Research Article Performance Analysis of a Modified SC-FDMA-DSCDMA Technique for 4G Wireless Communication Deepak Kedia and Arti Modi Department of Electronics and Communication Engineering, Guru Jambheshwar University of Science and Technology, Hisar, Haryana 125 001, India Correspondence should be addressed to Deepak Kedia; [email protected] Received 30 May 2014; Accepted 10 November 2014; Published 24 November 2014 Academic Editor: Eduardo da Silva Copyright © 2014 D. Kedia and A. Modi. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Single-carrier FDMA (SC-FDMA) is becoming more and more popular in multiuser communication because of its lower PAPR value. Apart from this, many other hybrid access techniques have also been explored in the literature for application to 4G wireless mobile communication. Still there is a need to explore newer techniques which could further reduce the PAPR value without any degradation in system BER. Keeping this in view, a modified hybrid technique SC-FDMA-DSCDMA has been proposed in this paper and it is found to provide significantly lower PAPR than SC-FDMA system with no degradation in BER performance. is paper extensively compares the BER and PAPR performance of various other multicarrier techniques for 4G wireless communications such as OFDMA, MC-DS-CDMA, and SC-FDMA with proposed SC-FDMA-DSCDMA scheme. Simulation results show that SC-FDMA-DSCDMA technique performs better than any other OFDM-CDMA based system for wireless communication. 1. Introduction e demand for high data rate services has been increasing very rapidly and there is no slowdown in sight. Demands for media-rich wireless data services have brought much atten- tion to high speed broadband mobile wireless techniques in recent years. Orthogonal frequency division multiplexing (OFDM), which is a discrete multitone modulation (DMT), consists of a large number of closely spaced orthogonal sub- carriers carrying user data. e user data is divided into sev- eral parallel data streams or channels, one for each subcarrier. Each subcarrier is modulated with a conventional modula- tion scheme (such as quadrature amplitude modulation or phase-shiſt keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth [1]. OFDMA is a multiple access scheme which is an exten- sion of OFDM to accommodate multiple simultaneous users. e advantage of OFDMA is its robustness in the presence of multipath signal propagation. OFDMA presents the benefits of flexible resource allocation and scheduling. Dynamic allocation of subcarriers in OFDMA can further improve performance compared to fixed allocation. Because of these advantages, OFDMA has been adopted in wireless stan- dards including WiMax and LTE. Despite many advantages, OFDMA suffers from various drawbacks; that is, it exhibits very pronounced envelope fluctuations resulting in a high PAPR, a need for an adaptive or coded scheme to overcome spectral nulls in the channel and high sensitivity to frequency offset. Frequency offset destroys the orthogonality of the transmissions, thus resulting in MAI. erefore, LTE uses OFDMA only on the downlink and not on the uplink. To overcome these drawbacks, 3GPP introduced a mod- ified form of OFDMA for uplink transmissions in the long term evolution (LTE). e modified version of OFDMA, ref- erred to as single-carrier FDMA (SC-FDMA), provides simi- lar throughput performance and complexity. As in OFDMA, the transmitters in an SC-FDMA system use different orthog- onal frequencies (subcarriers) to transmit information sym- bols. However, these transmitters transmit the subcarriers sequentially, rather than in parallel. Unlike in OFDMA, this arrangement reduces considerably the envelope fluctuations in the transmitted waveform. erefore, SC-FDMA signals have lower PAPR than OFDMA signals. However, in cellular Hindawi Publishing Corporation Journal of Computer Networks and Communications Volume 2014, Article ID 747824, 6 pages http://dx.doi.org/10.1155/2014/747824
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Research ArticlePerformance Analysis of a Modified SC-FDMA-DSCDMATechnique for 4G Wireless Communication
Deepak Kedia and Arti Modi
Department of Electronics and Communication Engineering Guru Jambheshwar University of Science and TechnologyHisar Haryana 125 001 India
Correspondence should be addressed to Deepak Kedia kedia29gmailcom
Received 30 May 2014 Accepted 10 November 2014 Published 24 November 2014
Academic Editor Eduardo da Silva
Copyright copy 2014 D Kedia and A Modi This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited
