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Routing for IP based Satellite Ad-Hoc Networks

Description:

TECHNOLOGY AREAS: Information Systems, Space Platforms

OBJECTIVE:  Demonstrate novel IP routing protocols onboard over satellites that would link user preferences and network conditions and improve end-to-end network performance, including heterogeneity of satellite nodes, interferences of satellite links, etc.

DESCRIPTION:  The defense satellite communication system (DSCS) is a satellite system designed to provide high-volume and secure communication infrastructure for supporting real-time military voice and data communication. A number of satellite communication system, including the DSCS III satellite constellation, have been deployed and successfully supporting military communication over the past decades. However, those systems cannot meet the modern military mission critical operation, which requires the high bandwidth for a large number of war-fighting users [1, 2]. One example of this was demonstrated in Afghanistan, where the DoD had to lease transponders on commercial satellites to extend communication reach and increase bandwidth for end-users in war-fight [3]. To address this issue, the DoD had an initiative to migrate the existing satellite-based circuit-switched communication systems to the packet switched system using Internet protocols. As shown in [4], the current MILSTAR II satellite communication system takes two minutes to transmit a 24 MB 8’’x10’’ image; while the next generation IP based satellite communication will be able to do that in less than one second. Cisco Systems Inc. and Intelsat General Corp. demonstrated the viability of conducting military communication via an Internet router in space [5].

In an IP-based satellite communication network, the satellite can be considered as nodes on a network or a router in 3-D space and a number of satellites can be formed an ad-hoc network in 3-D space. When designing routing protocols in such IP based satellite ad-hoc networks, there is a need to consider the following challenges due to the unique characteristics of satellite communication links, heterogeneous satellite nodes and end-users. First, satellite links have higher bit error rates than terrestrial links forming the Internet and round-trip time is from several hundred milliseconds to half-second. Hence, these will have significant impact on the performance of user datagram protocol and transmission control protocol over satellite, along with QoS requirements, including connection establishment delay, connection establishment failure probability, throughput, and transmit delay. Second, satellite nodes are heterogeneous and are in time-varying 3-D space. Satellite nodes can be located at low and medium-earth orbits. Those nodes have different up/down link bandwidth and computing resources. Because those nodes are not geostationary, the slant range varies, inter-satellite links are dynamic, and communication of one link may interfere with other links. Third, end-users of satellite communication systems, including remote-piloted aircraft and ground-based vehicles, are heterogeneous. Lastly, for mission critical operations, the satellite networks often have tight real-time requirements, e.g., end-to-end delay, bandwidth, etc.

To address those challenges, this STTR topic calls for novel theoretical constructs and effective designs of advanced IP routing onboard over satellite that will link user preferences and network conditions, including timeliness, availability, throughput, and heterogeneity of satellite nodes. To efficiently improve the usage of network resource and reduce end-to-end latency, the cross-layer design and multiple path/QoS routing mechanisms shall be developed to allow users to bargain and meet end-user QoS requirements given network conditions. In particular, the satellite ad-hoc network can be considered as a mesh network in a time-variant 3-D space, which consists of heterogeneous access satellite node, core satellite node, and client with satellite antenna. While this topic encourages novel solutions, the examples of state-of-the-art algorithms such as across-layer design [6] and multi-path QoS routing [7] in mesh network and ad-hoc networks can also be found in recent scientific publications.

PHASE I:  Develop IP-based satellite ad-hoc network architectures together with QoS for transmission control protocol (TCP) over satellite on connection establishment delay, connection establishment failure probability, throughput, transmit delay, residual error ratio, protection, priority and resilience. Demonstrate the feasibility through  proof-of-concept

PHASE II:  Refine the candidate solutions selected from Phase I results. Investigate options, e.g., maximum throughput vs. window size for various round-trip delays to improve performance of TCP over satellite. Assess computational requirements and communication overheads associated with centralized and decentralized implementation schemes for cross-layer algorithms and TCP over satellite. Document TCP research issues related to satellites.

PHASE III DUAL USE COMMERCIALIZATION:

Military Application:  Extend the architectures and/or technology components into real-time dynamic net-centric operations with security measures, e.g., IPSec to communicate at tactical edges where there exist users and warfighters with different priorities and credentials.

Commercial Application:  Transition the architectures and/or technology components into commercial systems. Anticipated benefits may include significant improvement of end-to-end performance of links with errors and enhancement of TCP over satellite channels.

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