varying delays are investigated. It is shown that with proper parameter design the system can achieve stabling behavior with close to pointwise proportional fairness among flows.},
	address = {Sardinia, Italy},
	booktitle = {The Ka and Broadband Communications Conference Navigation and Earth Observation Conference 2009 (KaConf2009)},
	pages = {pp. 1-8},
	organization = {Cagliari}
}
@conference {
	title = {Two-Level Dynamic Bandwidth Allocation for A Space-To-Ground Relay Network},
	author = {Zeng, Hui., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2006},
	month = {11/2006},
	abstract = {We address issues related to efficiency, fairness, end to- end delay minimization and Quality-of-Service in order to enable a flexible access and dynamic mission operation capability in the next generation NASA space-to-ground communication infrastructure. To provide efficient and fair utilization while guaranteeing specific service requirements for different traffic classes, we propose a two-level (long-term and short-term) sharing of a slotted high data rate satellite communication link. The implemented long-term optimal bandwidth allocation provides per-user/per-flow service guarantee and gives the inputs to the next level. In our short-term bandwidth allocation with threshold regulation, a small portion of bandwidth is still assigned to all active spacecraft in advance, but most bandwidth is dynamically allocated per frame by solving an optimal timeslot scheduling problem. We finally discuss simulation results and our design optimization approach.},
	address = {San Francisco, CA},
	booktitle = {2006 IEEE Globecom Technical Conference},
	pages = {pp. 1-6}
}
@conference {
	title = {Flexible and Dynamic Communication Architecture for Lunar Exploration},
	author = {Zeng, Hui., Roy-Chowdhury, Ayan., Rentz, Nicolas., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2006},
	month = {06/2006},
	abstract = {We present work related to designing a communication network for lunar exploration. We discuss the important requirements for future space missions that influence the design of this network. We list some characteristics of the network, and highlight important issues and constraint related to performance, cost, and future network evolution. We address issues related to efficiency, fairness, end-to-end delay minimization and Quality-of-Service (QoS) framework in order to enable a flexible access and dynamic mission operation. To provide optimal or near-optimal efficient utilization and fair allocation of bandwidth of the downlink channel while guaranteeing specific QoS requirements for different service classes, we propose two-level (long-term static and short-term dynamic) sharing of a slotted high data rate satellite communication link. The long-term optimal bandwidth allocation is implemented to provide per-stream/per-user QoS guarantee and give the inputs to the next level, short-term dynamic bandwidth allocation. In our time-varying short-term bandwidth allocation with threshold regulation, a small portion of bandwidth is still assigned to all active spacecrafts in advance, but most bandwidth is dynamically allocated by the requests from them, per frame, by solving an optimal timeslot scheduling problem.},
	address = {San Diego, CA},
	booktitle = {24th American Institute of Aeronautics and Astronautics},
	pages = {pp. 1-9}
}
@conference {
	title = {Flow Control and Active Queue Management for Integrated Services in an Aeronautical Satellite Network},
	author = {Shang, Yadong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2006},
	month = {06/2006},
	abstract = {The IP-based broadband aeronautical satellite network will provide numerous new applications and services for both airspace system operations and passenger communications. Application of commercial off the shelf technologies and techniques has the potential to make network operations economically and technically realizable. However the performance of data communication protocols and applications over aeronautical satellite networks is degraded dramatically. For the satellite channel, the window based flow control algorithm may cause transient congestion. The flow control mechanisms with or without explicit feedback from the congested resource are limited in performance and not effective. We propose a hierarchical scheduler for satellite gateways. Different service disciplines are used for integrated services. A Random Early Detection Flow Control (REDFC) algorithm is proposed for best-effort traffic at the satellite gateways. In REDFC, each packet is transmitted with a probability that is a function of the queue length. If the packet is not transmitted successfully, it will be retransmitted after certain time interval. We also propose a virtual parallel queue structure as a new active queue management scheme for short life and long life web traffic. The new flow control and active queue management schemes will provide better performance for integrated services in aeronautical satellite networks.},
	address = {San Diego, CA},
	booktitle = {24th American Institute of Aeronautics and Astronautics},
	pages = {pp. 1-10}
}
@conference {
	title = {Dynamic Bandwidth Allocation for a Space Relay Communications Network},
	author = {Zeng, Hui., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2006},
	month = {04/2006},
	abstract = {We address issues related to efficiency, fairness, end-to-end delay minimization and Quality-of-Service framework in order to enable a flexible access and dynamic mission operation capability in the next generation NASA space-to-ground communication infrastructure. To provide optimal or near-optimal efficient utilization and fair allocation of bandwidth of the downlink channel while guaranteeing specific service requirements for different service classes, we propose two-level (long-term static and short-term dynamic) sharing of a slotted high data rate satellite communication link. The long-term optimal bandwidth allocation is implemented to provide per-stream/per-user service guarantee and give the inputs to the next level short-term dynamic bandwidth allocation. In our time-varying short-term bandwidth allocation with threshold regulation, a small portion of bandwidth is still assigned to all active spacecraft in advance but most bandwidth is dynamically allocated by the requests from them per frame by solving an optimal time slot scheduling problem.},
