Performance Analysis ofW i-MAX with Matlab and Suitability of Its Existence Compared to O ther Technologies

M d·A hsan Habib, M onirM orshed, Tushar Kanti Roy

(1.M aw lana Bhashani Science and Technology U niversity,Tangail1902,Bangladesh; 2.Rajshahi U niversity of Engineering and Technology,Rajshahi6204,Bangladesh)

N ow a day several cellular phone companies are trying to upgrade their services to3G cellular phone system to fulfill users’dem and.The users are also trying to involvein broadband access service to fulfill their m odern necessitate.A s a result,the dem ands of the broadband services are increasing day by day.The cellular operators are providing the broadband services but their overall perform ance is not sufficient because of their required speed as w ell as cost of services.The speed is a vital factor in accessing broad band services, so the various companies are trying to get alternate service to fill up subscribers’requisite.In this case the W iMAX technology can play an important role.So it can create a revolutionary change in m odern hi-tech life.The W iMAX technology not only provides the high speed to its subscribers but also provides som e additional features that are unavailable to the existing cellular phones operators. The W iMAX technology can provide online gaming,online TV,radio,video conference,m ultim edia services,broadband accesses as w ell as m any others m odern services.The W iMAX has a great opportunity as the cost of services of W iMAX is comparatively low er than others technologies.So, people m ay be benefited by paying low er cost but getting superior services.

1 Flexibility of U sing W iMAX

W iMAX technology is quite flexible because of its easiness.There are so m any reasons for using the W iMAX.Am ong them som e important points are given below:

(1)W iMAX technology requires no w ire.

(2)It p rovides m odern billing system.

(3)It has higher speed than other technologies.

(4)It p rovides potentially low cost.

(5)It p rovides service in every w here (w ireless facilities).

(6)It p rovides broadband access.

(7)It is also provides extra m ulti-m edia as w ell as other m odern services.

(8)Both unlicensed&licensed spectrum.

2 Importance of W iMAX in N ew Technology

Educational researches as w ell as laboratory, experim ental facilities are quite large in develop countries.For this reason,technology is increasing day by day to fulfill m odern requirem ents w here people also get the latest technology for their specific purposes.But these phenom enon’s are rare in the under-developing or developing country like Bangladesh,N epal,Srilanka and so on.People have not sufficient funds to procure latest technology there.Governm ental right steps are also unavailable.For that reason,the latest technology is unavailable in developing country.But the situation is changing as the people of those countries are trying to change their life by connecting m odern technologies.

3 W iMAX M odulation

M odulation is a technique by w hich the one or tw o properties of the carrier frequency are being changed according to the m odulating signal.In another w ord,the m odulation is the process of encoding inform ation from a m essage source in a m anner suitable for transm ission[1].W iMAX uses digital m odulation technique.In digital m odulation, analog carrier signal is m odulated by digital bit stream.There are three basic types of m odulation, amplitude shift keying(ASK),frequency shift keying(FSK) and phase shift keying (PSK). W iMAX technology com bined ASK and PSK and form ed quardrature amplitude m odulation(QAM) w here both the amplitude and phase are changed. D epending on the w eather condition,interference of the signal and the client distance,base station dynam ically allocate the m odulation schem e w hich m akes W iMAX service profitable in this case the service p rovider is able to serve in a particular area,according to the need of the user[2].The IEEE 802.16/W iMAX only satisfied the four digital m odulation techniques.They are:BPSK;Q PSK; 16QAM;64QAM[3].If w e arrange the above four m odulation technique according to the order of m odulation then w e can that the arrangem ent below:64QAM ＞16QAM ＞Q PSK＞B PSK[higher order to low er order].

It should be m entioned that Q PSK and4-QAM are the sam e m odulation.16-QAM and64-QAM are the tw o amplitude m odulations that can be used according to the IEEE802.16standard. The m ost spectral efficientm odulation is64-QAM (6bits/sym bol are transm itted)[3].

4 A daptive M odulation

A daptive m odulation is nothing but a com bination of differentm odulation techniques.In adaptive m odulation technique,the m odulation technique is being changed according to the channel condition.It has the adaptive capability w ith the channel condition hence the nam e adaptive m odulation.W e can understand the adaptive m odulation w ith the help of the constellation diagram.A constellation diagram can help us define the amplitude and phase of a signal elem ent,particularly w hen w e are dealing w ith m ultilevel carriers(one in phase and one in quardrature).In a constellation diagram a signal elem ent type is represented as a dot.The bit or com bination of bits it can carry is often w ritten next to it[4].In constellation diagram,if w e plot the BPSK then w e get a s imple constellation diagram(Fig.1).

