# Cooperative Communication Based Protocols for Underwater Wireless Sensors Networks: A Review
## 5 Numerical Results
### Physical Layer Cooperative Communication Performance  
The first part of the analysis concerns the bit error rate (BER) performance considering a communication scenario like that one in Figure 3, including source, destination and a cooperative relay node. The link distance between source and destination has been set to 300 m, with the transmission being performed according to binary phase shift keying (BPSK). Regarding the relay position, we consider three cases, described as follows:  
* Case A: relay located 100 m from the source and 200 m from the destination;
* Case B: relay located at half way, that is 150 m from the source and 150 m from the destination;
* Case C: relay located 200 m from the source and 100 m from the destination. In Figure 5, we compare the performance of AF and DF mechanisms for the mentioned collaborative relay scenarios. Specifically, for both AF and DF we simulated the transmission of a \(10^{6}\) BPSK symbols over a noisy channel. The carrier frequency has been set to 20 kHz and the transmission bandwidth to 12 kHz, since representing typical working \begin{table}
\begin{tabular}{c c c} \hline \hline
**Authors** & **Year** & **Protocol/Strategy Type** \\ \hline [PERSON] and [PERSON] [45] & 2017 & Network nodes self-organization \\ \hline [PERSON] et al. [46] & 2020 & Clustering and AF-based nodes cooperation \\ \hline [PERSON] et al. [47] & 2020 & Energy optimization oriented clustering \\ \hline [PERSON] et al. [48] & 2015 & Clustering and AF-based nodes cooperation \\ \hline [PERSON] et al. [49] & 2022 & AF-aided sink mobility based routing \\ \hline [PERSON] and [PERSON] [50,51] & 2019 & DF-TDMA-based channel-aware cooperative routing \\ \hline [PERSON] et al. [52] & 2019 & Sink mobility based routing \\ \hline [PERSON] et al. [53] & 2018 & AF-aided energy efficient routing (nodes location unaware) \\ \hline [PERSON] et al. [54] & 2018 & Depth-based vertical routing (nodes location unaware) \\ \hline [PERSON] et al. [55] & 2019 & Sink mobility based vertical incremental cooperative routing \\ \hline [PERSON] et al. [56] & 2017 & Cooperative opportunistic routing \\ \hline [PERSON] et al. [57] & 2021 & Vertical cooperative opportunistic routing \\ \hline [PERSON] et al. [58] & 2017 & Fuzzy logic-based cooperative opportunistic routing \\ \hline [PERSON] et al. [59] & 2021 & Data priority and energy efficiency oriented cooperative routing \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of network layer protocols and strategies presented in the literature. parameters of commercial acoustic modems and considered in other works [60]. Each node transmit power is set to 1 W. Regarding AF, the signal received by the relay node is first band-pass filtered to remove the noise component out of the signal bandwidth. Then, before forwarding, the physical signal is amplified to match with the maximum amplitude dynamics allowed by the node transmit power. Finally, at the destination node, the received signal is once again first band-pass filtered. Demodulation is performed based on well known matched filtering, and the decision on the received symbol is taken following the maximum likelihood criterion. In DF case, simulation is essentially performed following the same steps, even though at the relay node the signal is first demodulated based on matched-filtering and then re-encoded before being forwarded to the destination. At destination, the BER is calculated as the ratio between the number of wrongly decoded bits and the total number of transmitted bits. Note that, with the employed BPSK modulation encoding one per symbol, we have that BER corresponds also to the symbol error rate. We consider different values of nodes transmit power, so BER is measured as a function of the SNR per bit \(E_{b}/N_{0}\) referred to the direct link between source and destination. By observing the curves it is possible to appreciate that, in general, DF outperforms AF.