# Comparative Study of Indoor Propagation Model Below and Above 6 GHz for 5G Wireless Networks
## 2 Related Work  
Mm-wave communications have recently attracted large research interest, since the huge available bandwidth can potentially lead to the rates of multiple gigabit per second per user [19]. The industry often uses the term mm-wave to define frequencies between 10 GHz and 300 GHz [20]. The wavelengthsof mm-wave frequencies ranges from 1 mm to 100 mm compared to the radio waves that serve today's devices, which measure wavelengths in the order of tens of centimeters.  
In the past, the mm-wave spectrum has been proposed for wireless local area networks (WLANs), intelligent transport systems (ITS's), personal communication network (PCN) systems and local multipoint distribution systems (LMDS) [21]. It has also been used in satellite communications, long-range point-to-point communications and military applications [20]. Currently, some cellular providers use mm-wave frequencies for data transmission between stationary points, such as two base stations [20]. However, using them to connect the base station with mobile terminals is an entirely different approach. The amount of available bandwidth in mm-wave bands including frequencies above 6 GHz i.e., the 28 GHz band help in the deployment of 5G. The future 5G wireless networks require a huge capacity to connect anything-anywhere at any time. With mm-wave bands, massive multiple-input multiple-output (MIMO) and other 5G technologies, the wireless network will be able to serve the future smartphone users, robotics [22], remote surgeries [23], and autonomous cars [24; 25]. Already, elevated expectations have been set for 5G by promising ultralow latency and record-breaking data speeds for consumers. However, there are some challenges for 5G wireless network, such as difficult propagation conditions using high frequency i.e., 28 GHz band [26]. These propagation difficulties can be countered by using multiple highly directional antennas [27]. The very short transmission time interval (TTI) that characterizes the mm-wave makes it very much suitable for indoors communications and for deployment in small city network, because of the high propagation path loss.  
Many studies have investigated the propagation for mm-wave bands in different indoor and outdoor environments [28; 29; 30; 31; 32; 33; 34]. In [35], the propagation measurements were conducted in the 28 GHz and 73 GHz frequency bands in a typical indoor office environment in downtown Brooklyn, New York on the campus of NYU and a large-scale path loss and temporal statistics was obtained. In [30; 33; 34; 36], extensive propagation measurement campaigns were conducted at 6-38 GHz, which measured path loss and delay spread in indoor corridors and dining rooms. Obtaining this information is vital for the design and operation of future 5G cellular networks that use the mm-wave spectrum. Few studies have made comparison between the frequency band below and above 6 GHz. Three candidate large-scale propagation pathloss models for use over the entire microwave and mm-wave radio spectrum were presented and compared in [37], while a comparative study of the two bands at 2.9 GHz and 29 GHz was provided in [38]. The motivation behind propagation measurements with varying azimuth and elevation angle parameters, using narrow beam width directional antennas in [35; 38], is to produce the omni-directional channel models. In this work, wide beam width directional antennas are used for propagation measurement in a closed space environment, i.e., the corridor. Using the wide beam width directional antenna is capable to cover the entire space of the corridor and provides the similar effect as using the omni-directional antenna. This implies that varying azimuth and elevation is not needed for the considered closed corridor environment. Despite this considerable progress in the 5G channel model, a complete characterization of the mm-wave link for next generation 5G mobile broadband is still needed. Thus, this paper will undertake a comparative study between two different bands below and above 6 GHz.