Single-carrier FDMA (SC-FDMA) is becoming more and more popular in multiuser communication because of its lower PAPRvalue Apart from this many other hybrid access techniques have also been explored in the literature for application to 4Gwireless mobile communication Still there is a need to explore newer techniques which could further reduce the PAPR valuewithout any degradation in system BER Keeping this in view a modified hybrid technique SC-FDMA-DSCDMA has beenproposed in this paper and it is found to provide significantly lower PAPR than SC-FDMA system with no degradation in BERperformance This paper extensively compares the BER and PAPR performance of various other multicarrier techniques for4G wireless communications such as OFDMA MC-DS-CDMA and SC-FDMA with proposed SC-FDMA-DSCDMA schemeSimulation results show that SC-FDMA-DSCDMA technique performs better than any other OFDM-CDMA based system forwireless communication
1 Introduction
The demand for high data rate services has been increasingvery rapidly and there is no slowdown in sight Demands formedia-rich wireless data services have brought much atten-tion to high speed broadband mobile wireless techniquesin recent years Orthogonal frequency division multiplexing(OFDM) which is a discrete multitone modulation (DMT)consists of a large number of closely spaced orthogonal sub-carriers carrying user data The user data is divided into sev-eral parallel data streams or channels one for each subcarrierEach subcarrier is modulated with a conventional modula-tion scheme (such as quadrature amplitude modulation orphase-shift keying) at a low symbol rate maintaining totaldata rates similar to conventional single-carrier modulationschemes in the same bandwidth [1]
OFDMA is a multiple access scheme which is an exten-sion of OFDM to accommodate multiple simultaneous usersThe advantage of OFDMA is its robustness in the presence ofmultipath signal propagation OFDMA presents the benefitsof flexible resource allocation and scheduling Dynamicallocation of subcarriers in OFDMA can further improve
performance compared to fixed allocation Because of theseadvantages OFDMA has been adopted in wireless stan-dards including WiMax and LTE Despite many advantagesOFDMA suffers from various drawbacks that is it exhibitsvery pronounced envelope fluctuations resulting in a highPAPR a need for an adaptive or coded scheme to overcomespectral nulls in the channel and high sensitivity to frequencyoffset Frequency offset destroys the orthogonality of thetransmissions thus resulting in MAI Therefore LTE usesOFDMA only on the downlink and not on the uplink
To overcome these drawbacks 3GPP introduced a mod-ified form of OFDMA for uplink transmissions in the longterm evolution (LTE) The modified version of OFDMA ref-erred to as single-carrier FDMA (SC-FDMA) provides simi-lar throughput performance and complexity As in OFDMAthe transmitters in an SC-FDMA system use different orthog-onal frequencies (subcarriers) to transmit information sym-bols However these transmitters transmit the subcarrierssequentially rather than in parallel Unlike in OFDMA thisarrangement reduces considerably the envelope fluctuationsin the transmitted waveform Therefore SC-FDMA signalshave lower PAPR than OFDMA signals However in cellular
Hindawi Publishing CorporationJournal of Computer Networks and CommunicationsVolume 2014 Article ID 747824 6 pageshttpdxdoiorg1011552014747824
2 Journal of Computer Networks and Communications
SC-FDMA
SC-FDMA-DSCDMA
Random data
sourceSpreading
Interleaver and
modulation
FFT
Subcarriermapping
IFFT
Add CP PS
DespreadingDeinterleaver
and demodulation
IFFT
Subcarrierdemapping
and equalization
FFT
Removal of CP SPBER
count
Channel
+
Figure 1 Modified SC-FDMA-DSCDMA system model CDMA spreading operation has been performed before interleaving andmodulation
systems with severe multipath propagation the SC-FDMAsignals arrive at a base station with intersymbol interferenceTherefore to cancel this ISI base station employs adaptive fre-quency domain equalization (FDE) This arrangement pro-vides useful model in cellular system because it reduces theburden of linear amplification in portable terminals at thecost of complex signal processing (frequency domain equal-ization) at the base station [2 3]
