Multicast communication support over satellite networks

In this dissertation, we focus on providing multicast communication support over satellite networks. We investigate the possible performance enhancements in terms of the throughput, capacity, and scalability of a Ka-band, multiple spot-beam satellite communication system that supports unicast and multicast services. The role satellite systems play in today's communication infrastructure is changing rapidly, fueled by the technological advance in the design of new satellite systems, and by the new multimedia service applications, such as on-demand multimedia content delivery, distance learning, and distributed software updates that would benefit from the wide-area coverage, direct and ubiquitous access capability of the satellite systems. These applications require concurrent transmission of the same content to multiple users. In order for multicasting-based services to grow over satellite networks, there must be an incentive to deploy them. We address the problem of user heterogeneity that occurs when multicast users that are located across several different spot-beam locations experience different channel conditions. We propose a novel power allocation scheme for smoothing out the heterogeneity experienced by the multicast groups, while making sure that unicast users get a fair share of system resources as well. Our power allocation scheme would benefit from user feedback in determining the channel conditions. However, collecting feedback from a large set of users is a challenging task in satellite systems, since access to the uplink bandwidth is to be shared between several users, and the resources are usually limited. We introduce a novel algorithm that reduces the volume of feedback information that is to be transmitted over the satellite segment of the network, while maintaining that the relevant information is collected in a timely manner. Finally, we focus our attention to the potential benefits of integrating packet level forward error correction coding to packet delivery for reliable multicast services over satellite networks. Forward error protection helps recover corrupted data, and minimizes the need for retransmissions over the satellite channel. We investigate the use of a special form of forward error correcting (FEC) code and couple it with an adaptive control mechanism to dynamically adjust the number of encoding packets forwarded to the users

A Multiple Subset Sum Formulation for Feedback Implosion Suppression over Satellite Networks

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%

A Feedback Implosion Suppression Algorithm for Satellite Reliable Multicast

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

Power Balancing in Multiple Spot-Beam Satellite Systems for Multicast Support

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

Load balancing in multi-beam satellite systems

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

Multicast-aware Power Allocation in Multiple Spot-Beam Satellite Communication Systems

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

A Reliable Multicast Transport Protocol for Satellite Communication Systems

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

IP Multicast via Satellite: A Survey

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 emph{building blocks}. However, for satellitemulticast services, several of these components have a differentdesign space. In this paper, we attempt to provide an overview of thedesign space and the ways in which the network deployment andapplication requirements affect the solution space. We maintain asimilar taxonomy 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