RESEARCH ARTICLE A high-speed long-haul wavelength division multiplexing– based inter-satellite optical wireless communication link using spectral-efficient 2-D orthogonal modulation scheme Mehtab Singh | Jyoteesh Malhotra Department of Electronics and Communication Engineering, Guru Nanak Dev University, Regional Campus, Jalandhar, India Correspondence Department of Electronics and Communication Engineering, Guru Nanak Dev University, Regional Campus, Jalandhar 144007, India. Email: mehtab91singh@gmail.com Summary In this work, we propose a novel multi-bit/symbol spectral-efficient optical orthogonal modulation scheme based on simultaneously modulating differen- tial quadrature phase shift keying (DQPSK)-polarization shift keying (PolSK) in a 16-channel wavelength division multiplexing (WDM)-based inter-satellite optical wireless communication (IsOWC) system. Through numerical simula- tions, we demonstrate a reliable transportation of 16 × 100 Gbps information over 25 000 km of transmission range with acceptable bit error rate (BER) using the proposed system. Further, the impact of space turbulences (ie, pointing error losses) on the BER performance of the proposed IsOWC link has been evaluated using numerical simulations. The simulation results report a successful transportation of information up to 2.7 μrad receiver pointing error angle with acceptable performance. KEYWORDS bit error rate (BER), inter-satellite optical wireless communication (IsOWC), orthogonal modulation scheme, space turbulence, transmission range 1 | INTRODUCTION The deployment of laser technology for communication purposes, specifically for space communication was first exploited in 1962. In the last five decades, individual researchers, government agencies, research institutes, and compa- nies have achieved tremendous progress in the field of optical wireless communication for inter-satellite links and deep-space applications. 1 In inter-satellite optical wireless communication (IsOWC) links, the information is transmit- ted between two satellites separated by a certain distance in space, orbiting either in same or different orbits. The first experimental IsOWC link was successfully demonstrated in March 2003, where 50 Mbps of information was transmit- ted between Advanced Relay and Technology Mission satellite (ARTEMIS) and Satellite Pour l'Observation de la Terre- 4 (SPOT-4) with 120 mW of transmission power and 850 nm of operating wavelength. 2 Inter-satellite links are considered crucial for communication purposes, mainly for providing global coverage. Three Geostationary satellites separated at 120  apart in space are capable of covering the entire globe for communication pur- pose. 3 IsOWC links have many merits including high-speed links, large bandwidth, small size and weight of equipment, low power requirement, and high efficiency. 4 Other merits of IsOWC links include copious spectrum with no licensing requirement, highly secure connections and immunity to electromagnetic and radio frequency interference. 5 However, narrow beam divergence angle owing to the use of high-frequency carrier signal makes the acquisition, tracking, and pointing very critical for IsOWC links. Any misalignment errors due to satellite vibration, background noise Received: 1 July 2019 Revised: 1 November 2019 Accepted: 2 December 2019 DOI: 10.1002/dac.4293 Int J Commun Syst. 2019;e4293. wileyonlinelibrary.com/journal/dac © 2019 John Wiley & Sons, Ltd. 1 of 13 https://doi.org/10.1002/dac.4293