Comparative BER Performance Analysis of OFDM System Using M-PSK and M-QAM Modulation Schemes over AWGN Channel

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1 S Scholar Knowlede i Power Auut 22 Volume, Iue 4 Article # IJCCet Reearch Paper ISS: Comparative BR Performance Analyi of OFDM Sytem Uin M-PSK and M-QAM Modulation Scheme over AWG Channel uhar Kanti Roy Department of lectronic and elecommunication nineerin, Rajhahi Univerity of nineerin & echnoloy, Rajhahi-624, Banladeh. *Correpondin author roy_anti@yahoo.com Abtract Orthoonal frequency diviion multiplexin (OFDM) i becomin the choen modulation technique for wirele communicatio It can provide lare data rate and i ufficiently robut in the face of radio channel impairment. Diital modulation technique contribute to the evolution of our mobile wirele communication by increain the capacity, peed and quality of wirele networ. In thi paper, I concentrate on diital modulation cheme, uch a M-PSK (M-ary Phae Shift eyin) and M-QAM (M-ary Quadrature Amplitude Modulation) over an additive white Gauian oie (AWG) channel to analye the performance of an OFDM ytem in term of bit error rate (BR). hi i evaluated throuh a computer imulation, the reult from which mae it clear that, for hih-capacity data rate tranmiion, the M-QAM modulation i better than the M-PSK modulatio Keyword: AWG, BR, OFDM, M-PSK, M-QAM. Citation: Roy. K., Comparative BR Performance Analyi of OFDM Sytem Uin M-PSK and M-QAM Modulation Scheme over AWG Channel, IJCCet (4): p. 5. Received: Accepted: Roy. K. hi i an open acce article ditributed under the term of the Creative Common Attribution 3. Licene. I. Introduction he rowth in the ue of information networ ha led to the need for new communication technique with hiher data rate. OFDM i a powerful modulation technique ued to achieve a hih data rate and i able to eliminate inter-ymbol interference (ISI). It i computationally efficient due to it ue of fat Fourier tranform (FF) technique for implementin modulation and demodulation functio In an OFDM cheme, a lare number of orthoonal, overlappin, narrow-band ub-channel or ubcarrier, tranmitted in parallel, divide the available tranmiion bandwidth. OFDM i the modulation technique ued in many new broadband communication cheme, includin diital televiion, diital audio broadcatin, ADSL and wirele LA. It alo allow diital data to be efficiently and reliably tranmitted over a radio channel, even in multipath environment [-3]. In OFDM, althouh ub-carrier overlap, thi doe not create any problem ince they are orthoonal, that i, the pea of one occur when that of other are at zero. hi i achieved by realizin all the ubcarrier toether uin the invere fat Fourier tranform (IFF). he analyi of BR performance have ueted that OFDM i better than CDMA which i currently incorporated in mot exitin 3G ytem [4, 5]. A major problem in mot wirele ytem i the preence of a multipath channel. In thi environment, the tranmitted inal reflect off everal objective and a reult, multiple delayed verion of the tranmitted inal arrive at the receiver which caue the received inal to be ditorted. Many wired ytem alo have a imilar problem with reflection occurrin due to impedance mimatche in the tranmiion line. A multipath channel will caue two problem for an OFDM ytem. he firt i ISI which occur when the received OFDM ymbol i ditorted by the previouly tranmitted OFDM ymbol and ha a imilar effect to the ISI that occur in a inle-carrier ytem. However, in uch ytem, the interference i typically due to everal ymbol other than only the previou one; and the ymbol period i typically much horter than the time pan of the channel, wherea the typical OFDM ymbol period i much loner than the time pan of the channel. he econd problem i unique to multi-carrier ytem and i called intra-ymbol interference which i the reult of interference amont a

