Optical Communications, 2nd Edition

10.4 DOUBLE-ENDED OPTICAL BEAM TRACKING

In Section 10.3, we analyzed a single-ended beam-tracking system, in which a receiver established a line of sight by tracking the arrival optical beam from a transmitter that was pointed perfectly toward the receiver. In this section, we extend to a double-ended tracking operation, where two terminals simultaneously track the optical beam from the other terminal. Pointing-error vectors can therefore develop at both ends of the system, and the pointing accuracy at one end effects the errors at the other end. The pointing-error vectors at the two ends therefore evolve as joint variables that are both temporally and statistically related. Such tracking scenarios will occur, for example, in establishing two-way optical communications between two moving spacecraft or orbiting space vehicles [10, 11].

The double-ended beam-tracking geometry is shown in Figure 10.18a. The optical terminals T₁ and T₂ are to simultaneously track optical beams transmitted toward each other and point their own beams back in the same direction We assume relative line-of-sight motion θ₁(t) observed from T₁ relative to its own coordinate system, and θ₂(t) observed from T₂. Let [ψ₁[(t), ψ₂(t)] be the corresponding pointing error vectors of each terminal. The above angles are each vector processes with both azimuth and elevation components.

Figure 10.18. (a) Double-ended ...