Interference analysis of the device-to-device communications model with regard to a signal propagation environment

Modern dense 4G and 5G networks allow placing a wireless access point in every indoor location to optimize wireless coverage. The paper analyzes the signal-to-interference ratio (SIR) for wireless systems operating in adjacent premises, and takes into account the loss of signal power during penetration of a signal through different environments. As analytical formulas for SIR are cumbersome, two approximations of the probability density function of interference are developed: an analytical expression for the total interfering signal in the form of the normal distribution and a three-parameter hyperexponential distribution with numerically assorted parameters for simulation of the interfering signal from each device. As a result, the last one gives the most accurate approximation, which can be used for lower-bound estimation of SIR. The authors analyzed SIR in the case of the uniform distribution of devices in the premises of the rectangular shape for five wall materials (glass, brick, concrete, masonry blocks, and reinforced concrete) and varying wall thickness, and found that the presence of walls between rooms fundamentally changes the structure of SIR density.