Search

Fast and reliable high-speed intersatellite communication (ISC) between small satellites is dependent on the physical layer (PL) design of the onboard communication system. However, as with nonlegacy systems, the lack of architecture and design information pertaining to the development of the PL of an LED-based visible light communication (VLC) system for ISC poses significant challenges to architecting the communication system. Addressing these challenges requires a holistic approach to the specification of the system design. To this end, we explore the use of model-based systems engineering (MBSE) principles in mitigating the design complexity of the PL architecture for the VLC system. Design concerns and gaps are addressed by developing an executable black-box system model that specifies the conceptual architecture of the system, and a parametric model that analyzes multiple system configurations based on generated values for the signal-to-noise ratio and bit error rate parameters. We utilize the structural, behavioral, and parametric semantics of SysML to define, specify, visualize, and analyze the various system design configurations. The resulting PL black-box system specification is verified through model execution.

Intersatellite communication (ISC), also known as intersatellite links (ISLs), comes with many benefits to distributed space systems (DSSs) including advanced capabilities, such as relative navigation among small satellites and a reduction in the need for the ground segment. Radio frequency (RF) has been the de-facto method for ISC in DSS missions. However, as new science missions evolve with advanced payloads and complex architectures, RF may not be able to meet the ISC requirements of high bandwidth and throughput without violating the size, mass, power, and cost (SMaP-C) constraints of small satellites. Laser communication has the potential of meeting the requirements for these more complex missions but may violate the constraints imposed on small satellites due to its high-precision pointing and tracking requirements. This work presents the progress made on the development of LED-based visible light ISC (VL-ISC). Key aspects of the system design are presented with regards to the physical and data link layers. The simulation of the nonorthogonal multiple-access scheme for VL-ISC in a cluster of small satellites indicates an overall system throughput sum rate of about 2 Mbit/s (for system bandwidth of 0.5 MHz) among others. The roadmap to the development of a future VL-ISC standard is discussed.

Unmanned Aerial Vehicle (UAV) swarms are promising solutions to conduct different military and commercial missions. However, highly varying environmental factors such as wind make the UAVs unable to maintain the minimum safe distance between each other, and the UAVs at the edge of the swarm more vulnerable to connectivity loss from the swarm. The paper extensively studies the effect of wind on the connectivity and safety of a large scale swarm with one leader and multiple follower UAVs. We examined the relationship between different parameters including UAV speed, UAV mass, wind speed, drag force, and number of UAVs maintaining the desired safety and connectivity requirement in a swarm. Our analysis demonstrates that planning to fly the swarm at a speed closer (equal, if possible) to the mean value of the wind speed at the desired altitude increases the number of connected and safely flying UAVs. This choice of UAV speed, however, might not be the best solution when one considers the time constraint to reach the desired destination. And, when the UAVs are flying with a speed less than the wind speed, we get a smaller number of critical UAVs whereas, such a selection leads to a higher number of UAVs that do not meet the safety requirement of the swarm. To address this challenge, we propose to optimally and adaptively select the UAV speed so that the swarm reaches the target destination with the minimum/desired flight time while maintaining the connectivity and safety of most (all, if possible) of the UAVs.

The emerging Digital Engineering demands digital representation of the system of interest and sharing models and data across the boundaries of organizations and the boundaries of the engineering lifecycle. Towards this direction, it is critical to develop systems modeling languages and tools that accommodate Digital Engineering. This paper presents our research on semantic mapping from System Modeling Language (SysML) to Functional Reactive Programming (FRP) with the goal of developing computing mechanisms with functional reactive programming to support executable and verifiable SysML model specification.

The System Modeling Language (SysML) is a visual modeling language that can be used to describe the structure and behavior of a system. Modeling tools can be used to capture the variety of diagrams and maintain the consistency of elements across the different structural and behavioral representations of the system. Current research is investigating using the XML Metadata Interchange (XMI) standard to convert the diagrammatic information captured in SysML into a format that can be used to produce software code that can then be simulated to ensure conformance with system requirements. The XMI standard can be used as an interim format to migrate the content from a diagrammatic representation, where system elements are sorted by the diagram that contains them, to an object approach, where all elements related to an entity reside in a tree structure below that element. This paper presents a method to ensure the consistency of the XMI representation regardless of whether a functional or physical system engineering approach is used for the design process. This has implications in maintaining the consistency of the XMI file when system development is initiated from a high level of abstraction, followed by iterative addition of detail. The goal is to ensure that XMI file maintains an authoritative representation of the modeled system.

