  We present analytical results on the effect of pointing errors on the average
bit-error probability (ABEP) of optically pre-amplified pulse-position
modulation (PPM) receivers. The results show that the beam width plays a key
role in the ABEP and that a significant power penalty is introduced by
utilizing sub-optimal widths, especially when pointing errors incorporate a
jitter component. We also present the optimisation the beam width for a number
of pointing error scenarios and show that increasing beam widths are required
as additional signal energy becomes available. The optimal beam width is also
affected by the PPM modulation order and the optical noise modes, with more
energy efficient (higher modulation order and lower noise) systems allowing for
broader beams.
