# Comparative Study of Indoor Propagation Model Below and Above 6 GHz for 5G Wireless Networks
## 1 Introduction  
Enabling consumers to do all the things they do today with mobile devices (such as smartphones and tablets) faster and more reliably, 5G may support new ways of using those mobile devices (e.g., new applications), and completely new types of mobile devices [1; 2]. As the number of mobile users increases, 5G communication networks/base stations must handle a greater amount of data and move toward considerably higher speeds than those of the base stations that make up today's cellular networks [3; 4]. 5G networks are also envisaged to use resource sharing for both heavily bandwidth thirsty video applications and for handling data traffic from large cluster of sensors i.e., the so-called Internet of Things (IOT) [5; 6]. The new IoT applications are enabling smart city initiatives worldwide [7]. Using IOT applications, the mobile users are able to monitor and control devices with high stream of real-time information. IoT requires huge amount of bandwidth, which is needed to support massive sensors [8; 9]. IoT based smart cities have various real-time applications which would be crucial and useful for the next generation of network [10]. The application can be classified into two major group i.e., smart energy and smart transportation [5]. Therefore, the main problem for current wireless networks is that a huge amount of data will be required more than before, which will be congested on the radio-frequency spectrum below 6 GHz. This implies that slower service and more dropped connections occur due to the low bandwidth. Therefore, the millimeter wave (mm-wave) band is chosen as a potential candidate for the next generation wireless networks, i.e., 5G, where more bandwidths are available with up to 10 times the capacity of today's cellular networks [11]. Moreover, the feasibility of mobile broadband systems in frequency bands above 6 GHz has been reported in academic and industry research [1; 12; 13; 14; 15]. For frequency bands below 6 GHz, it is worth to note that the licensed spectrum of 3.5 GHz could be potentially allocated for 5G applications [4; 16]. Various studies have been done which explains that the 3.5 GHz frequency band work as main access link for indoor communication whereas, the 28 GHz can be used as a backhaul link [4; 17; 18]. In this context, this paper investigates the diffraction loss (DL) and frequency drop (FD) based on comparative study for indoor propagation channel characteristics at 3.5 GHz and 28 GHz bands. DL is used to calculate the amount of loss due to the diffraction from wall edge in indoor environment. FD is used to estimate the signal degradation when the frequency is high (above 6 GHz) based on comparison with the received signal at lower band (below 6 GHz). The contributions of this paper can be defined in four folds as follows. * Firstly, the propagation characteristics for the 5G channel at frequencies of 3.5 GHz and 28 GHz are compared in an indoor environment. The line of sight (LOS) and non-LOS (NLOS) measurements were performed using the ultra-wideband correlation channel sounder with a higher chip rate of 1000 Megachips-per-second (Mcps) as well as a higher resolution of 1 ns. * Secondly, two physically based models; the close-in (CI) free space reference and the CI model with a frequency-weighted path loss exponent (CIF) are used to investigate the single and multi-frequency statistical path loss, respectively. Two 3 GPP path loss models; floating intercept (FI) and alpha-beta-gamma (ABG) models are also used to investigate the propagation characteristic for a single and multi-frequency statistical models, respectively. * Thirdly, DL and FD are used to analyze the signal degradation due to the shadow edge effect and high operating frequency. * In the last, the power delay profile, root mean square (RMS) delay spread and mean excess (MN-EX) delay, are considered to characterize the time dispersion parameters for both frequency bands. The remainder of this paper is organized as follows. Related work has been described in Section 2.