# Path Loss Measurements and Model Analysis in an Indoor Corridor Environment at 28 GHz and 38 GHz
## 2 Literature Review
Path loss (or path attenuation) is the decrease in the power density of an electromagnetic wave as it travels through space. Path loss can be caused by a variety of factors, including natural radio wave expansion, diffraction path loss caused by obstruction, and absorption path loss due to the presence of a form of media that is not transparent to electromagnetic waves. It is crucial to remember that even when a path is lost, the transmitted signal may still travel along other paths to its destination; this process is known as multipath. Since these waves or transmitted data travel along different paths, the wave may reconvuce at the destination point, resulting in significantly different received signals [38]. It also refers to the loss or attenuation that a propagating electromagnetic signal (or wave) experiences as it travels from the transmitter to the receiver. As a result, the received power is lower than the broadcast power level. Antenna gains, operational frequency, transmission power, and the range of separation between the transmitter and receiver are all elements to consider. The most common way to express path loss is in decibels(dB) [39]. Because the dependency of the distance between the transmitter and the receiver distance on the path loss is no longer linear, the path loss in wireless propagation is mostly a function of a logarithm factor. However, in LOS environments, signal attenuation over distance closely follows [PERSON] free space path loss equation, propagating signals attenuated according to the square power law [39; 40]. In the last 20 years, there has been substantial research into various propagation channels that could be used for indoor channels. While some have concentrated on both outdoor and indoor office spaces, others have concentrated solely on interior office environments [41; 42; 43; 44; 45; 46; 47]. [PERSON] et al. produced model descriptions with probability distributions; they relied on the parameters in research on an empirical path loss model for wireless channels in indoor short-range office environments. The model depicted appreciable variable values of route losses at different frequencies and produced a simpler model that simplified radio propagation in difficult situations. However, because this study was conducted in an office setting, it was necessary to evaluate this innovative prediction path loss model in a commercial setting with more obstacles [48]. Further research has revealed that most propagation models that work at frequencies less than 6 GHz are inapplicable when considering route loss models for millimeter wave frequency bands (which are generally above 6 GHz). [PERSON] et al. constructed channel models that could operate in indoor circumstances at frequency ranges of 4.5, 28, and 38 GHz in order to find a solution. Both LOS and NLOS measurements were taken in an inside office environment with the transmitting and receiving antennas separated by 23 m. The purpose of the study was to compare the new large-scale generic path loss models to existing path loss models, omnidirectionally and directionally, as well as multi-frequency and single-frequency path loss models. The investigation shows that when modeled with one parameter path loss exponent (PLE) and associated with transmitted power, the large-scale route loss model has a propensity to perform better [48]. Shadowing and attenuation, which were explored in [49], are another set of properties common to indoor environments. Wireless open-access research platform (WARP) equipment was used to model path loss and shadowing. As a result, the propagation path loss value was consistent with measurements in the literature, with an exponent of 4 and a standard variation of 6.4 dB. In millimeter wave propagation, the direct exchange of information between two near-distance devices in the absence of a base station (known as D2D, or device-to-device communication) has various advantages, including energy efficiency, increased data throughput, and shorter latency [31; 50].