The likelihood of line-of-sight (LoS) is an essential component in any radio channel model. It is particularly useful for radio network planning and urban coverage prediction. Empirical LoS models are hard to derive due to a strong dependency on local topology and the need for large measurement datasets. Since buildings are the major obstructions in a dense urban environment, we propose a new theoretical model to determine the LoS probability for air-toground channels based on local building geometry and knife-edge diffraction theory. The model takes into account key statistical parameters such as building height, building size, building coverage, street width and street angle distribution. The theoretical model is shown to agree well with ray tracing simulation results. The statistical parameters, such as mean building height, percentage of area covered by buildings (building coverage) and building density, can all be easily obtained for a specific location. We also derive equations for the likelihood of LoS for a direct slant path. These equations can be used in the analysis of air-to-ground channels.
Abstract-This paper provides new statistical models for air-toground channels in an urban environment. The model is derived to operate at frequencies from 200MHz to 5GHz. Issues such as path loss and shadowing are evaluated as a function of the elevation angle to the airborne platform, rather than the more usual separation distance used for terrestrial mobile communications. Results demonstrate the advantages of an airto-ground channel for urban communication, and relayed peerto-peer links in particular.
Abstract-Over the years peer-to-peer (P2P) multi-hop relays have been studied for mobile ad-hoc networks (MANETs) to overcome poor signal coverage and to improve connectivity. However, for an urban environment, particularly with a sparse mobile distribution, a ground relay is not able to achieve significant benefits, mainly due to the extremely high pathloss and shadowing encountered. Dedicated airborne relay nodes, at a height of hundreds or thousands of meters, can provide much better coverage, and hence improve the connectivity, decrease the number of hops, reduce the power consumption, and support co-operative relays when integrated into mobile ad-hoc networks. An air node can also act as the sink for current wireless sensor networks (WSNs). Despite these potential advantages, the coverage from an air node located directly above an urban operating environment has not been adequately investigated in the literature. This paper compares the advantages of airborne relaying compared to more conventional peer-to-peer mobile relays. Three channel types are considered, i.e. line-of-sight (LoS), obstructed LoS (OLoS), and non-LoS (NLoS), each with their own likelihood, pathloss, and shadowing models. The practical gain pattern of a hemispheric antenna, or a directional antenna, is also carefully considered for the air node. Comparisons of the air-to-ground (A2G) channel and the mobile P2P channel demonstrate that airborne relays can enhance the coverage and reduce the power consumption significantly.
In order to scientifically evaluate the thermal environment of the deep stope and its influencing factors, research was conducted on the thermal environment in Sanshandao Gold Mine, the theoretical calculations and structural analysis of heat release from 8 types of heat sources in the three sub-levels of -930 m, -945 m, and -960 m were carried out, and quantitative characterization was made on the influential degree of comprehensive heat release on the thermal environment, and it was clear that the heat release from the surrounding rock and mechanical and electrical equipment were the main parts at the deep mining site and the proportion of heat release from other heat sources is basically stable. Then, through the analysis of the influence factors of heat sources in the mining site, 17 evaluation indexes of the influence factors of the mining site thermal environment were sorted out, and the indexes’ weight was calculated based on the entropy weighting method, and it was learned that the largest weight of the influence on the thermal environment factors in a single excavation working face was the water gushing in the roadway. The TOPSIS method was used to comprehensively analyze and rank the thermal damage degree in the three middle sections. The results show that the degree of thermal damage in the -960 m is more severe than that in the -930 m and -945 m. This will provide some basic basis for the evaluation and prevention of thermal damage in deep mining projects, and is of great significance for improving mine production efficiency.
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