Kenneth Y. Jo

Optimal loading of satellite systems with subchannel gain-state control

This paper presents satellite loading methodologies for the wideband global system (WGS) satellites in which the gains of the subchannels are set differently to optimize the aggregate transponder and terminal powers. The methodologies employ classical optimization techniques to iteratively determine both the transponder gain of each subchannel and the transmit powers of the participating terminals. Given the transponder behavior with nonhomogeneous gain state, interference, and intermodulation (IM), efficient loading algorithms are devised to solve the optimal subchannel gains and link transmission powers based on the developed analytical methods. The optimal satellite loading can be achieved in a finite number of iterations to minimize the combined satellite and terminals powers simultaneously and to close involved links. A practical example in computing the optimum gains and transmission powers is also presented.

Non-homogeneous gain state optimization for transponding satellite communications

Recent advances in the design of transponding communications satellites the ability to switch transponder sub-bands among multiple up-link and down-link antennas. This feature increases the flexibility of traffic routing and improves spectral re-use characteristics. A side benefit of such a new system is the capability of applying different transponder gains to carriers in different sub-channels within a given transponder. Recently, techniques have been developed for analyzing link supportability and the transponder loading with these non-homogeneous gain states. However, these new analysis techniques require that the gains be known a-priori. to complement these analysis techniques a method is needed for selecting the best gains to be used in each sub-channel. This paper presents such a method for selecting transponder gains. We define the constraining equations, which ensure that each link can be supported, and propose a optimization metric that maximizes the overall supportability. We the suggest an optimization approach that can be sued to select the gains for each sub-channel and the overall transponder operating point. The approach described includes a means of selecting the starting point for the optimization. A numerical example is provided.

Global Command and Control System target architecture modeling

This paper presents methodologies for modeling and designing the target architecture for the Global Command and Control System (GCCS). The target GCCS architecture advances information processing and communications technologies to support a wide variety of command and control missions and functions. The GCCS requires reliable high-speed networking, multimedia conferencing, distributed simulation, and training. In addition, GCCS accommodates many information applications through shared processing, distributed data, multimedia communications, and centralized monitoring and control. All existing applications will be modernized and consolidated into a common operating environment. System characterization, interoperability of functional applications, target architecture design, capacity sizing, and optimum allocations of information technology resources are key design factors. The performance analysis, management and control, and operational effectiveness of involved systems are also discussed.<<ETX>>

Systems engineering and performance evaluation for the Defense Information Systems Network

This paper presents systems engineering and performance analysis and evaluation concepts for planning, designing, operating, and managing the Defense Information Systems Network (DISN). The DISN uses Asynchronous Transfer Mode (ATM) high-speed communications services to support a wide class of applications that require high-speed networking and will provide multi-media conferencing, distributed simulation, and training. DISN, via an ATM-based wide area network, will accommodate a wide variety of traffic types, each requiring proper traffic management and congestion control mechanisms. By doing so, new value-added communications services will be offered for the Department of Defense. This paper addresses key aspects of the multimedia services that the DISN will provide and discusses technical issues concerning the quality-of-service. Traffic modeling and characterization of the DISN, capacity management and sizing, and allocation of network resources in response to requirements are studied. The performance analysis, monitoring, and operational effectiveness are also described.<<ETX>>

Satellite communications with Internet Protocol (IP) efficiency

This paper presents an analysis of satellite communications (SATCOM) systems that use Internet Protocol (IP) with Quality of Service (QoS) metrics, and addresses IP efficiency measures. Key contributing elements for the IP efficiency are network structure, provisional efficiency, and bandwidth-on-demand features. IP bandwidth gains will also depend on the network size, the level of hierarchy, and the user applications. Small networks with packet-based traffic would show high IP gains while larger networks tend to show less IP gains. Large networks factoring in statistical multiplexing effects aided by less variability of traffic flows can be self-tuned with right-sized link capacities. Bursty traffic behaviors and duty cycles would further influence the IP gains. Case studies also demonstrate the delays and overflow probabilities for IP packets with different priorities.

