InsideGNSS || The Case for LEO GNSS at C-Band

This follow-up to a 2007 Inside GNSS article looking at the potential future role for C-band in navigation details how, nearly 20 years later, it’s moved from an interesting idea to critical for resilient position, navigation and timing (PNT).

PAUL ANDERSON, GEORGE SCHMITT, FURQAN AHMED, PATRICK SHANNON, TRUSTPOINT INC.

A 2007 Inside GNSS article examined C-band as a future for GNSS signals, with authors outlining its advantages and disadvantages when compared to L-band in context of the Galileo system and its potential role. Nearly 20 years later, we reexamine the cost/benefit trades for C-band for navigation in the context of the NewSpace economy and future commercial GNSS systems operating in low Earth orbit (LEO). In that time, C-band has become critical for resilient PNT, with TrustPoint beginning to deploy a proliferated LEO constellation of microsatellites broadcasting next-generation navigation signals in the 5010 to 5030 MHz Radionavigation Satellite Service (RNSS) allocation at C-band. TrustPoint’s future LEO GNSS service will enable rapid time-to-first-fix, meter and sub-meter positioning accuracy, improved jamming resistance due to frequency selection, diversity and increased signal strength, and an encrypted, spoof tolerant signal with built-in authentication.

The Paradigm Shift of Commercial GNSS
Over the past 50 years, the U.S. GPS and international GNSS counterparts have provided invaluable services in support of commercial, civil government, and military operations across the globe. Given the crucial role they play, it is difficult to envision a world without the ever-present support of these services streaming down from space. Recent reports estimate the global installed base of GNSS-enabled devices is projected to grow from 5.6 billion units in 2023 to almost 9 billion units across all markets by 2033, with the number of GNSS devices shipped per year increasing from 1.6 billion in 2023 to 2.2 billion units in 2033. As humanity exits the first complete epoch of the information age and boldly leans into the age of autonomy and ubiquitous connectivity, there is an expectation that GNSS-enabled devices will further proliferate and continue integrating more broadly and deeply into our way of life.

While humanity finds tens, if not hundreds, of new applications for GNSS every year, and develops an analogous number of unique receivers, the update rate for the satellite systems and the signals they transmit follow closer to decadal timeframes. This slow rate of technical progress is driven by a variety of factors, including the high costs of government system development, limited spectrum availability, and strict backwards compatibility requirements. Unfortunately, this rate of technical progress is severely outpaced by adversarial activity, new application requirements, and technologies from adjacent markets readily available for integration into the larger GNSS ecosystem. In response to this reality, TrustPoint has architected a responsive, resilient and evolutionary LEO PNT system and signal paradigm that enables rapid service upgrades to achieve receiver forward compatibility.

To date, all space-based PNT systems and services have been funded, owned and operated exclusively by world governments with significant budgets, lengthy schedules, and public Interface Control Documents (ICDs). A new era of space-based alternative PNT (A-PNT) is dawning with the emergence of venture-backed commercial companies seeking to fill capability gaps of heritage GNSS services with new technologies and solutions targeting a $260 billion plus total addressable market in navigation and location-based services enabled by commercial satellite platforms and advancements in microelectronics technology. This is a paradigm shift in that GNSS users will soon have access to commercial “PNT-as-a-Service” in addition to the heritage GNSS systems owned by world governments. Novel A-PNT business models and pricing strategies, proprietary signal ICDs, and service-level agreements specifying signal availability and signal-in-space accuracy will become standard—and this will fundamentally change the way global users subscribe to and access next-generation A-PNT services enabling secure, resilient and high-accuracy time and position solutions.

TrustPoint is deploying a purpose-built, commercial A-PNT service using a proliferated LEO constellation of microsatellites broadcasting next-generation navigation signals in the 5010 to 5030 MHz RNSS allocation at C-band. TrustPoint’s commercial, dual-use LEO PNT system and C-band service will enable rapid time-to-first-fix, meter and sub-meter positioning accuracy, improved jamming resistance due to frequency selection, diversity and increased signal strength, and an encrypted, spoof-tolerant signal with built-in authentication for all users. The solution is made possible by our constellation of low-cost LEO microsatellites that leverage commoditized space platforms, rideshare launch services, and patented innovations in navigation signal generation and processing at the RF physical and navigation data layers, enabling next-generation commercial GNSS services made possible by smaller wavelengths, smaller satellites and smaller orbits.

In this article, we summarize the cost and benefit trades of C-band versus L-band at LEO versus medium Earth Orbit (MEO), inclusive of considerations for space segment design, architecture, and size, weight, power, and cost (SWaP-C); signal and service design; and attenuation effects and path delay.

Commercial Space Segment Considerations
Why is it that after 50 years of satellite navigation technologies and services, LEO PNT has only become relevant in the past 5 years? The answer could lie in the trifecta of (1) the commoditization of microsatellite platforms spurred by the “NewSpace” ecosystem dominated by commercial players; (2) continued miniaturization of software-defined radios and other analog and digital electronics; and (3) the routine availability of low-cost rideshare launch opportunities to common LEO orbits. TrustPoint is leveraging all three of these factors to enable a commercially-funded space segment that is both affordable and high-capability—a combination that wasn’t possible at the scale needed for a new LEO PNT system even 5 years ago. Proliferated LEO architectures comprised of small-but-capable satellites have been technically, cost-prohibitively, or politically out of reach for First World governments, let alone commercial enterprises seeking to generate revenue from new PNT service offerings. As space technologies within the NewSpace economy have continued to relentlessly evolve on accelerated timelines, bootstrapped by venture capital and driven by new use cases arising from humanity’s increasingly interconnected and autonomous future, it is now possible for a commercial business to pursue—in fact, succeed in—delivering space-based LEO PNT services...