Time and Phase Synchronization Across Multiple Airborne Platforms

In Phase 1, 4S developed a synchronizing concept and demonstrated its feasibility through modeling and simulation.  Modeling included formation of an Unmanned Airborne System (UAS) swarm into a phase synchronized ensemble that was analyzed to quantify Radio Frequency (RF) beam pointing error as a function of frequency.  Investigations further included processing blocks that provide critical synchronizing functions and baseline requirements forming a point of departure for further development in Phase 2. 4S – Silversword Software and Services, LLC (4S) proposes to continue and extend our Phase 1 development of a novel synchronizing solution, starting with our proprietary Free Space Optical Communications (FSOC) technology termed Through the Air Link Optical Component (TALOC).  TALOC is a patented system designed explicitly for maintaining FSOC between airborne mobile platforms.  It is described in terms of platform 1 communicating with platform 2 and vice-versa for full duplex broad band connectivity.  Platform 1; 1) acquires and tracks platform 2 on a first dedicated wavelength via a platform 2 retroreflector, 2) measures range and 2 axis pose angle from platform 1 to platform 2, 3) transmits broad band optical information to platform 2.  Platform 2 operates in the same way to complete a bidirectional optical communications link.  TALOC links cooperate with parallel RF links among a swarm of UASs deployed randomly within a 1 mile diameter volume to simultaneously transfer a time reference from the command UAS to the remaining UASs.   A key element of the 4S solution is to make 2 independent time of flight (TOF) measurements simultaneously between the command UAS and each of the additional UASs.  The first measurement is a time reference code transmitted via RF from lead UAS to all other UASs; comparison with a swarm element UAS internal time reference code gives a TOF measurement bearing a timing error due to reference crystal drift.  The second measurement is a time reference code transmitted via TALOC from each UAS to the lead UAS retroreflector and back.  Comparison of the retroreflected time reference code with the UAS continuing internal reference code gives double the one way TOF with no oscillator drift present.  Comparison of the drift influenced and drift free measurements provides a value of drift correction to each UAS. The overall objective of this effort is to create a time and phase synchronization method that can be used to form a swarm of UAS into a collaborative and distributed phased array system in the air which reduces line-of-sight obstructions and extends the range of communications and EW applications.    A solution is needed that; 1) synchronizes multiple platforms without GPS or cooperative targets, 2) operates in a Group 3 UAS relevant temperature and vibration, environment, 3) meets the Group 3 UAS space, weight, power, and cooling (SWAP-c) requirements.