Blog: Solving Phase Noise Challenges in Space-based Cellular Networks

The latest generation of cellular networks have revolutionized connectivity with unprecedented speed and capacity. To extend these benefits globally, developments are shifting towards space-based cellular networks. Low Earth Orbit (LEO) satellite constellations are being deployed to provide service from orbit, bridging connectivity gaps in remote and underserved areas. However, in the challenging space environment, maintaining precise frequency control and minimizing phase noise has been a challenge for RF engineers. Phase noise can impact data transmission quality, especially at high frequencies. In this blog, we discuss phase noise challenges in space-based cellular networks and uncover several solutions that enable stable and interference-free communication.

What are Space-based Cellular Networks?

Space-based cellular networks are an extension of terrestrial networks, utilizing satellites in Low Earth Orbit (LEO) to provide service anywhere on earth. Still a new technology, space-based cellular networks will enable high-speed data transfers with low latency and support real-time applications like video conferencing. This summer, AT&T and AST SpaceMobile will launch the first ever space-based cellular network for wide-spread commercial use into orbit, a major milestone. Looking to the future of space-based cellular networks, we can expect even higher data transfer speeds and lower latency, further revolutionizing global connectivity and communication.

What is Phase Noise in Space-based Cellular Networks?

Phase noise, characterized by random fluctuations or jitter in signal phase, poses significant challenges in high-frequency applications like space-based cellular networks. Phase noise can manifest as a loss of synchronization between transmit and receive signals, leading to signal degradation, reduced data rates, and a decrease in coverage areas. These effects are particularly pronounced in space-based cellular networks due to the long distances involved and the need for highly reliable communication links. Phase noise is influenced by various factors, and space environments introduce additional complexities that can exacerbate phase noise issues in frequency control and timing systems. Specific environmental factors include but are not limited to:

• Vibration and Mechanical Shock
  During satellite launch and deployment, vibration and mechanical shock can introduce physical disturbances that affect the stability of frequency control components.

• Vacuum Conditions
  Space’s vacuum environment can impact the thermal management of electronic components, leading to temperature variations that affect oscillator stability and phase noise performance.

• Temperature Extremes
  Satellites experience wide temperature variations in space, altering the characteristics of electronic components and leading to changes in frequency stability and phase noise.

• Radiation Exposure
  Cosmic radiation in space can interact with electronic components, causing aging, degradation, and material changes that impact frequency control system performance.

• Long-term Reliability Requirements
  Satellites require high levels of reliability and durability from onboard electronics, necessitating stable frequency control and timing systems over extended missions.

• Electromagnetic Interference (EMI)
  Satellites are subject to EMI from internal and external sources, including cosmic radiation, which can introduce noise into frequency control circuits.

Phase Noise Solutions for Space-based Cellular Networks

To address these phase noise challenges and ensure high-performance levels in space applications, engineers can consider a range of design and technology solutions:

• Low-noise Designs
  Implementing frequency control and timing devices with low acceleration-sensitivity crystals can directly minimize the impact of phase noise. In addition, careful component selection and circuit layout can significantly reduce the noise contribution from external sources.

• Radiation Hardening
  Radiation itself may not directly influence phase noise, but its effects on electronic components within frequency control and timing systems can indirectly contribute to phase noise degradation in space-based cellular networks. To mitigate the effects of radiation on phase noise, source radiation-hardened components and materials.

• Redundancy and Fault Tolerance
  Design frequency control and timing systems with redundancy and fault tolerance features to ensure continuous operation and mitigate the impact of failures on phase noise performance.

• Thermal Management
  Implement efficient thermal management techniques to stabilize frequency control and timing system temperatures and mitigate temperature-related phase noise variations.

• Passive Vibration Isolation
  Shock mounting is the most common method used to isolate vibration from a frequency control or timing device. By analyzing and selecting shock mount stiffness and payload mass, engineers can design systems that attenuate vibration over a wide frequency range. This results in a reduction of the corresponding phase noise. Passive vibration isolation can perform well up to high frequencies but is limited at lower frequencies where shock mounts can resonate and amplify vibration content. Nonetheless, this method can well improve dynamic phase noise performance.

• Bootstrapping
  This technique, pioneered by the engineering team at Quantic Wenzel, employs two rugged crystal oscillators to compensate dynamic phase noise. A voltage representing the phase difference of the two oscillators, much like what a phase locked loop uses to phase lock, is used to create phase fluctuations that counteract those caused by vibration in real time.

• Combined Active and Passive Vibration Compensation
  This technique pairs together accelerometer and shock mount-based solutions to yield synergistic benefits. Active vibration compensation utilizes accelerometers to detect the acceleration seen by an oscillator and directly negates its effect on phase noise. Unlike passive compensation, active compensation is not limited at low frequencies. Therefore, the combined effect of the two techniques attenuates vibration over a fuller frequency range, significantly improving phase noise performance.

• Digital Signal Processing (DSP)
  Advanced DSP algorithms can be employed to compensate for phase noise in digital communication systems. Techniques such as phase estimation, equalization, and adaptive filtering can help mitigate the adverse effects of phase noise on data transmission.

• Adaptive Filtering and Equalization
  In systems where phase noise affects signal quality, adaptive filtering and equalization techniques can be employed to compensate for the distortion caused by phase fluctuations. These methods actively adjust the system parameters based on the observed phase noise characteristics.

Conclusion

Overcoming phase noise challenges in space-based cellular networks is a critical undertaking for RF engineers tasked with ensuring reliable system performance. For over 30 years, the expert RF engineers at Quantic Wenzel have been trusted to deliver low phase noise frequency control and timing solutions for space-based radio frequency and microwave applications. Quantic Wenzel’s heritage supporting space applications is extensive and includes X-Band synthesizers for the Mars Curiosity and Perseverance mission to manufacturing oscillators for broadband satellite constellations, and many more. Looking to the future, as our team continues to define and deliver the future of space-based connectivity, mitigating phase noise will remain a challenge. By pushing boundaries and developing new, innovative low phase noise solutions we will continue to help our customers usher in a more connected world, extending communication to the farthest reaches of the globe.  

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