Architecture, Modeling and Simulation for Communications Systems Design
In developing communications systems, we cannot always build a demonstration version to show how the system will operate. For a number of years, we have taken the alternate approach of understanding the architecture of the system, and then analyzing a model that simulates that architecture.
To develop the architecture of a communications system, we use the Raytheon Enterprise Architecture Process (REAP), which standardizes architecture development, description, evolution and assessment throughout Raytheon. The REAP is a systems architecting process extended with enterprise architecture concepts and techniques. This union of systems and enterprise architecting leverages best practices between the two and ensures that enterprise context, constraints and relationships guide the development.
For the modeling and simulation effort, we make use of the resources developed in conjunction with Raytheon's Enterprise Modeling & Simulation (EMS) effort. EMS has a Lego® brick-like structure with standard interfaces to allow rapid development and demonstration of high-fidelity simulations driven from desktop computers.
The Communication Reference Architecture comprises REAP architecture products and is one of the key enablers for the development of communications systems. The base applicable products (and associated framework products) are determined by the current lifecycle phase of the program or project that will be used as a starting point. The three lifecycle phases are: concept refinement, technology development and system development. The output of working with the Communication Reference Architecture is a set of architecture products that includes attributes that are key to architecture quality.
As an architect starts to work the reference architecture, understanding the mission objective (see figure) and the needs of a communications system allow for the selective tailoring of the artifacts within the Communication Reference Architecture to quickly develop the resulting system architecture. This system architecture is then used to pull together modeling and simulation modules for analysis of the system.
To perform the detailed modeling, simulation and analysis to support design and development of new communications systems, the modeling team employs a variety of commercial best-of-breed tools that are widely used in the civilian and defense communications sectors and are well suited to general analysis of both ground-based and airborne point-to-point links and communications networks. Selection and use of particular tools are dependent on the requirements of the individual program. However, a key characteristic of all of these tools is the ability to create and use custom-built models based on C- and C++ – like functions and structures. This translates into the ability to seamlessly transition from modeling and simulation into communications system software and protocol development. The architect is able to begin development using abstract models of basic system functionality and use an iterative approach to progressively increasing the detail and fidelity level of the models as the design matures. The ultimate result of this process is fully functional code that can be directly transitioned from the simulation environment into operational hardware. Likewise, this process can be reversed, where operational software from a communications system can be ported and executed in the simulation environment. Being able to test and evaluate the performance of communications-system protocols in a simulated RF environment can drastically reduce the risk associated with the traditional field-test approach.
In cases where the communications system is satellite-based, the modeling effort can integrate additional commercial best-of-breed satellite simulation tools for establishing and controlling satellite orbit characteristics, coverage footprints and link characteristics. Likewise, the perspective of the MS&A can be expanded to the platform level through the integration of multiple co-site and coverage analysis tools, as well as the use of specialized terrain models to reflect system performance in urban and subterranean environments.
For Mission Systems Integration initiatives, the perspective of architecture and simulation activities will often transition from one in which the performance of the communications system is the only question, to an environment where overall Mission Assurance and system-of-systems performance are the primary questions of interest. Thus, communications performance becomes only one of many second-order characteristics of the analysis. These efforts also frequently involve the incorporation of actual operational hardware, software and system users into an integrated test bed or experimentation environment commonly categorized as hardware-, software- or human-in-the-loop.
As a result of simulation run-time requirements and the limitations of traditional methods for federating simulations in these cases, our modeling groups developed the Distributed Communications Effects Module (DCEM). DCEM is a framework that supports integration of communications and networking models — of variable levels of fidelity — into a wide range of test-bed and experimentation architectures for the purpose of including the effects of communications system performance into larger mission-level analysis. DCEM has been specifically designed to achieve wall-clock simulation run-time requirements. It includes models of several current military communications systems, can be adapted to existing distributed test-bed architectures, and is fully integrated into EMS and our experiment test beds. In addition to models of specific communications systems, DCEM includes a "generic" communications model that allows architects to postulate the characteristics of future communications and networking systems and perform what-if analyses on them.
The future of architecture and communications we are looking at include the analysis of network communications centers and understanding mobile ad-hoc networks. The infrastructures needed to support the topics in this article are being built to accomplish tasks such as quickly transiting the Communication Reference Architecture into simulation and analysis models to determine the effectiveness of different systems and approaches to the customers' needs. This provides the ability to quickly trade different approaches for proposing the best solution for the problem. It also allows for developing and refining the requirements for the performance of the resulting communications system.
