Non-Terrestrial Networks (NTN)
Non-terrestrial networks promise global connectivity, but bringing satellite communications direct to mobile devices faces extreme technical challenges that expose OFDM’s fundamental limitations. LEO satellites travel at over 27,000 kilometers per hour, creating Doppler shifts up to ±50 kHz at typical cellular frequencies. Propagation delays stretch to 25 milliseconds or more. Massive cell footprints exceeding 100 kilometers create differential delays across the coverage area. Traditional signal-strength-based handovers fail when all users are roughly equidistant from the satellite, requiring new handover mechanisms every 10 seconds as satellites move across the sky.
“There comes a time when massive innovation is required to unleash new capabilities in global communications,” said Ray Dolan, Chairman and CEO at Cohere Technologies. “Many current industry leaders are once again planning to make incremental changes to existing OFDM-based 5G to improve connectivity in space-based networks for 6G, ignoring the many challenges that clearly mandate a fresh approach.”
Challenges in Space:
- Communicating with satellites in orbit traveling at hypersonic speeds creates obstacles in delay and Doppler that are nearly impossible to resolve with OFDM, yielding narrow solutions today that are mainly limited to text messaging.
- Connectivity at low angles of elevation creates coverage patterns that become elliptical in nature and hard to control at national boundaries, which are often limitations for spectrum licenses. Efforts to network satellites compound these issues.
Dolan continued, “A new approach is needed to enable NTNs to play a major role in overall space-based broadband solutions for public safety and defense. The entire area of sensing, and the integration of sensing with communications—often referred to as ‘ISAC’—is a massive opportunity for operators to drive revenue growth while providing new and valuable services to consumers, enterprises, and mission-first projects for governments. The growing awareness of the importance of sensing has created tremendous interest and partner support for our OTFS solution.”
Universal Spectrum Multiplier, as OFDM Companion Technology
Cohere’s Universal Spectrum Multiplier (USM) software platform improves the strength and efficiency of any generation (“any G”) mobile network. The USM is 3GPP standards-compliant and scalable software addresses the astronomical cost of acquiring new spectrum by enabling mobile network operators (MNOs) to improve the capacity, and increase the value, of all networks. The software leverages years of Cohere’s experience in advanced networking hardware development and offers SU- and MU-MIMO benefits to any network — with no changes to existing handsets, antennas and can integrate with existing base stations.
The USM software uses the geometric reciprocity of the Delay-Doppler model to increase both 4G and 5G spectrum performance. The Delay-Doppler channel detection method facilitates orthogonal beam management which leads to breakthrough MU-MIMO performance in both FDD and TDD spectrum, using the same time and frequency resources. The Delay-Doppler channel engine is waveform independent, thus making it possible for multiple dissimilar waveforms to operate in the same spectrum band via spatial multiplexing. The outcome is improved performance and maximized value of all spectrum assets.
Non-terrestrial networks already deployed in a OFDM 5G bent-pipe configuration (i.e. the base stations are on the ground), can benefit from the advanced beamforming and spatial multiplexing capabilities to increase spectral efficiency.
Cohere’s Pulsone Technology, Powered by Zak-OTFS is the Ideal NTN Waveform
Cohere’s Pulsone Technology powered by Zak-OTFS solves these challenges through native operation in the delay-Doppler domain, exactly where satellite channel impairments naturally occur. The delay dimension directly captures range information while Doppler captures relative velocity. Rather than fighting against satellite channel characteristics through compensation mechanisms, Zak-OTFS embraces them as signal features. The waveform remains coherent across the full range of LEO velocities without requiring position fixes or pre-compensation calculations. Channel estimation stays stable over frame duration even as satellites move, eliminating the constant re-estimation overhead that consumes OFDM’s capacity. The result is robust high-speed connectivity rather than stuttering, intermittent service.
Zak-OTFS transforms satellite channel impairments from obstacles into exploitable features. Operating in the delay-Doppler domain means rapid Doppler changes appear as static channel conditions over transmission frames. Multi-satellite diversity provides genuine performance gains rather than destructive interference. Spectral efficiency improves because channel estimation overhead drops dramatically as the stable Delay-Doppler representation requires far fewer pilot signals. Range and velocity information embedded in the Delay-Doppler domain enables integrated sensing alongside communications without additional overhead.
ISAC from Orbit: The Dual-Use Revolution
Beyond connectivity alone, OTFS-enabled LEO constellations unlock transformative sensing capabilities that create entirely new value propositions. A constellation running Zak-OTFS becomes a global, persistent, space-based multistatic radar network—simultaneously providing communications while tracking aircraft, ships, weather systems, and other targets across the planet.
The physics favors this approach fundamentally. Satellites at 500-700 kilometer altitude provide top-down viewing with no terrain masking. Orbital geometry creates constantly changing bistatic angles—transmitter on one satellite, receiver on another or on the ground—enabling target detection from multiple perspectives simultaneously. ISAC from orbit provides non-cooperative detection, tracking any aircraft or large UAV regardless of whether it transmits identification signals.
The beauty of ISAC implementation through OTFS is zero spectral efficiency overhead. Communications signals double as radar illuminators because the waveform already operates in the Delay-Doppler domain where both range and velocity information naturally appear. No dedicated sensing spectrum required. No separate radar transmissions needed. The satellites already deployed for connectivity provide sensing capability as an intrinsic feature rather than costly addition.
This dual-use architecture opens entirely new revenue streams for mobile operators beyond connectivity subscriptions. The ability to offer both communications and persistent wide-area sensing makes these systems significantly more valuable from national security and public safety perspectives. This strengthens regulatory positioning when negotiating spectrum allocations, subsidies for coverage expansion, or other policy benefits.