Future space missions will be driven by factors such as the need for reduced cost of spacecraft without diminished performance, new services, and capabilities including reconfigurability, autonomous operations, target observation with improved resolution and servicing (or proximity) operations. Small satellites, deployed as a sensor network in space, can through intersatellite communication (ISC) enable the realization of these future goals. Developing the communication subsystem that can facilitate ISC within this distributed network of small satellites require a complex range of design tradeoffs. For small satellites, the general design parameters that are to be optimized for ISC are size, mass, and power, as well as cost (SMaP-C). Novel and efficient design techniques for implementing the communication subsystem are crucial for building multiple small satellite networks with capability for achieving significant data-rates along the intersatellite links (ISLs). In this paper, we propose an alternative approach to radio frequency and laser ISLs for ISC among small satellites deployed as a sensor network in low earth orbit. For short to medium range ISLs, we present an LED-based visible light communication (VLC) system that addresses the SMaP constraints, including capability for achieving significant data rates. Our research is focused on the development of the physical layer for pico-/nano class of satellites with prime consideration for the impact of solar background illumination on link performance. We develop an analytical model of the intersatellite link (ISL) in MATLAB and evaluate its feasibility and performance for different intensity modulation and direct detection schemes. Using a transmitted optical power of 4 W and digital pulse interval modulation, a receiver bandwidth requirement of 3.5 MHz is needed to achieve a data rate of 2.0 Mbits/s over a moderate link distance of 0.5 km at a BER of 10−6.

In this paper, we develop the mathematical foundation for a formal requirements management of a systems engineering (SE) methodology called the Responsive and Formal Design (RFD) process. The RFD process relates a set of requirements, associated models, simulations, and the relationship between them, by integrating model-based systems engineering (MBSE) to manage system modeling complexity with formal methods to ensure that designs are verifiably correct against their requirements. In this paper, we formally define basic notions of the RFD process, develop algorithms to extract a set of logical expressions from a set of requirements, and present a technique that is used to map a behavior model to its simulation. We also present a formal way of refining requirements in the RFD process and show how properties are preserved along the way in a fundamental fashion. We demonstrate our development using three small satellites measurement system that images the colorful auroral ovals around Earth's magnetic poles.

Safety-critical systems must be engineered to be ultra-reliable. Redundancy is critical to tolerate faults that cannot be eliminated by using ruggedized or hardened computing. The use of small satellites allows new missions to be cost-effective, but it also introduces new problems in terms of robustness and fault handling. Apart from the inherent problems of working in a distributed setting, small sats normally lack the redundancy needed to deal with pernicious faults due to constraints on weight, cost and complexity. This paper presents and evaluates fault tolerance mechanisms in a swarm of satellites considered as a whole, making it robust to the failure of one or more satellites. The evaluation is performed with a computer model augmented with the properties desired from our system. We use a random testing tool to inject faults in different parts of our model and evaluate the fault detection and fault correction mechanisms we propose. Our results support the suitability of the proposed fault model, fault tolerant architecture, and evaluation methodology.

The verifiable design process (VDP) is a systems engineering methodology that integrates formal methods and model based systems engineering to achieve a correct-by-construction system. Formal methods are used in the design process to verify correct behavior of system as specified in the requirements. In order to aid development and analysis, the verifiable design process is organized in abstraction layers. The layers are represented using models that include requirements in natural language form, requirements in ontological form, specifications in logic form together with a proof process and interconnected models and their simulations. The models are intelligently coupled with each other to enable the formal verification and model-based validation of a system. In this work, we will show how to formalize the verifiable design process using category theory. We first show how to represent the different representations (models) of VDP as a category. Suitable categorical structures are employed to analyze them. Furthermore, we define each abstraction layer as a category (category of categories) with the models forming the objects and the relations among them forming the morphisms (functors). We then use pushout structure to represent the objects and their relations to provide analysis of the design process. The functors defined will formalize the relations between the different forms of representations.

Requirements that are understood and shared by all stakeholders as well as system engineers are highly critical in the development of a successful system. Natural languages (NL) are essentially preferred to represent requirements to advance this shared understanding. However, natural languages are inherently imprecise and ambiguous leading to inconsistent, incomplete, and incorrect requirements. Therefore, there is a need to represent requirements formally. In this paper, the use of ontologies for knowledge representation from requirements is presented for the responsive and formal design (RFD) process. The main goals are to (1) facilitate requirements engineering, (2) serve as an intermediate representation for automatic transition to logic-based modeling, and (3) formalize the process of transformation from requirements to logic-based modeling. Therefore, requirements engineering in the RFD process will be augmented using ontologies in the domain modeling of the system to be implemented. Ontologies are utilized to capture domain requirements, and formal mechanisms are used to check for inconsistency and incompleteness at each abstraction layer in the RFD process.

