Impact of Pointing Errors on the Error Performance of Intersatellite Laser Communications

The effect of pointing errors on the average bit error probability (ABEP) of an intersatellite laser communication link is studied. A closed-form expression in terms of the Marcum $Q$ -function is given for calculating the instantaneous channel gain. This expression provides great potential in further performance analysis and system optimization. In addition, tight, closed-form upper and lower bounds on the ABEP are derived, by using bounds on the Gaussian $Q$ -function. These bounds are in simpler form than existing results and are much more efficient in numerical evaluations. Further simplifications of these bounds are performed and invertible ABEP expressions are given. Via numerical comparisons, these invertible ABEP expressions are shown to be accurate approximations within a wide range of transmit power of interest and thus provide efficient error prediction methods. The diversity gain is easily obtained using the invertible ABEP expressions, which is related to the ratio of the equivalent beam radius to the pointing error displacement standard jitter at the receiver. Moreover, we show explicitly how the ABEP depends on different system parameters.