## 3 Proposed Quality of Service Routing Protocol (QoSRP) in UWSNs
### Underwater Acoustic Channel Detection (UWCD) Algorithm
#### 3.2.2 Distributed Cooperative Sensing (DCoS)  
In the UWCD scheme, the local channel detection made by the individual \(\mathcal{SU}\) for the desired capacity-aware channel is preferred. However, the high underwater noise, fading, and interferences have destructive effects caused by imperfect reporting channels on the wireless link quality leading to poor cooperative spectrum sensing in the network. This problem becomes more severe between the sender and the receiver secondary users due to an increasing probability of errors over the reporting channels of the transmitted signal in the network. Therefore, finding a channel with high data rates become more difficult in local spectrum sensing in UWEs. To this end, the distributed cooperative sensing (DCoS) provides better results in highly dynamic UWEs. The \(\mathcal{SU}_{\delta}\) in the proposed DCoS architecture performs the channel sensing tasks on demand only if the required capacity-aware channel is not found locally by the \(\mathcal{SU}\). To do so, the \(\mathcal{SU}\) that requires the channel information sends multicast request messages to its neighboring ASNs. The request message includes the required channel information, identity, and location information in the network. Upon receiving the request message, the neighboring \(\mathcal{SU}_{\delta}\) start to sense the required channels and share their channel detection statistics by exploiting the spatial diversity in the observations. Thus, each \(\mathcal{SU}\) based on its local sensing observation exchanges decision on the existence or non-existence of the primary signals in the UWSNs.  
The receiver \(\mathcal{SU}\) combines the received sensing information with its own information and after some necessary calculations makes an ultimate decision whether the \(\mathcal{PU}\) is active or not in the network. This decision information is disseminated to each sender \(\mathcal{SU}_{\delta}\) in the network. This combined decision mechanism significantly improves the performance of channel detection and relaxed sensitivity requirements for the \(\mathcal{SU}\) in the network. Thus, each receiver \(\mathcal{SU}\) acts as a fusion center as shown in Figure 2. In Figure 2, a \(\mathcal{SU}_{\ell}\) that requires a specific channel/s information sends a request message to its neighboring nodes. The neighboring \(\mathcal{SU}_{\delta}\) after successfully receiving the request message start to observe the channel activity in the network. Then each \(\mathcal{SU}\) based on local observation decides the presence or absence of the primary signal and forwards its final decision to the request \(\mathcal{SU}\) by considering the CSMA mechanism in the MCASNs. The selected \(\mathcal{SU}_{\delta}\) perform channel detection in a group manner in a way such that if required then more than one channel are sensed in parallel in every sensing interval as shown in Figure 2. During the information exchange process, an acknowledgment message is forwarded by the receiving node, which guarantees that the information has been received successfully.  
This mechanism significantly reduces the cooperation overhead in terms of latency for searching an appropriate spectrum since multiple channels are sensed in a single sensing interval. Moreover, it also significantly minimizes the network implementation cost by eliminating the need for centralized intelligent devices in the UWSNs. In addition, the fusion mechanism improves the robustness of the decision-making process at the fusion node on the presence or absence of \(\mathcal{PU}s\) in UWSNs. The cooperative decentralized parallel channel sensing architecture of our proposed scheme is indicated in Figure 3. It illustrates that different \(\mathcal{SU}s\) observe the designated channel/s and each of them makes an individual decision and forwards its one-bit decision to the fusion center in a parallel manner in UWSNs.