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Proceedings of the International Conference on Computer and Communication Engineering 2008 May 13-15, 2008 Kuala Lumpur, Malaysia

978-1-4244-1692-9/08/$25.00 2008 IEEE

Performance Study on Optimal Boundary per WiMAX Cell

Najma @ Thinzar Oo, Sidek Karim, Mohiuddin Ahmed

Department of Computer Science

Kulliyyah of Information and Communication TechnologyJalan Gombak, 53100, Kuala Lumpur, Malaysia

Email: mohiuddin@iiu.edu.my

Abstract

WiMAX can be considered as a new alternative

technology for the masses in most of the countries inthe world. This paper presents the results of WiMAX

performance study on optimal boundary per WiMAX

cell using NS-2 network simulator under differentWiMAX network models. The Performance metrics

measured in this study inclusive of packet loss,

throughput, and delay. From the results, it could bededuced that IEEE 802.16 networks perform

differently for different network traffic, number of

mobile nodes, distance from base station and mobile

speed. These results can be used as a guide line when

implementing WiMAX for developed urban areas likesuburbs of Kuala Lumpur.

I. INTRODUCTION

Wireless technology has become among the mostexciting area in telecommunication and computernetworking. The rapid growth of WiFi (IEEE 802.11standards) enabled mobile devices, cellular mobilephones, and wireless broadband Internet in generatingtremendous changes in the way people live. Thereduction of cost of Integrated Circuit (IC) andsophisticated technology in integrating very complexfunctionalities into a single module have increased thelevel of availability for wireless Internet access. 802.11standards or WiFi can be considered as ubiquitous

technology since it gained high popularity amongmobile devices. The latter wireless standards known asWiMAX (IEEE 802.16 standards) where as theoriginal standard dealt with radios operating inspectrum between 10GHz and 66GHz and currently itis considered as part of third generation (3G)communication standards. The second version ofWiMAX is the 802.11a where spectrum ranges of2GHz to 11GHz were added to the standards. Thisversion incorporated non-line-of-sight (NLOS)

capability for WiMAX transmission by usingOrthogonal Frequency Division Multiplexing (OFDM)modulation technique [1]. WiMAX 802.16c dealtmainly with updates in the 10GHz to 66GHz spectrum

range and it also addressed the issues of performanceevaluation, testing and detailed system profiling. The802.11e-2005 was released as a true mobile WiMAXstandard which enables high-speed signal handoffsnecessary for communications with users moving atvehicular speed [2]. The rest of this paper is organizedas follows: first we describe the simulation module andthe environments; second we analyze the simulationresults and evaluate the WiMAX networkperformance; thirdly discussion, and finally concludingremarks.

II.SIMULATIONMODELS

We have developed three different simulationmodels using NS-2 Tcl scripting. The trace filesproduced from the scripts were analyzed using AWKscripts and the output then was used for plotting usinggnuplot. The following simulations were performedinclusive of; 1) WiMax performance measurement fordifferent number of mobile nodes, 2) WiMax performance measurement for various distances, 3)WiMax performance measurement for different mobilenodes movements.

Figure 1. n-number of WiMAX subscribers per cell

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Figure 2. n-meter of WiMAX subscribers from base station

Figure 3. n-number of WiMAX subscribers moving ad v-ms-1speed

The three simulations were set up with the followingparameters:

TABLE 1: WIRELESS NODE AND TOPOLOGY PARAMETERS

Parameter Value

Wireless node parameters

Channel type WirelessChannelPropagation model TwoWayGround

Interface type OFDM

MAC layer protocol Mac/802_16/BS

Routing protocol DSDV

Interface Queue type Queue/DropTail/PriQueue

Maximum packet in ifq 50

Antenna model Antenna/OmniAntenna

Link layer type LL

Topology parameters

X-dimension 1100 m

Y-dimension 1100 m

Total simulation time 300 sec

WiMAX Cell Radius 500 m

Traffic pattern UDP agent with CBR trafficTCP agent with FTP traffic

Packet size 1500 bytesData rate 11Mbps

Bandwidth 11Mbps

Simulation (1) covers the performance of WiMAXcell when the number of mobile nodes was increasingas shown in Figure 1. The simulation measured thepacket loss, throughput, and average end-to-end delayof Transmission Control Protocol (TCP) and User

Datagram Protocol (UDP). The number of nodessimulated is stated in the Table 2.

