New adaptive link layer protocol using optimal packet length for free space optical communications

In this paper, the authors propose a new link layer protocol that adapts packet length and modulation and coding scheme (MCS) to propagation conditions for free space optical communications (FSO). In conventional FSO systems, only the MCS has been adapted with respect to propagation condition. For low signal to noise ratio (SNR), we reduce packet length and use robust modulation such as On Off Keying (OOK) and low rate channel coding. While, at high SNR, we increase packet length and use large modulation constellation. A significant enhancement in throughput is observed: the proposed link layer protocol offers 1-2 dB gain compared to the conventional one where all packets are transmitted with the same length.