Short-Length Raptor Codes for Mobile Free-Space Optical Channels

Free-space optical (FSO) links are competitive wireless links offering high data rate, security and low system complexity. For mobile applications, e.g., from a ground base station to an unmanned aerial vehicle (UAV), the FSO channel can suffer from severe instantaneous misalignment. This time varying misalignment is unknown to the transmitter and causes data packet corruption and erasure. As a result, the application of traditional fixed-rate erasure coding techniques is difficult. In this paper, we consider the application of rateless Raptor codes for such mobile FSO channels. Due to the high data rates required, short-length (16–1024) Raptor codes are designed and simulated on a severe jitter FSO channel. A key advantage of Raptor codes is their independence on channel state, no matter how large the misalignment. With a 1 Gbps transmitter, the designed Raptor code with $k = 64$ message packets offers 560 Mbps data rate and decoding cost of 4.14 operations per packet when transmitting power is 20 dBm. In contrast, a traditional automatic repeat-request (ARQ) algorithm technique on the same FSO jitter channel achieves a rate of 60 Mbps.