10.1117/2.1200709.0858 Free-space optics technology improves situational awareness on the battlefield Mouhammad Al-Akkoumi, Robert Huck, and James Sluss Using a new tracking algorithm, mobile vehicles can distribute video in real time. Free-space optics (FSO), or optical wireless, is an unlicensed line-of-sight technology that uses modulated optical sources to transmit information through the air. By using light beams, FSO can transmit and receive data, voice, and video, providing data rates ranging from 100Mbps to 2.5Gbps. It can function over dis- tances of several kilometers with a clear line of sight between the source and the destination. To maintain continuous line of sight and accurate alignment for high quality communications, FSO transceivers should be static. Thus, two essential challenges face FSO technology: first, severe weather conditions (fog, snow, etc.), and second, introducing mobility to this technology. If a reliable mobile FSO system can be achieved, the technology has excellent potential for scenarios requiring accurate situational awareness, such as battlefields. The popularity of FSO has grown since the 1990s. The main focus was on solving the ‘last-mile’ problem in telecommuni- cations: that is, the difficulty of providing high-speed access to information to distant users. The potential for FSO technol- ogy increases when mobility is added: many studies have been done to bring FSO strengths to mobile environments. 1–3 The use of a spherical antenna 3 covered with receiver modules has been demonstrated, using a small model train carrying trans- mitter modules—in that case, low-power light-emitting diodes (LEDs)—which moved on a 30cm-radius path around the an- tenna. The two modules did not remain aligned at all times, but when connectivity was lost, a new connection initialization algorithm was executed to promote alignment and re-establish communications. We introduce a tracking algorithm to maintain connectivity between FSO nodes on aerial and ground vehicles in battlefield scenarios. In our theoretical approach, two scenarios are studied: an unmanned aerial surveillance vehicle, the Global Hawk, with Figure 1. In the first scenario, a Global Hawk communicates with the M1 Abrams Tank using an FSO link. a stationary ground vehicle, an M1 Abrams Main Battle Tank; and a manned aerial surveillance vehicle, the E-3A Airborne Warning and Control System (AWACS), with an unmanned combat aerial vehicle, the Joint Unmanned Combat Air System (J-UCAS). FSO nodes are mounted on gimbals—mechanical de- vices used to rotate an object in multiple dimensions—which are placed on each vehicle. The tracking algorithm sends steering commands to the gimbals as the vehicles move to maintain laser alignment. An overview of the first scenario, using the Global Hawk and M1 Abrams Tank, is shown in Figure 1. The tracking algorithm specifies the gimbals’ angular po- sitions and velocities while taking into account the effect of different conditions. Examining the algorithm in a 2D system il- lustrates its feasibility in a simple case, such as two cars traveling in parallel lanes and moving toward one another. Both the vehi- cles’ locations and attitudes are taken into consideration while calculating the angular positions and velocities for the gimbals. Continued on next page