# Exploiting Outage and Error Probability
## 4 Simulation Results and Discussions
### Performance Trade-offs  
In this section, trade-offs (the cost at which the performance metrics are achieved) of the proposed protocols are discussed (refer to Table 3).  
ACE achieves more throughput by compromising on the network lifetime. Figures 8 and 9 demonstrate the decrease in lifetime and increase in energy consumption of the network respectively. In case of direct transmission failure, retransmission from the relay nodes causes increased energy consumption thereby reducing network lifetime. It can be clearly seen that when throughput is maximum in the initial seconds (see Figure 10), the energy consumption is more than double of EEDBR protocol. This is because transmission energy is used once or twice more for retransmission of data. After 230 s, when more than 100 nodes are dead in ACE (Figure 8), throughput is decreased, hence energy consumption is also decreased. Later on, energy consumption of ACE is almost similar to EEDBR and CARQ with throughput less than EEDBR. Decrease in throughput is due to less number of alive nodes to carry data to sink.  
E-ACE achieves throughput and reliability at the cost of reduced network lifetime. The reduction in network lifetime is due to increased energy consumption; retransmissions in case of direct transmission failure. Before 230 s (Figure 9), Relay transmissions are activated whenever direct transmission fails to achieve an acceptable BER, that is why, energy consumption of E-ACE is almost twice as compared to EEDBR (refer Figure 10). Later on, EEDBR and CARQ outperforms E-ACE (refer Figure 12) because they have more alive nodes to carry data to sink. Thus, we can say that E-ACE has less throughput and packet acceptance ratio than EEDBR, however, at the cost of more energy consumption. Reason behind this observation is that nodes decay rate of EEDBR is very slow as compared to E-ACE. Therefore, energy required by all the nodes for single transmission in EEDBR is almost equal to energy required for cooperative retransmissions in E-ACE.  
In both protocols, throughput is increased at the price of increased time delay. Cooperative diversity is implemented in time division channel. Source node broadcasts to destination and relay nodes in first phase. In case of direct transmission failure, first retransmission is performed by the retransmission node in the second phase, thus adding more delay. If it is again not acceptable, next retransmission is performed in the third phase, adding another delay, and so on. Therefore, more number of retransmissions enhance reliable reception, however, at the cost of surplus delay.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Protocol** & **Achieved Performance Parameter** & **Cost Paid** \\ \hline E-ACE & Highest throughput, least packet drop, & Highest delay, short network lifetime, \\  & highest reliability. & high energy consumption, high complexity. \\ \hline \multirow{2}{*}{ACE} & High throughput, less packet drop, & High delay, short network lifetime, \\  & high packet acceptance ratio, high reliability. & high energy consumption, complexity. \\ \hline \multirow{2}{*}{EEDBR} & Low throughput, low reliability, & Low delay, long network lifetime, \\  & high packet drop. & less energy consumption, low complexity. \\ \hline \multirow{2}{*}{CARQ} & Medium throughput, medium reliability, & Low delay, short network lifetime, \\  & medium packet drop. & high energy consumption, medium complexity. \\ \hline \hline \end{tabular}
\end{table}
Table 3: Performance trade-offs for ACE and E-ACE.