In this paper, we introduce a sophisticated path loss model incorporating both line-of-sight (LoS) and non-line-of-sight (NLoS) transmissions to study their impact on the performance of dense small cell networks (SCNs). Analytical results are obtained for the coverage probability and the area spectral efficiency (ASE), assuming both a general path loss model and a special case with a linear LoS probability function. The performance impact of LoS and NLoS transmissions in dense SCNs in terms of the coverage probability and the ASE is significant, both quantitatively and qualitatively, compared with the previous work that does not differentiate LoS and NLoS transmissions. Our analysis demonstrates that the network coverage probability first increases with the increase of the base station (BS) density, and then decreases as the SCN becomes denser. This decrease further makes the ASE suffer from a slow growth or even a decrease with network densification. The ASE will grow almost linearly as the BS density goes ultra dense. For practical regime of the BS density, the performance results derived from our analysis are distinctively different from previous results, and thus shed new insights on the design and deployment of future dense SCNs.
Notions that are similar to LoS and NLoS transmissions have been previously explored in the building blockage study in @cite_1 and the indoor communication network in @cite_10 . @cite_1 , the authors proposed a microscopic performance analysis framework to model the random blockage effect of buildings, and analyze its impact on cellular network performance. Further refinement and verification of the proposed model in @cite_1 is needed, especially to consider reflections which are an important contributor to coverage in urban areas. @cite_10 , the authors present an analytical study of indoor propagation through walls, and showed that the throughput does not scale linearly with the density of small cells. Different from @cite_10 , in this paper, we investigate outdoor dense SCNs.
@cite_10 @cite_1
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Cell splitting frequency reuse is a fundamental characteristic of cellular networks. In macrocellular networks, where pathloss is governed by the distance-to-a-power law, the SINR distribution is invariant to scale, i.e. the spectral efficiency per base (bps Hz base) remains constant, and hence the capacity increases linearly with the density of cells. We show for indoor networks, where signals suffer exponential loss in addition to the inverse square distance law, the median SINR decreases with the density of cells. This results in the capacity being proportional to the square-root of the improvement in the density of cells. Large-scale blockages such as buildings affect the performance of urban cellular networks, especially at higher frequencies. Unfortunately, such blockage effects are either neglected or characterized by oversimplified models in the analysis of cellular networks. Leveraging concepts from random shape theory, this paper proposes a mathematical framework to model random blockages and analyze their impact on cellular network performance. Random buildings are modeled as a process of rectangles with random sizes and orientations whose centers form a Poisson point process on the plane. The distribution of the number of blockages in a link is proven to be a Poisson random variable with parameter dependent on the length of the link. Our analysis shows that the probability that a link is not intersected by any blockages decays exponentially with the link length. A path loss model that incorporates the blockage effects is also proposed, which matches experimental trends observed in prior work. The model is applied to analyze the performance of cellular networks in urban areas with the presence of buildings, in terms of connectivity, coverage probability, and average rate. Our results show that the base station density should scale superlinearly with the blockage density to maintain the network connectivity. Our analyses also show that while buildings may block the desired signal, they may still have a positive impact on the SIR coverage probability and achievable rate since they can block significantly more interference.