## 4 Simulations
### Impact Analysis of Different Scheduling and Retransmission Techniques on EDETA-e Protocol  
As has been stated before, UWSN suffer from high propagation delays, which can make the traditional TDMA and CSMA medium access techniques inefficient [3]. Scheduling the transmissions allows to avoid collisions and can reduce the propagation delay. However, it is also necessary to introduce an extra time in the schedule to allow the retransmission of the packets in case packet errors occur.  
As mentioned in Section 3, nodes using EDETA and EDETA-e employ a TDMA schedule during the operational phase in order to send their data. Each destination node will send an acknowledgement back to the sender when a packet is correctly received.  
To evaluate the impact of different scheduling and retransmission techniques on the proposed underwater routing protocol, we will consider two different scheduling techniques, (i) the original TDMA schedule of EDETA and (ii) a delay-aware schedule. In order to perform the last one, the CH has to know the delay to its nodes. After that, the CH schedules the packets using the simplified set of schedule constrains proposed by [PERSON] _et al_. in [17].  
We consider three different retransmission techniques. In the first one, a backup transmission is scheduled right after the primary transmission and the node will only use it if there is a packet loss. In the second one a backup transmission is scheduled right after the primary transmission but, in this case, no ACK is sent back to the sender. Therefore, the sender always uses the backup transmission. Finally, in the third one, the transmissions are scheduled only once, however, a CSMA period is scheduled for the nodes to send their data again if there is a packet loss.  
In what follows, we introduce different combinations of the scheduling and retransmission techniques used to replace the simple TDMA scheduling and retransmission technique of EDETA.  
**TAck** is a TDMA schedule with acknowledgement and data packet loss. A TDMA schedule is used by the nodes to send their data and an ACK is sent back when the data is correctly received. Since this schedule is not delay-aware, the slots have to include the maximum propagation time. Each transmission is scheduled two times to provide a backup slot in case of a data packet error occurs.  
Figure 5: Effect of the \(T_{SuperFrame}\) on the network life time.  
**TnoAck** is a TDMA schedule without acknowledgement. A TDMA schedule is used by the nodes to send their data but no ACK is sent back. Hence, the TDMA slot will last for the time needed for the packet transmission and the signal to propagate to the maximum distance.  
**DAck** is a delay-aware schedule with acknowledgement and data packet loss. A delay-aware schedule is used by the nodes to send their data and an ACK is sent back when the data is correctly received. Each transmission is scheduled two times to provide a backup slot in case of a data packet error occurs.  
**DnoAck** is a delay-aware schedule without acknowledgement. A delay-aware schedule is used by the nodes to send their data but no ACK is sent back. Each packet is scheduled to arrive at the destination right after the previous one.  
**DnoAck2** is a delay-aware schedule without Acknowledgement. A delay-aware schedule is used by the nodes to send their data but no ACK is sent back. As explained in the previous section, each packet is scheduled to arrive at the destination right after the previous one but each packet is scheduled and transmitted twice.  
**DCsma** is a delay-aware schedule with acknowledgement and CSMA retransmission period. A delay-aware schedule is used by the nodes to send their data and an ACK is sent back when the data is correctly received. If the ACK is not received because of data packet loss, the node will wait until the CSMA period starts in order to send its data again.