Simultaneous Acquisition and Track Scheme with Multiple Terminals Based on Subspace Method for Optical Satellite Networks

This paper presents an inter-satellite optical multiple access scheme, which combines space division multiple access (SDMA) and code division multiple access (CDMA) in such way that a cluster of picosatellites communicate by means of a laser beam with a detector matrix receiver located on the master satellite and equipped with a common optical system for incoming beams. The detector has a field of view (FOV) large enough to include multiple terminals, in which signals arriving from different terminals with different directions are detected by different pixels. A spread spectrum technique is used, and each signal is modulated by its own unique pseudorandom (PN) sequence. Even though the two signals overlap, each pixel is de-spreading the desired signal according to the associated PN sequence. Furthermore, in order to acquire and track multiple terminals simultaneously, a blind algorithm is presented by exploiting the structure information of the data output of each pixel, which is based on a signal subspace approach using the sample matrix of the received signals. Performance measures in terms of the asymptotic performance and the signal-to-noise ratio (SNR) are obtained to assess the viability of the proposed scheme. Numerical results are presented to explain the impact on the performance of the proposed models. The approach significantly reduces stringent requirements of simultaneous acquiring and tracking multiple platforms instead of using a number of independent gimbaled telescopes by the master satellite and is easy to implement in real time applications.