TABLE 2: MAXIMUM NUMBER OF NODES PERSIMULATION.

Simulation Type Maximum number of

Nodes

TCP - Packet Loss 160

UDP - Packet Loss 200

UDP - Throughput 150

UDP - End-to-end delay 150

UDP End-to-end delay 150

The variation in number of nodes is due to the NS-2frameworks constraint and the hardware limitation.The number of nodes was set up as such since NS-2returned error messages such as segmentation fault asthe number of nodes were increased.

Simulation (2) dealt with the measurement ofWiMAX performance over different distances ofWiMAX subscriber stations from the base station inFigure 2.

The simulation traces were used to measure thepacket loss, throughput, and average end-to-end delayof Transmission Control Protocol (TCP) and UserDatagram Protocol (UDP) traffic. The maximumdistance of subscriber station from the base stationsimulated is stated in the Table 3 below:

TABLE 3: MAXIMUM DISTANCE OF NODE FROM WIMAXBASE STATION PER SIMULATION.

Simulation Type Maximum Distance of

Nodes from Base Station

(meter)

TCP - Packet Loss 800

UDP - Packet Loss 800

The maximum distance of the mobile nodes fromthe base station was set up as such since the topologywas set up with 50 nodes placed at different distances,ranging from 70 meters up to 800 meters from the basestation. Packet sent and losses were captured for eachnode based on its location.

Simulation (3) was developed in order to measurethe effects of mobility on WiMAX network as shownin Figure 3. This simulation is intended to capture andanalyze mobile nodes speed as an independentvariable and throughput and end-to-end delay as thedependent variables in Table 4.

TABLE 4: MAXIMUM SPEED OF NODES PER SIMULATION.

Simulation Type Maximum Speed (v) of

mobile node (ms-1)

UDP Throughput 40

UDP - Packet Loss 40

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III.SIMULATIONRESULTS &EVALUATION OFWiMAXNETWORKPERFORMANCE

In simulation (1), the characteristics of packet losses

are investigated through simulations of IEEE 802.16networks on different network settings with UDP/CBRtraffic and TCP/FTP respectively. UDP has likely beenused for real-time applications, such as video and audiowhile TCP is popular for HTTP and FTP applications.

For WiMAX networks with UDP/CBR andTCP/FTP traffic, we examined nine different caseswith 1, 3, 5, 7, 25, 50, 75, 100 and 150 mobile nodes.In networks with UDP/CBR traffic, shown in Figure 4,the number of packet sent, received and drop rate areshown; the drop rate increases as the number of mobilenodes in the network goes higher. However, theTCP/FTP traffic, shown in Figure 5, attains the fullutilization of the network resources up to a certain point; hence plotting of the number of packets sentincreases almost linearly. But the packet drop rate dueto bandwidth request collision goes higher as thenumber of mobile nodes increases.

The end-to-end delay for both traffic patterns,shown in Figure 6, is analyzed based on the abovementioned cases, the delay time increases as thetopology becomes bigger and apparently the UDPnetworks delay is much lower than the TCP trafficsince UDP achieves minimized transmission delay byomitting the connection setup process, flow control,and retransmission. [3]

Figure 4. Number of mobile nodes vs. Packet loss (UDP/CBR

traffic)

In simulation (2), 50 nodes were placed at differentdistances from the base station and different test casesof UDP/CBR traffic (Figure 7) and TCP/FTP traffic(Figure 8) are examined. The modulation scheme andfrequency of the topology was set up to cover 500meters from base station. The packet sent and dropparameters have been analyzed based on the simulationresults. From Figure 7, the number of UDP/CBR

packets sent goes significantly lower as the nodelocated further from the base station. However, in theTCP/FTP case, as shown in Figure 8, the performancegraph is almost constant regardless of the nodesdistance from base station while the node is located inthe coverage range.

Figure 5. Number of mobile nodes vs. Packet loss (TCP/FTPtraffic)

Figure 6. Number of mobile nodes vs. Average end-to-end delay(UDP/CBR and TCP/FTP traffic)

Figure 7. Distance of subscriber station from base station vs.packet loss (UDP/CBR)

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Figure 8. Distance of subscriber station from base station vs.packet loss (TCP/FTP)

TABLE5:THROUGHPUTFORUDP/CBRTRAFFICACHIEVEDWITHTHERESPECTIVENUMBEROFNODES.

