Optical high-rate pulse position modulation scheme and optical communications system based thereon
AssigneeOerlikon Space AG
InventorMichael Tuchler
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Abstract
It is an object of the present invention to provide a communications system for communication between two remote terminals, where even at very long distances between these two terminals and/or at very small signal-to-noise ratios a robust communication is possible. The invention achieves the goal set before by suggesting an inventive pulse position modulation scheme and a corresponding optical communications system. The system and method according to the invention are very well suited for communication with a satellite in deep space, for instance.
Claims28
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 provide 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, with B 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 number of time slots of each PPM symbol, 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 a number P of different pulse patterns contained in each of said PPM symbols is defined by
- P
- =
- (
- D
- ·
- M
- D
- )
- .
Laser communications system comprising a first transceiver and a second transceiver for establishing two optical channels there between, wherein
- said first transceiver comprises a first transmitter with a Laser light source for transmitting optical pulse position modulated signals into a first of said optical channels, said first transmitter comprising a bit interleaver followed by a symbol mapper mapping interleaved coded data bits into modulation symbols from a PPM symbol alphabet, said symbol mapper feeding a frame generator, followed by a pulse shaper so that an analog waveform is assigned to each modulation symbol, said pulse shaper providing said analog waveform for modulating said Laser light source,
- said second transceiver comprises
- a receiver for receiving said pulse position modulated symbols, said receiver comprising an all-digital PPM detector with a high-speed analog-to-digital converter followed by a frame and symbol detector, a symbol demapper mapping received pulse position modulated symbols to data bits, said symbol demapper forwarding said data bits to a bit deinterleaver.
Dependencies are inferred from the claim text.