	address = {Charlottesville, Virginia},
	booktitle = {2006 IEEE Systems and Information Engineering Design Symposium (SIEDS06)},
	pages = {pp.75-80}
}
@conference {
	title = {A Multiple Subset Sum Formulation for Feedback Implosion Suppression over Satellite Networks},
	author = {Akkor, Gun., Baras, John S., Hadjitheodosiou, Michael.},
	year = {2005},
	month = {11/2005},
	abstract = {In this paper, we present a feedback implosion suppression (FIS) algorithm that reduces the volume of feedback information transmitted through the network without relying on any collaboration between users, or on any infrastructure other than the satellite network. Next generation satellite systems that utilize the Ka frequency band are likely to rely on various fade mitigation techniques, in order to guarantee a service quality that is comparable to other broadband technologies. User feedback would be a valuable input for a number of such components, however, collecting periodic feedback from a large number of users would result in the well-known feedback implosion problem. Feedback implosion is identified as a major problem when a large number of users try to transmit their feedback messages through the network, holding up a significant portion of the uplink resources and clogging the shared uplink medium. In this paper, we look at a system where uplink channel access is organized in time-slots. The goal of the FIS algorithm is to reduce the number of uplink time-slots hold up for the purpose of feedback transmission. Our analysis show that the FIS algorithm effectively suppresses the feedback messages of 95\% of all active users, but still achieves acceptable performance results when the ratio of available time-slots to number of users is equal to or higher than 5\%.},
	address = {St. Louis, MO},
	booktitle = {Globecom 2005 Wireless Communications},
	pages = {pp. 3226-3230}
}
@conference {
	title = {An Authentication Framework for Hybrid Satellite Network with Resource-Constrained Nodes},
	author = {Roy-Chowdhury, Ayan., Baras, John S., Hadjitheodosiou, Michael.},
	year = {2005},
	month = {11/2005},
	abstract = {The new phase of space exploration involves a growing number of human and robotic space missions to remote planets with varying communication and service requirements. Due to the critical nature of the missions, security is a very important requirement that needs to be addressed. Among primary security requirements are user authentication and message integrity that are needed to ensure that the data in the network is transmitted without unauthorized modifications between the source and destinations, and that data from only authorized network nodes are accepted by other nodes. In this paper we focus on the issue of user authentication and data integrity for a specific space network architecture supporting lunar exploration. We consider a hybrid network consisting of a terrestrial network on Earth, a network on the lunar surface, and a satellite constellation that connects the two surface networks. The lunar network comprises sensor nodes serviced by stationary gateways and mobile robotic vehicles with sensing capability, while the network on Earth is envisioned as a combination of private and public networ:ks. The problem of authentication in this network is co~plex due to the presence of nodes with varying capabilities in terms of computation strength, storage and energy. The nodes on .Earth and the gatewayso n the lunar surfacew ould have higher computationa nd energyc apabilitiesc omparedto the satellites and the sensor nodes. In this situation, an authentication protocol that is optimized to the strengths and limitations of the different classeso f nodesw ould be most suited. We focus on a solution that will operate under the constraints of the space environment (delay, limited energy, limited processing capability at remote nodes). We present a framework for user authentication and data integrity based on an authentication algorithm that makes use of symmetric certificates and hash chains of keys used to compute Message Authentication Codes,to provide asymmetric authentication capabilities to the network nodes. nodes with more resources. We give a detailed description of the authentication protocol we develop for this network and p~ovide an analysis of the security of the protocol by considering various types of passive and active attacks. We also highlight the savings incurred in terms of processing, storage and network bandwidth, which we get in using the proposed protocol in comparison to standard public-key authentication protocols.},
	address = {Wuhan, China},
	booktitle = {International Conference on Spatial Information Technology (ICSIT 2005)},
	pages = {pp. 1-12}
}
@conference {
	title = {Hybrid Networks with a Space Segment - Topology Design and Security Issues},
	author = {Roy-Chowdhury, Ayan., Baras, John S., Hadjitheodosiou, Michael., Rentz, Nicolas.},
	year = {2005},
	month = {10/2005},
	abstract = {In this paper we investigate a hybrid network topology that is suitable for supporting interplanetary communications. We define an architecture comprised of a network of sensor nodes on a remote planetary surface, connected to a hybrid terrestrial network of wired and wireless LANs through a series of satellite relays. All the nodes in the network are IP-addressable and support public and symmetric key cryptography. The resulting network forms a hierarchical hybrid mesh that connects users on Earth to networks on or around a remote planetary surface. We describe the design of the network and present preliminary simulation results illustrating the network performance for various parameters. We also discuss how algorithms for user authentication, message integrity and data confidentiality can be incorporated in the network infrastructure for secure end-to-end communication.},
