## 4 Performance Evaluation
### Evaluation of MRSS-based Handoff Algorithm  
In this analysis, the performance of MRSS-based and DMRSS-based handoff algorithms were evaluated by a hexagonal cell based topology as shown in Figure 4(b). In the Mobile WiMAX environment, the size of simulation topology is 9000 m\({}^{2}\) and the distance between two adjacent APs is 1800 m. A random waypoint mobility model was adopted to simulate a user movement trajectory. Table 2 shows the radio propagation parameters and Table 6 shows the detailed parameters for the mobility model in the simulation. The performance of MRSS-based handoff method and DMRSS-based handoff method were compared with various RSS threshold-based handoff algorithms [9; 10], the geographic-based handoff algorithm [23] and the MACD-based handoff algorithm [27]. \begin{table}
\begin{tabular}{|c|c|c|c|} \hline Start & End & Duration (s) & Velocity (m/s) \\ \hline A & B & 80 & 1 \\ \hline B & B & 60 & 0 \\ \hline B & C & 80 & 1.21 \\ \hline C & C & 30 & 0 \\ \hline C & D & 80 & 1.12 \\ \hline D & D & 40 & 0 \\ \hline D & E & 80 & 1.12 \\ \hline E & E & 40 & 0 \\ \hline E & F & 30 & 1.2 \\ \hline \end{tabular}
\end{table} 
Table 5: The user motion parameters for the ping-pong effect analysis in WLAN. The RSS threshold-based handoff algorithms use two mechanisms, hysteresis (\(H\)) and dwell-time (\(D\)), to avoid the ping-pong effect. In the basic RSS threshold-based handoff algorithm (\(T\)), an MN triggers a handoff when the RSS of the current servicing base station (\(RSS_{old}\)) is lower than a pre-defined handoff threshold (\(TH_{HO}\)) and the RSS of a neighborhood base stations (\(RSS_{new}\)) is higher than \(RSS_{old}\). The hysteresis mechanism avoids the ping-pong effect by changing the handoff trigger \begin{table}
\begin{tabular}{|l|c|} \hline Environment & WiMAX \\ \hline Mobility model & Random waypoint \\ \hline Velocity (m/s) & 7 - 30 \\ \hline Max Pause (s) & 30 \\ \hline Duration (hour) & 24 \\ \hline Topology Size & 9000 m\({}^{2}\) \\ \hline Distance between AP & 1800 m \\ \hline \end{tabular}
\end{table} 
Table 6: Parameters for the mobility models in the handoff evaluation. Figure 14: The performance analysis of ping-pong effect. condition as \(RSS_{new}>RSS_{old}+H\). On the other hand, the dwell time is the time interval that an MN stays in the overlapped area of two APs. The handoff trigger condition must be satisfied and kept over the dwell time, then the MN is allowed to trigger a handoff. The RSS threshold based handoff algorithm can apply the dwell time mechanism and the hysteresis mechanism simultaneous. In the geographic-based handoff algorithm, an MN initiates a handoff according to a GPS and a location information server. In the simulation, a pre-processing delay was introduced to represent the latency of the network discovery procedure including the time required to turn on the interfaces, scan channels, associate with a chosen AP, etc. The parameters and thresholds of various approaches are presented in Table 7. Each case was simulated 1000 times. The simulations evaluated the performance of MRSS and DMRSS in terms of motion detection delay, power consumption, total number of handoff and total number of failure handoff. * **Motion detection delay**: The handoff delay strong impacts the quality of communications. If a motion detection method can detect the motion state quickly, an MN can have sufficient time to process handoff and can stop network discovery immediately when user becomes stationary. * **Power consumption**: In the network discovery, an MN turns on all its interfaces to search for new base stations and exchange the control information between mobility controllers. This procedure will consume much battery power. A larger accumulated all interfaces activated time represents larger power consumption. * **Number of handoff**: In some real-time applications, such as voice and video, delay and jitter will damage their quality. The transmission of the applications may be stopped for a while when an