International audienceThis manuscript presents a survey on new challenges in wireless communication systems and discusses recent approaches to address some recently raised problems by the wireless community. At first a historical background is briefly introduced. Challenges based on modern and real life applications are then described. Up to date research fields to solve limitations of existing systems and emerging new technologies are discussed. Theoretical and experimental results based on several research projects or studies are briefly provided. Essential, basic and many self references are cited. Future researcher axes are briefly introduced

Visible light communication (VLC) has become a promising technology for high data rate communications and an attractive complementary to conventional radio frequency (RF) communication. VLC is a secure, energy efficient and cost-effective technology that exploits the existing infrastructure, particularly in indoor environments, for wireless data transmission. Nevertheless, the main limitation of developing high data rate VLC links is the narrow modulation bandwidth of light-emitting diodes (LEDs), which is in the megahertz range. The power domain nonorthogonal multiple access (PD-NOMA) scheme is envisioned to address several challenges in VLC systems. In this paper, we present a detailed overview of PD-NOMA based VLC systems. Moreover, we introduce insights on some PD-NOMA VLC system constraints and challenges such as power allocation, clipping effect, MIMO and security. Finally, we provide open research problems as well as possible directions for future research to pave the way for the implementation of PD-NOMA VLC systems.

The importance of free-space optical (FSO) communication has increased during the last decade, introducing its unique features such as its high data rate, license-free spectrum, ease of deployability, and low power consumption. In the future, communication between low earth orbit (LEO) and geostationary earth orbit (GEO) satellites will be commonly established by using inter-satellite optical wireless communication (IsOWC) systems. That enables GEO satellites to relay information to and from LEO satellites and fixed Earth stations that otherwise cannot transmit/receive data permanently. IsOWC systems are the most effective application of the FSO, and they will be favorited shortly because of their features. In this work, we established an IsOWC between GEO and LEO satellites at a distance of 45000 km to achieve a target bit error rate (BER) equal to 10-6. Furthermore, we proposed an IsOWC system with suitable operating wavelengths. Physical techniques such as the multi-input multioutput (MIMO) technique and a wave division multiplexing (WDM) technique are employed.

In this paper, the bit error rate (BER) and the channel capacity of a multiple-input multiple-output (MIMO) system employing optical space shift keying (OSSK) scheme (termed as MIMO-OSSK) are investigated under combined effect of atmospheric turbulence (AT) and pointing errors (PEs). The analysis reveals that the diversity order of MIMO-OSSK remains intact over all AT regimes and under PE severity. This behavior is contrary to traditional pulse-based modulation schemes, where diversity order depends upon AT conditions and PE severity. In addition, the analysis also demonstrates that the MIMO-OSSK utilizes receiver diversity efficiently as compared to existing pulse-based modulations. In order to examine the effect of all ranges of AT along with PE severity on MIMO-OSSK, three different channel models are considered, i.e., log normal, gamma-gamma, and negative exponential. The probability density functions of the sum of squares of difference between two channel coefficients under these channel models are evaluated, to develop analytical expressions of average BER and ergodic channel capacity for the considered setup. On comparing MIMO-OSSK with the same rate MIMO-pulse amplitude modulation (MIMO-PAM) scheme employing repetition coding, it is observed that the MIMO-OSSK scheme outperforms the MIMO-PAM for a spectral efficiency of more than 2 b/s/Hz, provided that the number of receivers is sufficiently large.

Performance analysis of free-space optical (FSO) communication systems in different channel conditions has gained significant attention in literature. Nevertheless, most existing studies consider uncorrelated channel conditions. An uncorrelated channel requires sufficient spacing between transmitters and limits the receiver field of view and link distance. However, this might not be feasible in all applications. Thereby, this paper studies repetition code (RC) and orthogonal space time block code (OSTBC) performance in correlated log-normal FSO channels using intensity modulation and direct detection. An approximate analytical expressions using moment generating function for the average bit error probability are derived. Our simulation results show that RCs are superior to OSTBCs in correlated channel conditions.