# A Fair Cooperative MAC Protocol in IEEE 802.11 WLAN
## 5 Simulation and Results  
To evaluate the FC-MAC protocol, we simulate a mobile ad-hoc network (MANET) with IEEE 802.11 DCF, the CoopMAC protocol [6], and the FC-MAC protocol using an event-driven simulator developed in the INET Framework of the OMNET++ [29]. Simulations were configured as default parameters of the IEEE 802.11n standard, which are summarized in Table 3. The simulation time is 100 s with a transmitted power of 100 mW and a packet size of 1024 bytes generated at a constant bit rate (CBR) of 2 Mbps UDP. Packets are transmitted in multi-rate mode for BER < \(10^{-5}\) (Table 4). We used the Friis free space propagation model with a path loss exponent of 4. Nodes are uniformly distributed over an area of 600 m \(\times\) 600 m. In order to obtain established results, the curves presented were averaged over 50 runs.  
The throughput of the FC-MAC protocol is depicted in Figure 3. Comparing the FC-MAC protocol with the IEEE 802.11 DCF and CoopMAC protocols demonstrates the performance improvement of the FC-MAC protocol. Both the CoopMAC and FC-MAC protocols have better performance than the DCF protocol. When the number of nodes increases, the spectrum efficiency provided by the FC-MAC  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline RTS & 38.89 μs & Slot time & 9 μs \\ CTS and HTS & 32.23 μs & SIFS & 10 μs \\ CWmin & 15 slots & DIFS & 28 μs \\ CWmax & 1023 slots & ACK & 32.23 μs \\ \hline \hline \end{tabular}
\end{table}
Table 4: Simulation parameters of IEEE 802.11n.  
protocol is greater than the CoopMAC protocol because the FC-MAC protocol exploits the capacity of spectrum efficiency provided by all existing relay nodes, whereas the CoopMAC protocol is limited to the best relay node which presents the lowest transmission delay.  
The network lifetime improvement of FC-MAC can be seen in Figure 4 when the number of nodes changes. As expected, the CoopMAC protocol achieves the shortest lifetime because the best relay nodes always forward packets for other nodes. The continual use of the best relay nodes in cooperation results in relay node outage and a reduction of network lifetime. The energy of each node in the DCF protocol is only consumed by direct transmission to the destination and there is no overhearing and forwarding due to cooperation. Therefore, the lifetime of the DCF protocol indicates better performance in comparison to the two other protocols. The relay selection scheme of the FC-MAC protocol provides balanced energy consumption. The FC-MAC protocol exploits the energy capacity of all nodes in the network. Thus, its lifetime outperforms the CoopMAC protocol while the forwarding mechanism leads to its degradation in comparison to the DCF protocol.  
Figure 5 indicates the time fairness of the FC-MAC, CoopMAC, and DCF protocols as the number of nodes increases. It can be observed that FC-MAC provides better time fairness than the other  
Figure 4: Network Lifetime.  
Figure 3: Network Throughput.  
schemes. Since DCF and CoopMAC are not designed for time fairness, their fairness index is lower than that of FC-MAC. This is due to the fact that FC-MAC improves the time fairness based on high utilization of all existing relay nodes. Hence, all relay nodes with different cooperation gains have more chance to participate in cooperation and forwarding the packets.