Design and Simulation of MC-CDMA Transceiver via Slantlet Transform

Transcription

1 I.J. Informaton Technology and omputer Scence, 202, 3, 6-23 Publshed Onlne Aprl 202 n MES ( DOI: 0.585/jtcs Desgn and Smulaton of -DMA Transcever va Slantlet Transform Kattoush A. H. Electrcal Engneerng Department, Tafla Techncal Unversty, Jordan, Emal: aattoush@yahoo.ca Qasaymeh M. M. Electrcal Engneerng Department, Tafla Techncal Unversty, Jordan, Emal: qasaymeh@ttu.edu.jo Abstract Wreless communcatons s a rapdly growng pece of the communcatons manufacturng, wth the potental to provde hgh-speed hgh-qualty nformaton exchange between the portable devces located anywhere n the world. Mult-arrer ode Dvson Multple Access (-DMA) has emerged recently as a promsng canddate for the next generaton broad-band moble networs. Recently, t was found that Slantlet transform () based Orthogonal Frequency Dvson Multplexng (OFDM) s capable to reduce the Inter Symbol Interference (ISI) and the Inter arrer Interference (II), whch are caused by the loss of orthogonalty between the subcarrers. -OFDM can support hgher spectrum effcency than Fast Fourer Transform-based OFDM (-OFDM) due to the elmnaton of the yclc Prefx (P). In ths paper, a novel --DMA transcever desgn s presented based on the -OFDM that s used as a basc buldng bloc n the desgn of -DMA transcever to mantan the orthogonalty aganst the multpath frequency Selectve Fadng s (SF). Smulaton results are provded to demonstrate the sgnfcant gan n the performance of the proposed technque. The Bt Error Rate () of --DMA scheme s compared wth --DMA and tested n Addtve Whte Gaussan Nose (AWGN), Flat Fadng and Selectve Fadng s (SFH). The smulaton results confrmed that, the proposed system outperforms the reference one. Index Terms Slantlet Transform; Slantlet based OFDM; -DMA; Selectve Fadng.. Introducton Wreless communcatons [-4] s a rapdly growng pece of the communcatons manufacturng, wth the potental to provde hgh-speed hgh-qualty nformaton exchange between the portable devces located anywhere n the world. Mult-path fadng channels have a severe effect on the performance of wreless communcaton systems, even those systems that exhbt effcent bandwdth, le Orthogonal Frequency Dvson Multplexng (OFDM) and Mult-arrer ode Dvson Multple Access (- DMA). There s always a need for developments n the realzaton of these systems as well as effcent channel estmaton and equalzaton methods to enable these systems to reach ther maxmum performance []. DMA has been a robust canddate to support multmeda moble servces because t has the capablty to handle wth the asynchronous nature of the multmeda traffc and t can afford hgher capacty as opposed to the conventonal access schemes [2, 3]. The man problem n the desgn of a communcatons system over a wreless ln s to deal wth mult-path fadng, whch causes a sgnfcant degradaton n terms of both the relablty of the ln and the data rate [4]. Recently, a number of new -DMA systems have been proposed as an alternatve to the classcal sngle-carrer DMA systems [5-0]. The prncple of DMA was combned wth OFDM, whch allows one to use the avalable spectrum n an effcent way and mantan the many advantages of a DMA system []. Ths combnaton of OFDM-DMA or -DMA was frst proposed n []. It s a useful technque for 4-th generaton (4G) systems where varable data rates as well as relable communcaton systems are requred. ombnng OFDM wth DMA has one ey advantage; t can lower the symbol rate n each subcarrer compared to OFDM so that longer symbol duraton maes t easer to synchronze.

