The impact of random pointing and tracking errors on the performance and design of optical intersatellite communication links is analyzed. Given the rms transmitter pointing error and the desired probability of bit error (PBE), it can be shown that an optimal transmitter antenna gain exists which minimizes the required transmitter power. The product of this optimum antenna gain and the mean square pointing error is a constant which depends only on the PBE and the modulation format. For heterodyne systems, the performance of the receiver also depends on the tracking error between the local oscillator (LO) and the incoming signal. Given the rms LO tracking error, an optimum receiver antenna gain can be found which optimizes the receiver performance. The impact of pointing and tracking errors on the design of direct detection pulse-position modulation (PPM) and heterodyne noncoherent frequency-shift keying (NCFSK) systems are then analyzed in terms of constraints on the antenna size and the power penalty incurred. It is shown that in the limit of large spatial tracking errors, the advantage in receiver sensitivity for the heterodyne system is quickly offset by the smaller antenna gain and the higher power penalty due to tracking errors. In contrast, for systems with small spatial tracking errors, the heterodyne system is superior because of the higher receiver sensitivity.
ASJC Scopus subject areas
- Electrical and Electronic Engineering