Seeking to reduce costs and enhance control of satellite communications, a multi-service group in the Department of Defense is working to stimulate development of technology that will enable a switch from analog intermediate frequency (IF) to digital intermediate format (digital IF) technology for processing transmissions.
The Digital IF Working Group includes the Army Project Manager Defense Communications and Army Transmission Systems (PM DCATS), Defense Information Systems Agency (DISA), MILSATCOM Systems Directorate, Communications-Electronics Research, Development and Engineering Center (CERDEC), Air Force Life Cycle Management Center, Navy Program Executive Office C4I, Army Space and Missile Command, and other key communications-focused commands. It is pursuing a long-term strategy aimed at putting together standards and encouraging COTS production of systems that will bring the benefits of digitization to the analog systems currently used in SATCOM gateways.
“This fundamentally will change how we do business, and the way we strategically deliver SATCOM capabilities,” said Colonel Clyde E. Richards of PM DCATS, a working group participant who has referred to digital IF as “the next big thing” in military SATCOM.
“It’s a very familiar paradigm shift from analog to digital, and all the benefits that come from that,” Richards explained. “You can talk about greater capacity and reliability. You get better error correction and faster speed. We will have the ability to centrally manage the gateways, or terminals, and the services that are provided. Today, we operate and manage in a decentralized manner. The systems being introduced will provide greater capacity and speed to warfighters and decision makers, and enhance responsiveness in terms of making critical decisions and moving faster than the enemy.
“Finally, one the greatest benefits is that it will significantly reduce the costs and footprint of what we are doing today,” Richards added.
Randy Nash, chief of CERDEC’s Developmental Systems Branch, SATCOM Systems Division, Space and Terrestrial Communications Directorate (STCD), offered some historical perspective on the need for new SATCOM technology: “Historically, the evolution of the strategic SATCOM architecture has been relatively slow in comparison to the evolution of other telecommunications technologies. The component-level technology that you would typically find in a strategic SATCOM terminal subsystem has significantly evolved over time, due to demands in other growing technological areas. However, the system-level technology has significantly lagged with regards to breakthrough innovation, predominately due to the longer than expected lifecycle of the strategic terminals.
“SATCOM systems have not taken a significant technological leap forward, even in the last decade. Digitizing the transmission path entirely or by component would significantly improve their technical performance, resulting in efficiencies gained in both cost and space segment power/bandwidth resources,” added Nash, whose agency has been a leader in this area in recent years, sponsoring the Future Advanced SATCOM Technologies (FAST) initiative with the goal of developing the next-generation, all-digital IF architecture for strategic SATCOM.
Within a ground station, IF is the fabric that moves waveforms from the modems to the antennas and terminals. IF is used because it offers better signal processing than at the higher frequencies used for Radio Frequency (RF) propagation. In addition, it provides a fixed frequency for processing signals, instead of having to process multiple frequencies, Richards explained. “It’s much easier to process and handle, and costs less. Finally, it isolates the frequency, so it can filter out any other frequencies at a close range.”
Currently, all Army/DoD SATCOM operations rely on analog IF from the modem to the antennas. In order to make a switch from an analog to an all-digital format, modems capable of providing a digital IF format will have to be installed, along with new routing and switching.
“We want to implement this as soon as it is mature, available and affordable,” Richards said. “We’ll be prepared to make the investments where they make most sense. It will probably be a normal transition that fits into the tech refresh cycles that we already have planned for obsolescence.”
The issue is that digital IF technology today is not at the level of maturity where it could be acquired and deployed on a system-wide basis.
“It’s not available commercially, and what we are doing is trying to stimulate the market so that this capability becomes readily available. We know it can be done, it’s just a matter of getting it to market,” he noted, adding, “We’re looking at it from a COTS perspective, so we want a product that is being provided, not a developmental effort by the government—a product that we can procure that meets an open standard.”
Once available, however, the digital IF technology is expected to provide substantial operational and economic benefits. “From a performance standpoint, we get higher capacity and speed to meet what we see as a growing demand for SATCOM. That translates into wider satellite transponder bandwidth, so we will be able to transmit and receive higher carrier counts than we do today,” Richards said. “We also get higher reliability, and we can mitigate noise issues that we currently have with analog terminals, taking advantage of superior signal quality that comes with digital. So we reduce the number of transmissions we have to make to get the transmission right. There is no way we can do that today without a digital capability.”
From a distribution standpoint, terminals today operate in a decentralized fashion, each terminal being managed separately. With digital IF, however, the IF can be distributed globally from centralized points of operation.
“We can distribute over the existing high-speed terrestrial network at the high rate of speed that it brings,” Richards said. “We’ll be able to centralize the equipment and staffing operations, rather than distributing all the capability in a decentralized manner, and having all the overhead and staff costs at each location. It not only provides better management, but also better control and security, since it is now more centralized. It provides global flexibility, because once you have this infrastructure in place, you have the ability to move transmissions over any gateway. It also provides redundancy, which gives you more reliability.”
“When you talk about the economic standpoint, you will reduce costs because you won’t need to have as many modems and decentralized locations. We can reduce the floor space and costs of maintaining equipment and facilities. We also won’t have to pay as much over the life cycles of all the equipment we had. Finally, we get the benefits of digital capabilities and technology. As things get faster, we will be able to incorporate that into the capability and leverage it,” he added.
To that end, the working group has been collaborating for the past couple of years, bringing together a total of nine organizations focused on developing an open commercial standard that can be provided to industry and turned into products. “We hope to see standards established and production begin within the next four to six years,” Richards said. “We have made a lot of progress. One of our greatest challenges is the fiscal constraints we face. It isn’t happening fast enough for us, because we want to start integrating this technology and reaping its benefits. But we have to go through the process, and get the funding. Based on where we are, the business case indicates that from performance and cost standpoint, this is the way to go.”
With several years of experience in developing and demonstrating the technology, CERDEC STCD is serving as the subject matter experts in the digital IF SATCOM domain. The organization has been examining the issue for several years, undertaking several initial and proof-of-concept studies before launching the FAST program under STCD’s Joint SATCOM Engineering Center.
Lessons from the early prototyping efforts shaped digital IF development, Nash explained. “The need for standardization became a priority throughout the early development stages, as it became apparent that an all-digital SATCOM architecture can take on many variants, depending on the mission-specific requirements. It also became apparent that the architecture core subsystems can be functionally equivalent, but not interoperate when designed by different vendors.”
In response, the FAST Working Group was set up in fiscal 2012 to develop an Open Standard Digital-IF Interface (OSDI) for SATCOM systems. “The impetus behind this effort was to collaborate with industry to develop an open-system architecture and protocol standard for digital IF SATCOM, using practical design experience and practice,” Nash said. “The other objective was to stimulate industry development of digital IF SATCOM systems and subsystems. This development focused on fostering open market competition while not limiting creative ‘black box’ designs, non-proprietary technology, and designs that achieve compatibility, interoperability and interchangeability.”
The FAST Working Group has included STCD and DISA, teaming with Harris GCS, Comtech EF Data Systems, Welkin Sciences, Hughes Defense and Intelligence Systems, L-3 Communications West, and RT Logic.
This effort has resulted in a modular architectural framework defining the signal processing elements and the subsystem communication interfaces to create all-digital strategic fixed SATCOM terminals. The standard is currently being tested, and will subsequently be published in the public domain. ♦
- Issue: 4
- Volume: 18