2 Desgn and Smulaton of -DMA Transcever va Slantlet Transform 7 H(z) 2 H(z)H(z 2 ) 4 H(z) 2 H(z)F(z 2 ) 4 F(z) 2 F(z) 2 F(z) 4 z -2 F(z) 4 (a) Two-scale terated flter-ban (b) Equvalent form usng the DWT Fg. : Two-scale terated flter-ban and ts equvalent form usng the DWT. -DMA not only mtgates the ISI but also explots the multpath [2]. The same dea was proposed agan and the performance of maxmum lelhood detecton for -DMA systems was analyzed [3]. The Fourer based complex exponental carrers of the OFDM system was nterchanged wth some orthonormal wavelets n order to reduce the level of nterference. The wavelets are derved from multstage tree-structured Haar and Daubeches orthonormal Quadrature Mrror Flter ban. omparng wth the conventonal OFDM, t was found that the Haar and Daubeches-based orthonormal wavelets are capable of reducng the power of ISI and II [4]. The -OFDM has currently drawn most of attenton n the area of wreless communcaton. To combat ISI and II, yclc Prefx (P) s nserted between -OFDM symbols whch tae around 25 percent of bandwdth. To mprove the bandwdth effcency and reduce the ISI and II Dscrete Wavelet Transform (DWT) based OFDM was proposed and studed extensvely. A comparson between -OFDM and DWT-OFDM at dfferent transmsson scenaros can be found n [5, 6]. DWT-based -DMA has lately ganed popularty n lterature due to very hgh spectral contanment propertes of wavelet flters [7-9]. Waveletbased -DMA can better combat narrowband nterferences and more robust to II than tradtonal flters. Moreover, snce the classc noton of a guard band does not apply for DWT--DMA; data rates can be enhanced over those of mplementatons. In order to further reduce the level of nterference, ncrease the spectral effcency, and reduce the computaton complexty s replaced wth Slantlet Transform () n -DMA desgn n ths paper. The performance comparsons of --DMA and --DMA on three dfferent channel models: AWGN, flat fadng and selectve frequency fadng s provded. Smulaton results show that proposed desgn acheves much lower Bt Error Rates (),ncreases Sgnal to Nose power Rato (), and can be used as an alternatve to the conventonal - DMA. In ths paper, a novel --DMA transcever desgn s presented based on the -OFDM that s used as a basc buldng bloc n the desgn of -DMA transcever to mantan the orthogonalty aganst the mult-path frequency SF. The rest of ths paper s organzed as follows. Secton two ntroduces the Slantlet based OFDM system. Secton three presents the proposed realzaton of -based -DMA. Secton four provdes the performance analyss of the proposed --DMA ncludng smulaton results to demonstrate the sgnfcant gan n the performance of the proposed technque. 2. Slantlet based OFDM system The was frst proposed by Selesnc [20]. It s an orthogonal DWT wth two zero moments and wth mproved tme localzaton. It uses a specal case of bass [20], the constructon of whch reles on Gram Schmdt orthogonalzaton. Selesnc descrbed the bass from a flter-ban vewpont, gave explct solutons for the flter coeffcents, and descrbed an effcent algorthm for the transform. The usual terated DWT flter-ban and ts equvalent form are shown n Fg.. The Slantlet flterban s based on the equvalent structure that s occuped by dfferent flters that are not products. Wth ths extra degree of freedom obtaned by gvng up the product form, flters of shorter length are desgned satsfyng orthogonalty and zero moment condtons. For two-channel case the Daubeches flter [22] s the shortest flter whch maes the flter-ban orthogonal and has K zero moments. For K=2 zero moments, flters H(z) and F(z) are of length 4. For ths system, the terated flters n Fg. are of length 0 and 4. Wthout the constrant that the flters are products, an