2 iven OFDM ymbol own ub-carrier. An adaptive modulation and codin technique for overcomin any inter-ymbol interference (ISI) and analyin the performance of the BR i propoed in [6]. Comparative BR performance of diital modulation technique under multipath fadin are addreed in [4] in which the performance of the OFDM ytem i teted for M- PSK and M-QAM uin MALAB. he performance of different modulation cheme for the OFDM-baed WLA tandard I 82.a are dicued in [7]. he concept of OFDM i quite imple but it practical implementation involve many complexitie. A inle tream of data i plit into parallel tream, each of which i coded and modulated on to a ub-carrier, a term commonly ued in OFDM ytem. hu, a the hih bit rate previouly een on a inle carrier are reduced to lower bit rate on it ub-carrier, it i eay to ee that ISI will be dramatically reduced. he main purpoe of thi paper i to preent the commonly ued modulation cheme in wirele communication ytem, demontrate the performance of the M-QAM and M-PSK modulated ytem with OFDM in the preence of a noiy channel alon and indicate way of reducin the BR. herefore, throuhout thi paper, I preent BR performance comparion of different diital modulation cheme uin the OFDM technique over an AWG channel. he ret of thi paper i oranized a follow. Section II briefly introduce the OFDM ytem model in which I decribe the OFDM tranmit and receive inal mathematical equation with relationhip between / and b / for the OFDM ytem and the cyclic prefix for OFDM. Section III dicue the imulation reult and concluion are preented in ection IV. II. Sytem Modellin A. OFDM ranceiver In thi ection, I decribe the OFDM tranceiver ytem. Before tranmittin information bit over an AWG channel throuh the OFDM tranmitter, I ue the M-PSK and M-QAM modulation cheme hown in Fi.. he tranmitter ection convert the diital data to be tranmitted, into a mappin of the ub-carrier amplitude and phae uin modulation technique. he pectral repreentation of the data i then tranformed into the time domain uin an IFF which i much more computationally efficient and ued in all practical ytem [8, 9]. he addition of a cyclic prefix to each ymbol olve both ISI and inter-carrier interference (ICI) [, ]. he diital data i then tranmitted over the channel. After the time-domain inal pae throuh the channel, it i broen down into the parallel ymbol and the prefix i imply dicarded. he receiver perform the revere operation to that of the tranmitter. he amplitude and phae of the ub-carrier are then elected and converted bac to diital data. In OFDM, multiple inuoidal with frequency eparation / are ued, where i the active ymbol period. he information to be ent on each ub-carrier i multiplied by it correpondin carrier j2t the tranmit inal. herefore, the inuoidal ued in OFDM can be defined a [2]: e and the um of uch modulated inuoidal form j2t e w( () where, =,,...- correpond to the frequency of the inuoidal and w( =u(-u(t-) i a reular window over [, ]. Since the OFDM ytem ue multiple inuoidal inal with frequency eparation of /, each inuoidal i modulated by independent informatio Mathematically we can write a tranmit inal over the channel a, S( e j2t... w( where, i the th ymbol in the meae ymbol equence for in [, -],where i the number of carrier. (2) 2

3 Diital Modulation S/P Conv. IFF Cyclic Prefix Addition Channel (AWG or Rayleih ) Diital Modulation P/S Conv. FF Cyclic Prefix Removal Fi.: Bloc diaram of a baic OFDM tranceiver In an OFDM receiver, we multiply the received inal by a ban of correlator and interate it over period. herefore, the information ent on ubcriber i j2mt ( e,, m m (3) where, m tae it value from to -. A we conider the AWG channel, we can remove the frequency domain equalizer bloc from the above OFDM tranceiver ytem becaue a frequency domain equalizer i helpful only if the channel introduce multipath fadi B. Relationhip between / or b / for OFDM Sytem hi ection preent the relationhip between the / and b / for the OFDM ytem. o conduct a Monte Carlo imulation of an OFDM ytem, the required amount of channel noie to be enerated ha to be repreentative of the required / or b /. In MALAB it i eay to enerate a Gauian noie with a zero mean and unit variance which ha to be caled accordinly to repreent the required b / or /. ormally, for a imple BPSK ytem, the bit enery and ymbol enery are the ame a it b / and /. However, if we ue a M-QAM or M-PSK modulation cheme for the OFDM ytem then they are not the ame becaue each OFDM ymbol contain an additional overhead in both the time and frequency domai In the time domain, the cyclic prefix i an additional overhead to each OFDM ymbol bein tranmitted. In the frequency domain, not all the ub-carrier are utilized for tranmitted the actual data bit, rather a few ub-carrier are unued and are reerved a uard band. he relationhip between the ymbol enery and bit enery i [3]: b DSC d ( )( ) (4) FF d cp If we expre the above equation in db, we can write b DSC d db db lo( ) lo( ) (5) FF d cp where, d i the data ymbol duration, cp the cyclic prefix duration and DSC the number of ued ubcriber ued in the OFDM ytem. C. Cyclic Prefix of OFDM hi ection decribe the cyclic prefix of the OFDM ytem. Since orthoonality i an important property for an OFDM ytem, it ynchronization in frequency and time mut be extremely ood. Once orthoonality i lot, we experience ICI thi introduce 3

4 Bit rror Rate, BR interference from one ub-carrier to another. Another reaon for ICI in an OFDM ytem i that, if we add the uard time with no tranmiion that create problem for the IFF and FF, and reult in ICI. Althouh a delayed verion of one ub-carrier can interfere with another ubcarrier in the next ymbol period, thi can be avoided by extendin the ymbol into the uard period precedin it which i nown a a cyclic prefix. It enure that delayed ymbol have inteer number of cycle within the FF interation interval which remove ICI providin the delay pread i le than the uard period. We hould note that a FF interation period exclude the uard period. In an OFDM tranmiion, we now that tranmiion of the cyclic prefix doe not carry extra information over AWG channel. he inal enery i pread over time d + cp wherea the bit enery i pread over time d i.e. ( ) (6) d cp b d After implifyin we et the followin equation, d b ( d cp ) (7) III. Simulation reult In thi ection, I preent the BR performance of the OFDM ytem for different diital modulation cheme over an AWG channel invetiated by mean of a computer imulation uin MALAB. he performance of a data tranmiion ytem i uually analyed and meaured in term it of probability of error at a iven bit rate and SR. he parameter b /, where b i the bit enery and o the noie enery, i adjuted every time by chanin the noie in the deined channel. he BR performance of an OFDM ytem with M-QAM modulation over the AWG channel i hown in Fi.2 in which it can be oberved that when we continue to increae the b / value, the BR reduce. Alo it can be een that, althouh uin a hiher M- QAM i better for hih capacity tranmiion, the point on the contellation are very cloe to each other which mae the tranmiion le robut to error with the ame SR. Bit error rate of M-ary QAM over AWG M=24-2 M=2,4 M=8 M=6 M=52 M=256 M=32 M=64-4 M= SR, per bit, b / o (db) Fi.2: BR V b/ of M-ary QAM over AWG channel he BR performance reult for the OFDM ytem with M-PSK modulation over an AWG channel from the imulation are hown in Fi.3 in which it can be oberved that when we continue to increae the b / value, BR reduce. Alo uin a hiher M-PSK i better for hih-capacity tranmiio 4

