Wataru Yamada’s research while affiliated with Nippon Telegraph and Telephone and other places

Path loss in high frequency bands above 6 GHz is the most fundamental and significant propagation characteristic of IMT-2020. To develop and evaluate such high frequency bands, ITU-R SG5 WP5D recently released channel models applicable up to 100 GHz. The channel models include path loss models applicable to 0.5-100 GHz. A path loss model is used for cell design and the evaluation of the radio technologies, which is the main purpose of WP5D. Prediction accuracy in various locations, Tx positions, frequency bands, and other parameters are significant in cell design. This article presents the prediction accuracy of UMa path loss models which are detailed in Report ITU-R M.2412 for IMT-2020. We also propose UMa_A' as an extension model of UMa_A. While UMa_A applies different equations to the bands below and above 6 GHz to predict path loss, UMa_A' covers all bands by using the equations of UMa_A below 6 GHz. By using the UMa_A' model, we can predict path loss by taking various parameters (such as BS antenna height) into account over a wide frequency range (0.5-100 GHz). This is useful for considering the deployment of BS antennas at various positions with a wide frequency band. We verify model accuracy by extensive measurements in the frequency bands from 2 to 66 GHz, distances up to 1600 m, and an UMa environment with three Tx antenna heights. The UMa_A' extension model can predict path loss with the low RMSE of about 7 dB at 2-26.4 GHz, which is more accurate than the UMa_A and UMa_B models. Although the applicability of the UMa_A' model at 66 GHz is unclear and needs further verification, the evaluation results for 66 GHz demonstrate that the antenna height may affect the prediction accuracy at 66 GHz.

The International Telecommunications Union Radiocommunication Sector (ITU‐R) Study Group 3 identified the need for a number of radio channel models in anticipation of the World Radiocommunications Conference in 2019 when the frequency allocation for 5G will be discussed. In response to the call for propagation path loss models, members of the study group carried out measurements in the frequency bands between 0.8 GHz up to 73 GHz in urban low‐rise and urban high‐rise as well as suburban environments. The data were subsequently merged to generate site general path loss models. The paper presents an overview of the radio channel measurements, the measured environments, the data analysis, and the approach for the derivation of the path loss model adopted in Recommendation ITU‐R P.1411‐10 (2019‐08).

The user traffic in the mobile communication area has rapidly increased owing to the widespread of smartphones and various cloud services. To handle the increasing traffic, in the fifth-generation mobile communication system (5G), the millimeter-wave multiple-input and multiple-output (MIMO) communication technology is under development. Because the MIMO transmission performance heavily depends on the radio propagation characteristics, various MIMO channel measurements are needed for the performance evaluation and system design. The accurate and efficient parameter estimation algorithm which estimates the propagation delays and angle of arrivals (AoA) of radio waves is also indispensable for the purpose. In this paper, we extended the joint delay and azimuth estimation (JADE) method based on multiple signal classification (MUSIC) algorithm. In our proposal, the drawback of the MUSIC that the performance degrades for the estimation of coherent waves was solved by applying the smoothing technique in the frequency domain. It also makes the antenna calibration simpler. We implemented the proposed algorithm for the channel sounding system in the 66 GHz band, which is one of the candidate frequency bands for the International Mobile Telecommunications (IMT) system and evaluated the effectiveness through the experiment in an anechoic chamber. The result showed that our proposed method can de-correlate the signal components of coherent waves, and improved the parameter estimation accuracy significantly. The root means square error (RMSE) of the propagation delay estimation was improved from 2.7 ns to 0.9 ns, and the RMSE of the AoA estimation was improved from 20.3 deg. to 7.2 deg. The results are expected to be utilized for the millimeter wave band MIMO channel modeling.

This paper proposes a path loss model for crowded outdoor environments that can consider the density of people. Measurement results in an anechoic chamber with three blocking persons showed that multiple human body shadowing can be calculated by using finite width screens. As a result, path loss in crowded environments can be calculated by using the path losses of the multipath and the multiple human body shadowing on those paths. The path losses of the multipath are derived from a ray tracing simulation, and the simulation results are then used to predict the path loss in crowded environments. The predicted path loss of the proposed model was examined through measurements in the crowded outdoor station square in front of Shibuya Station in Tokyo, and results showed that it can accurately predict the path loss in crowded environments at the frequencies of 4.7 GHz and 26.4 GHz under two different conditions of antenna height and density of people. The RMS error of the proposed model was less than 4 dB.

This paper presents the characteristics of path loss produced by traffic sign blockage. Multi frequency bands including high frequency bands up to 40 GHz are analyzed on the basis of measurement results in urban microcell environments. It is shown that the measured path loss increases compared to free space path loss even on a straight line-of-sight road, and that the excess attenuation is caused by the blockage effects of traffic signs. It is also shown that the measurement area affected by the blockage becomes small as frequency increases. The blocking object occupies the same area for all frequencies, but it takes up a larger portion of the Fresnel Zone as frequency increases. Therefore, if blockage occurs, the excess loss in high frequency bands becomes larger than in low frequency bands. In addition, the validity of two blockage path loss models is verified on the basis of measurement results. The first is the 3GPP blockage model and the second is the proposed blockage model, which is an expanded version of the basic diffraction model in ITU-R P.526. It is shown that these blockage models can predict the path loss increased by the traffic sign blockage and that their root mean square error can be improved compared to that of the 3GPP two slope model and a free space path loss model. The 3GPP blockage model is found to be more accurate for 26.4 and 37.1 GHz, while the proposed model is more accurate for 0.8, 2.2, and 4.7 GHz. The results show the blockage path loss due to traffic signs is clarified in a wide frequency range, and it is verified that the 3GPP blockage model and the proposed blockage model can accurately predict the blockage path loss.