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SDR-Based SATCOM Monitoring
by Claus Vesterholt, Technical Program Manager, SATCOM, GateHouse A/S

This article offers an introduction to the challenges, opportunities and advantages associated with Satellite Communication (SATCOM) Monitoring, particularly in the perspective of the current state of Software Defined Radio (SDR) technology. Further, discussed will be the technological advances that enable ‘plug-and-play’ integration processes for RF-to-Ethernet components.

VesterholtGr1 SATCOM Monitoring, as category, spans over many different applications. Across the diversity in application, a common denominator in systems development has been a range of technological, financial and competence-related barriers. Current SATCOM Monitoring solutions are expensive, proprietary, restricted in use, and costly to maintain and keep updated. They offer limited interoperability with other IT systems and, in general, they fail to match the present and future potential complexity of the monitored devices.

A key argument in this article is that SDR technology addresses the aforementioned, listed barriers by enabling a system architecture where the complete range of RF-challenges are handled by one Commercial-Off-The-Shelf (COTS) hardware module that integrates seamlessly into a Software Communication Architecture (SCA)-compliant hardware framework.

Presented is an argument that SDR technology paves the way for a new generation of ‘plug-and-play’ SATCOM Monitoring solutions by offering the following advantages:

• Easy integration of Radio Frequency (RF) technology without the costly overhead of RF-expertise, prototyping, test labs and development tools
• Deployment-ready, cost-effective RF hardware platforms are available from multiple vendors in the market
• Reduced time-to-market and development risks for new SATCOM analysis systems
• Versatile, multi-service, and in-the-field programmable SATCOM monitoring and acquisition systems—lightweight solutions fit for tactical use
• A high quality platform for testing and feasibility studies (lab tests)

CPI_ad_MSM0113 Challenges + Limitations
Current SATCOM Monitoring systems are caught in a deadlock of technological, financial and competence-related barriers. The challenges are three-fold:

#1—Custom-built RF technology
The interception of radio signals by special purpose Radio Frequency (RF) systems requires custom-built RF hardware. Unfortunately, normal user terminal equipment is not applicable in satellite interception solutions, generally due to the optimization in cost and applications. In addition, the requirements in the signals interception domain with regard to robustness, flexibility and signal quality cannot be fulfilled with standard electronic devices.

In-house development of RF electronics has always been a big and complex challenge, and subsequently the resulting products and solutions expensive and proprietary. RF electronics development requires years of domain expertise, expensive test lab facilities and sophisticated, accurately calibrated RF instruments, and CAD development tools. Even the integration of generally available RF components implies a complex design, implementation and test process. As a consequence, the development of special purpose RF technology is associated with long development cycles and expensive prototyping.

#2 – Satellite services
The development of complex radio signal acquisition systems implies decoding and interpretation of binary data and protocols according to the service and standard used. The satellite-based radio frequencies are occupied by hundreds of old and new communication services with different communication topologies and protocols. Few old systems can be intercepted and decoded with standard available IT tools—and all current communication services apply complicated access, error correction and service-dependent mechanisms that in reality prohibit full-service analysis with do-it-yourself protocol and monitoring software.

Satellite services are no longer fixed services. The dynamic nature of communication services that is well-known in the Internet-domain also influences the satellite services enabling new software-based features and applications, and the possibility to introduce software upgrades as new technology becomes available or users push for it. Considerable resources and SATCOM competencies are thus required not only to develop a protocol stack and application features but also to maintain them as updates and changes in the satellite system(s) become available. This is pivotal for reliable and correct interpretation of critical information in a monitoring system.

#3 – IT integration
The integration of RF acquisition equipment into general information processing systems implies both integration of heterogeneous special-purpose electronics and the transformation of service-dependent data into standard protocols and storage formats for user data as well as meta data. Integration of RF front-ends in an interception scenario also involves selection and processing of individuals’ communication transactions to enable user-friendly presentation and intelligence analysis as part of a larger monitoring operation. Obviously, an important part of the challenge is to make the integration seamless across satellite services.