5 Bit rror Rate, BR Bit error rate of M-ary PSK over AWG 32-PSK -2 QPSK 64-PSK 8-PSK -4 6-PSK SR per bit, b / (db) Fi.3: BR V b/ of M-ary PSK over AWG channel From Fi.2 and Fi.3, it i clear that, for 6-QAM at a -4 BR, the SR i 2.5dB wherea, for 6-PSK, it i 6dB. Similarly, for 32-QAM it i 5.5dB and for 32-PSK 2.5dB. herefore, M-QAM require a lower SR than M-PSK to achieve the ame BR in an OFDM ytem. IV. Concluion In thi paper, I have evaluated the BR performance of an OFDM ytem with two diital modulation cheme, namely M-ary PSK and M-ary QAM, over an AWG channel. OFDM i a powerful modulation technique to achieve hih data rate and i able to eliminate ISI. It i computationally efficient due to it ue of FF technique for implementin modulation and demodulation functio It i oberved from the M-ary PSK BR plot that the BR i le in the cae of 4-PSK for a low b / than in the 8- PSK and 6-PSK cae. Hence, a a hiher value of M-ary PSK increae pectrum efficiency, but i eaily affected by noie, the OFDM ytem with the hiher M-PSK cheme i ued for lare-capacity, lon-ditance application at the cot of liht increae in b / while that with the QPSK cheme i uitable for low-capacity, hort-ditance applicatio he comparion of M-ary PSK and M-ary QAM cheme indicate that, the BR i lare in M-PSK a compared to M-QAM and it i enerally dependin on it applicatio For a hiher value of M, uch a M > 6, the QAM modulation cheme i uitable for OFDM. In both cae, I obtain ood performance but of thee two modulation cheme I conclude that for a hih capacity data rate tranmiion M-ary QAM modulation i better than the M-ary PSK modulatio Reference [] J. Chuan and. Sollenberer, Beyond 3G: Wideband wirele data acce baed on OFDM and dynamic pacet ainment, I Communication Ma., vol. 38, pp , July 2. [2] Saltzber, B. R., Performance of an fficient Parallel Data ranmiion Sytem, I ra on Communication, Vol. COM-5, o. 6, December 967, pp [3] A.G.Armada, Undertandin the ffect of Phae oie in OFDM, I ranaction on Broadcatin, vol. 47, o.2, June 2. [4] Mehul Jain and M. Mani Roja, Comparion of OFDM with CDMA Sytem in Wirele telecommunication for multipath delay pread, he t I and IFIP International Conference in Central Aia, Sept., 25, Pae 5. [5] Bernard Slar, Diital Communication Fundamental and Application, Second dition, Pearon ducation, Aia, 2. [6] Sami H. O. Salih, Mamoun M. A. Suliman, Implementation of Adaptive Modulation and Codin echnique uin Matlab, 53rd International Sympoium LMAR-2, 4-6 September 2, Zadar, Croatia. [7] Sanjeev Kumar, Swati Sharma, rror Probability of Different Modulation Scheme for OFDM baed WLA tandard I 82.a International Journal of nineerin (IJ), Volume: 4, Iue: 4 [8] L. Hanzo, W. Webb, and. Keller, Sinle and Multi-carrier Quadrature Amplitude Modulation, ew Yor, USA: I Pre-John Wiley, April 2. [9] S. B. Weintein and P. M. bert, Data tranmiion by frequency diviion multiplexin uin the dicrete Fourier tranform, I ranaction on Communication echnoloy, vol. COM 9, pp , October 97. [] X. Cai and G. B. Giannai, Low-complexity ICI uppreion for OFDM over time- and frequency-elective Rayleih fadin channel, in Proc. Ailomar Conf. Sinal, Sytem and Computer, ov. 22. [] Shaopin Chen and Cuitao Zhu, ICI and ISI Analyi and Mitiation for OFDM Sytem with Inufficient Cyclic Prefix in ime-varyin Channel I ranaction on Conumer lectronic, Vol. 5, o., February 24. [2] M. S. Ilam, G. R. Barai, and A. Mahmood, Performance analyi of different cheme uin OFDM technique in Rayleih fadin channel, International Journal of Fundamental Phyic Science, Vol., o., pp , June, 2. 5