Small satellites are becoming increasingly popular for several scientific missions due to their significantly lower cost of development and launch compared to large satellites. A network of multiple small satellites can be utilized to compensate the limited capability of individual small satellites. Therefore, developing a reliable inter-satellite communication among these satellites is a key design factor to enhance the performance of small satellites networks. In this paper, we propose a game-theoretic power optimization technique for interference management in inter-satellite communication network by taking advantage of computation and decision making capabilities of recent small satellites. In the proposed Stackelberg game model, the master satellite as the game leader determines the price of power transmission to optimize the network welfare and the slave satellites set their individual power to maximize their individual throughput. The proof of existence and uniqueness of the solution of the proposed game is provided.

Efficient multiple access (MA) schemes are one of the major components in enabling Visible Light Communication among multiple small satellites with the aim of optimizing throughput and lifetime of the network. Small satellites are becoming a popular choice for satellite missions involving multiple satellites due to their relatively low costs of production and deployment as well as improvement in temporal and spatial resolution which results in enhanced quality of data from these missions. These satellite missions involve communications among multiple satellites deployed as a wireless sensor network. Visible light communication using LEDs is preferred for inter-satellite communication due to the higher data rates it delivers. Non-Orthogonal Multiple Access has the potential of delivering high throughput relative to other multiple access schemes with Visible Light Communications. In this work, the feasibility of Non-Orthogonal Multiple Access (NOMA) is investigated for a cluster of small satellites with the aim of maintaining high throughput. Simulation results show a BER performance of 10−6 which is required for stable communications at a minimum transmit power of about 12W. This paves way for further development in aspects of multiple access involving VLC among small satellites.

Inter-Satellite Communication (ISC) is a relatively new and emerging technology for small satellite systems. The level of complexity associated with an inter-satellite communication system necessitates a Model-Based Systems Engineering (MBSE) approach towards the system design concept. Applying MBSE concepts in the early life-cycle phases of the ISC system development, will lead to a well-defined set of system requirements. In this direction, we present a model-based Concept of Operation (ConOps) for an ISC system using visible light communication (VLC). The ConOps model captures the scope definition process and the allocation of stakeholder requirements to stakeholder use cases. Also captured is the Operation Concept (OpsCon) and operational scenarios necessary for defining the system requirements.

In this paper, we formalize the Responsive and Formal Design (RFD) process using category theory. The RFD process combines Model-Based Systems Engineering (MBSE) to manage system modeling complexity and formal methods to ensure that designs are verifiably correct against their requirements. It consists of a set of levels of abstraction. Each level of abstraction represents a set of requirements and its associated models, simulations, and the relationship between them. Abstraction and refinement functions relate different levels of representation. In this paper, we represent and analyze the RFD process using category theory. Category theory provides us a means (using a collection of objects and arrows) to represent each level of abstractions and communications between them. We represent each level of abstraction using a pullback categorical structure (define the objects and morphisms). The facts and theorems in one level of abstraction will be passed to another via a refinement or an abstraction functor (function). The two functors operate in an inverse (adjoint) relationship. This means refinement traceability is met in the design process fundamentally. Additionally, since adjunction is a weaker relation than any other relations (such as equality, isomorphism, and equivalence) between two categories, it is a relatively better option for relaxing the design space. Finally, we introduce an idea of defining a category of refinements (i.e. a category of functors) and interpreting the universal properties.

In our previous paper, we examined the utility of LEDs for inter-satellite communication (ISC) in multiple small satellite networks and proposed an approach of the physical layer design that meets the requirements of the platform in terms of the critical physical layer design variables. These variables (or parameters) include the LED transmit power, photodetector active area, receiver bandwidth and link distance. One of the most important tasks for the visible light communication (VLC) system designer is how to ensure the required balance or trade-off among these variables in order to achieve the desired performance. In this work, we employed multi-objective optimization to determine physical layer design variables at which the signal-to-noise ratio (SNR) at the VLC receiver is maximized. We used the Non-dominated Sorting Genetic Algorithm II (NSGA-II) in MATLAB to determine the Pareto front of two conflicting objective functions, and then extracted the optimal solution using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). Analysis of the optimal solution showed that it yielded the maximum SNR within the set of non-dominated solutions at the Pareto front. We showed that using multi-objective optimization techniques for assignment of parameter values can yield more than 3 dB improvement in the SNR.