	address = {Atlantic City, NJ},
	booktitle = {2005 Military Communications Conference (MILCOM 2005),},
	pages = {pp.1414 - 1420}
}
@conference {
	title = {Integrated Packet Level FEC Coding for Bulk Data Transfer Over Satellite Network},
	author = {Akkor, Gun., Baras, John S., Hadjitheodosiou, Michael.},
	year = {2005},
	month = {09/2005},
	abstract = {Packet level forward error correction (FEC) coding has been widely accepted as an efficient way of reducing the number of retransmissions and recovering from packet losses for reliable multicast in satellite networks. While there has been a significant effort in defining packet level FEC schemes that detail the structure, organization and delivery of the encoding packets, little attention has been given to how the physical channel, channel coding, and the downlink power budget affect the design space of these schemes in the context of a satellite network architecture. In this paper, we take a step in this direction, and define the points of interaction between various components and build a simulation environment. Using this simulation setup, we provide design suggestions for integrating FEC coding into reliable multicast transport protocols.},
	address = {Rome, Italy},
	booktitle = {23rd AIAA International Communications Satellite Systems Conference and Exhibit (ICSSC)}
}
@conference {
	title = {Modeling and Design of a Communication Architecture Supporting Lunar Exploration},
	author = {Roy-Chowdhury, Ayan., Hadjitheodosiou, Michael., Baras, John S., Rentz, Nicolas.},
	year = {2005},
	month = {09/2005},
	abstract = {We discuss some basic requirements and trade-offs for designing a communication network supporting the needs of lunar exploration missions. We describe the unique characteristics of this network and outline a prototype network architecture. The proposed network consists of three distinct segments - a terrestrial network on Earth, a network on the lunar surface, and a space segment comprising a satellite constellation that connect the two surface networks.~We develop a simulation platform that includes the network topology, node orbits and mobility, and test the network performance with different applications and traffic loads. We present simulation results obtained with our models that illustrate the network connectivity and delay for varying satellite orbital patterns and traffic characteristics. We also discuss the requirements and constraints for providing a secure infrastructure for end-to-end communication in space exploration networks~and suggest algorithms and protocols for implementing end-to-end encryption, authentication and secure group communication.},
	address = {Rome, Italy},
	booktitle = {23rd AIAA International Communications Satellite Systems Conference and Exhibit (ICSSC)},
	pages = {pp. 1-10}
}
@conference {
	title = {Dynamic Resource Allocation for an IP-based Communications Network Supporting Space Exploration},
	author = {Zeng, Hui., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2005},
	month = {09/2005},
	abstract = {We address issues related to efficiency, fairness, end-to-end delay minimization and Quality-of-Service (QoS) framework in order to enable a flexible access and dynamic mission operation capability in the next generation NASA space-to-ground IP-based communication infrastructure. In our scenario, the downlink channel of the NASA Tracking and Data Relay Satellite System is shared by a number of spacecraft, which we model as streams with different priority levels going through a common queue and a router. Both the current and future potential architectures for this relay system are addressed. We formulate an optimization problem for long-term static bandwidth allocation and present its solution to serve as initial bandwidth allocation algorithm and periodical regulation approach. Along with it, a hybrid Time Division Multiple Access (TDMA)-based protocol is proposed and then an assignment problem for the short-term dynamic optimal timeslot scheduling is studied. By using simulation, the performance of a suitable Medium Access Control (MAC) protocol with timeslot scheduling is analyzed and compared with that of the existing static fixed-assignment scheme.},
	address = {Rome, Italy},
	booktitle = {23rd AIAA International Communications Satellite Systems Conference and Exhibit (ICSSC)},
	pages = {pp. 1-12}
}
@conference {
	title = {AeroTCP: A Splitting Transport Protocol for an IP-based Satellite Network Supporting Aeronautical Communications},
	author = {Shang, Yadong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2005},
	month = {09/2005},
	abstract = {The IP-based Broadband Aeronautical Satellite Network will provide numerous new applications and services for both airspace system operations and passenger communications. However, the performance of data communications protocols and applications over such systems is dramatically degraded, especially the Internet TCP/IP protocol suite. In this paper, we propose a new transport protocols for satellite network supporting Internet and data services. Based on the observation that it is difficult for an end to- end TCP solution to solve the performance problem effectively, we propose a new splitting based TCP protocol, called Aeronautical Transport Control Protocol (AeroTCP), which takes advantage of the specific properties of satellite channel. Our simulation results show that AeroTCP improves satellite channel utilization and fairness.},
	address = {Rome, Italy},
	booktitle = {23rd AIAA International Communications Satellite Systems Conference and Exhibit (ICSSC)}
}
@conference {
