## 3 Routing Protocols for UWSN
### Protocols Facturing Node Mobility
#### 3.1.3 Cooperative Depth Based Routing (CoDBR)  
Incorporating co-operation with an existing routing protocol called DBR, a unique scheme called cooperative DBR (CoDBR) has been proposed by [PERSON] et al. The main aim of this protocol is to improve reliability and throughput [54]. In DBR, a source node broadcasts the data to its neighboring node. These neighboring nodes compare their depth with their respective previous hop distance and a forwarder is selected on the basis of minimum depth. By recursion of this depth based single link procedure, eventually data from source reaches to the surface sinks by multi-hop. But this technique is prone to high bit error rate and low reliability due to multi-path fading, noisy underwater environment and hindrance posed by marine life. So, authors suggested Cooperative Path diversity via multiple paths to subdue this problem in CoDBR. CoDBR is also a localization free protocol like DBR which only needs to know the depth of the sensor nodes. Every node has the depth information of their neighboring nodes. A source node compares the depth of its neighboring nodes and the node with the minimum depth is selected as the destination for the next hop. The nodes with the second and third lowest depth are selected as relay node. CoDBR has two phases--(1) path setup (2) data transmission. A cooperative multi hop path is established from source to the sink in the first phase. Data transmission in Co-DBR is explained by Figure 5.  
All the black and blue nodes of the figure take part in the data transmission whereas the gray nodes remain idle. Node 1 is the source and it sends the data to the node 2 as next hop. The blue nodes relay the same data from node to the node 2. This improves the reli  
Figure 5: Data transmission in Cooperative Depth Based Routing (CoDBR) [54]. bit error rate of the transmission. If the sink is within the range of the source node, then the sink becomes the next hop destination. If the sink is not within the range of the source then, source node selects next hop destination from its neighbor on the basis of the lowest depth recursively until the source node finds the sink as its next hop destination. Moreover, in both the cases two relay nodes are selected for simultaneous transmission of the same data to the destination. In data transmission phase, data is transmitted to the sink through multi hop paths which was established in path setup phase. Source node broadcasts its data to the next hop destination node and relay nodes. Relay nodes employ Amplify and Forward (AF) technique to deliver the received data to next immediate destination. Relay nodes do not forward their own sensed data rather they only amplify the data received from the source and send it to the next destination. Upon receiving these three independently faded copies of data at the next hop destination node are merged together by maximal ratio combining technique. If the Bit Error Rate (BER) of the received data crosses the threshold value T, the data packet is simply dropped. T is the maximum allowable Bit Error rate. This is done recursively until the data from the source reaches the sink. As a two relay node also transmits along with the source node, CoDBR has the higher reliability than DBR but the energy consumption of CoDBR is higher than that of DBR. It leads to shorten the network life of CoDBR significantly. In comparison with DBR, it offers 83% more throughput and 90% less packet drop. But due to relay nodes it incurs higher power consumption and higher delays. This trade off must be considered to get higher reliability. Its data delivery ratio can be improved further, if the destination node asks for re-transmission, in case the BER of the received data crosses the threshold value instead of just dropping the data. This will improve packet delivery ratio and throughput as well. It is also noticeable that relay nodes do not send their own data to the destination at a time in one round.