3. LITERATURE REVIEW
6.1 Kiyotaki-Moore Model Approach to Performance Devolution in Mobile
Mobile WiMAX is developed to meet the demand for personal broadband ser-vices. Kiyotaki-Moore is an economic model that shows how small shocks to the economy might be amplified by certain factors, causing large output fluctuations.
In this dissertation, we have taken a novel approach to the degradation of perfor-mance in mobile WiMAX by applying this model. We have produced a small shock by accidentally increasing the number of simultaneous users and then ana-lyzed the output explaining the meaningfulness and applicability of this model. In this dissertation the performance of mobile WiMAX under special circumstances has been investigated. The performance degradation of mobile WiMAX is ana-lyzed according to the system parameters which are the number of simultaneous users per each channel, the fixed height of antenna plus the fixed distances be-tween the BS and the MSs. Four scenarios have been conducted for running the experiments. NCTUns 6.0 has been selected for simulating the scenarios. This simulation program provides the real world environment with a complete set of equipment’s and application configurations. This simulation program has facili-tated the process of setting up a network and running the analysis and experi-ments. In order to achieve the research target, four mobile WiMAX scenarios have been designed to simulate mobile WiMAX topology.
Objectives and Approaches
The objective was set to analyze and investigate the performance of mobile Wi-MAX under the condition of increasing the number of simultaneous users being increased at once. For this purpose and obtaining reliable results, an economic theory has been deployed to define and explain the occurred degradation which appears to the performance of the mobile WiMAX. A shock has been created and then analyzed the aftermath. Moreover it was observed that as the number of us-ers increases the performance faces a logical decrease.
6.1.2 Results
NCTUns provides the possibility for configuring the network topologies and pa-rameters, surveillance of traffic flows, and gathering statistics about a simulated network (Chin-Liang Wang 2010; R. B. Ramle et al. 2010).
Table 2. Simulation parameters
Parameters Values
Frequency Bandwidth 5 MHz
Modulation Type OFDM-QPSK
Length of the Frame 5ms Simulation Time 100s Routing Protocol OSDV Mean Length of Packet 1024 bytes Number of Nodes Scenario-based
Table 2 shows the simulation parameters. As one can see in Figure 27 the pa-rameters are set to ensure a standard test condition. The frequency bandwidth is fixed at 5 MHz. The length of frame is of 5ms. The simulation duration is circa 100 seconds and the number of nodes is variable and based on scenarios defined through the process to make sure conditions do not interfere with the output.
Figure 27. Creating the shock by an increase in the number of simultaneous users
In Figure 28, as one can observe, we have worked on the case where the number of simultaneous users have drastically increased. Therefore, by this way accord-ing to Kiyotaki-Moore model we have designed a small shock to the WiMAX network and as one can see the simulation results this small shock has led to a decrease of average data rate and finally resulted in a visible decline when it comes to the performance of the mobile WiMAX network. Therefore when the height of the base station and the distance between the BS and MS’s are fixed at values of 25 meters and 1000 meters respectively, then if the number of simulta-neous users is continuously increasing, the performance of the WiMAX network faces a decline.
The performance decline of Mobile WiMAX is analyzed according to the system parameters which are the number of simultaneous users per each channel, and the height of antenna. We have conducted 4 scenarios for running the experiments.
NCTUns 6.0 has been selected for simulating the scenarios. This simulation pro-gram provides the real world environment with a complete set of equipment’s and application configurations. This simulation program has facilitated the process of setting up a network and running the analysis and experiments. In order to achieve the research target, four mobile WiMAX scenarios have been designed to simulate mobile WiMAX topology. The scenarios can be seen listed in Table 3.
There are four MSs used in this simulation and then the number has been
in-creased to forty MSs for creating the required small shock. It is to be mentioned that all the MSs are connected to one BS. The distance between the BS node and MS nodes is a fixed value of 1000 meters. In each of the scenarios, the number of the simultaneous users per channel has been increased by 20.
After running the test with the before mentioned parameters and values, we got the following results as shown in Figure 28:
Table 3. Simulation settings and outcomes
No Scenario Base Station
Height
Number of Simulta-neous Users per Channel
Average Data Rate bits/second
Scenario 1 25 40 848
Scenario 2 25 60 842.78
Scenario 3 25 80 837.98
Scenario 4 25 100 832.78
Figure 28. Performance decline of mobile WiMAX (x axis: number of simulta-neous users per channel; y axis: average data rate)
In this economic model, by considering some factors a small shock to the econo-my can cause a large amount of fluctuations in the output of the system. The Ki-yotaki-Moore model can be observed in Figure 29 as follows:
Figure 29. Kiyotaki-Moore Model (N. Kiyotaki et al. 1997)
WiMAX technology can be affected by various issues like the distance from the base station, environmental effects and many others (A.Vinel et al. 2011; Q. Ni et al. 2012; R.B. Ramle et al. 2010). In this dissertation we have analyzed the case when the numbers of simultaneous users have drastically increased. Hence, by this way based on Kiyotaki Moore model we have created a small shock to the WiMAX network and as one can see the simulation results this small shock has resulted in a sharp decrease of average data rate and eventually led to a visible decline when it comes to the performance of the mobile WiMAX network. This can be observed that when the height of the base station is fixed and the number of simultaneous users are constantly increasing, the performance of the WiMAX network faces a devolution.
6.1.2 Contribution to the Research Area
In this dissertation, we have presented the performance evaluation for mobile WiMAX utilizing the NCTUns 6.0 simulation program. The evaluation is deter-mined based on the system parameters that are the height of BS and the number of simultaneous users. Eventually it can be observed that when the height of the base station is fixed and the numbers of simultaneous users are constantly increas-ing, the performance of the WiMAX network faces a decline. Hence, by this way based on Kiyotaki-Moore model we have created a small shock to the WiMAX network and as one can see the simulation results this small shock has resulted in a sharp decrease of average data rate and finally led to a visible decline when it
comes to the performance. This research is restricted to the number of the simul-taneous users. It has been mentioned that other parameters like the height of the BS and the distances between the BS and MS’s are fixed.