Next direct sequence code division multiple access (DS-CDMA) is a multiple access technique based on spread spec-trummodulation A spread spectrum system is one in whichthe transmitted signal is spread over a wider bandwidth requ-ired to transmit the information being sent [4 5] Spreadingis accomplished with the help of a code which is independentof the data At receiver the same code is used to despread andrecover the transmitted dataDS-CDMAsystemoffers severaladvantages in cellular environments including easy frequencyplanning high immunity againstMAI if high processing gainis used and flexible data rate adaptation [5]
The combination of DS-CDMA and OFDM leads tothe development of MC-DS-CDMA The multicarrier DS-CDMA transmitter spreads the SP converted data streamsusing a given spreading code in the time domain [6] and afterthat multicarrier modulation (OFDM) is performed by IFFToperation [4]This combination is very effective in combatingsevere multipath interference and provides multiple accesssimultaneously However MC-DS-CDMA suffers from highPAPR value because of multicarrier
Now we have considered in this paper amodified hybridtechnique SC-FDMA-DSCDMA obtained by combinationof SC-FDMA and DS-CDMA A similar technique has alsobeen considered earlier by Luo and Xiong [5] However inthis paper a modified technique is proposed where CDMAspreading operation is performed before interleaving andmodulation operation (Figure 1) We call this technique ldquoSC-FDMA-DSCDMArdquo which inherits merits of SC-FDMA aswell as DS-CDMA In addition to this the available literaturelacks the exhaustive analysis and comparison of this hybridtechniqueThis technique could prove to be a good alternativeto the SC-FDMA technique and thus simultaneously provid-ing better PAPR performance
This paper is organized as follows Section 2 provides thebackground that led to the formulation of problem consid-ered in this paper Section 3 covers a brief overview of themodified SC-FDMA-DSCDMA technique Furthermore inthe subsequent sections we discuss the comparative BERper-formance of SC-FDMA-DSCDMA with respect to differentmulticarrier techniques over different fading channel con-ditions Next PAPR performance of SC-FDMA-DSCDMAwith respect to different FFT size is analyzed and then compa-rative PAPR performance analysis of the proposed techniquewith different multicarrier techniques is also done Finallythe relevant results of the paper are concluded
2 Background and Problem Formulation
As already mentioned a CDMA system coupled with multi-carrier modulation offers many potential benefits but it alsosuffers from a major drawback due to multicarrier transmis-sion that is high PAPR Depending on the user data thesummation of subcarriers may result in a signal with largeamplitude or small amplitude And as a result the peak powerof signal is much greater than the average power The highPAPR causes out-of-band radiations due to nonlinear poweramplifier Therefore the transmit power amplifier must beoperated in linear region but it results in poor power conver-sion efficiency The multicarrier modulation (OFDMA) hasnow been replaced with SC-FDMA which provides furtherreduction in PAPR value of the transmit signal
A number of approaches have been proposed in theliterature [7] for reducing high value of PAPR in OFDMsystems Broadly speaking these PAPR reduction techniquescan be divided into two categories namely distortion-basedand distortionless techniques The distortion-based tech-niques achieve significant PAPR reduction but at the cost ofincreased BER high computational complexity data rate lossand so forth On the other hand distortionless techniquesachieve PAPR reduction without any degradation in BERand spectral efficiency The distortionless techniques mainlyrely on hybrid structures without introducing any deliber-ate distortion in the transmit signal Keeping in view this
Journal of Computer Networks and Communications 3
advantage of distortionless techniques we have proposed amodified hybrid technique that is SC-FDMA-DSCDMAwhich is a combination of SC-FDMA and DS-CDMA Asimilar technique has also been considered earlier by Luo andXiong [5] But in this paper we have explored an idea thatPAPR can be reduced further by proper placement of spread-ingdespreading block in hybrid OFDM-CDMA systems Inthe technique proposed by us CDMA spreading operationis performed before interleaving and modulation operation(Figure 1) However Luo and Xiong [5] have used the spread-ing process after modulation
