Improved upper bound on capacity of optical IM/DD channels using binary pulse amplitude modulation

A new upper bound on the channel capacity of power- and bandwidth-constrained optical intensity channels corrupted by white gaussian noise is derived when equiprobable binary pulse amplitude modulation is used. a new closed-form upper bound on the capacity is found through a sphere-packing argument, presenting a tighter performance at lower optical signal-to-noise ratio when compared with previously reported bounds.