	title = {TCP Splitting Protocol for Broadband Aeronautical Satellite Networks},
	author = {Shang, Yadong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2004},
	month = {10/2004},
	abstract = {In this paper, we recommend suitable transport protocols for an aeronautical network supporting Internet and data services via satellite. For the future IP-based aeronautical satellite hybrid network, we describe TCP protocol and focus on the problems that cause dramatically degraded performance of the Transport Protocol. Based on the observation that it is difficult for an end-to-end solution to solve these problems effectively, we propose a new TCP-splitting protocol, termed Aeronautical Transport Control Protocol (AeroTCP). The main idea of this protocol is to use a fixed window for flow control and one duplicated acknowledgment (ACK) for fast recovery. We also study the Gilbert-Elliott channel model for satellite channel since protocol behavior often depends strongly on the channel behavior. Our simulation results show that AeroTCP can maintain higher utilization for the satellite link than end-to-end TCP, especially in burst error-environment.},
	address = {Salt Lake City, Utah},
	booktitle = {23rd Digital Avionics Systems Conference (DASC)},
	pages = {pp. 11.C.3 (1-9)}
}
@conference {
	title = {Transport Protocol Support for Aeronautical Satellite Communications},
	author = {Shang, Yadong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2004},
	month = {05/2004},
	abstract = {We recommend suitable transport protocols for an aeronautical network supporting Internet and data services via satellite. We study the characteristics of an aeronautical satellite hybrid network and focus on the problems that cause dramatically degraded performance of the Transport Protocol. We discuss various extensions to standard TCP that alleviate some of these performance problems. Through simulation, we identify those TCP implementations that can be expected to perform reasonably well. Based on the observation that it is difficult for an end-to-end solution to solve these problems effectively, we propose a new TCP-splitting protocol, termed Aeronautical Transport Control Protocol (AeroTCP). The main idea of this protocol is to use a fixed window for flow control and one duplicated acknowledgement (ACK) for fast recovery. Our simulation results show that AeroTCP can maintain higher utilization for the satellite link than end-to-end TCP, especially in high BER environment.},
	address = {Monterey, California},
	booktitle = {22nd AIAA International Communications Satellite Systems Conference \&amp; Exhibit 2004 (ICSSC22)}
}
@conference {
	title = {An Optimization-based Approach to Flow~Control and Resource Allocation Problem in Satellite Communication Systems},
	author = {Akkor, Gun., Baras, John S., Hadjitheodosiou, Michael.},
	year = {2004},
	month = {05/2004},
	abstract = {We propose an approach to optimize resource sharing and flow control in a multi-beam broadband satellite system that supports both unicast and multicast flows. We show that, in this architecture, the load on every spot-beam queue could be different, depending on the type of the flows and the distribution of the receivers across spot-beam coverage areas. This load imbalance may significantly under-utilized the system resources and decrease the system throughput when both unicast and multicast flows are active in the system. In this paper, we formulate an optimization problem for Intra- and inter-beam resource sharing such that the variance of the session rates experienced by users of a flow located in different beam coverage areas is minimized. The result of our resource allocation also determines the maximum sustainable rate of each flow. We present results that compare the beam utilization and maximum sustainable sessions rates with and without optimization. We conclude that this method improves the average session rates up to 40\% and average utilization of the system up to 15\% when both unicast and multicast flows are active.},
	address = {Monterey, California},
	booktitle = {22nd AIAA International Communication Satellite Systems Conference \&amp; Exhibit 2004, (ICSSC)}
}
@conference {
	title = {Protocol Support for A New Satellite-Based Airspace Communication Network},
	author = {Shang, Yadong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2004},
	month = {04/2004},
	abstract = {We Recommend suitable transport protocols for an aeronautical network supporting internet and data services via sattelite.We study the characteristics of an aeronautical satellite hybrid network and focus on the problems that cause dramatically degraded performance of the Transport Protocol. We discuss various extensions to standard TCP that alleviate some of these performance problems. Through simulation, we identify those TCP implementations that can be expected to perform well. Based on the observation that it is difficult for an end-to-end solution to solve these problems effectively, we propose a new TCP splitting protocol, termed Aeronautical Transport Control Protocol (AeroTCP). The main idea of this protocol is to use a fixed window for flow control and one duplicated acknowledgement (ACK) for fast recovery. Our simulation results show that AeroTCP~can maintain higher utilization for the satellite link than end-to-end TCP, especially in high BER environment.},
	address = {Fairfax, Virginia},
	booktitle = {4th Integrated Communications, Navigation, and Surveillance (ICNS) Conference},
	pages = {pp. 81-90}
}
@conference {
	title = {A Feedback Implosion Suppression Algorithm for Satellite Reliable Multicast},
	author = {Akkor, Gun., Baras, John S., Hadjitheodosiou, Michael.},
	year = {2003},
	month = {12/2003},
