Home' RTCA Documents for Review : C2 Link Systems MASPS_Draft Contents Appendix D
© 2018 RTCA, Inc.
C2 Link System Latency for the Aviate, Navigate and Integrate Remote Pilot
Other than for the Communicate activity discussed in Subsection E.3 of this Appendix, no
standards currently exist to support the direct assessment of the latency requirements for
C2 Link Systems. However, latency must be considered when assessing the TETs
associated with the C2 Link System’s ability to support the remote pilot’s Aviate, Navigate
and Integrate activities described in OR-1.1, 1.3, 2.4, 1.4 and 2.3.
To resolve this situation, a combination of standards, measured data and Subject Matter
Experts’ opinions were used to estimate latencies for the components of the C2 Link
System that could be realistically provided by various architectures (see Figure 1-3 for
example architectures) and those estimates were then applied as normative requirements to
enable the TETs to be specified.
Note D-10: Even though the scope of this version of the MASPS does not include network
requirements, estimates of the latencies do include them. This was done to
avoid having to change, for example, TET requirements in future versions of
these C2 Link System MASPS when networks are introduced.
Note D-11: The estimate for the latency requirement supporting the remote pilot’s Aviate
activity assumes that the UA is equipped with a Flight Guidance System. As
such, the C2 Link System’s latency was not part of the inner-loop control of
the UA’s trajectory, i.e., this MASPS assumes the C2 Link System does not
support the pilot’s direct control of the UA’s aerodynamic surfaces.
Note D-12: The latency estimates herein assume a DO-362  defined 50 milliseconds
(ms) Time Division Duplex (TDD) C2 Link System design.
The data in Table E-6 and Table E-7 contain all latency estimates of the components of the
C2 Link System made for this MASPS.
The endpoints for these latency estimates, as shown in the SV-2 (Figure C-7) are the
interfaces between the UA and CS C2 Link Systems Data Transfer, Security and Routing
subsystems (inside the C2 Link System) and the C2 Data Mux/Demux and Voice Codec
subsystems (outside of the C2 Link System) in both the UA and the CS.
Additional latencies, in the CS and the UA, will also need to be included; those would be
identified when a system designer performs an overall “Stick to Aerodynamic Surface”
Since these are estimates, they do not assess the absolute worst or best cases but are
representative, per Subject Matter Experts opinion, of the higher and lower limits of what
can be achieved with realistic technology.
As can be seen at the bottom of Table E-6, the estimates assess the highest one-way
(telecommand or telemetry) latency for a Networked Terrestrial C2 Link System as being
225 ms and the lowest as 135 ms. Based on the data in the tables, this variation is mostly
attributed to the difference between the International Telecommunication Union-
Telecommunication (ITU-T) Y.1541 specified maximum latency for a Class 0 Quality of
Service (QoS) network and a typical business level Internet Protocol (IP) service provider’s
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