VesterholtFig1 In tactical scenarios, processing resources are scarce and relaying data to a central hub requires not only standard interfaces and protocols but also intelligent data mapping between systems, i.e., accurate alignment of the interception process and objectives to the selection criteria, be it an individual, a terminal or a location. Effective monitoring coverage is only obtained if this information can be used real-time to (re-)configure the RF electronics.

In case the satellite topologies uses small spot beams, e.g., Inmarsat BGAN and Thuraya, a distributed monitoring set up with multiple connected receiving stations is required with radio interception equipment placed in the relevant spot beams. This represents a significant challenge in terms of achieving complete monitoring coverage.

Summarizing, providing a SATCOM Monitoring solution with receive-only operation and enhanced robustness, and which meets the demands of tomorrow, calls for alternatives to the current barriers (or excess of resources).

Critical Limitations
Today’s SATCOM Monitoring solutions are mainly provided by a few satellite interception companies. However, the handling of different satellite services becomes an overwhelming challenge as new and complicated satellite services are launched—some in isolated regions of the world—and available solutions risk being insufficient and unable to meet the specific needs in certain markets.

Being based on existing, proprietary RF-platforms, these systems tend to miss even minimum requirements for interoperability. In other words, none of them cover the whole range of satellite services used, and they are not able to integrate with each other.

Developing monitoring capabilities in this domain is driven by new services and new user applications. As satellite service providers may want to change core parameters of their systems, satellite acquisition solutions need to be swiftly reprogrammable to cater for such changes. Existing solutions will allow updating and upgrading, but are often limited to the upper layers of the monitoring applications—all other modifications will need to be carried out as ‘factory-upgrades’.

VesterholtFig2 In tactical scenarios, there may be a need for covering multiple satellite services on the same location. This is especially important if critical information is deliberately spread across multiple services, or if the satellite service of interest is unknown prior to initiating the analysis process.

The analysis of satellite services can have many purposes, and organisations interested in this field of activity possess different skills and experiences. However, a common denominator could be to break the current critical limitations and explore the possibility of:

• A development platform enabling ‘plug-and-play’ reception of RF signals using standard software development tools
• A completely reprogrammable, lightweight solution fit for tactical use
• A high quality platform for complete testing and feasibility studies

SDR Opportunities
The SDR technology is able to address quite a few of the issues mentioned above. SDR allows for a technical architecture where the complete range of RF-challenges is handled by one COTS hardware module that integrates seamlessly into a so called SCA-compliant hardware framework.

Satellite acquisition systems based on a ‘plug-and -play’ set up with well-defined, generic Application Programming Interfaces is thus no longer a distant future vision—it is reality now.

Not only will this dramatically reduce the RF barriers and technical risks for all organisations working with satellite analysis today, it will also facilitate cost-effective innovation projects and feasibility studies on satellite signals and satellite services.

Rapid prototyping is, by definition, a baseline benefit. However, in this case, differences between prototype and real deployment will not occur as the hardware, the interfaces and the modules are all completely identical.

VesterholtFig3 One of the most important benefits that will actually grow over time is the synergy from using a standard framework for special-purpose systems. As multiple sources for software and hardware will become available at a reasonable cost, the flexibility of the platform will increase.

Being completely re-programmable from RF to software-API the analysis capabilities are in fact unlimited and can be supplied by third party vendors or home-grown. This will enable special multi-purpose satellite analysers or in-the-field re-programmable receivers for tactical deployment.

SDR Technology
Over the last 30 years, radios have changed from mere hardware-based devices to containing more and more software. The term Software Defined Radio is used for a radio where the essential functions are implemented in software and consequently can be reconfigured for different communication standards.

