Laser communication system using wavelet-based multi-rate signaling

Free space optics (FSO) communication is a promising candidate for broadband applications, achieving bit rates far beyond possible by radio frequency (RF) technology. Communications via RF signals are generally reliable and well understood but cannot support emerging data rate needs unless they use a large portion of the precious radio spectrum, FSO communications offer enormous data rates but operate much more at the mercy of the environment. The perennial limitations of FSO communications are manifested in the channel attributes of scintillation (optical turbulence) and path obscurations. Both phenomena reduce the availability of the optical channel to support reliable communications. Since RF paths are relatively immune to the same phenomena, combining the attributes of a high data rate but bursty link (FSO) with the attributes of a low data rate (by comparison) but reliable link (RF) could yield attributes better than either one alone: high availability with high data rates. This transmission configuration is normally referred to as a hybrid RF/FSO wireless system [Kavehrad, M et al., 1990, 1991]. Increased FSO availability can ease the design of a hybrid radio, significantly. The focus of this paper is on a specific approach; fractal transmission on an FSO link, leading to improved availability of such links.