The welcome and adaptation of optical wireless technology by the modern era has brought forward the concept of an inter-satellite free-space optical communication system. In the present work, I study the combined effect of selection of different operating wavelengths and detector types along with the pointing errors at the transmitter and receiver side on the performance of an inter-satellite free-space optical link. The link performance has been optimized by measuring and analyzing the bit error rate and quality-factor of received signal under different scenarios. Performance of the inter-satellite link has also been investigated considering different modulation formats and data rates for LEO and MEO distances.

Underwater wireless optical communication is the best alternative for many applications especially for high bandwidth data communication between underwater objects and vehicles. The implementation of coding scheme along with advanced modulation technique and equalisation methods is identified as a key research scope for enhancing the performance of the system. In this paper, the coded generalised frequency division multiplexing (GFDM) technology is employed to provide high-data rates and less out-of-band emission. The Bose-Chaudhuri-Hocquenghem (BCH) and Reed-Solomon (RS) coding schemes along with equalisation techniques namely normalised least mean square (NLMS)-based decision feedback equalisers (DFE), minimum mean square error (MMSE) and zero forcing (ZF) are utilized to reduce inter symbol interference (ISI). The bit error rate (BER) performance is evaluated in the presence of pointing error (PE) and turbulence using Monte Carlo channel modelling simulations. The results showed that RS coding with NLMS-DFE outperforms other techniques and achieves a BER of roughly 10−5 with a signal-to-noise ratio levels below 20 dB. The simulation results demonstrate that RS code with 15 total symbols per code word and 3 data symbols, i.e., RS (15, 3) and BCH code with 31 total symbols in a code word and 6 data symbols, i.e., BCH (31, 6) provided the best error performance among other coding schemes employed. It is inferred that RS (15, 3) coded 2 × 2 multiple input multiple output systems with NLMS-DFE achieved a BER value of 1.1925 ×  10−5 at 11 dB which is 16 dB less than uncoded system. Thus, the coded GFDM improves overall BER performance and has the potential to provide higher reliability for internet of underwater things (IoUT) applications.

This paper investigates the differential binary modulation for decode-and-forward (DF) based relay-assisted free space optical (FSO) network under the effect of strong atmospheric turbulence together with misalignment error (ME). The atmospheric fading links experience K-distributed turbulence. First we derive novel closed form expression for average bit error rate (BER) and outage probability (OP) in terms of Meijer’s G function. Further, the OP of differential DF-FSO system with multiple relays is derived. We also analyze the asymptotic performance for the sake of getting the order of diversity and the coding gain. The power allotment term is utilized to examine the effect of different power allotment techniques on BER and OP. The simulation results have been used to validate the derived analytical results.