Fig.1 BPSK constellation diagram

For this reason,it is not difficult to detect the tw o points in the presence of higher noise.O n the other hand,if w e plot16QAM or the64QAM in the constellation diagram then w e get the complex diagram.In the case of the plotting16QAM or 64QAM,the all points in the constellation diagram are too close so that it is complicated to detect them simply in the presence of higher channel noise.So it is understood that,the higher order m odulation techniques require higher SNR,on the other hand the low er order m odulation techniques require low er SNR.

The Fig.2is64QAM constellation diagram.

Fig.2 64QAM constellation diagram

The Fig.2show s that all points in the constellation diagram are too close to each other,so it is intricate for the receiver to detect or differentiate them in the presence of high channel noise.But 64QAM hashigher data ratescompared w ith BPSK or low er orderm odulation technique.So the higher order m odulation techniques require higher SNR but having higher data rates.Low er order m odulation techniques require low er SNR but having low er data rates.

4.3 我院信息系统上实现了中心审方功能，但实际工作中存在人力不足、人员专业水平差异等诸多影响因素，中心审方的深度有待探讨。未来，借助嵌入前置性审方软件，再结合临床药师的在线审核能力，才能做到真正意义上的中心审方[8]。

5 W iMAX A daptive M odulation

The adaptive m odulation enables a W iMAX system to opt im ize the throughput based on the propagation conditions.A daptive m odulation and coding schem e can connectm ore users[2]. W iMAX uses adaptive m odulation so the physical layer(PHY)can employ the follow ing m odulation schem es:Q PSK,16-QAM or64-QAM m odulation adaptively changing on the basis of channel conditions[3].

W hen the signal to noise ratio in the channel is low it uses the low er order m odulation technique,on the other hand w hen the signal to noise ratio is high then it uses the higher order m odulation.Thus it has the adaptive capability w ith the channel condition w hich increases the overall perform ance of the system.A daptive m odulation technique is the m odern advanced m odulation technique w hich increases the overall perform ance as w ell as data rates and throughputs.W e know that the channel condition is not sam e for all the t im e. It is being changed due to various factors.Environm ental factors also can change the SNR in the channel.In such a case,if w e use the adaptive m odulation schem e then w e can get the best output from the system.A s the SNR is very good or high near the BS/base station(due to high value of the signal)higher order m odulation is used.The cell boundary areas have low er SNR (due to low er value of the transm itted signal that the signal travels long path from the BS/TX);in this situation the adaptive m odulation uses low er order m odulation techniques.D epending on the channel condition,adaptive m odulation perm its the w ireless system to select the higher-orderm odulation. W iMAX uses both Q PSK and QAM as m odulation techniques.Q PSK,16QAM and64QAM is compulsory in dow nlink for both m obile and fixed W iMAX w hereas64QAM is optional in uplink. W hen use64QAM is op tional in uplink[3].W hen use64QAM as a m odulation technique,w e have to take care of the signal to noise ratio(SNR) to el im inate the interference.A daptive m odulation is useful to elim inate fading and other interference, optim ize throughput w hile m aintaining also the long distance[2].

6 Application of A daptive M odulation

The adaptive m odulation has m any advantages or purposes.They are given below:

It m aintains connection quality.

A lso m aintains link stability.

Increases data rates/throughput.

H igh perform ance.

Feedback procedure.

B ut,increases system complexity.

7 Sim ulated M atlab O utput for A daptive M odulation

From the Fig.3to Fig.7,it is presented the generalized concept ofthe adaptive m odulation technique in W iMAX by m atlab sim ulation.The m odulation technique is being changed according to the channelcondition/SNR.The B PSK & Q PSK w ork in sm all SNR channel but having lower data rate,on the other hand the16QAM or 64QAM w ork in large SNR channel.B ut64QAM has the higher data rate than the16QAM orQ PSK or the BPSK.

Fig.3 BER vs.SNR for BPSK

Fig.4 BER vs.SNR for QPSK

Fig.5 BER vs.SNR for16QAM

Fig.6 BER vs.SNR for64QAM

Fig.7 BER vs.SNR for differentm odulations technique

8 Conclusion and D iscussion

The broadband speed of theW iMAX is m uch higher than the existence technology in the w orld. For this reason people of developing country can getconnected w ith this m odern technology. W iMAX has generated a trem endous am ount of interest in the w ireless comm unity and it can be one of the m ost deployed technologies in the future.The m ain advantage of it is that it can provide w ireless broadband service w ith higher speed and low cost.So it can be deployed in rural areas w here w ired structure is difficult to implem ent.It has capability of providing other beneficial entertainm ent facilities along w ith w ireless broadband service.The W iMAX can deliver both of the real tim e and non real tim e features.Finally W iMAX has great opportunity that has been com e in develop country w ith its latest advanced facilities for the users.A daptive m odulation is one of its integrated techniques that can increase the system performance to fill subscribers’dem and.That is m andatory for any comm unication system.

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[4] Behrouz A Forouzan.D ata Comm unications&N etw orking[M].Fourth Edition.,N ew York:M cgraw H ill,2006:1-68.