Thus the main focus of this paper is on the reduction inPAPR value without any BER degradation through the use ofmodified hybrid SC-FDMA-DSCDMA technique Further itis aimed at establishing the proposed technique as a suitablealternative to the technique proposed by Luo and Xiong [5]and other existing techniques like SC-FDMA MC-DS-CDMA and OFDMA by comparing the PAPR and BER per-formance under different channel conditions Firstly it will beensured that no degradation in BER performance takes placedue to the modified systemThen the extent of improvementin PAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique will be analyzed
3 Overview of Proposed SC-FDMA-DSCDMA
Figure 1 shows the modified SC-FDMA-DSCDMA systemstructure Unlike OFDMA or OFDM-CDMA SC-FDMA-DSCDMA is a single-carrier spread spectrum technique Inthis technique the signal is generated by serial concatenationof DS-CDMA and SC-FDMA The key model of this systemis SC-FDMAmodelTheprinciple of SC-FDMA-DSCDMA isfirstly to map the chips of a spread data symbol in frequencydomain
The transmitter of this system groups the modulationsymbols into blocks each containing 119873 symbols The SC-FDMA system involves an119873-point FFT operation and thenit maps each of the 119873-FFT outputs to one of the 119872 (gt 119873)
orthogonal subcarriers that can be transmitted Then an119872-point IFFT transforms the subcarrier amplitudes to a complextime domain signal After that it inserts cyclic prefix to pro-vide guard time [8 9]
Therefore transmitted data propagating through the cha-nnel can be modelled as a circular convolution between thechannel impulse response and the transmitted data blockthrough the use of cyclic prefix At receiver side the receivedsignal is converted into frequency domain via DFT and thenfrequency domain equalization is performed after demappingthe subcarriers The equalized symbols are transformed backto the time domain via IDFT and decoding takes place inthe time domain At last despreading is done by multiplyingeach symbol with the same pseudorandom code and thendetection takes place [8]
4 PAPR of SC-FDMA-DSCDMA Signals
In this section we analyze the PAPR of the SC-FDMA-DSC-DMA signal for localized FDMA The information symbolsare represented by 119887119896 = 119887119896(119899) 119899 = 1 2 119873 for user 119896
where 119896 = 1 2 119870 The random data 119887119896 is first multipliedwith the spreading code yielding 119910119896 It is Kronecker productof 119887119896 and 119862119896radic119871 as shown in
119910119896 = 119887119896 ⊙119862119896
radic119871
(1)
Each data symbol is mapped into complex-valued data sym-bol that is 119889119896 In the process of spreading the spreading codewill be normalized We call the elements in 119910119896 ldquochipsrdquo Then119910119896 is passed to SC-FDMA modulation after DFT precodedoperation yielding 119884119896 [5] Let 119884119896 119896 = 0 1 119873 minus 1 denotethe frequency domain samples after DFT of 119910119896 Define 119896 119896 = 0 1 119872 minus 1 as the frequency domain samples aftersubcarrier mapping which can be described as follows
119896 = 119884119896 0 le 119896 le 119873 minus 1
0 119873 le 119896 le 119872 minus 1(2)
Define 119910119898 119898 = 0 1 119872minus1 as the time domain symbolsafter IDFT of 119896 Then let119898 = 119876119899 + 119902 where 0 le 119902 le 119876minus 1
and 0 le 119899 le 119873 minus 1 Then 119910119898 can be expressed as follows[10]
119910119898 = 119910119876119899+119902
=
119910119899
119876 119902 = 0
1 minus 1198901198952120587(119902119876)
119876119873sdot
119873minus1
sum
119901=0
119910119901
1 minus 1198901198952120587((119899minus119901)119873+119902119876119873) 119902 = 0
(3)
As expressed in (3) 119910119898 has 1119876 weighed copies from theinitial sequence 119910119898 in positions where 119902 = 0 However inthose positions where 119902 = 0 119910119898 is the linear combination of119910119898 which can be regarded as the interpolation process thatleads to PAPR Hence the PAPR of LFDMA can be definedas [10]
PAPR =max0le119905le119872119879
1003816100381610038161003816119910 (119905)1003816100381610038161003816
2
(1119872119879) int119872119879
0
1003816100381610038161003816119910 (119905)1003816100381610038161003816
2119889119905
(4)
where 119910(119905) represents the analog time domain signal of SC-FDMA-DSCDMA data block after considering the effect ofbaseband pulse shaping filter and 119879 is the period
5 Simulation Results
To evaluate the BER and PAPR performance of the proposedSC-FDMA-DSCDMA system theMATLAB Simulinkmodelhas been developed for uplink over different fading channels(AWGN Rayleigh fading and Rician fading) and withrespect to different size of FFT Table 1 shows the various par-ameters considered in the Simulink model for performanceevaluation
