# Path Loss Measurements and Model Analysis in an Indoor Corridor Environment at 28 GHz and 38 GHz
## 2 Literature Review  
We review heavy path loss, wide bandwidth, narrow wavelength, and high penetration that characterize millimeter wave communication. These features are mentioned as follows:  
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2. Abundant bandwidth: At the moment, the overall bandwidth available for a mobile network is insufficient to meet the increased data demands of devices (in fact, the available bandwidth is less than 780 MHz for 2G, 3G, and 4G networks). The most significant advantage of millimeter communication over classical communication is the increased bandwidth, which allows the transmission at frequencies exceeding 150 GHz [15]. 3. Short wavelength: Because mmWave signals have wavelengths in the order of millimeters, they must be communicated using MIMO, and they are particularly well suited to packing a large number of half-wavelength-spaced antennas into tiny spaces. The combination of mmWave with massive MIMO can considerably improve wireless access and throughput performance [23]. 4. Propagation loss: Path loss and penetration loss are two different types of propagation losses. Under the assumption of the line-of-sight (LOS), the free space route loss is proportional to the square of the carrier frequency, according to the Friis transmission formula. Because microwave frequencies start at 26.5 GHz, there is more propagation loss than in the microwave band. For example, at 60 GHz, it is 28 dB higher than at 2.4 GHz. This has been a key drawback of mmWave, but with the introduction of device to device (D2D) communications, a high-gain directional antenna may compensate for the loss, improving network capacity and enhancing security against eavesdropping and jamming. The increased penetration loss in NLOS settings makes it difficult for mmWave nodes placed outdoors to reach indoor spaces. Signals/propagation may suffer from large penetration losses in the case of indoor users with outdoor base stations (BSs), lowering data throughput, spectrum efficiency, and energy efficiency. The separation of outside and indoor scenarios is, therefore, unavoidable [24; 25]. According to [PERSON] et al. [26], there are unallocated spectra in millimeter wave bands, preventing the full use of massive antenna arrays for high-speed data transfers. Although gigabit data transmissions in these bands necessitate accurate channel modeling, the shadowing effect and the necessity for adaptive beam formations in areas with significant mobility persist. As a result, it was suggested that in addition to end-channel sounders, detailed measurements for full radio characterization should include angular spread and delay time in the evaluation of multipath make-ups. However, in order to provide input to standard organizations, the lack of channel models must be addressed. [PERSON] et al. [27] emphasized the relevance of millimeter bands as a proven solution for high data rate transmissions, particularly in indoor environments. However, millimeter wave propagation technology has been reported to suffer from propagation loss of 25 to 30 dB due to impediments, such as walls, furniture, and human blocking. Another study used a frequency domain and a vector network analyzer (VNA) to investigate millimeter wave propagation at 60 GHz in an indoor environment. The results suggest that an access point (AP) can be placed in the center of the network to reduce shadowing caused by human impediments. It has a high frequency that could be solved with a frequency lower than 60 GHz. As mentioned in [28], millimeter wave measurements were made in China with the goal of determining the influences of atmospheric variables on transmission. There was a difference between the theoretical rain-induced signal attenuation and the practically recorded signal attenuation during the rainfall. It was founded on the idea of rain fore casting and monitoring in real-time.