## 5 Performance Evaluation
### Single-Spot Deployment Scenario
#### 5.1.1 Throughput Gain of MLO  
First, we consider one MLD deployed with various numbers of overlapping BSSs (OBSSs) with legacy SLDs. The MLD is contending on both link 1 and link 2. OBSSs are added to each of the links at the same time, i.e., one OBSS means one legacy BSS on link 1 and link 2. The performance gain of MLO is evaluated in terms of throughput enhancement.  
The throughput performance results of MLO using different channel access schemes with coexisting legacy devices are presented in Figure 18. In the case with the STR capability, as shown in Figure 18a, the throughput of MLO is approximately double that of SLO (the legacy-only case) when a single MLD system exists with no legacy devices (STAs). However, with coexisting legacy devices, the throughputs under Sync and Sync-PL are greatly reduced. Sync fails to provide TXOPs on either link and shows a throughput lower than that in the legacy-only case. Under Sync, the existence of one link occupied by transmission involving other devices can severely affect performance because it can cause the Sync process to become stuck in the step of repicking the backoff counter because of busy channels. Sync-PL achieves performance close to the legacy-only case since its TXOPs  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Value** \\ \hline Frequency & 5 GHz \\ \hline Number of links per MLD & 2 \\ \hline Channel bandwidth of a & 80 MHz \\ link & \\ \hline Total number of devices & Single-spot: 1–11, 4, [8, 16, 40, 80, 160] \\  & Indoor random: [8, 16, 40, 80, 160] \\ \hline MCS & Single-spot: 7 (680.6 Mbps) \\  & Indoor random: Adaptation (0\(\sim\)9) \\ \hline Traffic generation & Full buffer \\ \hline Max aggregation size & 64 MPDUs \\ \hline MPDU size & 1500 bytes \\ \hline Slot length & 9 μs \\ \hline SIFS & 16 μs \\ \hline DIFS & 34 μs \\ \hline CWmin & 16 (32 for set B) \\ \hline CWmax & 1024 (2048 for set B) \\ \hline Tx power & 18 dBm for both AP and user device \\ \hline Energy detection threshold & \(-\)62 dBm \\ \hline Preamble detection threshold & \(-\)82 dBm \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation parameters.  
Figure 17: Coexistence evaluation scenario.  
are limited by the contention on the primary link. However, the other access schemes still show higher throughput than the legacy-only case, implying that MLO can significantly increase throughput performance. Async without power leakage always achieves double throughput due to the independent transmissions on both links. Sync-FT shows similar performance as Async because of its ability to allow fast transmission when a multi-link TXOP is available. While the other variants of Sync-FT show similar performance to each other, Sync-FT-Repick + Comp shows decreasing throughput as the number of legacy STAs increases.  
Figure 18b shows the throughput performance without the STR capability. The extent to which Sync-FT suffers from power leakage is limited, and it becomes the best scheme. The variants of Sync-FT show similar performance trends as in the case with the STR capability. Async suffers from power leakage and achieves limited throughput, especially in the case of an EHT system alone. This means that Async fails to fully exploit the benefits of MLO with power leakage. As the number of legacy STAs increases, the performance gap between Async and Sync-FT decreases, showing that its throughput is predominantly limited by contention in this case. As in the case without power leakage, Sync and Sync-PL still suffer in the presence of legacy STAs.