	abstract = {In this paper, we propose a knapsack-based feedback suppression algorithm for reliable multicast transport protocols operating over a satellite network. A reliable transport protocol needs to identify the packets which failed to reach a given destination. This is achieved through feedback packets returned to the source. For multicast services, receive feedback has been shown to lead to the feedback implosion problem. Feedback implosion is a well-studied problem and various solutions exist in the literature. However, these solutions mainly focus on wireline terrestrial networks and do not take into account the inherent characteristics of the satellite channel and the architecture of the deployed network. Therefore, we need to revisit the problem and provide a new set of solutions for efficient integration to next-generation satellite systems. In this paper, we introduce a feedback implosion suppression algorithm, which effectively suppresses the amount of feedback relayed through the satellite channel, while ensuring that the critical information is conveyed in a timely fashion. The performance of the algorithm is evaluated through simulations.},
	address = {San Francisco, California},
	booktitle = {IEEE Globecom 2003},
	pages = {pp. 3765-3769}
}
@conference {
	title = {Using Broadband Satellite Systems to Support Aeronautical Communication},
	author = {Shang, Yadong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2003},
	month = {04/2003},
	abstract = {In this paper we discuss the possibility of using a broadband satellite-based system to support aeronautical communications. First, we investigate the applications and service requirements for current and future aeronautical communications. Then the communication system and network architecture are outlined and some of the system components are discussed in detail, including the satellite transmission channel, the airplane on-board network, and various aspects of aeronautical terminals. Finally we present a simulation analysis of the system with the focus on meeting the Quality of Service requirements for identified service categories.},
	address = {Yokohama, Japan},
	booktitle = {23rd AIAA International Communications Satellite Systems Conference and Exhibit (ICSSC)},
	pages = {pp. 1-9}
}
@conference {
	title = {Alternative Network Architectures for Supporting Communications From the International Space Station},
	author = {Nguyen, Alex T., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2002},
	month = {05/2002},
	abstract = {In order to support the communications needs of the International Space Station (ISS), alternative communications architectures to provide broadband support need to be considered. We address three communications options and evaluate an architecture for the direct to ground option, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. We focus on a particular user{\textquoteright}s requirements, and examine the system{\textquoteright}s communications links, and coverage availability. These parameters, along with high-level cost estimates, are compared to using commercial relay satellites, and an enhanced TDRSS. The direct to ground option is viable for store-and-forward applications and cost comparable to commercial constellations, but TDRSS is the choice for realtime or continuous data applications.},
	address = {Quebec, Canada},
	booktitle = {20th AIAA International Communication Satellite systems Conference and Exhibit},
	pages = {pp. 1-10},
	organization = {Montreal}
}
@techreport {
	title = {A direct-to-ground architecture for supporting Commercial Communications from the International Space Station},
	author = {Nguyen, Alex T., Zhou, Xiangrong., Hadjitheodosiou, Michael.},
	year = {2002},
	month = {01/2002},
	abstract = {We outline the first steps of an effort to start defining a communications architecture for supporting broadband data communications from the International Space Station. We address three communications options and focus on a direct-to-ground architecture, which could serve as an intermediary solution to satisfy near-term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. A high-level analysis of the architecture for the direct to ground option is performed, focusing on a particular user{\textquoteright}s requirements, communications links, and coverage availability. We also discuss system, mobility support and protocol issues that need to be addressed for this solution to be a feasible alternative.},
	address = {New York, NY}
}
@conference {
	title = {A direct-to-ground architecture for supporting commercial communications from the International Space Station},
	author = {Nguyen, Alex T., Zhou, Xiangrong., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2002},
	month = {04/2002},
	abstract = {We outline the first steps of an effort to start defining a communications architecture for supporting broadband data communications from the International Space Station. We focus on a direct-to-ground architecture, which could serve as an intermediate solution to satisfy the near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. We address three communications options and evaluate an architecture for the direct-to-ground option, focusing on a particular user{\textquoteright}s requirements, communications links, and coverage availability. We also discuss system, mobility support and protocol issues that need to be addressed for this solution to be a feasible alternative.},
	address = {New York, NY},
	booktitle = {IEEE International Conference on Communications},
	pages = {pp. 2989-2993}
}
@article {
	title = {Multicast-Aware Power Allocation in Multiple Spot-Beam Satellite Communication Systems},
	author = {Akkor, Gun., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2006},
	month = {01/2006},
