A Flexible OFDM System Simulation Model. with BER Performance Test

Transcription

1 Contemporary Engineering Science, Vol. 5, 2012, no. 8, A Flexible OFDM Sytem Simulation Model with BER Performance Tet Aladdin Amro Al-Huein Bin Talal Univerity, Jordan Department of Communication Engineering amroru@ hotmail.com Viiting profeor in Taibah Univerity, Saudi Arabia Fadi Abu-Amara Al-Huein Bin Talal Univerity, Jordan Department of Computer Engineering fadiabuamara@yahoo.com Ahmed Mua Al-Huein Bin Talal Univerity, Jordan Department of Computer Engineering a_horman@yahoo.com Abtract Thi wor aim at developing flexible imulation model for orthogonal frequency diviion multiplexing (OFDM). In thi model, the ytem parameter uch a modulation cheme ymbol order, or the number of ubcarrier can be changed eaily according to pecific OFDM ytem implementation. Thi ytem can erve a a ey tool for reearcher in the area of OFDM ytem. In thi wor, the propoed model i ued to conduct different experiment to examine the performance of OFDM ytem. For intance, the Bit Error Rate (BER) of OFDM ytem under different noie condition have been computed. In

2 366 Aladdin Amro, Fadi Abu-Amara and Ahmed Mua addition, a comparion between BER reulting from different contellation cheme have been performed. Simulation reult indicate that the propoed model i woring efficiently. Keyword: AWGN, Bit Error rate, orthogonal frequency diviion multiplexing, Signal to Noie Ratio I. Introduction Orthogonal Frequency Diviion Multiplexing (OFDM) ha been uccefully applied to a wide variety of digital communication application over the pat everal year[5][4]. While OFDM principle wa adopted a a phyical layer for many important communication ytem uch a aymmetric digital ubcriber loop(adsl), Digital Audio Broadcating (DAB),Digital Video Broadcating (DVB), high-definition televiion (HDTV), wirele local area networ (WLAN)and the fourth generation of mobile cellular[5][4],the theory, algorithm, and implementation technique of OFDM are topic of high interet[3][4]. Depite that OFDM ytem have lot of advantage in providing high data rate with ufficient robut againt radio channel impairment. OFDM ytem have uffered from everal drawbac uch a high dynamic range of the tranmitted ignal. Thu intenive wor have to be performed to improve the OFDM ytem performance. Thi paper i intended to develop an efficient and flexible imulation model for OFDM ytem uing Matlab. The ret of thi paper i organized a follow: ection II preent the mathematical model of OFDM ytem. Section III decribe the propoed Simulation model. Section IV preent the propoed model tet by performing bit error rate ( BER)performance analyi for different ytem configuration a an example of the propoed model uage while ection V conclude the paper. II. Mathematical Model of OFDM Sytem It i worth mentioning that OFDM i a pecial cla of Multicarrier modulation (MCM).Figure 1 (a) how a general implementation of MCM ytem[6]. The tructure of a complex multiplier (IQ modulator/demodulator) which i commonly ued in MCM ytem, i alo hown in Figure1 (b). The MCM tranmitted ignal S(t) can be repreented by Equation 1-3 [6].

3 Flexible OFDM ytem imulation model 367 S( t) = + N SC i= = 1 C S ( t it ) i (1) S ( t) = Π( t) e j2πf t (2) 1,0 < t T Π( t) = 0, t 0, t > T (3) Where C i i the i th information ymbol at the th ubcarrier, S i the waveform for the th ubcarrier, N c i the number of ubcarrier, f i the frequency of the ubcarrier, T i the ymbol period, and π(t) i the pule haping function. Figure 1 The optimum detector for each ubcarrier ue a filter that matche the ubcarrier waveform. In other word, thi filter i wored a a correlator that matche the ' C ubcarrier, ee Figure 1. Therefore, the detected information ymbol i at the output of the correlator i given by C ' i = T 1 T T * 1 j 2πf t r( t its ) Sdt = r( t its ) e S T 0 S 0 dt (4)

4 368 Aladdin Amro, Fadi Abu-Amara and Ahmed Mua Where r(t) i the received time domain ignal. Becaue claical MCM ue nonoverlapped band limited ignal it require exceive bandwidth [6]. The main advantage of OFDM ytem i it ability to employee the overlapped yet orthogonal ignal et. Thi orthogonality originate from a traightforward correlation between any two ubcarrier, given by δ T 1 1 l = l dt T = T 0 = exp( jπ ( f exp( j2π ( f in( π ( f f l ) T ) f l ) T ) π ( f f ) T l f ) t) dt = l (5) For the two ubcarrier to be orthogonalthe following condition hould be atified f f l 1 = m T OFDM modulation/demodulation can be implemented by uing invere dicrete Fourier tranform (IDFT)/dicrete Fourier tranform (DFT).Thi i evident by analyzing equation (1)and(4)[5].The OFDM technology divide a wideband frequency elective channel in to Narrow band flat fading channel. Thu it ha a trong reitance to multipath fading and anti-carrier interference [3]. III. Simulation Model Decription An OFDM model i built uing MATLAB. In thi model, the number of bit in the tream, the number of ubcarrier, and the modulation cheme are uer input parameter. Figure 2 diplay the bloc diagram of the propoed OFDM model.

