## 4 Analytical Results
Figure 1 illustrates the ABER evolution for single-hop \((N=1)\) or the quad-hop \((N=4)\) LOS THz link configuration over a wide range of transmitted power through a weak turbulent channel with clear, rain or fog weather conditions and moderate air humidity along with the presence of FSPL and strong ZB or NZB pointing errors. It is depicted that for the same transmitted power and water vapor concentration values along with identical turbulence conditions, the weather effects and NZB pointing errors, the single-hop outperforms the quad-hop link configuration in terms of ABER. This is in accordance with other multi-hop configurations in the wider outdoor wireless communications literature [22; 23; 55], while it can be explained by the fact that most of the effects that affect the THz ABER performance such as FSPL, water vapor attenuation and atmospheric turbulence are distance-dependent. Thus, quadrupling the total THz coverage area becomes at the expense of this ABER performance degradation. Additionally, by focusing on single-hop configuration's ABER results, we can observe that higher corresponding ABER values are obtained when NZB pointing errors are considered instead of ZB pointing errors with the same spatial jitter. The latter indicates that as is the case with FSOs [2; 28; 67], the boresight component should not be neglected when stochastic pointing errors are estimated between THz transmitter and receiver terminals. Consequently, our initiative to include NZB pointing errors for THz links alike seems to be reasonable. Furthermore, for each  
Figure 1: ABER vs. Transmitted power for single-hop and quad-hop THz link configurations under different weather conditions, weak turbulence, FSPL, moderate water vapor concentration and strong generalized pointing errors. illustrated configuration, i.e., single-hop with ZB pointing errors, single-hop with NZB pointing errors and quad-hop with NZB pointing errors, three different weather scenarios are depicted, i.e., fog, rain or clear weather conditions. The performance comparison between them reveals that corresponding ABER values under rain are the largest. Likewise, ABER values under fog are slightly larger than their corresponding ABER values under clear weather conditions. This behavior indicates that rain is the most detrimental weather effect for THz signal transmissions while fog slightly aggravates the attenuation of the propagating THz signal. It is worth noting that the latter is qualitatively consistent with the experimental findings in [11; 12; 15; 16; 17]. It should be also recalled here that contrary to THz, the most detrimental weather effect for FSO transmissions is fog due to the comparable size of fog droplets with IR optical wavelengths [78; 12], while conversely, FSO transmissions suffer only slightly from rain. This fact enables THz as a key complementary wireless technology to FSOs, paving the way for the development of hybrid FSO/THz links which will be able to efficiently operate in both rain and fog conditions. Finally, it is shown that higher transmitted power values lead to lower ABER values, as it was expected. Figure 2 illustrates the ABER evolution for single-hop (\(N=\)1) or the quad-hop (\(N=\)4) LOS THz link configuration over a wide range of transmitted power through the same weak turbulence, FSPL, weather and air humidity conditions, but along with the presence of weak ZB or NZB pointing errors this time. The ABER qualitative behavior of Figure 2 is very similar to the one of Figure 1, which further enhances the accuracy of the analysis performed along with the conclusions discussed above. Nevertheless, all the ABER values from Figure 2 are lower than their corresponding ABER values from Figure 1, owing to the weaker amount of pointing mismatch which is assumed in the corresponding configurations of Figure 2. It is also worth noting that the detrimental impact of boresight component is now becoming more evident due to the lower spatial jitter values.