Figure 2 shows the BER performance of modified SC-FDMA-DSCDMA obtained for fixed number of users withQPSK modulation over AWGN channel
4 Journal of Computer Networks and Communications
Table 1 Simulation parameters
Parameter ValueModulation scheme QPSKNormalization factor 1radic2
FFT size 64Spreading code Pseudorandom codesCoding mode (rate) Convolutional (12)Cyclic prefix 14
Channel AWGN Rayleigh and RicianChannel estimation IdealChannel equalization Zero-forcing equalizer
0 2 4 6 8 10 12
Multicarrier transmission with QPSK modulation over AWGN channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 2 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overAWGN channel) BER performance of the proposed technique isbest and very close to that of SC-FDMA and Luo and Xiong [5] Nodegradation in BER
Simultaneously it is compared with BER performanceof other multicarrier techniques such as SC-FDMA MC-DS-CDMA and OFDMA The figure shows that the BERperformance is improved with increase in SNR value It canbe very clearly observed from Figure 2 that at BER of 10minus3over AWGN channel the SNR requirement of SC-FDMAsystem and SC-FDMA-DSCDMAsystem is 92 dB and 96 dBrespectively Further MC-DS-CDMA system requires SNRvalue around 105 dB whereas the OFDMA systemrsquos require-ment is 117 dBThus it can be concluded from this figure thatBER vs SNR performance of the proposed SC-FDMA-DSC-DMA system is best when compared to MC-CDMA as wellas OFDMA and very close to that of SC-FDMA system Ithas also been observed that the BER performance of the pro-posed technique does not show any degradation in BER with
0 2 4 6 8 10 12 14 16 18 20
Multicarrier transmission with QPSK modulation over Rayleigh channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 3 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overRayleigh channel) BER performance of the proposed technique isagain best and very close to that of SC-FDMA No degradation dueto modified technique
respect to technique described in [5] Figure 3 shows the com-parative BER curves for the different systems that is SC-FDMA-DSCDMA SC-FDMA MC-CDMA and OFDMAover Rayleigh fading channel
The comparative BER curves in Figure 3 depict similarbehaviour to that of Figure 2 under AWGN It can beobserved from Figure 3 that to achieve a BER of 10minus3 overRayleigh channel the SC-FDMA SC-FDMA-DSCDMAMC-DS-CDMA and OFDMA systems require SNR valueof 168 dB 175 dB 20 dB and 21 dB respectively The BERperformance of SC-FDMA-DSCDMA is again found to bevery close to that of SC-FDMA and no degradation inBER has taken place due to the use of proposed techniqueFigure 4 also shows a similar BER performance of differentmulticarrier systems over Rician channel
The different relevant parameters are clearly marked inFigure 4 We have used localized subcarrier mapping forSC-FDMA-DSCDMA Thus it can be concluded that BERvs SNR performance of the proposed SC-FDMA-DSCDMAsystem shows no degradation in the BER due to change inthe placement of CDMA spreading blockThe proposed tech-nique is best when compared to MC-CDMA as well as OFD-MAand very close to that of SC-FDMAsystem Further theseresults are clearly in line with earlier reported research workby Luo and Xiong [5]
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique now it is imperative to determine the extent ofimprovement in PAPR performance offered by the proposedtechnique PAPR is a performance measurement that is
Journal of Computer Networks and Communications 5
0 2 4 6 8 10 12 14 16 18
Multicarrier transmission with QPSK modulation over Rician channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 4 BER performance of the proposed SC-FDMA-DSCDMAtechnique comparedwith othermulticarrier techniques (over Ricianchannel) BER performance of the proposed technique is again bestand very close to that of SC-FDMANo degradation due tomodifiedtechnique
indicative of the power efficiency of the transmitter A posi-tive PAPR in dBmeans that we need a power backoff to oper-ate in the linear region of the power amplifier and high PAPRdegrades the transmit power efficiency performance Wecalculate the CCDF (complementary cumulative distributionfunction) of PAPR which is the probability that PAPR ishigher than a certain PAPR value PAPR0 (PrPAPR gt
PAPR0) Figure 5 shows the PAPR performance of SC-FDMA-DSCDMAwith respect to different119873-point FFTwithQPSK modulation
It has been observed that as the FFT size increases thePAPR value is also increased For example in Figure 5 64-point FFT has PAPR of 64 dB 128-point FFT has PAPR of755 dB whereas 256-point FFT has PAPR of 86 dB Next thePAPR performance of the proposed SC-FDMA-DSCDMAtechnique is being illustrated in Figure 6
