# Cross-Technology Interference-Aware Rate Adaptation in Time-Triggered Wireless Local Area Networks
## 3 CTI-Aware Rate Adaptation Framework  
### Overview of the CARA Framework  
This paper aims to mitigate performance degradation caused by CTI when WLAN devices operate in a time-triggered communication framework without direct communication with CTI-causing devices. The scenario where APs and STAs in a time-triggered WLAN are affected by CTI is illustrated in Figure 1. When \(N\) STAs engage in time-triggered communication with an AP under access time management, they may experience CTI from devices operating in the same frequency band at specific times, using various wireless technologies. In this scenario, each STA is allocated a time duration, \(T_{slot}\), during which it can transmit packets for low-latency communication. In the 2.4 GHz ISM bands, various devices such as ZigBee, Bluetooth devices, and non-communication devices like microwave ovens operate; we represent them as CTI-A, CTI-B, and CTI-C, respectively. Each device exhibits different interference patterns depending on the type of wireless technology it uses, as shown in Table 1.  
The proposed framework to achieve the interference mitigation objective (RQ1) in the given network environment is shown in Figure 2. This framework performs CTI \begin{table}
\begin{tabular}{l l l l} \hline \hline  & **Time Domain** & **Frequency Domain** & **Power Domain** \\ \hline \multirow{3}{*}{WLAN [34]} & \multirow{3}{*}{Max 5.5 ms wavelength} & 2400\(\sim\)2480 MHz, & \multirow{3}{*}{Max 100 mW} \\  & & 14 channels, & (20 dBm) \\  & & 20 MHz BW & \\ \hline \multirow{3}{*}{Bluetooth [35]} & 0.625 μs slot, & 2400\(\sim\)2480 MHz, & \multirow{3}{*}{100 mW (20 dBm)} \\  & 1600 hops/s, AFH & 79 channels, & 2.5 mW (4 dBm) \\  & & 1 MHz BW & 1 mW (0 dBm) \\ \hline \multirow{3}{*}{ZigBee [36]} & \multirow{3}{*}{Max 5 ms wavelength} & 2400\(\sim\)2480 MHz, & \multirow{3}{*}{1 mW} \\  & & 16 channels & (0 dBm) \\ \hline \multirow{3}{*}{MWO [37]} & \(\sim\)5 ms On, \(\sim\)15 ms Off & \multirow{3}{*}{2450\(\sim\)2465 MHz} & \multirow{3}{*}{60 dBm} \\  & repeat 60 Hz & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Features of wireless technologies. Figure 1: Cross-technology interference in time-triggered WLAN. identification (addressing RQ2) and uses the identified information to enable CTI-aware rate adaptation (addressing RQ3). Each STA transmits a WLAN packet during its allocated slot duration, and the AP receives radio frequency (RF) signals from the STAs. The received signal waveform reflects interference effects due to CTI. Through a CTI identification process, the AP distinguishes signals generated by other devices operating in the same band and estimates their interference strength. Based on this information, and considering the CTI patterns mentioned earlier, the AP projects the CTI occurrence times for each device and performs CTI-aware rate selection. Finally, the rate selection results, which account for the impact of CTI, are fed back to each STA via modulation and coding scheme (MCS) feedback messages [34], guiding the STAs to adjust their rate control to mitigate performance degradation due to CTI. To better understand the operation and effectiveness of the framework, we examine a simple scenario in Figure 3a,b, illustrating cases where our framework is not applied and when it is applied. In this scenario, WLAN STAs sequentially transmit uplink data to the AP during each time-triggered interval. In this scenario, CTI-A periodically generates interference every six slots. As shown in Figure 3a, when STA-2 transmits a packet to the AP in the first slot (\(t_{1}\)-\(t_{2}\)), the signal is subject to interference from CTI-A. The AP measures the SNR of the received packet and detects a low SNR. Consequently, it sends feedback to STA-2 via an MCS feedback message, instructing it to lower its transmission rate (Rate \(\downarrow\)). Following this feedback, STA-2 transmits packets at a reduced rate during the second slot (\(t_{4}\)-\(t_{5}\)), but this time, there is no interference from CTI-A during the slot.