3 8 Desgn and Smulaton of -DMA Transcever va Slantlet Transform Input Data Output Data Seral to Transmtter to Seral Sgnal Plots carrers generaton Sgnal De- -OFDM Modulator Zero Pad ompensaton I Remove Zero Pad to Seral -OFDM DeModulator h(t) AWGN + Seral to Recever Estmaton Fg. 2: Bloc Dagram of -OFDM System orthogonal flter-ban wth K=2 zero moments can be obtaned where the flter lengths are 8 and 4. That s a reducton by two samples, whch s a dfference that grows wth the number of stages. Ths reducton n length, whle mantanng desrable orthogonalty and moment propertes, s possble because these flters are pecewse lnear. Even though there s no tree structure for, t can be effcently mplemented le an terated DWT flter-ban [20]. Therefore, a computatonal complexty of the s of the same order as that of the DWT. The bloc dagram of the -OFDM system s depcted n Fg. 2. It s very smlar the -OFDM wth some dfferences n the OFDM modulator-demodulator blocs. The processes of seral to parallel (S/P) converson, sgnal de-mappng, and tranng sequence nserton are the same. The -based OFDM modulator conssts of zero paddng and Inverse (I) blocs whle the -based OFDM demodulator conssts of and zero-pad removal blocs. The man dfference between -OFDM and -OFDM s that n - OFDM there s no need for addng a P to OFDM symbols; therefore the spectral effcency and the data rate of -OFDM are better than those of -OFDM. 3. Proposed realzaton of -based - DMA The -DMA transmtter spreads the orgnal data stream over dfferent sub-carrers usng a gven spreadng code n the frequency doman [, 3]. Fg. 3 and Fg. 4 show the -DMA transmtter of the th user for BPSK scheme and the power spectrum of the transmtted sgnal respectvely [9], where d (t) s the data bts for th user, G denotes the processng gan, N s the number of sub-carrers and (t) s the spreadng Pseudo-random Nose (PN) sequence of the th user. It s assumed that N = G []. In -DMA systems, the orgnal data stream from a user s spread wth the user s specfc spreadng code n the frequency doman. In other words, a fracton of the symbol correspondng to a chp of the spreadng code s transmtted through a dfferent subcarrer. The narrowband subcarrers are generated usng BPSK modulated sgnals, each at dfferent frequences, whch at baseband are multples of harmonc frequency /T s. That s, Δ f = f f = () T where, T s s the symbol duraton of data stream. The subcarrer frequences are orthogonal to each other at baseband. The transmtted sgnal of the th user s gven by: N S S ( t) = d ( t) c cos( ω t) (2) = The total bandwdth requred for transmsson s: β = ( N +)G N T S (3) The receved sgnal of -DMA systems [9] for all K users as Fg. 5 shows s gven by: K = N r( t) = d ( t) h( ) c cosω t + n( t) = (4)

4 Desgn and Smulaton of -DMA Transcever va Slantlet Transform 9 d 2 3 f G d (t) d (t) d t t t ( ) 2 t ( ) N (t) cos( ω t) cos( ω t) 2 cos( ω N t) Fg. 3: -DMA transmtter system model Σ s (t) r(t) cos( ωt) cos( ω t) 2 LPF LPF LPF q q 2 Σ cos( ω G t) q g. 5: -DMA recever system model. dˆ F f f 2 f 3 f N f Fg. 4: Power spectrum representaton of the transmtted sgnal. I/P Data Spreadng ode Transmtter Seral to Sgnal Sgnal Plots carrers generator -OFDM Modulator To Seral h(t) AWGN + O/P Data DeSpreadng ode Recever To Seral Sgnal De ompensaton Estmator -OFDM De- Modulator Seral to Fg. 6: Bloc Dagram of proposed --DMA System where n(t) s the Addtve Whte Gaussan Nose (AWGN) and h() s the complex sgnal channel coeffcent of the th subcarrer. The receved sgnal s demodulated wth correspondng subcarrer followed by low pass flterng to generate the baseband sgnal. The baseband sgnal s weghted by some coeffcents, and then all baseband sgnals are combned together. It can be seen that the receved sgnal s combned n the frequency doman therefore the recever can always employ all the receved sgnal energy scattered n the frequency doman. Ths s the advantage of -DMA [, 3]. Dfferent combnng technques to enhance the system performance can be used, whch correspond to dfferent choces of coeffcents. Typcal combnng technques nclude maxmum rato combnng, equal gan combnng [] and mnmum mean square error combnng [3]. The drawbac of ths system s that, t does not consder the multpath and fadng effects. The bloc dagram of the proposed system for based -DMA s depcted n Fg. 6. In ths desgn the -Based OFDM s replaced wth a -based OFDM whch has a better performance and a reduced ISI and II n comparson wth -based OFDM. Each data symbol s multpled wth a spreadng sequence, the Gold sequence can be used snce t has a relatvely good correlaton values. Other spreadng codes that have a relatvely good correlaton values le Walsh-Hadamard (WH) code can be used, but t can be used when a small number of users are consdered, snce the orthogonalty of the code s reduced due to the multpath propagaton [23]. Bnary Phase Shft Keyng (BPSK) or Quadrature Phase Shft Keyng (QPSK) sgnal mappng can be used for mappng the spreadng and the tranng sequences. After that a plot-carrer (tranng sequence) whch may be a bpolar sequence prevously nformed to recever s generated. The channel frequency response s estmated by usng the tranng and the receved sequences as follows:

