## 5 Computer Simulation
### Evaluation Metrics  
Simulative evaluation compares three metrics defined as follows. * _System throughput_ (bps): It is defined as the sum of throughputs for all sessions wherein packets are successfully delivered to a destination. \[System\,throughput = \frac{1500\times 8N_{r}}{T_{sim}}\] (5) \begin{table}
\begin{tabular}{c|c c|c|c|c|c|c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c|}{**(A)**} & \multicolumn{2}{c|}{**(B)**} & \multicolumn{2}{c|}{**(C)**} & \multicolumn{2}{c|}{**(D)**} & \multicolumn{2}{c}{**(E)**} \\  & **DCH-Mono-IPT** & **DCH-Dual-IPT** & **DCH-Conv.** & **DCH-Previous** & **SCH-Conv.** \\ \cline{2-8}  & **Ch.1** & **Ch.2** & **Ch.1** & **Ch.2** & **Ch.1** & **Ch.2** & **Ch.1** & **Ch.2** & **Ch.1** \\ \hline \hline \multirow{2}{*}{Wireless IF} & \multicolumn{8}{c|}{IEEE 802.11a [47]} \\ \cline{2-8}  & Tx rate & \multicolumn{8}{c|}{54 Mbps} \\ \cline{2-8}  & Channel model & \multicolumn{8}{c|}{IEEE 802.11 TGn channel model D [48]} \\ \cline{2-8}  & Routing protocol & \multicolumn{8}{c|}{Minimum path loss routing [46]} \\ \cline{2-8}  & & & & & & \\ \hline \multirow{2}{*}{Traffic model} & \multicolumn{8}{c|}{Poisson origination, log-normal distribution} \\  & & Avg. DL: 20 packets, UL: 3 packets [50] & \multicolumn{8}{c}{Packet size: 1500 bytes,} \\ \cline{2-8}  & & & & & & \\ \cline{2-8}  & & & & & & \\ \hline \multirow{2}{*}{Relay scheme RTS/CTS Off (slot)} & IPT & CSMA/CA & IPT & Bi-IPT & CSMA/CA & IPT & CSMA/CA & CSMA/CA \\  & Off & On & Off & Off & On & Off & On \\  & 7 & 15 & 7 & 7 & 15 & 7 & 15 \\ \hline \multirow{2}{*}{Buffering} & Round Robin & FIFO & Round Robin & FIFO & Round Robin & FIFO & FIFO \\ \cline{2-8}  & Traffic handling & DL & DL+UL & DL & DL+UL & DL & UL & DL+UL \\ \hline \multirow{2}{*}{Ch. switching threshold} & 100 & 100 & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{\begin{tabular}{} \end{tabular} } \\  & & & & & & & \\ \cline{2-8}  & packets & packets & & & & & \\ \hline \multirow{2}{*}{\
\begin{tabular}{} \end{tabular} } & Tx period & \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & \multirow{2}{*}{0, 100} & \multirow{2}{*}{0} & \multirow{2}{*}{0, 100} & \multirow{2}{*}{0} & \multirow{2}{*}{0, 100} & \multirow{2}{*}{0} \\  & (user) & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. * _Average packet delay_ (s): Average time period from the instant when a packet occurs at a source node to the instant when a destination node completes reception of the packet. \[Average\,delay\,=\,\frac{1}{N_{r}}\sum_{i=1}^{N_{r}}D_{i}\] (6)
* _Packet loss rate_ (%): Ratio of the number of discarded packets to the total number of packets to be received. \[Packet\,loss\,rate\,=\,\frac{N_{d}}{N_{r}+N_{d}}\times 100\] (7) where \(N_{r}\) denotes the number of packets successfully received by destination nodes. \(D_{i}\) denotes the elapsed time period from the \(i\)-th packet's occurrence at the source node to the reception completion at the destination node. \(N_{d}\) denotes the number of discarded packets due to excess of the retry limit. Simulation is carried out for \(T_{sim}=240\) s. This simulation period has been ensured to exhibit a good convergence. We compare five schemes to be defined as follows. The same forwarding path is used for all schemes as shown in Figure 5.  
**(A)**: _DCH-Mono-IPT_--RR-IPT is applied to Ch.1 and it accommodates downlink traffic only. Uplink and partially downlink traffic are forwarded via Ch.2 using CSMA/CA. **(B)**: _DCH-Dual-IPT_--RR-IPT is applied to Ch.1 and it accommodates downlink traffic only. In Ch.2, uplink and downlink traffic are forwarded by RR-IPT in bi-directional manner (Bi-RR-IPT). **(C)**: _DCH-Conventional_--Conventional scheme is defined as that does not apply IPT but only CSMA/CA-based packet relaying.