Patent ID: 8081882

Claim:
Method comprising the steps: at a transmitting side of an optical channel providing bits for transmission across the optical channel, processing the bits by performing a bit-to-symbol mapping in order to map said bits into PPM symbols, where each PPM symbol has a symbol duration comprising D*M time slots and a blank time of blank time duration, each time slot has a slot duration, the blank time duration is D*B times the slot duration, where B defines the number of blank time slots, being an integer number ≧1, the parameter D is an integer number ≧2 defining the number of pulses located at D of the D*(M+B) time slots, M defines the alphabet size, or number of pulse positions that a modulated pulse can assume, in the PPM scheme, with M being an integer number ≧4, where each pulse has a pulse duration, and where said slot duration is shorter than said pulse duration so as to provide for theoretically overlapping pulses inside each PPM symbol; where said theoretically overlapping pulses are provided inside each PPM symbol in order to provide for an increased raw data rate for the transmission of the bits across said optical channel, where an overlap ratio is defined by pulse duration/slot duration said ratio preferably being equal to 2 or equal to 3; and between two consecutive pulses of the PPM symbol there is al least one blank time of one blank time duration and the last pulse of the respective PPM symbol is at least one blank time of one blank time duration away from the end of the respective PPM symbol, an amplitude modulation is applied so that each of said pulse of a PPM symbol can take A different amplitude levels, where A is the number of available amplitude levels, said amplitude modulation being applied to further increase said raw data rate, where a number P of different pulse patterns contained in each of said PPM symbols is defined by P = A D · ( D · M D ) .