This paper presents an application of a fuzzy relation in system modeling (from requirements) to be used for a Systems Engineering (SE) methodology. We define fuzzy classifications (models for distributed systems), extract component and system theories (sets of logical expressions), and ensure consistency of requirements for the Responsive and Formal Design (RFD) Process. The RFD process is a SE methodology that relates a set of requirements, associated models, simulations, and the relationship between them, by integrating Model-Based Systems Engineering (MBSE) to manage system modeling complexity with formal methods to ensure that designs are verifiably correct against their requirements. To translate informal requirements to logical expressions in the RFD process, we first model requirements using a 3-tuple structure called a classification formulated from Barwise and Seligman's channel theory. A classification consists of "tokens" (observed situations) and "types" (situation features) and a binary relation classifying tokens with types. However, classifying tokens using types as present (represented as ‘1’) or absent (represented as ‘0’) as used in channel theory is not always possible (since it involves vagueness and imprecission) and the representation lacks expressiveness to reason about relations among such types (vague situation features). Hence, a binary classification doesn't capture uncertainity. In this paper, we consider a degree of truth in the relation between tokens and types to define a fuzzy classification. We then develop an algorithm that extracts a theory from a fuzzy classification. This helps in formal proof for checking consistency (no contradiction) and deducing to requirements (verifying properties). We demonstrate our development using three small satellites measurement system whose goal is to image the colorful auroral ovals seen around Earth's magnetic poles.

An Architectural framework for defining Inter-Satellite Communication system architectures based on Model-Based Systems Engineering concepts will facilitate the development of reliable and consistent system models that can be simulated, verified and validated. However, such a framework does not exist, thereby limiting our ability to define comprehensive and effective inter-satellite communication system architectures. As a means of addressing this challenge, we present an architectural framework design for defining and representing ISC system architecture for Small Satellite Systems based on an MBSE approach. The Systems Modeling Language SysML is used as the modeling tool for the framework design.

The goal of this paper is to explore the need for Systems Engineering (SE) in East African countries and how best to educate engineers in the field of SE. It provides a comprehensive overview on the usefulness of SE education for East African nations and proposes SE curriculum. Presently SE has been given little attention in East African countries. However, these countries are in the beginning of industrialization with many new mega projects and infrastructure expansions that demands SE professionals. This motivates the need to introduce SE education in the region. Systems engineering education demands the development of SE curriculum, which will be multidisciplinary and considers social and psychological factors by taking into account the active participation of the community. Towards this end, the paper demonstrates the necessity of SE education via designing and managing ongoing mega projects. It also proposes SE curriculum by incorporating courses covering both foundations of SE and the practice of SE. Furthermore, it suggests that these courses will be delivered in collaboration with industry and government entities.

Requirements, stakeholders' visions, drive any systems engineering (SE) process. But in design process practices, there is a gap often present between stakeholders' visions and requirements representation. This limits the impact that the stakeholders can provide input to the SE process. Then, the process may end up with errors or provide a product which is unwanted. We proposed a design methodology called the Responsive and Formal Design (RFD) process that directly involves the stakeholders input at each level of the requirement elicitation, shows its effect on the total system performance, and integrates high level requirements with domain specific considerations and verifies formally. It consists of a set of levels of representaion. Each level represents a set of requirements and its associated models, simulations, and the relationship between them. The levels of representation are related with refinement and abstraction relations. The refinement helps to make clear the connection with parametric considerations. As levels of RFD proceed towards refinement, the design process becomes a local or discipline specific activity, though always with a global perspective. Following our framework, this paper presents the implementation of the refinement process. Each level of the RFD process has its own level of granularity. This is true for the model, logical representation, and simulation of the requirements. In this paper, we define the pair of functions, refinement and abstraction, that exist between two models (system and component models in table form called classifications) and their logical representations (called theories) with different levels of granularity. We also show how high level requirements are interpreted in the refined level. We use an example of data from three small satellites, whose goal is to image the auroral ovals around Earth's magnetic poles, to demonstrate our development.

Future space missions will be designed to take advantage of multi-satellite network deployment because of their potential for providing improved spatial and temporal resolutions of a target and/or can provide a more comprehensive observation of the Earth. To enable interoperability within this satellite network particularly for autanomous operations and provide on-orbit data handling through distributed processing, a reliable inter-satellite communication (ISC) is required. In this paper, we examine the suitability of Light-Emitting Diodes (LEDs) for ISC in multi-satellite networks, and further propose an approach of the physical layer design that meets the requirements of the platform in terms of the size, weight and power (SWaP) of the satellite. An analytical model of the ISL is developed to test feasibility of using LEDs for reliable data communication in the presence of steady solar background illumination. Finally, the performance of the ISL is evaluated in terms of the Bit Error Rate (BER) and achievable data rates for four different intensity modulation and direct detection (IM/DD) schemes.

