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SUMMARYThis paper introduces architectures for next-generation high throughput satellite (HTS) systems comprising various satellite payload options, ground terminal advances, and scalable system-level software control and management techniques. It describes a model to estimate aggregate system capacity as a function of radio band, available spectrum, spot beams, waveforms, and payload capability, including antenna size, power, and digital/ analog connectivity across various links and availability objectives. This system model has been used to evaluate aggregate capacity of representative Ka-Band low earth orbit and geosynchronous orbit systems. A system implementation approach is described for next-generation HTS systems based on widely used Industry standards. Modulation and coding techniques are based on Digital Video Broadcasting -S2 extensions (DVB-S2X), which comprises spectrally efficient modulation schemes combined with low-rate codes. Several implementation technologies are analyzed related to configurable onboard payload and ground-based, software-defined resource control and management, key enablers of next-generation HTS systems. Basic architectural building blocks are introduced for design of end-to-end systems across low earth orbit, medium earth orbit, and geosynchronous orbit satellite constellations, with and without onboard processing and inter-satellite links, and including several efficient scenarios to achieve lossless handovers.

Mega satellite constellations in low earth orbit (LEO) will provide complete global coverage; rapidly enhance overall capacity, even for unserved areas; and improve the quality of service (QoS) possible with lower signal propagation delays. Complemented by medium earth orbit (MEO) and geostationary earth orbit (GEO) satellites and terrestrial network components under a hybrid communications architecture, these constellations will enable universal 5G service across the world while supporting diverse 5G use cases. With an unobstructed line-of-sight visibility of approximately 3 min, a typical LEO satellite requires efficient user terminal (UT), satellite, gateway, and intersatellite link handovers. A comprehensive mobility design for mega-constellations involves cost-effective space and ground phased-array antennas for responsive and seamless tracking. An end-to-end multilayer protocol architecture spanning space and terrestrial technologies can be used to analyze and ensure QoS and mobility. A scalable routing and traffic engineering design based on software-defined networking adequately handles continuous variability in network topology, differentiated user demands, and traffic transport in both temporal and spatial dimensions. The spacebased networks involving mega-constellations will be better integrated with their terrestrial counterparts by fully leveraging the multilayer 5G framework, which is the foundational feature of our hybrid architecture.

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Software Defined Satellite Network (SDSN), similar to SDN [1], decouples data plane functions from control plane functions. SDSN benefits from logically centralized network state knowledge and decision making that enables optimal resource allocations for dynamic packet processing and transmission. An SDSN network node uses forwarding tables configured by a centralized system controller to govern packet routing with embedded Layer 2 switch without requiring elaborate Layer 3 control plane software implementation in every satellite node. Besides upper layer packet queuing and switching, SDSNs also involve radio transmission links and encompass associated modulation, coding, and resource allocation functions with dynamic control. SDSN architectural concepts can be illustrated with the SPACEWAY system which uses a GEO satellite comprising Ka band spot beams and a 10 Gbps packet processing switch. The onboard switching function is orchestrated by a ground-based system controller, with centralized support for addressing, routing, and packet flow management. The SDSN building blocks and performance objectives can be extended to address inter-satellite packet routing using a constellation of satellites with inter-satellite links and enhanced routing and resource management function at the controller. Besides GEO, LEO, and MEO satellites the SDSN architecture and techniques for addressing, routing, QoS, traffic engineering, and resource management can also be utilized for aerial and high altitude networking platforms.

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We propose using a tree-structured piecewise linear filter as an adaptive equalizer. The tree equalizer is constructed as follows. Each node in a tree is associated with a linear filter restricted to a polygonal domain, and this is done in such a way that each subtree is associated with a piecewise linear filter. A training sequence is used to adaptively update the filter coefficients and domains at each node, and to select the best subtree and the corresponding piecewise linear filter.The tree-structured approach offers several advantages. First, it makes use of standard linear adaptive filtering techniques at each node to find the corresponding conditional linear filter. Second, it allows for efficient selection of the subtree and the corresponding piecewise linear filter of appropriate complexity. Overall, the approach is computationally efficient and conceptually simple. Numerical experiments are performed to show the advantages of tree-structured piecewise linear and piecewise decision feedback equalizers over linear, polynomial and decision feedback equalizers for the equalization of channels with severe intersymbol interference.