## 5 Experiments with Frame Aggregations  
In this section, we evaluate the performance of the proposed MAB algorithms when the frame aggregation and multiple spatial streams are available. For this, we use the IEEE 802.11 ax standard that is recently developed to achieve high efficiency in wireless networks \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Moving away** & **Moving toward** & **Average** \\ \hline KL-UCB & +30.4\% & +36.2\% & +36.3\% \\ Thompson sampling & +10.9\% & +6.6\% & +8.8\% \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Performance improvements in IEEE 802.11g networks. Figure 4: (a) Average of the final application throughputs when the sender moved away from the receiver, (b) average of the final application throughputs when the sender moved toward the receiver in IEEE 802.11g networks. (it is also known as the high-efficiency (HE) standard). The IEEE 802.11 ax standard can support the frame aggregation using A-MPDU and A-MSDU. However, we considered only A-MPDU in the experiments because A-MPDU is known for performing better than A-MSDU, particularly in high packet error rate situations [40]. This is primarily because A-MPDU can selectively acknowledge successfully delivered packets among the aggregated packets transmitted as a single frame. For the experiments described in this section, we set the A-MPDU size to 65,535 bytes, which is the maximum size in the ns-3 version we used for the experiments. When the A-MPDU frame aggregation is enabled, in addition to the BAck and BAckR frames, several control frames are also used. They are add block acknowledgment (AddBA) request/response frames and delete block acknowledgment (DelBA) frames [15]. These control messages are exchanged between a sender and receiver to manage aggregated packet transmission sessions. Among these control messages, we control the MCS levels of BAckR frames as if they were data packets and their transmission results are used in the proposed MAB algorithms. This is because the BAckR frames play an important role in the frame aggregation particularly when the packet error rates are high. For this, we modified the ns-3 implementation to make the sender adjust the MCS levels of BAckR frames in the same way as it does for the data packets when the sender adopts the proposed MAB algorithms. In addition, the IEEE 802.11 ax standard supports multiple spatial streams (i.e., multiple links) between a sender and receiver. Therefore, wireless nodes can use the MIMO technology if they are equipped with multiple antennas in the IEEE 802.11 ax standard. According to the standard, there are 12 possible MCSs for each combination of the bandwidths and guard intervals. Although the IEEE 802.11 ax standard supports up to eight spatial streams, for simplicity, we assume that wireless nodes can be equipped with maximum two antennas each, such that they can use the \(2\times 2\) MIMO mode in addition to the \(1\times 1\) SISO mode. By fixing the bandwidth to 20 MHz and the guard interval to 800 ns, senders can choose one MCS and the number of spatial streams to be used for each frame transmission. Thus, in our experiment setting, \(K=24\) if \(2\times 2\) MIMO mode is available and the set of all the corresponding data transmission rates is [8,6, 17.2, 25.8, 34.4, 51.6, 68.8, 77.4, 85.0, 103.2, 114.7, 129.0, 143.4, 17.2, 34.4, 51.6, 68.8, 103.2, 137.6, 154.9, 172.1, 206.5, 229.4, 258.1, 286.8] Mbps. However, if each wireless node is equipped with only one antenna, \(1\times 1\) SISO mode is used. In this case, \(K=12\) and the set of all the corresponding data transmission rates is [8,6, 17.2, 25.8, 34.4, 51.6, 68.8, 77.4, 85.0, 103.2, 114.7, 129.0, 143.4] Mbps. Except for the IEEE 802.11 ax standard, we used the same wireless network environments as we used for the experiments with the IEEE 802.11g standard described in Section 4. Specifically, we used the same path loss model (i.e., Equation (6)) with the same parameters. We used the same packet error probability model (i.e., NIST error rate model) for the packet error rates.