| Popis: |
Transmit power control, as in the mobile wireless channels, can enable a robust and spectrally efficient communication through atmospheric turbulence in terrestrial free-space optical (FSO) channels. With optical bandwidths in excess of several GHz and eye safety regulations limiting the transmit optical power, the per hertz signal-to-noise ratio (SNR) in terrestrial FSO systems can possibly become limited. This is especially true for future high-bandwidth and long-haul terrestrial systems based on coherent optical communications. Hence, power control becomes significant in terrestrial FSO communication systems. However, a comprehensive assessment of the impact of dynamic power adaptation in the existing terrestrial FSO systems is lacking in the literature. In this paper, we investigate perfectly beam power-controlled terrestrial FSO communication systems with heterodyne detection and direct detection based receivers operating under shot noise-limited conditions. Under these systems considerations, we derive unified exact and asymptotic capacity formulas for the Gamma-Gamma turbulence channels with and without pointing errors. The numerical results highlight the intricate relations of atmospheric turbulence and pointing error parameters in typical terrestrial FSO channel settings. More importantly, a concrete assessment of the impact of the key channel parameters on the capacity performances of the aforementioned FSO systems is performed revealing several novel and interesting insights. |