Adaptive infinite impulse response (IIR) filters provide significant advantages over equivalent finite impulse response (FIR) implementations because they are able to more accurately model physical plants that have pole-zero structures. Additionally, they are typically capable of meeting performance specifications using fewer filter parameters. This savings in parameters, which can be as much as 5-10 times, leads to the use of fewer multiplier blocks and therefore, lower power consumption. Despite these advantages, adaptive IIR filters have not found widespread use because the associated mean squared error (MSE) cost function is multimodal and therefore, significantly difficult to minimize. Additionally, the filter can become unstable during adaptation. These two properties pose several problems for adaptive algorithms, causing them to be sensitive to initial conditions, produce biased solutions, unstable filter configurations or converge to local minima. These problems prevent the widespread use of adaptive IIR filters in practice and if such filter structures are to become more practical, new, innovative solutions are required. This paper proposes a new algorithm for minimizing the MSE cost function of adaptive IIR filters aimed at addressing some of the aforementioned issues. We adopt the approach of using a branch-and-bound algorithm, which is an exhaustive search method, and employ interval arithmetic for all computations. Simulation results show that the resulting algorithm is viable and competitive and, when compared with a number of existing state-of-the-art algorithms, outperforms them in terms of the MSE of the final point.

Small satellite systems enable whole new class of missions for navigation, communications, remote sensing and scientific research for both civilian and military purposes. As individual spacecraft are limited by the size, mass and power constraints, mass-produced small satellites in large constellations or clusters could be useful in many science missions such as gravity mapping, tracking of forest fires, finding water resources, etc. Constellation of satellites provide improved spatial and temporal resolution of the target. Small satellite constellations contribute innovative applications by replacing a single asset with several very capable spacecraft which opens the door to new applications. With increasing levels of autonomy, there will be a need for remote communication networks to enable communication between spacecraft. These space based networks will need to configure and maintain dynamic routes, manage intermediate nodes, and reconfigure themselves to achieve mission objectives. Hence, inter-satellite communication is a key aspect when satellites fly in formation. In this paper, we present the various researches being conducted in the small satellite community for implementing inter-satellite communications based on the Open System Interconnection (OSI) model. This paper also reviews the various design parameters applicable to the first three layers of the OSI model, i.e., physical, data link and network layer. Based on the survey, we also present a comprehensive list of design parameters useful for achieving inter-satellite communications for multiple small satellite missions. Specific topics include proposed solutions for some of the challenges faced by small satellite systems, enabling operations using a network of small satellites, and some examples of small satellite missions involving formation flying aspects., 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications Surveys and Tutorials

This chapter introduces an application of small satellite for environmental monitoring using real-time data that focuses on measured soil moisture and temperature using in situ sensor network. Soil Moisture Active Passive Mission (SMAP) uses microwave radar and radiometer to sense surface soil moisture condition but gives coarser result than the in situ data. To overcome the limitation of accuracy in SMAP mission, the proposed architecture will provide sensor data via a Ground Monitoring Wireless Sensor Network (GM-WSN) where data is collected by small satellite(s) operating in Lower Earth Orbit (LEO). The satellite will store the data until it passes over a ground station whereby it is communicated back to earth. The motivation for developing satellite accessible in situ measurements is to retrieve information from remote areas like Lake Tana in Ethiopia, where human accessibility is difficult. Hence, those important and unattended places would be covered by the proposed system. Another key attribute of this architecture is that it addresses four (climate, carbon, weather, and water) out of six NASA’s earth science strategic focus areas. The GM-WSN will consist of a sensor network that will measure soil moisture and temperature. The base station function is to fuse the data from the sensors, provide a time stamp, and format the data to be transmitted to satellite. It will also act as transceiver for ground to space communication using the amateur VHF/UHF radio band that has a maximum data rate of 9.6 kbps and will provide health maintenance and power management of network.

In this paper, we study the problem of multi-user inter-satellite communications in a network of small satellites and design and implement of an optimum CDMA-based multiple access communication using Software Defined Radios. Inter-satellite links (ISL) enable small satellites to exchange information and share resources while reducing the traffic load to the ground. The ISL assist in performing advanced functions including distributed processing and autonomous applications. By utilizing the ISL in maintaining the relative distance between the satellites, navigation, and positioning accuracy is improved greatly. The ideology proposed here is to implement remote modifications in inter-satellite communication after launch using Software Defined Radios (SDRs), while accommodating an adaptive autonomous small satellite network. Remote upgrades from the ground as well as the potential to accommodate new applications and future services without hardware changes is very promising. Software defined radio-based implementation of an ISL can assist in enabling an adaptive and reconfigurable communication system, which can achieve higher data rates and modification of frequencies. In this paper, we designed and implemented a multi-user inter-satellite communication network using SDRs, where Code Division Multiple Access (CDMA) technique is utilized to manage the multiple access to shared communication channel among the satellites. This research is the first work to study and implement the utilization of SDRs for inter-satellite communications in small satellite systems.

