Motivated by unique atmospheric scattering properties of optical waves at petahertz frequencies, we present a novel maximal selective transmit diversity scheme based on the selection of maximum irradiance optical path with a continuous waveform detector employed for petahertz wireless communications. The proposed scheme is designed to significantly improve the performance of a nonline-of-sight (NLOS) petahertz link in a turbulence-induced fading channel. We characterize the received signal by a continuous wave detector and quantify the cumulative distribution function (CDF) of the largest order statistics of the received irradiance. Furthermore, we derive closed-form expressions of important performance metrics including the average bit error rate, the outage probability, and the optical channel capacity with each scattered path experiencing the Gamma-Gamma distributed turbulence-induced fading. From the analytical expressions derived, the performance of the proposed NLOS petahertz communication system is analyzed and validated. Simulation results show that the proposed scheme effectively overcomes the channel impairment without increasing the transmit power. Even under strong turbulence fading, when the number of transmit diversity branches increases from 1 to 2 and 4, the required average signal-to-noise ratio (SNR) to maintain an outage probability of 10 −5 is found to be significantly reduced by 13 dB and 21 dB, respectively.INDEX TERMS Average bit error rate, continuous waveform detector, free-space optical communications, optical channel capacity, outage probability, petahertz communications, transmit diversity.
I. INTRODUCTIONT HE desire for low-cost, high-speed, and low-power communication links has motivated recent interest in optical wireless communications (OWC). Infrared (IR) and visible light communication (VLC) based OWC systems have been extensively used in indoor and outdoor optical communication applications through line-of-sight and diffused links.The conventional OWC employing IR or VLC is a promising technology capable of offering high data rate. However, these links are always susceptible to blockage due to their strict requirement of pointing, acquisition, and tracking (PAT). Furthermore, atmospheric turbulence produces fluctuations in the irradiance of the received beam, thereby severely degrading the communication performance. Various performance improvement techniques have been reported to address the performance impairments in the conventional OWC systems. A performance enhancement scheme for a wavelength division multiplexing for the OWC channel impaired by interchannel crosstalk, pointing error, and amplified spontaneous emission was reported [1]. The receiver sensitivity over the turbulence channel was shown to improve significantly by utilizing spatial modulation and pulse position modulation. Another interesting technique by the same authors to improve the performance of an orbital angular momentum-based multiplexed link over the OWC