Satellite communications networks with IP quality of services

This paper presents a satellite communications (SATCOM) architecture that uses packet switched technologies and addresses the relationships between SATCOM and IP quality of service (QoS). The onboard satellite processing with fast-packet switching rather than traditional circuit switch or bent pipe SATCOM connections, is described first. The performance of such an architecture may improve or degrade with IP QoS services depending on how they interact. The network architecture incorporates a bandwidth-on-demand concept through demand-assigned multiple-access (DAMA) protocols, and achieves multiple levels of QoS services through IP class-of-service (CoS). This concept improves application performance, increases network utilization and throughput, and reduces message/file transfer times. The bit error rates that are inherent to SATCOM networks do not apply directly to the architecture. Underlying performance evaluation methodologies as well as related implementation issues for the proposed architecture are addressed. The onboard switching architecture generally brings about performance improvements, but one case that degrades performance is presented. In this example, excessive delays occur when transmitting moderate-to-high bit error rates due to an IP error recovery procedure that induces more lower-layer packet segmentation and reassembly processes. Thus, the higher bit error rate caused by satellite links can be critical for the performance. This observation along with related protocol and performance issues leads to the conclusion that the essential IP features will only be operative for the fast-packet switching SATCOM architecture.

Satellite communications representation in network simulation

This paper presents methodologies to represent satellite communications (SATCOM) behaviors in network simulation. This paper is based on tasks performed for generic network warfare simulation that employs traditional network simulation models. The methodologies also include the integration issues of SATCOM tools and the network simulation models. We first characterize space segments and assets involved in warfare operations and exercises, and then analyze system behaviors to measure space-link performance design results. The techniques adopted in effect will augment traditional network models with SATCOM capabilities through specialized satellite analysis models. The SATCOM tools produce detailed satellite orbit characteristics and radio frequency (RF) performance analyses for public and commercial satellites with multiple microwave bands. Automated interface mechanisms between the SATCOM and network simulation models are being developed to provide more interactive model collaboration.

Performance of Combatant Command satellite (COCOMSat) communications in contested environments

This paper presents satellite loading methodologies for loading satellite communications (SATCOM) requirements on commercial Ka-band satellites in contested environments experiencing jamming. Future high-capacity Ka-band commercial satellites will rely on ground concentration nodes (GCNs) and adaptive coding and modulation (ACM) techniques to provide digital video broadcasting/return channel via satellite (DVB/RCS) services for forward and return links to achieve high throughput. Traffic flows between user beams are coordinated through GCNs thus requiring double hops for peer-to-peer traffic while reachback traffic requires single hops relying on terrestrial networks. Cell-like user beams are assembled in arrays designed to enhance user coverage and supportability. Optimal satellite loading in the presence of uplink jamming is derived to minimize satellite and terminals powers and to maximize the supported data rates. Throughput degradation in contested environments results when the transponders begin to operate in a non-linear mode approaching saturation.

Design and analysis of large-scale wireless communications networks

This paper presents fundamental design and performance assessment methodologies for modern large-scale enterprise wireless communications networks comprised of many system components. Large-scale wireless networks are needed to serve mobile users in a region and to satisfy their intra- and inter-region communications requirements by adopting network-on-the-move (NOTM) concepts. For global access, the NOTM systems will connect to wireless and terrestrial networks and will also support communications-on-the-move (COTM) users. For the design and analysis of such wireless networks, several key areas need to be addressed. These are Internet Protocol (IP) gain assessment, optimal wireless network architecture design, and wireless link analyses. For architectural assessment, new approaches have been developed to meet the design and performance requirements given system capacities. Numerical representations of the optimal wireless network design methodologies are presented to demonstrate the assessment of end-to-end enterprise-wide network performance levels in benign and hostile jamming environments. The aggregate results of these approaches can be effectively applied to provide improved forward-link services to remote mobile users and bandwidth-efficient wireless communications link support to dispersed enterprise users

Simulation methods for analysis of traffic processes in ATM networks

This paper presents efficient simulation methods for analyzing modern, large-scale networks and evaluating their performance attributes. Characterizing traffic flows from multiple sources and applications is key in assessing overall network performance measures. It is essential to have quantitative network cost and performance measures in order to plan, design, and implement modern, large-scale networks such as the Advanced Distributed Learning Network (ADLN). ADLN requires integrated, multimedia network services for distributed, collaborative processing among globally dispersed users. ADLN will interconnect multiple categories of users and provide integrated voice, video, and data services, which can be enabled through the use of Asynchronous Transfer Mode (ATM) technology (ATM Forum 1992). Through efficient multiplexing and networking, ATM can interconnect multiple classes of users and transport ADLN applications cost-effectively with guaranteed performance. A combined approach of simulation and analysis is used to assess the performance of the large-scale, distributed network such as ADLN. Topics include the multi-source traffic characterization, performance analysis of ATM networks, capacity sizing, and optimal allocation of network resources.