Robust Data Detection for the Photon-Counting Free-Space Optical System with Implicit CSI Acquisition and Background Radiation Compensation

摘要

Since atmospheric turbulence and pointing errors cause signal intensityfluctuations and the background radiation surrounding the free-space optical(FSO) receiver contributes an undesired noisy component, the receiver requiresaccurate channel state information (CSI) and background information to adjustthe detection threshold. In most previous studies, for CSI acquisition, pilotsymbols were employed, which leads to a reduction of spectral and energyefficiency; and an impractical assumption that the background radiationcomponent is perfectly known was made. In this paper, we develop an efficientand robust sequence receiver, which acquires the CSI and the backgroundinformation implicitly and requires no knowledge about the channel modelinformation. It is robust since it can automatically estimate the CSI andbackground component and detect the data sequence accordingly. Its decisionmetric has a simple form and involves no integrals, and thus can be easilyevaluated. A Viterbi-type trellis-search algorithm is adopted to improve thesearch efficiency, and a selective-store strategy is adopted to overcome apotential error floor problem as well as to increase the memory efficiency. Tofurther simplify the receiver, a decision-feedback symbol-by-symbol receiver isproposed as an approximation of the sequence receiver. By simulations andtheoretical analysis, we show that the performance of both the sequencereceiver and the symbol-by-symbol receiver, approach that of detection withperfect knowledge of the CSI and background radiation, as the length of thewindow for forming the decision metric increases.