LOSS FACTORS ASSOCIATED WITH SPATIAL AND TEMPORAL TRACKING ERRORS IN INTERSATELLITE PPM COMMUNICATION LINKS.

The performance of an optical PPM intersatellite link (ISL) in the presence of spatial and temporal tracking errors is investigated. It is shown that for a given rms spatial tracking error, an optimal transmitter beamwidth exists that minimizes the probability of bit error. The power penalty associated with the spatial tracking error when the transmitter beamwidth is adjusted to achieve optimal performance is shown to be large ( greater than 9 dB) when the rms pointing jitter becomes a significant fraction ( greater than 30%) of the diffraction-limited beamwidth. The power penalty due to temporal tracking error, on the other hand, is relatively small ( less than 0. 1 dB) when the tracking loop bandwidth is less than 0. 1% of the slot frequency. By properly allocating losses to spatial and temporal tracking errors, it is seen that a 10** minus **9 error rate can be achieved for a realistic link design with an approximately equals 3 dB signal power margin.