Atmosfer olukları ve troposferik saçılım ile ufuk ötesi haberleşme kanalları ve ağları

Network centric operations (NCO) aim to provide a competitive advantage through information superiority. Modern military communication systems require communication links having low transmission delays and high data rates in order to provide effective command and control in challenging warfare areas. Available wireless communication systems are inefficient at b-LoS ranges. For this reason, new b-LoS communication techniques are required to provide high data rates, reliability and security. The main motivation of the proposed thesis is to analyze b-LoS wireless communications and networks with troposcatter and atmospheric ducts in order to tackle these problems. Tropospheric scatter that is widely known as troposcatter, is the scattering of the propagating signals in all directions due to the irregularities in the troposphere. The scattered signals are directed especially in the forward direction, but some of the signal power is directed to the receiver. As a result, the effects of troposcatter can be utilized as a b-LoS communication medium. To this end, we investigate the viability of troposcatter channel as a b-LoS communication medium through physical layer channel modeling studies. In addition, we propose models for the fading correlation and rain attenuation in troposcatter links. At the end, our models show that troposcatter communication is especially promising for fixed links with low probability of detect/intercept, low transmission delays and high data rates. 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. Although the wave propagation in atmospheric ducts has been studied, there are only a few papers which consider the ducting channel as a high data rate communication medium. Therefore, the communication aspects of this channel is mostly missing. To this end, we assess the viability of ducting communications for modern naval communications. Our results show that ducting communication can be utilized in challenging naval warfare conditions with secure and high data rate communications. To this end, we develop a channel modeling approach based on parabolic equation and ray-tracing methods. We analyze the viability of diversity techniques and investigate physical layer parameters of the ducting channels. At the end, we introduced a beam-forming method for ducting channels and investigate the feasibility of ducting ad hoc networks.