Figure 6 shows the CCDF curves of PAPR for differentmulticarrier systems while modulation technique is QPSKand FFT size is 256This plot clearly shows that the proposedmodified technique that is SC-FDMA-DSCDMA providesbest PAPR performance among all multicarrier systemsconsidered in this paper From the figure it is observed thatOFDMAhas the highest PAPRof 112 dB followed byMC-DS-CDMA (98 dB) SC-FDMA (95 dB) and the proposed SC-FDMA-DSCDMA (86 dB) respectively SC-FDMA-DSC-DMA thus provides the best PAPR performance around 1 dBbetter than SC-FDMA Further an improvement of around2 dB has also been obtained by the proposed modified tech-nique as compared to the technique by Luo and Xiong [5]
0 1 2 3 4 5 6 7 8 9 10
SC-FDMA-DSCDMA system with N-point FFT with QPSK modulation
z (dB)
CCD
F
N 64N 128N 256
10minus2
10minus1
100
Figure 5 PAPR performance of the proposed SC-FDMA-DSCDMA technique for different FFT size with QPSK modulationFFT size 119873 indicates the number of subcarriers PAPR increaseswith increase in FFT size
Therefore we can say that the modified SC-FDMA-DSCD-MA technique is best suited for uplink in next generationwireless communication
6 Conclusion
The main objective of this paper was to propose such a tech-nique which could provide improved PAPR performancewithout any degradation in the system BER In view of thiswe proposed amodified hybrid technique that is SC-FDMA-DSCDMA which is a combination of SC-FDMA and DS-CDMA In this paper we have explored an idea that PAPRcan be reduced further by proper placement of spread-ingdespreading block in hybridOFDM-CDMA systemsTheproposed technique has been obtained by modifying thetechnique considered by Luo and Xiong [5]
In order to justify the relevance of the proposed tech-nique firstly it was ensured that no degradation in BERperformance takes place due to the modified technique whensimulated under different fading channel conditions (AWGNRayleigh and Rician) Then the extent of improvement inPAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique has been analyzed
Simulation results prove that BER vs SNR performanceof the proposed SC-FDMA-DSCDMA system shows nodegradation in the BER due to change in the placementof CDMA spreading block The proposed technique is bestwhen compared to MC-CDMA as well as OFDMA and veryclose to that of SC-FDMA system Further these results are
6 Journal of Computer Networks and Communications
1 2 3 4 5 6 7 8 9 10 11
Different multicarrier systems with QPSK modulation
SC-FDMA-DSCDMASC-FDMA
MC-DS-CDMAOFDMA
10minus2
10minus1
100
Pr (P
APRgt
PAPR
0)
PAPR0 (dB)
Figure 6 PAPR performance of the proposed SC-FDMA-DSCDMA technique compared with other multicarrier techniquesQPSK modulation with FFT size being 256 PAPR performance ofthe proposed technique is best 1 dB better than SC-FDMA and 2 dBbetter than Luo and Xiong [5]
clearly in line with earlier reported research work by Luo andXiong [5] without any degradation
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique the main objective of determining the extent ofimprovement in PAPR performance offered by the proposedtechnique has been realized Simulation results showed thatthe proposed modified technique that is SC-FDMA-DSCD-MA provides an improvement of around 1 dB over SC-FDMA technique and 2 dB over the technique reported byLuo and Xiong [5]
Thus it can be concluded that the proposedmodified SC-FDMA-DSCDMA technique provides improved PAPR per-formancewith no degradation in the systemBER It performsbetter than any other existing OFDM-CDMA based systemfor next generation wireless communication and thus couldprove to be a good alternative technique However the BERand PAPR performance could further be improved throughvarious equalization techniques and by implementing othercodingspreadingPAPR reduction techniques
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] S C YangOFDMA System Analysis and Design Artech House2010
[2] H GMyung J Lim andD J Goodman ldquoSingle carrier FDMAfor uplink wireless transmissionrdquo IEEE Vehicular TechnologyMagazine vol 1 no 3 pp 30ndash38 2006
[3] D Falconer S L Ariyavisitakul A Benyamin-Seeyar andB Eidson ldquoFrequency domain equalization for single-carrierbroadband wireless systemsrdquo IEEE Communications Magazinevol 40 no 4 pp 58ndash66 2002
[4] S Hara and R Prasad ldquoOverview of multicarrier CDMArdquo IEEECommunications Magazine vol 35 no 12 pp 126ndash133 1997
