## 4 Direct Cooperation via In-Band Energy Level Patterns
### Enhanced LTE LAA  
Cooperation techniques among LTE and Wi-Fi can further enhance the current coexistence techniques such as LTE LAA, providing improved use of the available spectrum towards an enhanced user experience. 3 GPP has introduced four different channel access priority classes for DL LTE LAA. Table 2 shows the different priority classes, where the smaller the number of the class, the higher the priority. This table is defined in the 3 GPP specifications describing the channel access procedure for LTE LAA [15]. As can be seen from the table, each priority class uses different T\({}_{\rm{m\,cot,p}}\), which refers to the maximum channel occupancy time for priority class p. For the priority Classes 3 and 4, T\({}_{\rm{m\,cot,p}}\) is 10 ms if the absence of any other co-located technology sharing the same spectrum band can be guaranteed on a long-term basis. In a different case, it is limited to 8 ms. According to the LTE LAA standards, an eNB cannot continuously transmit in the unlicensed spectrum for a period longer than T\({}_{\rm{m\,cot,p}}\). On the other hand, when frame aggregation is not used, Wi-Fi transmits only one packet when it gains access to the medium performing CCA. A Wi-Fi packet transmission typically lasts a few hundreds of \(\mu\)s. It is clear that the ratio among LTE and Wi-Fi channel occupancy is not balanced. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Channel Access Priority Class (p)** & \(\mathbf{m}_{p}\) & \(\mathbf{CW}_{\text{min}p}\) & \(\mathbf{CW}_{\text{max}p}\) & \(\mathbf{T}_{\text{m\,cot,p}}\) & **Allowed CW\({}_{\text{p}}\) sizes** \\ \hline
1 & 1 & 3 & 7 & 2 ms & 3, 7 \\
2 & 1 & 7 & 15 & 3 ms & 7, 15 \\
3 & 3 & 15 & 63 & 8 or 10 ms & 15, 31, 63 \\
4 & 7 & 15 & 1023 & 8 or 10 ms & 15, 31, 63, 127, 255, 511, 1023 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: LTE LAA channel access priority classes. Figure 9: Enhanced CSAT flowchart. To render LTE LAA fairer for Wi-Fi, we propose a scheme according to which LTE will transmit using an adaptable maximum channel occupancy time. Moreover, a variable mute period of LTE-LAA after a transmission can also be introduced, as is depicted in Figure 10, in order to avoid consecutive LTE burst transmissions. The proposed scheme can be further enhanced by introducing cooperation using in-band energy level patterns. In this case, a Wi-Fi or an LTE network can announce its presence by transmitting a corresponding identification special energy pattern. This way, an LTE network will be informed about the presence of other LTE or Wi-Fi networks. LTE can use this information to select and adjust both the burst duration and the mute period. The decision of the channel occupancy time and the length of the mute period will be made based on a combination of parameters. One important parameter is the number of present Wi-Fi and LTE networks, which have been identified by an identification special energy pattern. This information can assist LTE to keep a balance of channel occupancy in time. Another important parameter that can further enhance this balance is the channel utilization during the silent periods of LTE, meaning the backoff period and the LTE mute period. The LTE must continuously sense the medium to identify the amount of transmitted traffic. Then, it can decide the maximum transmit duration and the length of the mute period. The type of traffic, such as delay-sensitive traffic, can be part of the decision. However, delay-sensitive traffic can be transmitted via the licensed anchor if the unlicensed channel utilization is high. Hence, a quiet channel will result in a short or zero mute period and a high channel occupancy time. On the other hand, an active channel will result in a higher mute period and a shorter occupancy time. It is clear that the algorithm that controls the LTE transmission duration and the LTE mute period is critical. As a first approach, the LTE network can use a slow start type of algorithm.