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Next Generation Half-Duplex Common Data Link

Common Data Link (CDL) is the US Department of Defense's standard RF communication system for airborne intelligence, surveillance, and reconnaissance (ISR) systems. It has evolved over the past 30+ years to include a large family of data rates and waveform variants and is used in a number of applications. Two important capabilities are attracting increasing attention in recent years: networking and spectral efficiency. The current point-to-point, full-duplex architecture does not allow a moderate number of terminal modes to form an ad-hoc mesh network. Moreover, if the number of nodes within a network exceeds a small threshold, the available CDL spectrum can be easily exceeded. If not resolved, these issues will significantly limit future CDL applications and deployment. This paper discusses the history of the networking and spectrum aspects of CDL. It explains why the existing CDL architecture, if unmodified, is not suitable for the next generation ad-hoc mesh networking. It proposes a new, spectrally efficient, half-duplex CDL (HD-CDL) waveform as the candidate for the next generation wideband mesh networking data link waveform, and explains how the proposed HD-CDL extension enables CDL mesh networking. It also discusses challenges that a system integrator may face in transitioning from the current point-to-point full-duplex implementation to the proposed HD-CDL. The focus of the discussion is the physical layer specification, but other network layers and functions will also be briefly discussed.