System engineering has experienced multiple successes over the years in various industrial projects with a strong emphasis in defense and aerospace. Recently, system engineering has gained several contributions from theory, however the field still lacks a strong theoretical foundation. This request for more theoretical foundations come from both academia and industry in order to make the best of system engineering practices and experience in increasingly multidisciplinary projects. Several research topics need to be addressed such as formal definitions of system engineering terms and concepts, systems semantics, complexity theory of multidisciplinary systems, and formal analysis of system engineering processes and standards. The impact of theoretical computer science on languages (e.g. SysML) and tools used by system engineers, the integration of quantitative methods (e.g. formal methods, value driven design, petri-nets, design space optimization, etc.) with MBSE methods and processes, along with system engineering languages (SysML) and its variants will also be included. This paper proposes a short review on the first special session - THEFOSE - Theoretical Foundations of System Engineering held at the IEEE SYSCON 2015 Conference on System Engineering.

In this paper, we present the formal requirement management of the Responsive and Formal Design (RFD) process that extracts a formal theory from requirements written in a natural language. The RFD process was developed as a procedure used in designing Cyber-Physical Systems (CPS) and represents an integration of Model-Based Systems Engineering (MBSE) with formal methods to ensure a “correct-by-construction” design. The extraction of a formal theory is based on Channel Theory as developed by Barwise and Seligman, which is established as a framework for the “flow of information” in terms of category theory. A system consists of components connected via channels. Each component is viewed as an information-flow network and mathematically modeled using a notion of a classification. A classification is a table representation of an information-flow network. Regularities (that represent global behavior of the system) of a classification are captured using a theory (a set of formulas or constraints). One goal of the RFD process is to insure that the requirements are formally consistent. In this paper, we develop a set of algorithms that extracts a theory from a classification, though the theory is not necessarily unique. This work is inclusive of an algorithm which checks whether a regular closure (based on structural rules) of a theory is a theory of a given classification. An example of this work is demonstrated through a satellite communication Store and Forward operation.

Present design processes for satellite networks mainly involve interconnected system models and their parameter-based simulations without emphasizing high level requirements in the process. What is missing is a systems engineering approach and a system of verification and validation based on formal representation and analysis. We propose a systems design methodology for inter-satellite communication based on the Responsive and Formal Design (RFD) [1]–[3], which addresses the need for a model-based system engineering approach coupled with a system of validation and verification based on formal representation and analysis. The goal is to apply the RFD process to provide a solution for the Inter-Satellite Communications (ISC) problem within the Open Systems Interconnection (OSI) framework. The OSI represents a standard framework for communication between devices. It divides the communication process into seven layers, with each one providing well-defined functions and services. We will address the integration of the RFD process with the OSI framework for ISC. The RFD process involves levels of design abstraction and refinement which correspond to layers or groups of layers of the OSI model. The process illustrates how the complete framework for ISC unfolds in an iterative manner.

Consider the class of d-dimensional causal filters characterized by a d-variate rational function H(z)=\frac{P(z)}{Q(z)} analytic on the polydisk {\Bbb D}^{d}=\{ z=(z_{1}, \ldots ,z_{d})\, :\,\mid z_{i}\mid \lt 1 \}. The BIBO stability of such filters has been the subject of much research over the past two decades. In this paper we analyze the BIBO stability of such functions and prove necessary and sufficient conditions for BIBO stability of a d-dimensional filter. In particular, we prove if a d-variate filter H(z) analytic on {Bbb D}^{d} has a Fourier expansion that converges uniformly on the closure of {\Bbb D}^{d}, then H(z) is BIBO stable. This result proves a long standing conjecture set forth by Bose in [3].

This paper presents an initial investigation into the design of a solar thermal propulsion concept for an increasingly important class of spacecrafts. Small satellites have been receiving renewed attention over the last decade. The proposed heat exchanger solar thermal propulsion concept attempts to move away from traditional solar thermal propulsion concepts. In this concept thermal energy in the form of heat is moved from the solar array to the propellant. Excess thermal energy is radiated into space. Initial thrust force and specific impulse values obtained by the use of established mathematical relations, produce numerical values that are not only comparable with the traditional solar thermal concept, but also with other small satellite propulsion types. A small satellite with an on-board propulsion system will expand the capability of small-satellites for the use in formation flying and station keeping. It will also provide a viable option for de-orbit at the end of mission life, thereby contributing to the effective removal of orbital spacecrafts once have completed their missions.

