## 3 Co-Channel Coexistence Mitigation Methods
### M\({}_{\text{C}}\)-Preamble Brief description  
In the M\({}_{\text{C}}\)-preamble, the superframes are known only by V\({}_{\text{NR}}\). With this method, as illustrated in Figure 4, an IEEE 802.11p preamble is added at the beginning of each NR-V2X transmission to inform the V11p that the channel is occupied for a given duration (up to 10 ms using the standard preamble). Please note that the \"IEEE 802.11p preamble\" here is actually the \"preamble field\" + \"signal field\" in the physical layer protocol data unit (PPDU) format; the information of the packet length is included in the signal field [17]. The preamble uses a 10 MHz channel and lasts 40 us. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Numerology** & **TTI Duration [ws]** & **TOPDM [ws]** & **Fitting Preamble** & \(\mathbf{v2\times T_{\text{OFDM}}}\) **[ws]** & **Fitting Preamble** \\ \hline
0 & 1000 & 71.4 & ✓ & 142.9 & ✓ \\ \hline
1 & 500 & 35.7 & ✗ & 71.4 & ✓ \\ \hline
2 & 250 & 17.9 & ✗ & 35.7 & ✗ \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Options for the numerology of 5G NR-V2X in FR 1 and number of symbols required to allocate the IEEE 802.11p preamble. Figure 3: Illustration of M\({}_{\text{B}}\)-E-signals, only V\({}_{\text{NR}}\) know the superframe structure and they would transmit 3 types of energy signal during the idle TTI, just before S\({}_{\text{NR}}\), and at the 14 th OFDM symbol in each TTI to inform V11p the S\({}_{\text{NR}}\) is busy. The subfigure (**a**) is from the V\({}_{\text{NR}}\) perspective, and the subfigure (**b**) is from the V\({}_{\text{11p}}\) perspective. For the transmission of the preamble, the gap before each transmission and the first OFDM symbol can be used; the first OFDM symbol, in fact, carries a copy of the second symbol and is used for automatic gain control (AGC), thus using it does not reduce the data rate of NR. The IEEE 802.11p preambles added to each NR-V2X packet are identical. Thus, given the OFDM properties, multiple preambles sent in the same TTI by different VNR are treated by the generic receiver as a single signal affected by multi-path. ConfigurationsThis method can be implemented with a static or dynamic slot configuration. As discussed in [10], the static configuration performs similarly to the eM\({}_{\text{A}}\)-time-split, thus in this paper we only consider the dynamic configuration (hereafter called dMC-preamble) where each of the VNR estimates the NR slot \(T_{\text{NR}}\) locally, based on the perceived technology percentage. The perceived technology percentage can be derived by VNR for example from the equation  
\[\text{Tech}_{\%}=\frac{\text{CBR}_{\text{NR}}}{\text{CBR}_{\text{NR+11p}}} \tag{1}\]  
where CBRNR is the channel occupation measured only considering the NR-V2X signals, and CBRNR+11p is measured considering also the other signals, as suggested in [4] and used hereafter. The PHY header always indicates 1 TTI, which is dependent on the numerology, to cope with different possible estimations of the slot duration. The time assigned to the SNR and S11p/bd cannot be less than 5 ms [4]. Modifications requiredThis method does not require any change to IEEE 802.11p. NR needs instead to be modified to include the IEEE 802.11p preamble (reported in Table 2) and the technology proportion estimation. At the same time, it can be noted that the preamble is always the same, thus it can be implemented as a fixed sequence of IQ samples, and the technology proportion may not be required if a static or controlled configuration is used. Implications of NR instead of LTEIt is worth noting that the preamble needs at least a 40 us time space to be inserted. As shown in Table 3, the time period that can be inserted is different depending on the numerology. With numerology 0, which corresponds to the LTE, it is possible to transmit the preamble within either the gap or the first symbol. With numerology 1, both of them (71.4 us in total) need to be used. Finally, with numerology 2 one additional symbol is needed, with an impact on the NR data rate.