Airborne laser communications using wavelet packet modulation and its performance enhancement by equalization

Free Space Optics (FSO) through cloud has lately attracted substantial attention for a variety of applications[ 1][2]. FSO is a promising candidate for emerging broadband applications, considering that RF spectrum is already congested, rendering assignment of additional RF channels costly. Combining the attributes of a higher data rate but bursty link (FSO) with the attributes of a lower data rate but reliable link (RF) can yield attributes better than either one alone, enabling a high availability link at high data rates. This transmission configuration is typically called a hybrid RF/FSO wireless system [3][4]. Recently, there have been interests in filterbank transceivers, and both OFDM and wavelet modulation technologies can be understood as examples. In FSO, normally we are given huge optical bandwidth, but in fact, use of the huge bandwidth is limited due to both enabling technologies and the severe channel distortion. Therefore, not only in RF but also in FSO, we also need efficient use of resources. In this research, we aim at the following goals. First, wavelet packet modulation (WPM) will be applied to FSO to find the resource-efficient optimal spectral decomposition of the optical channel. Then, equalization will be applied to further enhance FSO performance.