# Path Loss Model for Outdoor Parking Environments at 28 GHz and 38 GHz for 5G Wireless Networks
## 1 Introduction  
It is expected that mobile traffic volumes can increase a thousand times over the subsequent decade. It is expected that fifty billion devices will be connected to the network by 2020 and share information anytime and anywhere [1; 2; 3]. Due to the increasing number of connected devices, the overall capacity of the entire existing network structure needs to increase. This increasing of capacity can be done by improving energy efficiency, cost and coming up with a better system for spectrum and bandwidth utilization. Hence, better scalability options for handling the increasing number of connected devices will need to be provided. To successfully achieve the vision of increasingthe number of interconnected devices, a system has to come up with a network structure that can support up to a 1000 times increase in the projected data volume, 100 time increase in the cell capability and over a 100 times increase in the entire system capacity [3; 4]. One of the key solutions for future wireless networks is device to device (D2D) communication [5; 6]. With the exponential growth of mobile traffic and the improvement of local service flexibility requirements, D2D communications can alleviate the huge infrastructure investment [5]. The D2D communications allow the communication between mobile users in cellular networks directly [7]. Future 5G networks are 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) [8; 9; 10]. It will be able to monitor and control devices with high stream of real-time information [11]. The IOT applications are enabling Machine to Machine (M2M)-driven services [8; 12]. To support various IOT applications, a joint interest, physical and energy-aware cluster formation mechanism has been proposed in [8] to create clusters among the M2M devices. The adaptive clustering architecture for multimedia support in a multihop mobile network has been presented in [13]. In [12], the problem of energy and physical aware coalition formation and resource management in smart IoT applications has been addressed based on M2M communication. With the use of innovative ideas, technologies and the efficient utilization of frequency bands such as millimeter waves (mmWaves), some of the solutions can adequately meet these rising demands [14]. In fostering the development and wide spread of the fifth-generation (5G) wireless communication network, new wireless communication systems are required to offer revolution in technology with potential new spectra and novel architectural concepts [15]. As for any wireless communication system, the study of signal propagation is important for designing and modeling the 5G systems [16]. Channel characterizations at mmWave frequencies are needed in developing new standards and channel models to help engineering teams in system design and construction. The study of mmWave began as early as 1989 [17], to characterize the path loss using a low-height base station antenna in micro-cell environments at a frequency of 11 GHz. In downtown Denver, wideband non-line-of-sight (NLOS) channels at 9.6 GHz, 28.8 GHz and 57.6 GHz were measured [18]. Recently, extensive propagation measurements were conducted at frequencies of 28 GHz, 38 GHz and 73 GHz in urban microcellular and urban macro-cellular cases [19; 20; 21]. Omnidirectional path loss models in dense urban environments at frequencies of 28 GHz and 73 GHz were thoroughly investigated in [22]. Different path loss models were investigated at different frequencies between 2 GHz to 73 GHz in urban microcellular and urban macro-cellular cases [23]. The experimental channel characterizations for short distance in outdoor corridor environment using ultra-wideband channel sounder at 4.3 GHz were investigated in [24; 25]. Probabilistic omnidirectional path loss models in densely populated urban areas at 28 and 73 GHz were proposed in [26].