	abstract = {In this paper, we address the problem of user heterogeneity in satellite multicast from the perspective of resource allocation in a multiple spot-beam satellite system that supports both unicast and multicast flows. Satellite communication systems, with their wide-area coverage and direct access to a large number of users, clearly have an inherent advantage in supporting multicast applications. In order to remain competitive against other broadband technologies, however, next generation satellite systems will be required to support both unicast and multicast flows and offer optimal sharing of system resources between these flows. We show that user heterogeneity across spot-beam queues may result in lower allocated session rates for active flows, and be perceived as unsatisfactory by potential users when both unicast and multicast flows are active in the system. We propose an optimization-based approach that allocates resources with the goal of smoothing user heterogeneity and show that resulting session rates are higher on the average for both unicast and multicast flows. This is achieved through the re-distribution of system power among spot-beam queues, by taking into account the load on the queues and the channel states. We conclude that it is possible to increase the average session rates of multicast flows by 25{\textendash}100\%, and the rates of unicast flows by 15{\textendash}40\% compared to the pre-optimization levels.},
	pages = {pp. 49-71},
	volume = {Vol. 24},
	number = {Issue  1},
	journal = {International Journal of Satellite Communications}
}
@article {
	title = {Security Issues in Hybrid Networks with a Satellite Component},
	author = {Roy-Chowdhury, Ayan., Baras, John S., Hadjitheodosiou, Michael., Papademetriou, Spyro.},
	year = {2005},
	month = {12/2005},
	abstract = {Satellites are expected to play an increasingly important role in providing broadband Internet services over long distances in an efficient manner. Most future networks will be hybrid in nature {\textemdash} having terrestrial nodes interconnected by satellite links. Security is an important concern in such networks since the satellite segment is susceptible to a host of attacks, including eavesdropping, session hijacking, and data corruption. In this article, we address the issue of securing communication in satellite networks. We discuss various security attacks that are possible in hybrid satellite networks and survey the different solutions proposed to secure data communications in these networks. We look at the performance problems arising in hybrid networks due to security additions like Internet Security Protocol (IPSec) or Secure Socket Layer (SSL) and suggest solutions to performance-related problems. We also point out important drawbacks in the proposed solutions and suggest a hierarchical key-management approach for adding data security to group communication in hybrid networks.},
	pages = {pp. 50-61},
	volume = {Vol. 12},
	number = {Issue 6},
	journal = {IEEE Wireless Communications Magazine}
}
@techreport {
	title = {Hybrid Networks with a Space Segment - Topology Design and Security issues},
	author = {Roy-Chowdhury, Ayan., Hadjitheodosiou, Michael., Rentz, Nicolas.},
	year = {2005},
	month = {01/2005},
	abstract = {In this paper we investigate a hybrid network topology that is suitable for supporting interplanetary communications. We define an architecture comprised of a network of sensor nodes on a remote planetary surface, connected to a hybrid terrestrial network of wired and wireless LANs through a series of satellite relays. All the nodes in the network are IPaddressable and support public and symmetric key cryptography. The resulting network forms a hierarchical hybrid mesh that connects users on Earth to networks on or around a remote planetary surface. We describe the design of the network and present preliminary simulation results illustrating the network performance for various parameters. We also discuss how algorithms for user authentication, message integrity and data confidentiality can be incorporated in the network infrastructure for secure end-to-end communication.},
	number = {Number: CSHCN TR 2005-6}
}
@article {
	title = {Transport Protocols in Multicast via Satellite},
	author = {Akkor, Gun., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2004},
	month = {11/2004},
	abstract = {In a wide variety of broadband applications, there is a need to distribute information to a potentially large number of receiver sites that are widely dispersed from each other. Communication satellites are a natural technology option and are extremely well suited for carrying such services because of the inherent broadcast capability of the satellite channel. Despite the potential of satellite multicast, there exists little support for multicast services over satellite networks. Although several multicast protocols have been proposed for use over the Internet, they are not optimized for satellite networks. One of the key multicast components that are affected when satellite networks are involved in the communication is the transport layer. In this paper, we attempt to provide an overview of the design space and the ways in which the network deployment and application requirements affect the solution space for transport layer schemes in a satellite environment. We also highlight some of the issues that are critical in the development of next generation satellite multicast services.},
	pages = {pp. 611-627},
	volume = {Vol. 22},
	number = {No. 6},
	journal = {International Journal of Satellite Communication}
}
@article {
	title = {Broadband Communication Support for Earth Observation from the International Space Station},
	author = {Nguyen, Alex T., Hadjitheodosiou, Michael., Baras, John S.},
	year = {2004},
	month = {10/2004},
	abstract = {In order to support the communications needs of Earth-observing instruments on the International Space Station (ISS), alternative communications architectures to provide broadband support need to be considered. In this paper, we evaluate the direct-to-ground option in terms of coverage. We show that a direct-to-ground option is a feasible solution to enhance the limited communication capabilities provided by the current ISS infrastructure. In order to ensure efficient end-to-end communication support and deal with the complications of the space environment, COTS equipment with recently demonstrated protocol modifications needs to be adopted. We also demonstrate that selecting the most appropriate location for placement of the ground stations is an important design issue that can ensure optimal coverage and maximize throughput. As both the need for broadband services from the ISS and from other upcoming space missions increases, this option will play a role in enhancing the currently limited space-relay architecture until a next generation relay system is deployed.},
