Using a GPS-aided inertial system for coarse-pointing of free-space optical communication terminals

Abstract

In the Capanina project, it has been shown that it is possible to use solely GPS positions for coarse-pointing of a stratospheric free-space optical communication terminal. Although this system design has been shown to be functional, it has to deal with acquisition and reacquisition times of up to 20 seconds. Whenever the line of sight is blocked, the Capanina terminal has to do a reacquisition of the partner terminal.In land-mobile systems, e.g. transmission between a moving vehicle and a fixed station, where objects like trees or buildings can frequently block the line of sight, this type of acquisition/reacquisition is not acceptable.In this paper a revised system design will be shown, which reduces the initial acquisition time to below a second by using information from a GPS-Aided Inertial System (GPS-INS). It will also be shown how reacquisition times and coarse-pointing errors can be reduced to a minimum by using feedback from the optical fine-pointing device. Finally a demonstrator setup and some test results will be presented.

Concepts for fast acquisition in optical communications systems

“…Normally, as the quality (and weight) of the components increases, the errors decrease and the cost increases. These errors are not discussed in great detail in this paper, however [3] provides a more detailed analysis.…”

Autonomous reconfiguration and control in directional mobile ad hoc networks

“…These two schemes are based on the use of GPS information and optical beacons, respectively. Much previous work on PAT systems has depended on optical devices [26][27][28][29][30] or Inertial Navigation Systems (INS) combined with GPS [28][29][30]; GPS or DGPS acts as a secondary device for providing position updates and correcting INS drift error, whose position accuracy is at the meter level.…”

“…Hence, it is essential to have complete information as to where nodes are (position coordinates) as well as where they are heading (pointing vectors) as shown in Figure 6. The use of various kinds of position and angular sensor devices is therefore natural in pointing techniques [26][27][28][29][30]. GPS (Global Positioning System) might be the alternative for providing such complete information in all weathers and global regions.…”

“…In previous work, low-cost and lightweight PAT systems for mobile nodes, such as aircraft or ground vehicles have been described [28,29]. These pointing systems used both Differential GPS (DGPS) and INS to measure a coarse pointing vector as well as a camera to provide a fine pointing vector.…”

Investigation and design of short-range free-space optical communication system for flight platforms

“…Inaccurate beam pointing can result in pointing losses and degrade the performance of FSOC, therefore these losses must be kept to a minimum through the PAT process. Moreover, it is desirable to achieve short duration from the start of pointing phase to the tracking phase so that FSOC can commence quickly when required [56]. The factors to consider for PAT, duration of PAT and probabilities for successful PAT are discussed in [57][58].…”