SATCOM Digital IF Stream Rate Considerations for Earth Segment Transport

Abstract

Digital IF shows significant promise as a SATCOM Earth segment architecture, offering solutions for gateway congestion, Earth segment resilience and long term growth. One resilience aspect of Digital IF is the ability to transport IF long distances for the sake of redundant RF aperture locations. The ANSI/TIA-5041 FAST OSDI standard has been developed for universal adoption by SATCOM stakeholders as a common Digital IF protocol to ensure interoperability within the Digital IF Earth segment architecture. This standard is presently computationally efficient at the expense of transport efficiency. Sample rate and sample size are standardized to simplify implementation of computational functions at the expense of higher Digital IF stream rates. This presents an issue to terrestrial transport where higher Digital IF stream rates increase terrestrial WAN consumption. FAST OSDI stream rates are typically 50–100 times a carrier's symbol rate, corresponding to 8 to 100 times the data traffic rate at 1 to 6 bits per symbol. To reduce Digital IF stream rates, potential updates to the FAST OSDI standard are considered, first by reducing sample rate and sample size, then by analyzing waveform performance. Digital IF stream rate can be reduced, for purposes of terrestrial transport, by factors of 2 to 6 over these same 1–6 bits per symbol while preserving signal integrity for demodulation. Additional Digital IF transport considerations include transport of multiple carriers, reconstruction of uplink modulation spectra and adoption of Earth segment transport as an explicit Digital IF functional element.