Optimality of the users strength in optical PPM-CDMA channels

An upper bound on the users strength in direct-detection optical code-division multiple-access communication systems, which employ pulse-position modulation techniques, is developed. This upper bound is consistent with the lower bound derived previously, as long as the transmitted information per photon is less than some positive threshold. The concept of users strength was introduced by the author in a previous paper, where it provides a measure to the maximum number of simultaneous users that can communicate simultaneously with arbitrary small probability of error.