Number of

nodes

Throughput

(Mbps)

%Data

rate

1 8.270 75%

3 8.213 74.66%

5 8.204 74.58%

7 8.200 74.55%

25 7.878 71.6%

50 7.683 69.8%

75 8.096 80.96%

100 7.893 71.75%

150 7.782 70.75%

Mobility has become the real potential of wirelessnetworks. Our third simulation examined the effects ofmobile nodes speed towards network performance.The simulation is set up as a network of 50 mobilenodes with UDP/CBR traffic as shown in Table 6.Parameters such as throughput and average end-to-enddelay are analysed based on different test cases ofspeed 0.0, 1.0, 10.0, 20.0, 30.0 and 40.0 m/s.

TABLE6:THROUGHPUTFORUDP/CBRTRAFFICACHIEVEDWITHTHERESPECTIVESPEEDOFTHENODES.

Speed

(ms-1)

Throughput

(Mbps)

Avg end-to-

end delay (ms)

0.0 8.156 8.92

1.0 8.1534 8.95

10.0 8.156 8.84

20.0 8.156 8.69

30.0 8.1574 8.80

40.0 8.1574 8.80

IV.DISCUSSION

Based on the analysis of the simulation (1), it can be concluded that WiMAX network simulated could

support up to 100 concurrent nodes in a cell forTCP/FTP traffic before it showed significant network performance degradation. This signifies that if therewere fewer nodes transmitting and receiving TCP/FTP packets, the network would be fully utilized and thenetwork is congested once additional nodes joined thecell. For UDP/CBR traffic, the simulation showedexponential increase of packets for the cell, henceconclusion can be drawn that WiMAX is better suitedfor UDP/CBR traffic rather than TCP/FTP traffic. Thisresult also could be extrapolated that WiMAX has high potential in providing multimedia streamingapplications [4].

Simulation (2) demonstrated reliable TCP/FTPtransmission of packets inside the cell up to the 500meter. In the context of UDP/CBR traffic, significantpacket loss occurred as the node located further awayfrom the cell. Both cases prove that WiMAX issuitable for wide area networks implementation andalso proves the reliability of TCP connections till thelast mile.

According to the results analysed in Table 6, weconclude that the movement of the mobile nodesdoesnt have much effect on the network performancewhen the nodes are in coverage range of the basestation. However, the mobile nodes speed will greatlyaffect the network performance once the handover is

involved [5].

V.CONCLUSION

Hence, with wide coverage area introduced insimulation (2), it could be concluded that it is alsopossible to deploy UDP based application for the massusing WiMAX network in urban areas.

The performance of WiMAX cell could be furtherenhanced with proper changes made to the antennagain, MIMO/BF gain, output power of BS, TDD ratio,type of modulation, noise figure, CPE (CustomerPremise Equipment) output power, CPE antenna gain,

and receiver gain of BS [6].

REFERENCES

[1] Sanders, T. WiMAX/802.16 Revealed. Retrieve:

http://www.wifiplanet.com/tutorials/article.php/3550476

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[2] WiMAX.Retrieve: http://en.wikipedia.org/wiki/WiMAX[3] Nmeth, Z. and Szab, C. A. 2006. Measurements to assist

access network design with fixed WiMAX in urbanenvironment. In Proceedings of the 1st internationalConference on Access Networks (Athens, Greece, September04 - 06, 2006). AcessNets '06, vol. 267. ACM, New York, NY,

10.[4] Bakshi, M. VoIP / Multimedia over WiMAX (802.16).

Retrieved 20th Aug, 2007 fromwww.cse.wustl.edu/~jain/cse574-06/ftp/ wimax_voip.pdf

[5] Chang, C. 2005. A Mobile-IP Based MobilitySystem for Wireless Metropolitan Area Networks. In

Proceedings of the 2005 international Conference on Parallel

Processing Workshops (June 14 - 17, 2005). ICPPW. IEEEComputer Society, Washington, DC, 429-435.

[6] Cao, M., Ma, W., Zhang, Q., Wang, X., and Zhu,

W. 2005. Modelling and performance analysis of thedistributed scheduler in IEEE 802.16 mesh mode. In

Proceedings of the 6th ACM international Symposium on

Mobile Ad Hoc Networking and Computing (Urbana-Champaign, IL, USA, May 25 - 27, 2005). MobiHoc '05.ACM, New York, NY, 78-89.

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