5 20 Desgn and Smulaton of -DMA Transcever va Slantlet Transform receved Tranng Sample () H ( ) = (5) transmtte d Tranng Sample () The channel frequency response prevously found s used to compensate the channel effects on the data. 4. Performance Analyss of proposed -- DMA In ths secton the results of performance smulatons usng MATLAB 7 for --DMA are provded and compared wth the conventonal - - DMA under dfferent channel condtons. AWGN channels, Flat Fadng s (FF), and mult-path frequency selectve Raylegh dstrbuted wth AWGN channels are consdered durng smulatons. The system parameters used n the smulaton are as follows: 5MHz bandwdth, BPSK modulaton, Walsh-Hadamard spreadng code, and 64 sub-carrers. 4. Performance of --DMA n AWGN The performance of the proposed -- DMA and the conventonal --DMA system n AWGN channel s shown n Fg. 7. The s changed from 0dB to 40dB. From whch t can be noted that - -DMA has an gan of 6dB compared wth --DMA system to acheve of. Also t has an gan of 6dB compared wth -- DMA system to acheve of. 4.2 Performance of --DMA n a Flat Fadng The performance of -based -DMA n a Flat Fadng s tested under a two-ray Rayleghdstrbuted mult-path fadng channel model s assumed. The second path gan and delay was set to -8dB and µsec respectvely. It s assumed that all frequency components of the transmtted sgnal are changed and correlated n phase and magntude Fg. 7: Performance of -DMA n AWGN channel. Fg. 8: Performance of --DMA n FF at maxmum Doppler shft = 5Hz Fg. 9: Performance of --DMA n FF at maxmum Doppler shft = 500Hz. Three maxmum Doppler shfts are used n the smulaton: 5Hz, 500Hz, and 00Hz. The results of smulaton are shown n Fg. 8, Fg. 9 and Fg. 0. It can be seen from the fgures that performance of - -DMA system s stll better than the -- DMA system. For example, Fg. 8 shows that - -DMA has = at =25dB, whle - -DMA system has = at about =40dB. Ths s a 5dB gan n. 4.3 Performance of proposed --DMA system n Selectve Fadng In Selectve Fadng (SF), the frequency complements of the transmtted sgnal are affected by uncorrelated changes, where the parameters of the channel correspond to two path system. For SF many models are used n smulaton and performance s compared for -based and -based -DMA systems, the effect of path attenuaton, delay and maxmum Doppler shft of an echo was also taen n

6 Desgn and Smulaton of -DMA Transcever va Slantlet Transform 2 account. Fg. shows the performance smulaton of the --DMA and the --DMA systems for a SF wth path delay equal sample, path gan equal -8dB, and Doppler shft equal 5Hz. Fg. 2 and Fg. 3 plot the performance smulaton of the systems for SF wth the same channel parameters except changng Doppler shft to 500Hz and 00Hz respectvely. It s seen that --DMA system has better performance than - -DMA system. Fg. 4, Fg. 5, and Fg. 6 show the performance smulaton of the - -DMA and -- DMA systems for a SF wth path delay equal sample, Doppler shft equal 5Hz, and path gan equal - db, -5dB and -2dB respectvely. It can be seen from plots that the performance of --DMA s better than that of --DMA for less than 35 db, but for greater than 35 db --DMA outperforms --DMA system. Fg. 7, and Fg. 8 show the performance smulaton of the - -DMA and --DMA system for a SF wth path gan equal -5dB, Doppler shft equal 5Hz, and path delay equal sample and 2 samples respectvely. It can be seen from plots that performance of - -DMA system s always better than that of - -DMA system. For example from Fg DMA has = at =2.5dB, whle - -DMA system has = at about =37.5dB. Ths s a 6dB gan n. Fg. 0: Performance of --DMA n FF at max. Doppler shft = 00Hz Fg. : Performance of --DMA n SF at maxmum Doppler Shft=5Hz. Fg. 2: Performance of --DMA n SF at maxmum Doppler Shft=500Hz. Fg. 3: Performance of --DMA n SF at max. Doppler Shft=00Hz.