	pages = {pp. 375-388},
	volume = {Vol. 46},
	number = {Issue 3},
	journal = {Computer Networks Journal}
}
@techreport {
	title = {Power Balancing in Multiple Spot-Beam Satellite Systems for Multicast Support},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2004},
	month = {01/2004},
	abstract = {We address the problem of optimizing resource sharing and flow control in a multiple spot-beam broadband satellite system that supports both unicast and multicast flows. Satellite communication systems, with their wide-area coverage and ubiquitous access to large number of users, clearly have an inherent advantage in supporting distributed applications that require concurrent transmission of content to multiple users. In order to remain competitive against other broadband technologies, next generation satellite systems will be required to support both unicast and multicast flows and offer optimal sharing of system resources between these flows. We show that a high load variation across the spot-beam queues may significantly under-utilize the system and be perceived unsatisfactory by potential users when both unicast and multicast flows are active in the system. We propose an optimization based-approach to balance the load in the system and conclude that it is possible to increase the average session rates of all active flows by up to 30\% after this optimization is applied.},
	number = {Number: CSHCN TR 2004-15}
}
@techreport {
	title = {A Multiple Subset Sum Formulation for Feedback Implosion Suppression over Satellite Networks},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2004},
	month = {01/2004},
	abstract = {In this paper, we present a feedback implosion suppression (FIS) algorithm that reduces the volume of feedback information transmitted through the network without relying on any collaboration between users, or on any infrastructure other than the satellite network. Next generation satellite systems that utilize the Ka frequency band are likely to rely on various fade mitigation (compensation) techniques ranging from adaptive coding to dynamic power control, in order to guarantee a service quality that is comparable to other broadband technologies. User feedback would be a valuable input for a number of such components, however, collecting periodic feedback from a large number of users would result in the well-known feedback implosion problem. Feedback implosion is identified as a major problem when a large number of users try to transmit their feedback messages through the network, holding up a significant portion of the uplink resources and clogging the shared uplink medium. In this paper, we look at a system where uplink channel access is organized in time-slots. The goal of the FIS algorithm is to reduce the number of uplink time-slots hold up for the purpose of feedback transmission. Our analysis show that the FIS algorithm effectively suppresses the feedback messages of 95\% of all active users, but still achieves acceptable performance results when the ratio of available time-slots to number of users is equal to or higher than 5\%.},
	number = {Number: CSHCN TR 2004-21}
}
@techreport {
	title = {Multicast-aware Power Allocation in Multiple Spot-Beam Satellite Communication Systems},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2004},
	month = {01/2004},
	abstract = {We address the problem of optimizing resource sharing and flow control in a multiple spot-beam broadband satellite system that supports both unicast and multicast flows. Satellite communication systems, with their wide-area coverage and direct access to large number of users, clearly have an inherent advantage in supporting multicast applications. In order to remain competitive against other broadband technologies, however, next generation satellite systems will be required to support both unicast and multicast flows and offer optimal sharing of system resources between these flows. We show that, in a multiple spot-beam system, a high load variation across spot-beam queues may force lower allocated session rates for active flows, and be perceived as unsatisfactory by potential users when both unicast and multicast flows are active in the system. We propose an optimization framework for balancing the spot-beam queue service rates such that the sum of the rate variances of all active multicast flows is minimized. This is achieved through the re-distribution of system power among spot-beam queues, by taking into account the load on the queues and the channel states. We conclude that it is possible to increase the average session rates of multicast flows by up to 16\%, and the rates of unicast flows by up to 4\% after this optimization is applied.},
	number = {Number: CSHCN TR 2004-19}
}
@techreport {
	title = {Load balancing in multi-beam satellite systems},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2004},
	month = {01/2004},
	abstract = {We propose an approach to optimize resource sharing and in a multi-beam broadband satellite system that supports both unicast and multicast flows. We show that in this architecture, the load on every spot-beam queue could be different, depending on the type of the flows and the distribution of the receivers across spot-beam coverage areas. This load unbalance may significantly under-utilize the system resources and decrease the system throughput when both unicast and multicast flows are active in the system. In this paper, we formulate an optimization problem for intra- and inter-beam resource sharing such that the variance of the session rates experienced by users of a flow located in different beam coverage areas is minimized. The result of our resource allocation also determines the maximum sustainable rate of each flow. We calculate the beam utilization and maximum sustainable sessions rates with and without optimization and compare the results. We conclude that this method significantly improves the session rates and overall utilization of the system when both unicast and multicast flows are active.},