We propose to develop a model-based systems engineering process that results in high-confidence designs for small satellite systems in the pico-/nano-class, i.e. < 50kg. This objective will be achieved through the integration of formal methods and model based systems engineering to develop an agile framework for high-confidence designs for these small systems. We propose, Reliable and Formal Design (RFD) process whose results are correct by construction, formally verified, and responsive to system requirement changes. This paper develops an intelligent framework that ties requirements, models, and simulations in a cogent manner. Furthermore, this papers provides a formulation for consistency and traceability, where the latter enforces a condition on the relationship between abstraction layers, that is, the function that refines any layer of abstraction into a successive layer must have a dual. An example of this refinement is illustrated using PVS to express the logical requirement formulation and for providing type checking proof.

Lyman et al. (2000) developed some important properties of a continuous-time linear predictor applied to a bandlimited random process, and discussed how such a prediction could be applied to the problem of mobile radio fading. In this paper, we solve explicitly for the optimal predictor, in the mean-square sense, when the process spectral density is not within the band limits and the predictor impulse response is energy constrained. As basis functions, we use time-shifted versions of the prolate spheroidal wave functions, leading to a simple algebraic optimization problem that is solved using a Lagrange multiplier. We show how to use the solution to compute the minimum mean squared prediction error under the energy constraint. Then, we discuss the case of a bandlimited process embedded in white noise, showing how to determine if a certain mean squared prediction error can be attained.

In communications and signal processing, we can find examples of applications that could benefit from the prediction of a bandlimited random process. We consider a continuous-time linear predictor applied to a bandlimited process. We show that if the past values of the process are known over an interval of arbitrary positive length, the mean squared prediction error may be made arbitrarily small, regardless of how far in the future we wish to make the prediction. We also show that this is no longer true when a certain energy constraint is applied to the predictor. Furthermore, we discuss what this means for the case in which the prediction is based on past values that are corrupted by estimation errors.

In this paper, we address the problem of determining maximum-likelihood estimates of sinusoid parameters from a signal that consists of sinusoids and additive noise. We present three algorithms that integrate interval methods for global optimization with procedures that decompose the problem into smaller ones. Interval methods represent a global optimization technique that is based upon the branch and bound principle. More specifically, we decompose the problems via the expectation-maximization algorithm and variations of the coordinate descent algorithm. Although, we have not proven that the proposed algorithms converge to the global optimum, their performance in our simulation example was much superior to that of the popular iterative quadratic maximum likelihood (IQML) method.

In this brief, we develop a least mean square (LMS) algorithm that converges in a statistical sense to the global minimum of the mean square error (MSE) objective function. This is accomplished by estimating the gradient as a smoothed version of the MSE, The smoothed MSE objective begins as a convex functional in the mean. The amount of dispersion or smoothing is reduced, such that over time it becomes the true MSE as the algorithm converges to the global minimum. We show that this smoothing behavior is approximated by appending a variable noise source to the infinite impulse response (IIR)-LMS algorithm. We show, experimentally, that the proposed method does converge to the global minimum in the cases tested. A performance improvement over the IIR-LMS algorithm and the Steiglitz-McBride algorithm has been achieved.

Current video compression algorithms are increasingly complicated and difficult to analyze and profile. Design tools and system level languages often prove to be inefficient and incapable of providing complexity analysis as a first step directed toward at the implementation of video compression algorithms. This paper proposes framework that will help to develop a methodology that facilitates the derivation of analytical dataflow models. The framework proposes dataflow models for quantifying the underlying algorithm's memory complexity, related timing considerations, and verification of the correctness of the video compression algorithm.

Late 2008, at SCAN 2008 in El Paso, TX, an effort to standardize interval computations was started by a working group of the IEEE Microprocessor Standards Committee, titled the Interval Arithmetic Working Group of the IEEE P1788 Standard. This paper describes the goals of this effort, the history of the working group, and how it relates to the IEEE 754 Standard. It gives a brief overview of the policies and procedures for constructing the standard, and its expected structure. It also presents some of the questions the group may have to solve in the future.

A major drawback of recursive adaptive filters based on gradient methods is that convergence to a global minimum is not always achieved. This is due to a nonconvex mean square error (MSE) performance surface. This article develops a continuous-time least mean square algorithm that converges to the global minimum with probability one.