An SDR contains generic processing elements namely General Purpose Processors (GPP), Digital Processing Processors (DSP) and Field Programmable Gate Arrays (FPGA). These processing elements are loaded and configured during startup of the receiver to make the receiver perform as required to implement a particular communication standard. The term Waveform refers to the software that executes and controls the communication functions.

The development of SDR technology has been encouraged by the rapid development over recent years in integrated circuits, where size and power consumption has decreased and performance has increased, enabling very high performance generic platforms.

The U.S. Department of Defense (DoD) has invested in SDR through the Joint Tactical Radio System (JTRS) program. The JTRS program has produced a number of SDR radios and waveforms as well as the SCA standard which specifies how radio platform and waveforms must be designed and implemented to ensure interoperability, and in particular that a SCA-compliant waveform can run on different radio platforms as long as they are SCA-compliant.

The GateHouse BGAN Waveform contains all the common functionality required to build a BGAN terminal and is therefore an essential building block for a SDR-based satellite monitoring system.

VesterholtFig4 The BGAN Waveform is developed for SDRs and can be made compliant with the SCA specification version 2.2.2. This means that the waveform can run on generic SDR hardware conformant to the SCA specification. The BGAN Waveform can run as the only waveform on the radio or run as one of several waveforms on a multimode radio. Due to the SCA specification, the effort to port the waveform from one radio to another is considerably less than for a conventional radio design where the software typically interfaces custom designed hardware.

The traditional approach has been to develop inflexible purpose-specific hardware to implement a BGAN terminal, whereas by using the SDR approach the complete functionality (waveform) is implemented in the software, leaving the underlying hardware generic and fit for other purposes as well.

In addition to giving the advantage of reusing radio platforms and allowing for coexistence of waveforms on a single radio, the SDR approach also allows for easy upgrades of the BGAN terminals as the BGAN standard evolves (e.g., support of higher data rates).

The GateHouse BGAN waveform is structured internally according to the Inmarsat BGAN specifications and contains multiple layers of functionality.

There are numerous benefits for organizations already working with SATCOM Monitoring and for those considering activities in this area. A non-exhaustive list of perspectives, i.e., the direct benefits, for different players, follows next.

For companies investing in end-to-end SATCOM Monitoring solutions:
• Reduced initial cost due to standard hardware platforms
• Increased flexibility of real-life applications— scalability and expendability
• Supplier-independence
• Increased interoperability

For organizations carrying out in-house technical development of SATCOM Monitoring capabilities:
• Facilitate own internal development of SATCOM interception capabilities—either as supplement to commercially available solutions or as a direct replacement
• Conduct feasibility studies and use rapid prototyping to verify capabilities
• Additional waveforms will become available for standard platforms

For non-SATCOM companies striving to penetrate this area and other organizations who wish to conduct feasibility studies and sand-box activities:
• Inexpensive RF-to-Ethernet reference modules
• Perform rapid prototyping to minimize risks and cut development time
• Develop new applications based on the capabilities ‘out of the box’

Over and above the direct benefits for end-users and organizations the general perspective for the industry is a synergetic increase in availability of technology and waveforms:
• Market growth will gradually encourage development of additional waveforms
• New combined solutions will be possible based on compatible satellite services

For about 10 years, GateHouse has been involved in the satellite communications industry and has developed a range of satellite communications products and services for both governmental/military and commercial use.

More information at the Company website

VesterholtHead About the author
Claus Vesterholt is the Technical Program Manager for the Satellite Communication activities in the Danish software company GateHouse A/S. He has a Master degree in Electrical Engineering from Aalborg University and has taken various positions in the wireless communication industry over the last 18 years. He has been leading a number of programs and projects on the development of communication systems, mainly GSM/GPRS terminals and Inmarsat BGAN terminals. Claus has experience in developing and testing communication software for terrestrial systems and satellite systems. Currently, Claus is responsible for all technical activities in the satellite communication area of Gatehouse and is leading the engineering team.