	number = {Number: CSHCN TR 2004-9}
}
@techreport {
	title = {A Reliable Multicast Transport Protocol for Satellite Communication Systems},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2003},
	month = {01/2003},
	abstract = {In this paper, we propose a reliable multicast transport protocol for satellite communication systems. Many of the emerging applications in the Internet would benefit from reliable multicast services, and broadband satellite communication systems have attractive characteristics for supporting such services. However, many of the protocols designed primarily for terrestrial networks do not perform well over satellite networks. Therefore, it is necessary to look at the problem of reliable multicast in the solution space of satellite communications. Our protocol makes use of a special form of forward error correcting codes and couples it with an adaptive window based control mechanism to dynamically adjust the number of encoding packets forwarded to the users. Protocol makes very good use of the broadcast nature of the satellite channel and attempts to minimize the feedback from users. We evaluate the protocol performance by extensive computer simulations.},
	number = {Number: CSHCN TR 2003-17}
}
@techreport {
	title = {A Feedback Implosion Suppression Algorithm for Satellite Reliable Multicast},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2003},
	month = {01/2003},
	abstract = {In this paper, we propose a knapsack-based feedback suppressionalgorithm for reliable multicast transport protocols operating over asatellite network. A reliable transport protocol needs to identify thepackets which failed to reach a given destination. This is achievedthrough feedback packets returned to the source. For multicastservices, receiver feedback has been shown to lead to thefeedback implosion problem. Feedback implosion is awell-studied problem and various solutions exist in the literature.However, these solutions mainly focus on wireline terrestrial networksand do not take into account the inherent characteristics of thesatellite channel and the architecture of the deployed network.Therefore, we need to revisit the problem and provide a new set ofsolutions for efficient integration to next generation satellitesystems. In this paper, we introduce a feedback implosion suppressionalgorithm, which effectively suppresses the amount of feedback relayedthrough the satellite channel, while ensuring that the criticalinformation is conveyed in a timely fashion. The performance of thealgorithm is evaluated through simulations.},
	number = {Number: CSHCN TR 2003-3}
}
@techreport {
	title = {IP Multicast via Satellite: A Survey},
	author = {Akkor, Gun., Hadjitheodosiou, Michael.},
	year = {2002},
	month = {01/2002},
	abstract = {Many of the emerging applications in the Internet, such astele-conferencing, distance-learning, distributed games, softwareupdates, and distributed computing would benefit from multicastservices. In many of these applications, there is a need todistribute information to many sites that are widely dispersed fromeach other. Communication satellites are a natural technology optionand are extremely well suited for carrying such services. Despite thepotential of satellite multicast, there exists little support forsatellite IP multicast services. Both Internet Engineering andInternet Research Task Forces (IETF and IRTF) have been involved in aresearch effort to identify the design space for a general purposereliable multicast protocol and standardize certain protocolcomponents as building blocks. However, for satellite multicastservices, several of these components have a different designspace. In this paper, we attempt to provide an overview of the designspace and the ways in which the network deployment and applicationrequirements affect the solution space. We maintain a similartaxonomy to that of the IETF efforts, and identify which keycomponents of a general multicast protocol are affected by two of themost common satellite network deployment scenarios. We also highlightsome of the issues which we think are critical in the development ofnext generation satellite IP multicast services.},
	number = {Number: CSHCN TR 2002-35}
}
@techreport {
	title = {Alternative Network Architectures for Supporting Communications from the International Space Station},
	author = {Nguyen, Alex T., Hadjitheodosiou, Michael.},
	year = {2002},
	month = {01/2002},
	abstract = {In order to support the communications needs of the International Space Station (ISS), alternative communications architectures to provide broadband support need to be considered. We address three communications options and evaluate an architecture for the direct to ground option, which could serve as an intermediary solution to satisfy near term communications needs of commercial experiments and payloads on the ISS and overcome certain limitations of the current ISS communications infrastructure. We focus on a particular user\&rsquo;s requirements, and examine the system\&rsquo;s communications links, and coverage availability. These parameters, along with high-level cost estimates, are compared to using commercial relay satellites, and an enhanced TDRSS. The direct to ground option is viable for store-and-forward applications and cost comparable to commercial constellations, but TDRSS is the choice for real-time or continuous data applications.},
	number = {Number: CSHCN TR 2002-9}
}