7 22 Desgn and Smulaton of -DMA Transcever va Slantlet Transform Fg. 4: Performance of --DMA n SF wth path gan = db. Fg. 7: Performance of --DMA n SF wth path delay = sample. Fg. 5: Performance of --DMA n SF wth path gan = -5dB. Fg. 8: Performance of --DMA n SF wth path delay = 2 sample. 5. onclusons DWT Fg. 6: Performance of --DMA n SF wth path gan = -2dB. In ths paper a novel -DMA system s desgned and mplemented, -OFDM transcever scheme s used n proposed -DMA system nstead of conventonal -OFDM. A robust to nose nterference s used to mprove the performance of the communcaton system wthout a need to use the cyclc prefx. omparng the performance of --DMA and --DMA n AWGN channel, FF, and SF ndcated that for AWGN channel --DMA has performance gan about 5dB compared wth -- DMA to acheve =. For FF and for dfferent maxmum Doppler shft, --DMA system has better performance than conventonal system, t has performance gan of about 2dB compared wth - -DMA to acheve =. In SF proposed --DMA has better performance than -- DMA n all cases even when changng all channel

8 Desgn and Smulaton of -DMA Transcever va Slantlet Transform 23 parameters. Maxmum Doppler shft badly affects the performance of --DMA compared wth other channel parameters. It can be noted that DMA when combned wth OFDM, has performance better than just usng OFDM only. Ths can be addressed to spreadng the orgnal data stream and then modulatng dfferent carrers wth each chp. References [] Goldsmth A., Wreless ommuncatons, ambrdge Unversty Press, [2] Mng K. and hee T. Hybrd OFDM-DMA: A omparson of /DS-DMA, -DMA and OFDM, Dept of Electrcal & Electronc, Adelade Unversty, SA 5005, Australa [3] Ryu K. W., Par J. O. and Par Y. W., Performance of multcarrer S/DMA n frequency-selectve Raylegh fadng channels, 2003 Sprng IEEE 57th Semannual Veh. Tech. onf., vol. 2, pp , Aprl [4] Ngh H. Tran, Nguyen Ha H., and Tho Le-Ngoc, Bt- Interleaved oded OFDM wth Sgnal Space Dversty: Subcarrer Groupng and Rotaton Matrx Desgn, IEEE Transactons On Sgnal Processng, 55 (2007) pp [5] Daslva V. and Sousa E. 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A., Wavelet-based multcarrer DMA system and ts correspondng multuser detecton, IEE Proc. ommun., vol. 50, no. 6, pp , December [8] Haxa Zhang, Dongfeng Yuan, and Matthas Patzold, Novel Study on PAPRs Reducton n Wavelet Based Multcarrer modulaton Systems, Dgtal Sgnal Processng, vol. 7, no., pp , Jan [9] Xangbn Yu; Guangguo B; Performance Analyss of Multcarrer DMA System Based On omplex Wavelet Pacet And Space Tme Bloc odes In Raylegh Fadng, World Scentfc Publshng, Journal of rcuts, Systems, and omputers, Vol. 5, No. (2006) [20] Selesnc I. W., The slantlet transform, IEEE Trans. Sgnal Processng, 47 (999), pp [2] Alpert B., Beyln G., ofman R., and Rohln V., Wavelet-le bases for the fast soluton of second-nd ntegral equatons, SIAM J. Sc. omput., 4 (993), pp [22] Daubeches I., "Ten Lectures on Wavelets", Phladelpha, PA: SIAM, 992. [23] Yew T. J., Multwavelets and Scalable Vdeo ompresson, Ph.D. Thess, Department of Electrcal and omputer Engneerng, Natonal Unversty of Sngapore, Abbas Hasan Kattoush receved hs M.S., and Ph.D. degrees n communcaton Eng. from former USSR n 979 and 984 respectvely. For 0 years Dr Kattoush was a techncal manager of a leadng SAKHER computers company. He was a poneer n computer networng and software engneerng n Jordan. From 993 to 2000 he wored at Appled Scence Unversty Amman Jordan where he was a foundng member of the department of electrcal and computer engneerng. From 2000 to 2008 Dr. Kattoush was an assocate professor at Electrcal and omputer Engneerng department at Al-Isra Unversty, Amman-Jordan. urrently he s an assocate professor at Tafla Techncal Unversty, Jordan. Hs areas of research nterest nclude DSP, dgtal communcaton systems, phase unwrappng, flterng, and nterpretaton. He has authored several tenths of research artcles, textboos, and computer software systems. Mahmoud Qasaymeh has done hs Ph.D n Electrcal Engneerng / Telecommuncatons at Wchta State Unversty (WSU), Kansas He dd hs MSc and B.Sc n Electrcal Engneerng / Telecommuncatons and Electroncs at Jordan Unversty of Scence and Technology. Dr. Qasaymeh s currently wth Tafla Techncal Unversty, Jordan.