# Handover-Driven Interference Management for Co-Channel Deployment of Femto- and Macro-Cells
## 6 Performance Evaluation
### Numerical Results
Figure 8: Probability distribution of users’ achieved SINRs under various numbers of macrocell and femtocell users when the range control is considered (the target SINR of macrocell users and that of femtocell users are \(-\)5 dB and 5 dB, respectively). Figure 6: Probability distribution of users’ achieved SINRs under various numbers of macro- and femtocell users when handovers are not considered (the target SINR of macrocell users and that of femtocell users are \(-\)5 dB and 5 dB, respectively). Figure 7: Probability distribution of users’ achieved SINRs under various numbers of macrocell and femtocell users when the per-user handover control is considered (the target SINR of macrocell users and that of femtocell users are \(-\)5 dB and 5 dB, respectively). Next, the effect of the target SINR is studied. The corresponding simulation results are plotted in Figure 9 when \(M=30\) and \(F=30\). According to the considered power control mechanism described in Equation (4), the transmitting power of a user is proportional to his target SINR. Thus, it is clear that a higher target SINR will generate a larger interference and thus degrade the performance of the users having insufficient room to increase their transmit power. However, a change in macrocell users' target SINR and a change in femtocell users do not result in the same level of performance degradation. When the target SINR of macrocell users is changed from \(-5\) dB to \(0\) dB, some macrocell users achieve better SINRs (due to the increased target SINR) and others achieve lower ones, but femtocell users are unaffected. This is because macrocell users are likely to experience larger path losses to their serving cells (either macro- or femtocells) than femtocell users and thus, they are less robust against interference. Figure 9: Probability distribution of users’ achieved SINRs for (macrocell users’ target SINR (dB), femtocell users’ target SINR (dB)) (\(M=30\), \(F=30\)). Two different handover options in the per-user control are investigated in Figure 10 (\(M\) = 50, \(F\) = 100): (1) allowing macrocell-to-femtocell (inbound) handovers of macrocell users only; and (2) allowing femtocell-to-macrocell (outbound) handovers of femtocell users as well. Most femtocell users are expected to be better served by femtocells, since they may experience smaller wall losses to their own femtocells (as can be inferred from the considered channel models). However, it is also probable that some femtocell users, when handed over to a macrocell, achieve better SINRs if they happen to be closer to a macro BS or their serving femtocells experience significant interference from nearby macro- and femtocell users. Accordingly, as shown in the figure, allowing outbound handovers makes a slight improvement of users' performance. However, this phenomenon is difficult to observe when the level of interference is low due to a small number of users. Finally, the number of handovers is shown for different schemes in Figure 11 (\(M\) = 30, \(F\) = 50). The range control triggers a large number of handovers at the first iteration, thus incurring significant handover overhead at once. Thanks to the finer control granularity, HO-FIM triggers a smaller number of handovers at each iteration, which even decreases over iterations. HO-FIM with inbound handovers triggers an even smaller number of handovers, but at the expense of reduced performance gain (as seen in Figure 10).