The development of approaches for understanding the complex dynamics of biological systems is a growing research area in electrical engineering, particularly in the fields of signal processing and controls. The focus of our research is the exploitation of the parallels between engineering and biology through the development of optimization and identification methods. Specifically, this research consists of developing methods for the estimation of unmeasured states, the identification of parameters of kinetic models and the validation of biochemical models. This work falls under the general research topic of systems biology. We explore the use of interval analysis in developing numerical algorithms for optimization and validation of systems biology problems. A major attribute of this method is that convergence to global minima is guaranteed. This paper includes a development of an adaptive interval optimization method based on the branch-and-bound method known as smooth interval branch-and-bound. One potential impact of this research is the development of more accurate models of biological systems. This will aid in the design of drugs for cancer and disease treatment and aid in the study of how they propagate

We present two case studies of different architectures for H.264 video decoder. The objective of this case study is to show the design methodology that can maximize the flexibility of video decoder. First, H.264 is designed based on configurable processor. The configurable processor was used to complement the existing functional units with instruction extensions for the H.264 hardware kernel. Secondly, we profile the H.264 application to capture the amount of data traffic among modules. We will use this information to guide the placement of H.264 hardware modules in the dataflow architecture. A simulated annealing based placement algorithm produces the final placement aiming to optimize the communication costs between the modules in a dataflow architecture. With both our design methodologies, emerging embedded applications requiring several GOPS to meet real-time constraints can be drafted within a reasonable amount of design time with maximum design flexibility

There are many applications within digital signal processing (DSP) that require the user to know how various numerical errors (uncertainty) affect the result. This uncertainty is represented by replacing non-interval values with intervals. Since most DSPs operate in real time environments, fast processors are needed to implement interval arithmetic. The goal is to develop a platform in which interval arithmetic operations are performed at the same computational speed as present day signal processors. We have proposed a design for an interval based arithmetic logic unit (I-ALU) whose computational time for implementing interval arithmetic operations is equivalent to many digital signal processors. Many DSP and control applications require a small subset of arithmetic operations that must be computed efficiently. This design has two independent modules operating in parallel to calculate the lower bound and upper bound of the output interval. The functional unit of the ALU performs the basic fixed-point interval arithmetic operations of addition, subtraction, multiplication and the interval set operations of union and intersection. In addition, the ALU is optimized to perform dot products through the multiply-accumulate instruction. Division traditionally is not implemented on digital signal processors unless computed with a shift operation. In this design, division by shifting is implemented. The ALU is designed to have maximum throughput while minimizing area.

We present an algorithm for adaptive IIR filters that is designed to yield stable filters while guaranteeing convergence to the global minima of the mean square error (MSE) cost function. The algorithm is based on the global optimization technique of branch-and-bound along with interval arithmetic to compute bounds on the cost function. By so doing, we ensure that infinite precision results are not lost due to rounding errors that occur naturally in digital computations. The effectiveness of the algorithm is demonstrated through simulation results which show that it is capable of locating global minimum points in the presence of local minima.

Optimization is critical in the development and implementation of techniques for estimating the unmeasured dynamics of biological systems. Local-search algorithms present an attractive option for implementing this optimization due to their low complexity. These algorithms can, however, produce sub-optimal results when estimating these unmeasured dynamics using noisy measurements. In this work, we implement a global-search constrained optimization based on real-coded genetic algorithms (RC-GA) to estimate the unmeasured dynamics of the Caspases signal transduction network. We show that RC-GA performs better than gradient-based local search algorithms by providing estimates that more closely match the "true" dynamics of the biological system.

As mandated by the President, the vision for space has generated a renewal of interest in on-orbit servicing, and many of the individual technologies inherent to the concept, as a result of the sophisticated capabilities required to ensure realization of the vision’s aggressive objectives. In response to these needs, the Heterogeneous Expert Robots for On-orbit Servicing (HEROS) architecture was conceptualized. The fundamental baseline of HEROS is driven by the paradigm shift away from the monolithic servicing platforms of the 1980s toward a more pragmatic approach of conglomerate teams of smaller, agile agents. Utilizing a fleet of small, specialized service platforms working symbiotically to achieve a common task requires no single platform to perform all servicing subtasks. Thus, the individual platforms can be made less complex and hence should be more robust, albeit at the cost of complexity introduced by requirements of cooperation. This paper presents a discussion of the advantage/challenges and current research in path planning algorithms for the HEROS architecture.

A decision-directed adaptive channel-tracking scheme can fail in a fading environment. We propose a method for overcoming this problem using a prediction of the complex fading envelope, which is modeled as a bandlimited random process. Making use of the prolate spheroidal wavefunctions, we solve the bandlimited linear prediction problem for the special case in which the process spectral density is flat within the band limits. How these findings may be applied to the channel tracking problem, as well as other more complex fading compensation measures, is also discussed.

The authors present a new algorithm for computing the initial state of a N-D DLSI system. The algorithm is based on suppression of any transients due to initial conditions and can be applied to initialize 1-D and 2-D systems as well. They present a 1-D example on the use of the algorithm to show its effectiveness, and also successfully use the algorithm for suppressing transients associated with the implementation of spatial domain filters. >