TRANSMISSION SCHEME AND ERROR PROTECTION FOR SIMPLEX LONG-DISTANCE ATMOSPHERIC FSO SYSTEMS

Theoretical investigations and channel measurements clearly show that the atmospheric optical communication channel is often interrupted by strong and very slow fades. Using on/off keying modulation, synchronous communication schemes suffer from channel interruptions, therefore asynchronous datagram communication seems to be favourable. Furthermore the error protection codes must be able to cope with very long fades compared to the bit duration. For envisaged high data-rates, physical-layer bit wise coding can not deal with burst errors longer than codewords. Further, interleaver with technically feasible depth fail in splitting long burst errors produced by the slow fading. Therefore packet-layer coding with an implicitly longer codeword length can overcome this problem. Packet-layer coding performance investigations and code dimensioning are discussed in this paper