5 Flexible OFDM ytem imulation model 369 Data In Symbol Mapping Serial to parallel IDFT Channel Data Out Symbol Demapping parallel to Serial DFT Noie + Figure 2: OFDM model bloc diagram The propoed OFDM model can be ummarized a follow. Bit tream with the given length i generated uing the random function randint(nbit,1,2). In thi function, nbit denote the length of the bit tream that hould be diviible by number of ubcarrier. Conequently thee generated bit are modulated uing Matlab "modem.qammod" object. Thi built in object allow the uer to et the deired M-ary value a well a the ymbol order which can be binary, gray, or uer defined. afterward, the bit tream i converted to a parallel tream where the number of tream i correpond to the deired number of ubcarrier. Now, the invere Fourier tranform can be computed. To demontrate and imulate the channel condition and effect, a white Gauian noie of different power i added to the OFDM ignal At the receiver end, revere operation are performed which include Fourier tranform computation, parallel-to-erial converion,, and demodulation, repectively. Thu the propoed model allow the uer to imulate the OFDM ignal formulation, tranition, and receiving. Here, a wa previouly mentioned, the uer can elect the deired modulation cheme, ymbol order, bit tream ize, and number of ubcarrier. IV.OFDM Model Teting Here, the imulated OFDM model i crutinized uing different SNR value. A a reult, a figure that how the behavior of BER veru the (Eb/No)change i obtained. The acquired reult are compared with thoe tandard reult obtained

6 370 Aladdin Amro, Fadi Abu-Amara and Ahmed Mua from the Matlab BERTool [7]. Fortunately, a cloe match between the imulator reult and the tandard one ha achieved. A wa previouly mentioned, thi tudy aim at tudying the OFDM ytem performance(i.e., meauring BER) according to the change of the following ytem parameter. 1. BER performance for different contellation ize The model wa run for 4, 16, and 32 QAM contellation. Figure 3 diplay BER v. Eb/No for thee contellation. Figure 3 how that the BER performance of the ytem i inverely dependent on contellation ize. Thi mean that when the contellation ize increae the BER increae accordingly For intance, to achieve BER =10-4 for 4 QAM contellation we need 7 db SNR. However, a 12 db SNR i required to achieve the ame BER for 16 QAM QAM 4 QAM 32 QAM 10-2 BER Eb/N0 Figure 3: BER v. SNR for different contellation ize Similar reult are achieved in for 2 (i.e., BSK),4, and 16 contellation a hown in Figure 4.

7 Flexible OFDM ytem imulation model QAM 4 QAM BSK 10-2 BER Eb/N0 Figure 4: BER v. SNR for different contellation ize 2. BER Performance for Different Number of Subcarrier To crutinize the effect of number of ubcarrier on BER performance, the model ha been run for different number of ubcarrier. Figure 5 how the BER v. Eb/NO for 512, 256, and 1028 ubcarrier are. From the BER curve (Fig. 5), it can be oberved that the BER performance i almot independent of the number of ubcarrier except at very high SNR.

8 372 Aladdin Amro, Fadi Abu-Amara and Ahmed Mua car 256 car 1028 car 10-3 BER Eb/NO Figure 5:BER v. SNR for different number of ubcarrier 3. BER performance for different Symbol mapping The propoed model give the uer the opportunity to chooe ymbol order (binary, gray,etc). Figure 6 how the BER curve for two ymbol mapping; gray and binary.

9 Flexible OFDM ytem imulation model Binary Gray 10-2 BER Eb/N0(dB) Figure 6: BER v. SNR for Binary and Gray mapping V. CONCLUSION In thi paper, a flexible OFDM imulation model ha been developed. In thi model the ytem parameter can be eaily changed according to pecific ytem requirement. The BER v. SNR carve for OFDM ytem are obtained for different ytem parameter. The analyi of the obtained reult how that the developed model can efficiently imulate and demontrate the effect of changing of OFDM ytem parameter. Thu, the developed model can be ued a a reearch tool (or educational tool) to perform deepen tudy and invetigation to improve OFDM ytem performance. Reference [1] A. R. Bahai and B. R. Saltzberg "Multi-Carrier Digital Communication: Theory and Application of OFDM" Kluwer Academic Publiher, 2004.

10 374 Aladdin Amro, Fadi Abu-Amara and Ahmed Mua [2] LIAN HuaZhAOruimei HU boning PANG Huawei," Simulation and Analyi of OFDM Communication Sytem", nd International Conference on Indutrial Mechatronic and Automation. [3] Lun Zhang, Qing Zhao, Simulation and Analyi of MIMO-OFDM Sytem Baed On Simulin, IEEE International Conference. [4] Taewon Hwang; Chenyang Yang; Gang Wu; Shaoqian Li; Ye Li, G.;"OFDM and It Wirele Application: A SurveyVehicular Technology, IEEE Tranactio [5] Theodore S. Rappaport, A. Annamali, R. M.Buehrer, and W.H. Tranter "Wirle Communication: Pat event and a future perpective",ieee Communication Magazine 50th Anniverary Commemorative Iue/May [6] William Shieh and Ivan Djordjevic" OFDM for Optical Communication ", Elevier, [7] Received: May, 2012