Time and Phase Synchronization Across Multiple Airborne Platforms

The objective of this effort is to create a time and phase synchronized swarm of Unmanned Airborne Systems (UAS) that can be used to create a collaborative and distributed phased array antenna system in the air which reduces line-of-sight obstructions and extends the range of communications and EW applications.  Each node includes an embedded Radio Frequency (RF) transceiver that is synchronized in both time and phase (i.e. coherent carrier frequency) across the swarm.  Current techniques rely on GPS or cooperation from the target/receiving end to synchronize multiple UASs.  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.  4S - Silversword Software and Services, LLC (4S) proposes to develop 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.  As shown in Figure 1-1, TALOC links cooperate with parallel RF links among a swarm of 10 UASs deployed randomly within a 1 mile diameter volume to simultaneously transfer a time reference from the swarm lead UAS to the remaining UASs.  A key element of the 4S solution is to make 2 independent time of flight measurements simultaneously between the lead UAS in line and each of the additional UASs.  The first measurement is a time reference code transmitted from lead UAS to all other UASs; comparison with a swarm element UAS internal time reference code gives time of flight 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 time of flight with no oscillator drift present.  Comparison of the drift influenced and drift free measurements provides a value of drift correction to each UAS.