# Modeling of Downlink Interference in Massive MIMO 5G Macro-Cell +
## 4 Simulation Studies
### Results for NLOS Conditions  
Due to modeling of the transmission properties of the propagation environment, the 3 GPP simulation test procedure is strictly statistical. On the other hand, the procedure used in the MPM is based on the PDP, which provides the creation of a geometric structure for the determined analysis of propagation paths. The DS (\(\sigma_{\tau}=363\) ns) is the only joint parameter that describes the transmission properties of the environment. Under LOS conditions, the signal arriving at the Rx via the direct path is the dominant component of the received signal. Hence, according to 3 GPP and MPM procedures, simulation tests give us results with a similar set of values and the nature of changes. Under NLOS conditions, the 3 GPP approach gives a statistical estimate of the SIR as a function of the beam separation angle and the distance from the gNodeB. In contrast, the MPM procedure is associated with specific transmission properties of the propagation environment, which define the PDP and constitute one random set of parameters in the 3 GPP procedure.  
For NLOS conditions, we carried out the simulation tests based on the assumptions described in Section 4.1. The obtained results are shown in Figures 9 and 10. Charts in Figure 9 depict the SIRs versus \(\Delta\alpha\) for various \(D\) obtained for (a) the MPM and (b) the 3 GPP model, respectively. The corresponding CDFs of SIR are illustrated in Figure 10.  
Figure 9: SIRs versus angle of beam separation for non-line-of-sight (NLOS) conditions and different distances between UE and gNodeB obtained for the (**a**) MPM and (**b**) 3 GPP model.  
As can be expected, an increase in \(\Delta\alpha\) reduces the DL interference between the reference beam (providing services to the UE) and the interference beam. However, the spreading effect of the propagation environment causes significant angular dispersion in the power of the received signals. This is the reason for an increase in the level of co-channel inter-beam interference, i.e., a decrease in the SIR by about 15 dB in reference to corresponding LOS results. The results obtained in the 3 GPP simulation test process show little differentiation in relation to the EU position. This effect is due to the multiple uses of averaging in the 3 GPP procedure. It consists of a random selection of the transmission parameters of the propagation environment in the next simulation step. The selection randomness of these parameters is limited only by the condition of ensuring a constant the DS value.  
On the other hand, use of the MPM makes it possible to assess the impact of the UE position on SIR changes. In this case, the PDP unambiguously defines the transmission environment parameters that are the basis for determining the MPM spatial structure. Thanks to this, it is possible to map the Rx position in relation to scattering element locations, which determines the individual propagation path trajectories. The simulation test results clearly indicate that estimation of the intra-cell interference and SIR with MPM use demonstrates greater detail in comparison to the 3 GPP channel model [27]. Therefore, the MPM seems to be a reasonable alternative to the commonly used 3 GPP channel model, especially if we want to obtain an assessment for strictly determined PDP.  
It should be highlighted that the 3 GPP model is currently considered a standard in the analysis of 5G systems and beyond. However, this does not mean that the results obtained by this model always faithfully reflect the simulated scenario. This may be due to differences between the modeling approaches, i.e., statistical, stochastic, geometric, or deterministic. Many models in the literature also show divergence from the 3 GPP model, e.g., [41; 42; 43; 44]. The authors of [41; 42] propose models based on empirical measurements carried out in Vienna and New York, respectively, whereas ray-tracing approaches are described in [43; 44]. In the last, differences in the CDFs of the received interference power are shown.