This article focuses on the design of transmitters and receivers for molecular communication (MC). It also reviews existing literature on transmitter and receiver architectures for realizing MC, including both nanomaterial-based nanomachines and/or biological entities.

Atmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower atmosphere, can trap the propagating signals. The trapping effects of the atmospheric ducts can be utilized as a communication medium for beyondline-of-sight (b-LoS) links. Although the wave propagation and the refractivity estimation techniques for the atmospheric ducts are well studied, there is no work that provides a channel model for the atmospheric ducts. Therefore, we develop a large-scale path-loss model for the surface ducts based on the parabolic equation (PE) methods for the first time in the literature. In addition, we develop a ray-optics (RO) method to analyze the delay spread and angle-ofarrival (AOA) of the ducting channel with the surface ducts. Using the developed RO method, we derive an analytical expression for the effective trapping beamwidth of the transmitter to predict the ranges of the beamwidth that can be trapped by the surface ducts according to the refractivity and the channel parameters.

Near-surface wave propagation at microwave frequencies especially 2 GHz and above shows significant dependence on atmospheric ducts that are the layer in which rapid decrease in the refractive index occurs. The propagating signals in the atmospheric ducts are trapped between the ducting layer and the sea surface, so that the power of the propagating signals do not spread isotropically through the atmosphere. As a result, these signals have low path-loss and can travel over-the-horizon. Since atmospheric ducts are nearly permanent at maritime and coastal environments, ducting layer communication is a promising method for beyond-Line-of-Sight (b-LoS) communications especially in naval communications. To this end, we overview the characteristics and the channel modeling approaches for the ducting layer communications by outlining possible open research areas. In addition, we review the possible utilization of the ducting layer in Network Centric Operations (NCO) to empower decision making for the b-LoS operations.

In the near future, the available radio-frequency (RF) bandwidth will not be sufficient to meet the ever increasing demand for wireless access. Visible light communication (VLC) is an alternative method to reduce the burden of RF-based communication, especially in indoor communications. 70% of the communication is indoors, and light emitting diode (LED) arrays are spreading for illumination purposes thanks to their low energy and higher lifetime. VLC can be realized as a secondary application in LED arrays that are placed for lighting. In this way, some of the wireless traffic can be sent using light, with less cost and less carbon footprint. For these reasons, VLC attracts significant research interests. We provide an extensive survey of the current literature by outlining challenges and future research areas in order to facilitate future research in this area.

Troposcatter communications provide a good alternative for beyond-Line-of-Sight (b-LoS) communication because it can provide reliable high data rate applications with the advancement in the modem and high power amplifiers. The employment of the high data rate applications with troposcatter communications requires the investigation of the troposcatter channels. However, available channel models for the troposcatter communications are not able to take the non-homogeneities of the air turbulence into account. Therefore, the main motivation of this paper is to develop a ray-based MIMO troposcatter channel model in which the beamwidths of the antennas are divided to small parts and, the associated delay and power of the rays are calculated in order to consider the non-homogeneities and time variations of the channel. Also, in order to show the time varying behaviour of the channel this paper provides the simulation results for the maximum data rate of the channel by using real world measurements first time in the literature.