Patent ID: 7277644
Filing Date: 2007-10-02
Classification: H03M,H04B,H04J,H04L

Abstract:
1. A fade-resistant forward error correction (FEC) method for a free-space optical communications system, comprising: encoding user input data with a forward error correction (FEC) code to produce encoded user data; producing a plurality of encoded user data channels from said encoded user data, wherein each particular channel of said encoded user data channels comprises a unique delay relative to all of the other channels of said plurality of encoded user data channels; a step for transmitting said plurality of encoded user data channels across a free space optical channel to produce transmitted channels; a step for receiving said transmitted channels and separating each channel from said transmitted channels to produce a plurality of received channels; detecting each channel of said plurality of received channels; adjusting selected ones of said received channels so all of them are temporally equal; decoding said received channels to produce decoded channels; and sending the first successfully decoded received channel of said decoded channels as a recovered user data output, wherein said step for transmitting said plurality of encoded user data channels across a free space optical channel comprises: in a first quadrature phase shift keying (QPSK) encoder, QPSK encoding a first group of at least two channels of said encoded user data channels and combining said first group in said first QPSK encoder into a first QPSK transmission channel; driving a first optical phase modulator (OPM) with said first QPSK transmission channel; modulating a first laser beam produced by a first UDWDM laser with said first OPM to produce a first OPM channel; in a second quadrature phase shift keying (QPSK) encoder, QPSK encoding a second group of at least two channels of said encoded user data channels and combining said second group in said second QPSK encoder into a second QPSK transmission channel; driving a second optical phase modulator (OPM) with said second QPSK transmission channel; modulating a second laser beam produced by a second UDWDM laser with said second OPM to produce a second OPM channel; combining said first OPM channel and said second OPM channel in a wavelength division multiplexing multiplexor (WDM-MUX) to produce combined channels; and transmitting said combined channels across said free-space optical channel to produce said transmitted channels; wherein said step for receiving said plurality of encoded user data channels and separating each channel from said plurality of encoded user data channels comprises: demultiplexing said plurality of encoded user data channels of said combined channels in a wavelength division multiplexing de-multiplexor to reconstruct said first OPM channel and said second OPM channel to produce a reconstructed first OPM channel and a reconstructed second OPM channel; in a first QPSK optical phase decoder, decoding said first reconstructed OPM channel to produce a first group of light beams corresponding to said first group; and in a second QPSK optical phase decoder, decoding said second reconstructed OPM channel to produce a second group of light beams corresponding to said second group, wherein said first group of light beams and said second group of light beams are referred to as a plurality of received beams.