LOS and NLOS Channel Modeling for Terahertz Wireless Communication with Scattered Rays Anamaria Moldovan 1 , Michael A. Ruder 1 , Ian F. Akyildiz 2 , and Wolfgang H. Gerstacker 1 1 Institute for Digital Communications, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Cauerstr. 7, D-91058 Erlangen, Germany, {moldovan, ruder, gersta}@LNT.de 2 Broadband Wireless Networking Lab, Georgia Institute of Technology, Atlanta, USA, ian.akyildiz@ee.gatech.edu Abstract—In this paper, the wireless communication over indoor Terahertz (THz) channels is studied. The physical mech- anisms governing a wireless transmission in the 0.1 – 10 THz band are a very high molecular absorption and spreading loss which result in a very high and frequency-selective path loss for the line-of-sight (LOS) links. For the non-line-of-sight (NLOS) propagation, a very high reflection loss depending on the shape, material, and roughness of the reflecting surface affects the THz wave propagation. Taking these peculiarities of the THz radiation into account and applying a ray tracing approach for scattered rays, a novel deterministic equivalent channel model is developed that accounts for both the LOS and NLOS propagation cases. Furthermore, the channel capacity of the proposed model is investigated. Simulation results demonstrate that for distances, up to 1 m, data rates in the order of Terabit per second (Tbps) are obtained for a transmit power of 1 Watt. Moreover, the capacity of only the NLOS component is around 100 Gigabit per second (Gbps). These results are highly motivating to develop future wireless THz communication systems. I. I NTRODUCTION To satisfy the growing demands for high data rates in wireless communication systems, the network capacity has been enhanced by increasing the spectral efficiency by means of advanced modulation schemes and signal processing techniques [1]. However, the efficiency of these methods is limited due to the narrow bandwidth of legacy systems. Another approach for throughput enhancement is increasing the operation frequency. In this respect significant effort is devoted to research in the field of millimeter-waves, which allow for data rates up to 10 Gigabit per second (Gbps) [2]. Yet, the increasing demand for even higher data rates in wireless communications will eventually lead to the allocation of wider bandwidths in the Terahertz (THz) frequency range. For this purpose, the IEEE 802.15 Terahertz Interest Group (IGthz) has been established in 2008 to explore the feasibility of the Terahertz band for wireless communications [3]. Since January 2014 there is an official IEEE standardization committee called 100Gbps. The THz band, or so-called sub-millimeter band, covers the frequency range between 100 GHz and 10 THz, with corresponding wavelengths between 3 mm and 30 μm. In contrast to X-ray radiation, THz radiation is non-ionizing and therefore it can be used in close proximity to the human body. Other important advantages of THz radiation include the penetration of many opaque materials and the high selectivity due to the fact that many molecules have resonance frequencies within the THz band, enabling their detection when they are present. Many applications of THz waves, some of them already available, like THz body scanners at airports or medical imaging, are based on these properties. So far, THz waves have not been utilized for wireless communications because of the lack of devices for generating and detecting them [1]. Currently, though there are three major technologies such as Silicon- Germanium (SiGe), Galium-Nitride (GaN), and Graphene that are being considered for the development of ultra-high-speed transceivers in the THz band [4]. The physical mechanisms governing a wireless transmission in the THz band are different from those which affect schemes operating in the lower frequency bands where the propagation is mainly influenced by the spreading loss. Therefore, already existing channel models cannot be re-used for THz commu- nications. The peculiarities of THz radiation are a very high molecular absorption and spreading loss which result in a very high and frequency-selective path loss for line-of-sight (LOS) links. For non-line-of-sight (NLOS) propagation, a very high reflection loss depending on the shape, material, and roughness of the reflecting surface governs the THz wave propagation. So far, the existing literature on the channel modeling in the THz band is sparse. In [5], an LOS propagation model for the entire THz band was developed by analyzing the impact of molecular absorption on the path loss. To account for the NLOS propagation, it is necessary to characterize the reflection of electromagnetic (EM) waves at obstacles in the THz frequency range. The properties of typical indoor materials have been measured in the 0.1 to 1 THz frequency range [6], [7]. Furthermore, the scattering behavior of rough surfaces both in the specular [8] and non-specular [9], [10] directions has been analyzed at 300 GHz band. To this end, these works employ Kirchhoff scattering from rough surfaces theory [11]. The few existing channel models in the THz band [12], [13] characterize the multipath channel at 0.3 THz based on ray- tracing simulations. They are mainly based on measurements and consider specular reflections only. In this paper, we propose a novel deterministic channel model for the 0.1 to 1 THz frequency range, based on Kirchhoff scattering theory and ray tracing that includes the effects of LOS and NLOS propagation. We improve the LOS propagation model proposed in [5] by adopting an updated molecular High Resolution Transmission (HITRAN) 2012 database and realistic values for the fraction of water vapor in the air. Our improved LOS propagation model in Section II shows a significantly lower molecular absorption loss as compared to [4]. For the NLOS propagation, in Section III we model the reflection loss as discussed in [10], including also the effects of the molecular absorption loss and spreading loss on the indirect paths. Furthermore, the channel capacity is determined in Section V by employing the proposed deterministic channel model for LOS and NLOS propagation from Section IV and optimizing the transmit power allocation via water-filling. Our simulation results show that for relatively short distances, up to 1 m, data rates in the order of Terabit per second (Tbps) can be obtained for a transmit power of 1 Watt. This result encourages the use of the THz band for wireless short range Globecom 2014 Workshop - Mobile Communications in Higher Frequency Bands 978-1-4799-7470-2/14/$31.00 ©2014 IEEE 388