# Atmospheric Effects on OFDM Wireless Links Operating in the Millimeter Wave Regime
## 1 Introduction  
The rapid growing use of cellular services and the expanding line of products that are based on the wireless communications technologies have led to an increasing interest in the standardization of the 5 th Generation (5G) mobile communication technology. The 5G technology is expected to use millimeter waves (MMW) to offer unprecedented spectrum and extremely high data rates to the wireless communications. The implementation of MMW technology has led to the recognition of the necessity of a consistent standardization of networks, channels, and modulation techniques that are relied on corresponding modeling efforts [1]. The US Federal Communications Commission (FCC) has stated their intention to establish the U.S. as leaders in the field of 5G [2]. One of the options considered for application was the allocation of bandwidth in the Extremely High Frequency (EHF) range, 30-300 GHz that can lead to the development of practical consumer applications of MMW technologies. The spectrum available for licensed use was set in three bands within the Ultra High Frequency (UHF) 850 MHz, 2.4 GHz, as well as MMW in the 28 GHz, 37 GHz, and 39 GHz bands. Furthermore, the 64-71 GHz band was recently designated for unlicensed use, which increases the total amount of unlicensed spectrum to 14 GHz as well as 600 MHz in the 37 GHz band for shared access. Different modulation techniques have been proposed for usage in 5G systems in order to provide greater flexibility and thereby increase transmission efficiency and reliability. Currently, the orthogonalfrequency-division multiplexing (OFDM) scheme is used in the 4G as a digital multi-carrier modulation method and is one of the popular techniques considered for the 5G cellular wireless communications [3]. The communication in the EHF range has many advantages; however, it is subjected to atmospheric propagation issues. In general, atmospheric effects are due to absorption and dispersion phenomena. In short wavelengths, the MMW propagation is significantly affected by weather conditions, such as air pressure, temperature, relative humidity, fog, and rain. Almost all of the studies on the effect of atmospheric conditions on the performance of communication links are referring to the attenuation only [4]. The signal phase shift and time delay effects are usually ignored, although they can be significant in extreme conditions [5; 6]. [PERSON] et al. presented in their previous studies on MMW atmospheric propagation, theoretical and experimental results of absorptive and dispersive propagation effects and their influence on the signal strength and phase dispersion [7; 8; 9; 10; 11]. It was found that apart from attenuation, the dispersive effects like group delay should be considered in the design of MMW and THz radar and wireless communication links. In the present work, the performance of an OFDM wireless communication link operating in the MMW regime is studied under different weather conditions such as humidity, fog, and rain. The atmospheric effects on the OFDM waveform were formulated theoretically and demonstrated by simulation model. For this purpose, an atmospheric channel model for wireless communication was developed, combining our MMW propagation model with 5G Toolbox of MATLAB R2019b (MathWorks, Natick, MA, USA) [12]. MMW propagation model is applied to the transmitted baseband OFDM complex envelope and the performance of the wireless link is presented by using constellation diagram and BER (Bit Error Rate) performance chart. The present work is focused on the dispersive effects like group delay and phase shift and their effect on the OFDM communication link. The current paper presents an integration of several issues as sub-models: the MMW propagation model (Section 2), the frequency dependent attenuation and phase dispersion factors for different weather conditions (Section 3), transmission of OFDM waveform in a medium (Section 4), technical specifications of the next generation cellular network and the simulation parameters (Section 5).