Acquisition, Tracking, and Pointing

  • Hemani Kaushal
  • V. K. Jain
  • Subrat Kar
Part of the Optical Networks book series (OPNW)


For ground-to-satellite laser communication link, it is essential to establish line-of-sight (LOS) path between ground-based station and the onboard satellite to ensure reliability of the system. Since the optical beam is very narrow, it requires a very accurate acquisition, tracking, and pointing (ATP) subsystems especially for long-distance communication. The process of aligning the transmitter in the field of view (FOV) of receiver is called “pointing,” and the process of aligning the receiver in the arrival direction of the beam is called “spatial acquisition.” It is a process defined by the ability of the receiver to search within initial uncertainty region for detecting the optical beam from the transmitter. Maintaining both “pointing” and “acquisition” throughout the communication time period is referred as “spatial tracking.” For FSO communication system, it is desirable to have an efficient performance of acquisition system within shortest acquisition time. Very fast and precise pointing and tracking system with good accuracy has to be incorporated into the system to maintain the LOS between transmitter and receiver. One of the major sources of pointing errors also called “boresight errors” arises due to stress, noise, structure fabrication, etc., of various electronic and mechanical components in the satellite. The pointing error is further increased due to turbulence-induced beam wander (discussed in Chap.  2) which may deviate the optical beam from its LOS. Further, the vibration of satellite platform and ATP assembly may complicate the pointing process and results in random pointing jitter. This will lead to significant displacement of transmitted beam at the receiver which will increase pointing error and cause significant degradation of the system performance. This chapter begins with the description of acquisition link in Sect. 4.1. It covers mathematical modeling, beam divergence, and power criteria required to establish the acquisition link. Details of tracking and pointing errors are given in Sect. 4.2. In Sect. 4.3, the concept and importance of ATP system is highlighted. Finally, ATP link budget is discussed in Sect. 4.4.


Beam Divergence Beacon Signal Beat Noise Dichroic Beam Splitter Uncertainty Area 
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Copyright information

© Springer (India) Pvt. Ltd. 2017

Authors and Affiliations

  • Hemani Kaushal
    • 1
  • V. K. Jain
    • 2
  • Subrat Kar
    • 2
  1. 1.Electronics and CommunicationThe NorthCap UniversityGurgaonIndia
  2. 2.Electrical EngineeringIndian Institute of Technology DelhiNew DelhiIndia

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