## 4 Simulation Results and Discussion
### Effects of the OIS's Load Ratio on Various Aspects of Performance  
#### 4.3.1 Connection Hold Rate  
Figure 22 shows the performance of the OIS's connection hold rate in relation to its load ratio in various channel environments. It can be seen from Figure 22a that when no fading is employed, the toss-and-catch algorithm performed better than Control Groups 1 and 2 at all OIS load ratios. This is because the OIS of the toss-and-catch algorithm has a higher chance of selecting SBSs (which are mostly MSBSs) with a larger coverage radius, and effective assistance is provided by the overload support mechanism; hence, performance is practically unaffected. Moreover, according to Figure 22a, for Control Group 1, when the OIS load ratio is smaller than or equal to 50%, the connection hold rate declines gradually and slightly in response to increasing OIS load ratios. This can be explained by the score-based selection mechanism, as the OIS has a higher chance of selecting SBSs with a smaller coverage radius and there are gradually less suitable SBS options. On the other hand, when the load ratio of the OIS exceeds 50%, Control Group 1 has a higher chance of selecting SBSs with a larger coverage radius, and there are gradually more SBS options (in comparison with the SBS options when the load ratio of the OIS is equal to 50%), which slightly increases the connection hold rate.  
Figure 22: Comparing the performance of the OIS’s connection hold rate in relation to its load ratio using the three methods in (**a**) nonfading environments; (**b**) Nakagami-3 fading environments; (**c**) Nakagami-1 fading environments; and (**d**) Nakagami-1/2 fading environments.  
In all fading conditions, as seen in Figure 22b-d, the toss-and-catch algorithm also performed better than Control Groups 1 and 2. When Nakagami-3 fading is employed, the degree of fading is marginal, and the toss-and-catch algorithm is practically unaffected, while the performance of both control groups declined significantly by around 10%. This is because the two control groups lacked an overload support mechanism, and there were fewer SBS options, which reduced the chances of the OIS to continuously select an SBS that can undertake its load and thereby decreased the connection hold rate. When Nakagami-1 fading is employed, the degree of fading and its effects increased, thus reducing the assistance provided by the overload support mechanism to the toss-and-catch algorithm and resulting in a marked decline in the connection hold rate. On the other hand, the OISs of the two control groups had even fewer SBS options compared to the toss-and-catch algorithm, and the coverage area was even smaller. Therefore, the two control groups had more significant declines in their connection hold rates in comparison with the toss-and-catch algorithm. For example, as shown in Figure 22c, when the OIS load ratio is 50%, the connection hold rate of the toss-and-catch algorithm decreases by around 20%, while the rates of the two control groups decreases by around 30%. When Nakagami-1/2 fading is employed, severe fading had occurred in the channels, which largely reduced all three methods' effective signal coverage of the track paths, and hence, the connection hold rates decreased significantly. This is because under this fading condition, there were very few SBS options for the OISs of all three methods, and the overload support mechanism of the toss-and-catch algorithm had no effect whatsoever. Nevertheless, the connection hold rate of the toss-and-catch algorithm remained two times higher than those of the two control groups, which can be attributed to the fact that the MSBSs of the former were in super mode and the SBSs were selected through the score-based selection mechanism. Therefore, the toss-and-catch algorithm still performed better than the two control groups.