# FD-LTDA-MAC: Full-Duplex Unsynchronised Scheduling in Linear Underwater Acoustic Chain Networks
## 4 Results and Discussion  
Here, we consider simulation results of FD-LTDA-MAC, LTDA-MAC, and LTDA-MAC with FD enabled nodes. The comparison is performed using the frame duration, i.e., the frame duration is time taken to complete transmitting a frame from the beginning of the frame to end of the frame. Where frame is a network digital unit that defines a segment of data on a network or communication link in data-link or physical layer usually consisting of preamble, destination, and sources addresses, data payload, and error-checking information. It is important, because it defines the rate at which each node can send a new sensor reading. It is also important to state here that the frame duration is equal to the inverse of the monitoring rate, in other words, the shorter the frame duration, the higher the monitoring rate.  
Simulated MAC schedules for FD-LTDA-MAC and LTDA-MAC for a 10-hop 2 km pipeline are presented in Figure 7. It shows packet schedules for data transmission and reception in the presence of interference. FD-LTDA-MAC shows, a 44% reduction in the frame duration and packets are still correctly received at the desired destination nodes despite the overlap in time between the transmit and interference packets compared to the LTDA-MAC with HD enabled nodes as can be observed in Figure 7b. This also provides a 10% compression of frame duration against LTDA-MAC with FD enabled nodes presented in [24]. This compression in the frame duration given correct reception of packets in the presence of overlap in time is made possible by the ability of the FD-LTDA-MAC to fully exploit spectrum reuse. In contrast, Figure 7a shows a longer frame duration because the half-duplex nodes do not allow simultaneous in-band transmission and LTDA-MAC lacks the capability to handle full-duplex transmissions. As a result, frame durations and end-to-end packet delays are shorter with the FD-LTDA-MAC protocol compared to the LTDA-MAC protocol with HD enabled nodes and LTDA-MAC protocol with FD enabled nodes scenarios.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Transmit power (Small scale scenarios) & 140 dB re \(\mu\) Pa\({}^{2}\)m\({}^{2}\) \\ Transmit power (Medium and large scale) & 170 dB re \(\mu\) Pa\({}^{2}\)m\({}^{2}\) \\ Noise power & 85 dB re \(\mu\) Pa\({}^{2}\)m\({}^{2}\) \\ \(\tau_{dp}\) (Small/Medium and Large scale) & 200 ms/500 ms \\ \(\tau_{rp}\) (Small/Medium and Large scale) & 50 ms/100 ms \\ \(\tau_{g}\) (Small/Medium and Large scale) & 25 ms/100 ms \\ Acoustic modem range & 1 km/2 km \\ Centre frequency/Bandwidth & 24 kHz/7.2 kHz \\ Acoustic data rate & 640 bits/s \\ Shipping activity factor & 0.5 \\ Wind speed & 10 m/s \\ Interfering link detection threshold & 0 dB SNR \\ Sound speed profile & North Atlantic Ocean SSP \\ Pipeline length (L) & 2 km to 1000 km \\ Number of hops (H) & 2 to 1000 hops \\ \hline
**Scenario** & **Description** \\ \hline Small\_L\_H & Small scale scenario \\ Medium\_L\_H & Medium scale scenario \\ Large\_L\_H & Large scale scenario \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation parameters.  
Figure 8a,b show sections of Figure 7a,b representing a time interval of 1.4-2.5 s involving N3 and N4 nodes. It can be seen that the FD-LTDA-MAC protocol exploits spatial re-use better by scheduling simultaneous in-band transmission and reception, which reduces transmit delays and compresses the overall frame duration, as can be seen as FD gain in Figure 5b. The LTDA-MAC protocol has the limitation of this capability as shown in Figure 5a, this causes waste of resources (time), thus, resulting in longer transmit delays.  
The following subsections discuss the impact of the frame duration enhancement on the monitoring rate and end-to-end packet delays.  
Figure 8: _Cont._  
Figure 7: Simulated MAC schedules for the 2 km 10-hop scenario. Tx: Transmission, Rx: Reception. (**a**) LTDA-MAC [11]. (**b**) FD-LTDA-MAC.