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In this paper, we report the results of a field measurement campaign carried out inside a pedestrian tunnel at 24 GHz in two conditions, namely, empty tunnel scenario and busy tunnel scenario with pedestrian movement. The experiment measures the fading effects of various groups of pedestrian crowds using directional antennas at the transmitter and receiver for millimeter-wave radio communications. Having presented and analyzed the measurement data in several diverse scenarios, we have further investigated human scattering effects in the crowded pedestrian tunnel and performed ray-tracing simulation for an empty pedestrian tunnel condition. Because tunnel is an enveloped scenario that is not bound by any geographic areas, the results of this study can be applied to a wider scenario like other pedestrian tunnels across the globe. Above all, these findings contribute towards ensuring wireless connectivity for everyone even in a remote scenario like underground passages.

Caves have been used as a natural habitat since ancient times, and our ancestors once resided in them. As time and age evolve, caves slowly lose their original functionality, yet never ever lose their significance as a place. In this letter, we present field measurement results taken from inside a beautiful cave-turned-into-a-wine-cellar site, which is the first of its kind for such tourist caves rich with stalagmites and stalactites. This cave, named Jeff's cellar operated by the Sunway Group, is one of the famous tourist hot spots in Malaysia, and it has never failed to attract tourists from near and far each year. Needless to say, ensuring that wireless communications are available inside this cave fondly frequented by tourists is important. In this letter, we present field measurement results taken from inside Jeff's cellar at three frequencies, namely, 900 MHz, 2.4 GHz, and 5.8 GHz in both line-of-sight and non-line-of-sight scenarios. These measured results are useful for the practical planning and implementation of wireless communications not only in the said cellar but also other tourist caves such as meditation cave, thermal steam cave, crystal cave, and others.

This paper investigates the impacts that open-trench drains make on the accuracy of radio propagation prediction in an urban city environment. Compared with conventional prediction styles that assume the ground to be flat, in this paper, we have considered for the first time the real scenario in many Asian cities to make open-trench drains inclusive in radio propagation modeling. The aims of this paper are twofold. First, to scrutinize one narrow L-shaped structure, modeled after an open-trench drain, by means of comparing ray-tracing simulation results with the actual field measurement results at 2.4 and 5.8 GHz. Second, to compare one city model built without and with the inclusion of open-trench drains for running ray-tracing simulation in yielding radio propagation prediction results. The findings from this paper are especially beneficial to the improvement of mobile communications in extraordinary environments such as open-trench drains, caves, coal mines, underground passageway, and others. Besides, they provide a unique insight into how the presence of the open-trench drains may affect radio wave propagation in an urban city environment.

Despite the fact that cave communication has an abundant history, when an accident happened, some of the major problems are seemed to be left untreated yet. A year ago, thousands of people from around the world gathered in Thailand to help rescue one Thai soccer team who was trapped inside a cave. Tragedy could be avoided or better resolved with wireless communication inside cave. In this work, we have built an uneven terrain model for potential applications in cave environment since the ground in cave is oftentimes not flat but uneven. We performed field measurement on this uneven terrain model at 2.4 GHz. Subsequently, the measured result is compared with two ray-tracing results – one original one and another one with a scattering factor incorporated. The comparison shows that the latter ray-tracing simulation matches the measured result better, with an improved standard deviation value.

Making wireless communications available in caves is important, it will benefit several activities that are caves-related such as volcanology, speleo-biology, speleo-archeology, hydrology, military reconnaissance, and cave exploration. Besides, it will also enhance the safety of the operation of show caves like the tourist caves and furthermore, may assist in the search and rescue operation in caves. In this paper, we study the behavior of radio waves on a random rough surface using ray tracing technique that incorporates a special twist to the Fresnel reflection coefficient to account for the scattering effects arising from that rough surface. The findings of our work lays a foundation for further investigation to be conducted in actual cave environment, since the ground surface inside a cave is definitely not smooth but rough.

Ray tracing method has conventionally played an important role in radio propagation modeling, which outputs an estimation of signal strength given certain input parameters. Being a time-honored method, ray tracing is expected to continue to play an important role in next generation propagation modeling. In this paper, we place our focus on a narrow L-shaped structure which oftentimes at first glance appeared simple, yet presents technical complexity that even commercial propagation tool might fail to yield accurate prediction results. The L-shaped structure under scrutiny has a very narrow width, which found its applications in a wide variety of scenarios, ranging from mining and tunnel activities, to speleology and spelunking exploration, and others. Our findings suggest that contrary to what is commonly perceived, in the non-line-of-sight (NLoS) section of the L-shaped structure, reflection turned out to be a very complex propagation mechanism when the width of the structure is very narrow. Instead, diffraction, which in many instances is ignored due to its mathematical complication, emerged as one alternative propagation mechanism that should be explored.