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Digitization and Virtualization of SATCOM Networks – Part II

January 6, 2022

Digitization of SATCOM Network Architecture

By Dr. Juan Deaton and Carlos Placido

At the most basic level, digitization of modems means separating the digital modem processing from the Radio Frequency (RF) front end and introducing the new digital IF interface between these two components. In a purpose-built modem, as shown in Figure 1, these functions are combined into a single device. The digital modem transmutes the signals between data bits and digital samples, and the RF front end then transmutes signals between digital samples and L-band IF. As shown in Figure 2, these two functions are separated in a digitized modem architecture, where we call the RF front end an “edge device.” The digital modem and the edge device are connected using the digital IF interface, which is IP-based transport protocol used to communicate digital samples and their contexts across a data network.

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While the differences between Figure 1 and Figure 2 may seem subtle, there are significant implications for SATCOM networks. Digitized SATCOM modem architectures provide the following advantages6:

  • Reduced Total Cost of Ownership (TCO)
  • Increased Radio Frequency (RF) Performance
  • Increased Network Agility and Capability.

 

Reduced TCO

Managing SATCOM networks’ costs is important in maintaining profitability and longevity. When comparing capital expenditures, instead of expensive analog transmission lines and distribution equipment, digital IF transmissions are based Commercial-Off-the-Shelf (COTS) IP routers and switches, which, generally, have lower capital and operation costs. Additionally, network reconfiguration or migration doesn’t require operators to disconnect transmission cabling for equipment replacement. These network operations can be entirely managed by reassigning digital IF IP addresses or simply plugging in a new digital modem into a router.

 

Increased RF Performance

Increasing Signal-to-Noise Ratio (SNR) improves signal quality and SATCOM network throughput. The major disadvantages of using analog L-band IF are cable power loss and distortion from L-band switching systems, which degrade the SNR. In digitized architectures, L-band switching equipment is replaced with more efficient IP switched systems. Additionally, since the edge device is not fixed to the modem, edge devices can be placed much closer to the antennas, minimizing L-band IF cable length, transmission power loss, and maximizing SNR.

 

Increased Network Agility and Capability

Network and terminal agility are becoming more important due to the rapidly changing space layer. Agile networks and terminals will enable easier migration to waveforms and constellations, streamline network resource reconfiguration, and modernize deployment of new capabilities. In a digitized architecture, digital modems are decoupled from edge devices, supporting easy reconfiguration of the network. With a standardized digital IF interface, digital modems could replace and back up one another for redundancy through simple IP network configurations. Additionally, digital IF streams could be duplicated, combined, and separated digitally to provide new capabilities like diversity gain, beam forming, and amplifier distortion correction. Finally, with a reliable digital IF transport, digital modems can communicate to distant edge devices adding additional network redundancy and even leverage cloud computing.

 

Dr. Juan Deaton is a Research Scientist for Envistacom’s Advanced Technology Group and Carlos Placido is a Consultant for Northern Sky Research.

 

[6] A. J. Vigil and J. Hicks, “The Case for an All Digital Military Satellite Communications Earth Terminal,” MILCOM, 2009 [Online]. Available: https://bit.ly/3ypEnxv

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