Abstract—Mobile communication technology is evolving toward the Sixth Generation (6G), which is designed to deliver ultra-high data rates and support advanced applications including the Internet of Everything (IoE), virtual reality, and artificial intelligence. Realizing such performance demands millimeter-wave (mmWave) and early sub-terahertz frequencies; these bands offer broad bandwidth yet are vulnerable to propagation impairments, especially in tropical environments. Taking Banda Aceh, Indonesia as a tropical urban case, this paper investigates the propagation characteristics of 6G mmWave signals at 28, 38, 73, and 142 GHz. Simulations are built upon the 3rd Generation Partnership Project Technical Report 38.901 (3GPP TR 38.901) channel model integrated within the NYUSIM simulator, with standard Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) propagation scenarios configured. To faithfully replicate tropical atmospheric conditions, local meteorological parameters (temperature, humidity, air pressure, and rainfall) are imported into baseline simulation outputs via an external attenuation model. This work evaluates core channel metrics: path loss, received power, and Root Mean Square (RMS) delay spread, and compares baseline and climate-aware simulation cases to quantify atmospheric attenuation impacts. The simulation results reveal that path loss and delay spread rise alongside frequency and transmission distance, while the received power drops considerably at higher frequencies. Climate-induced attenuation exerts a limited influence on low mmWave bands over short distances; however, its effect becomes far more prominent at higher frequencies, particularly at 142 GHz, due to intensified atmospheric absorption. These observations demonstrate the frequency-dependent characteristics of climatic impacts and identify critical deployment obstacles for high-frequency wireless communication systems in tropical cities. This study delivers valuable references for preliminary 6G network planning and deepens the understanding of climate-sensitive propagation in mmWave and early sub-terahertz spectrums.

Keywords—Sixth Generation (6G), millimeter-wave (mmWave), tropical urban environment, propagation, NYUSIM