## 3 Spectrum Management Issues
### High-Spectrum Access
#### 3.4.4 Outdoor Investigation  
In [190], the authors have demonstrated a 26 GHz mmWave propagation measurement model for outdoor parking spaces in areas, such as Kuala Lumpur, Malaysia. The research is conducted by implementing a technique of Close-In Free Space (CI) and Floating Intercept (FI) path loss models. Besides, the directional horn and omni antennas are used for Tx (Transmitter) and Rx (Receiver), respectively. They have concluded that the CI model outperforms the FI model. However, a more robust model is required for a moving car scenario. The architects in [191] have focused on the capability of the channel at the mmWave frequency band of 15 GHz by using MIMO technology in outdoor rural and urban environments. Moreover, the Okumura Hata model for rural regions and the microcell path propagation model in urban areas are used as a path loss model to validate the performance. Results have suggested that it is a viable option for future networks because it provides a substantial amount of throughput due to diversified MIMO systems in this frequency band. A study [192] has figured out the free space propagation path loss model for LOS and NLOS environments. It has developed a CI and FI propagation model at various frequency ranges. As a result, the probabilistic path loss model can deliver high bandwidth data rates in mmWave frequency bands, where CI and FI cases show an almost equal output. For a more effective approach, we can apply advanced path loss models, such as Alpha-Beta-Gamma (ABG) and Close-In Frequency Weighting (CIF). The scholars in [193] have analyzed the channel characteristics of the mmWave frequency bands at 28 and 73 GHz and compared the output within the operation of the LTE-A frequency band at 2.14 GHz. They have implemented the ABG model and evaluated results in terms of average user throughput and spectral efficiency average cell throughput for various user capacity. Therefore, the results have proved that the mmWave frequency band has a higher overall network performance compared with the 2.14 GHz frequency band of LTE-A. Nonetheless, the interference effect, such as intercell interference, is higher in mmWave, especially for the cell-edge users, due to the signals coming from the adjacent sector of the same cell; cochannel interference also occurs due to the usage of the same frequency in the adjacent. The effect of interference will be analyzed for the multiple-cell scenario for LOS and NLOS environments, thus requiring an efficient methodology to overcome this problem before being implemented in a real-world scenario.  
In [194], outdoor propagation parameters are observed with various antenna deployment scenarios at 32 GHz frequency band for LOS and NLOS environments. FI and CI free space path loss models are observed for the outdoor environment. The results have proved that the CI model is more effective than the FI path loss model for NLOS measurement, and cross-polarization increases slower than co-polarization under LOS conditions. Nevertheless, FI shows better performance for the NLOS environment in the horn-horn and horn-omni antenna deployment. For future work, 26, 28, and 38 GHz bands will be inspected under the same environmental conditions. In [195], the investigators have discussed the joint contribution of channel models at 28, 38, 60, and 73 GHz and mmWave propagation measurements at four particular scenarios, such as BS-mobile, BS-BS, peer-peer, and V2V. They have applied wideband sliding correlator channel sounder with horn-horn antenna configuration for the outdoor environment. The results have achieved high values of path loss exponent (PLE), whereas a more scrupulous antenna setting is required.