[5] Z Luo and X Xiong ldquoPerformance comparison of SC-FDMA-CDMA and OFDM-CDMA systems for uplinkrdquo in Proceedingsof the International Conference on Consumer Electronics Com-munications and Networks (CECNet rsquo11) pp 1475ndash1479 April2011
[6] A C McCormick and E A Al-Susa ldquoMulticarrier CDMAfor future generation mobile communicationrdquo Electronics andCommunication Engineering Journal vol 14 no 2 pp 52ndash602002
[7] S H Han and J H Lee ldquoAn overview of peak-to-average powerratio reduction techniques for multicarrier transmissionrdquo IEEEWireless Communications vol 12 no 2 pp 56ndash65 2005
[8] H G Myung ldquoIntroduction to single carrier FDMArdquo in Pro-ceedings of the 15th European Signal Processing Conference(EUSIPCO rsquo07) pp 2144ndash2148 Poznan Poland September2007
[9] H G Myung and D J Goodman Single Carrier FDMA ANew Air Interface for Long Term Evolution John Wiley amp SonsLondon UK 2008
[10] P Li Y Zhu Z Wang and N Wang ldquoPeak-to-average powerratio of SC-FDMA systems with localized subcarrier mappingrdquoin Proceedings of the Global Mobile Congress (GMC rsquo2010) pp1ndash6 Shanghai China October 2010
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2 Journal of Computer Networks and Communications
SC-FDMA
SC-FDMA-DSCDMA
Random data
sourceSpreading
Interleaver and
modulation
FFT
Subcarriermapping
IFFT
Add CP PS
DespreadingDeinterleaver
and demodulation
IFFT
Subcarrierdemapping
and equalization
FFT
Removal of CP SPBER
count
Channel
+
Figure 1 Modified SC-FDMA-DSCDMA system model CDMA spreading operation has been performed before interleaving andmodulation
systems with severe multipath propagation the SC-FDMAsignals arrive at a base station with intersymbol interferenceTherefore to cancel this ISI base station employs adaptive fre-quency domain equalization (FDE) This arrangement pro-vides useful model in cellular system because it reduces theburden of linear amplification in portable terminals at thecost of complex signal processing (frequency domain equal-ization) at the base station [2 3]
Next direct sequence code division multiple access (DS-CDMA) is a multiple access technique based on spread spec-trummodulation A spread spectrum system is one in whichthe transmitted signal is spread over a wider bandwidth requ-ired to transmit the information being sent [4 5] Spreadingis accomplished with the help of a code which is independentof the data At receiver the same code is used to despread andrecover the transmitted dataDS-CDMAsystemoffers severaladvantages in cellular environments including easy frequencyplanning high immunity againstMAI if high processing gainis used and flexible data rate adaptation [5]
The combination of DS-CDMA and OFDM leads tothe development of MC-DS-CDMA The multicarrier DS-CDMA transmitter spreads the SP converted data streamsusing a given spreading code in the time domain [6] and afterthat multicarrier modulation (OFDM) is performed by IFFToperation [4]This combination is very effective in combatingsevere multipath interference and provides multiple accesssimultaneously However MC-DS-CDMA suffers from highPAPR value because of multicarrier
Now we have considered in this paper amodified hybridtechnique SC-FDMA-DSCDMA obtained by combinationof SC-FDMA and DS-CDMA A similar technique has alsobeen considered earlier by Luo and Xiong [5] However inthis paper a modified technique is proposed where CDMAspreading operation is performed before interleaving andmodulation operation (Figure 1) We call this technique ldquoSC-FDMA-DSCDMArdquo which inherits merits of SC-FDMA aswell as DS-CDMA In addition to this the available literaturelacks the exhaustive analysis and comparison of this hybridtechniqueThis technique could prove to be a good alternativeto the SC-FDMA technique and thus simultaneously provid-ing better PAPR performance
This paper is organized as follows Section 2 provides thebackground that led to the formulation of problem consid-ered in this paper Section 3 covers a brief overview of themodified SC-FDMA-DSCDMA technique Furthermore inthe subsequent sections we discuss the comparative BERper-formance of SC-FDMA-DSCDMA with respect to differentmulticarrier techniques over different fading channel con-ditions Next PAPR performance of SC-FDMA-DSCDMAwith respect to different FFT size is analyzed and then compa-rative PAPR performance analysis of the proposed techniquewith different multicarrier techniques is also done Finallythe relevant results of the paper are concluded
2 Background and Problem Formulation
As already mentioned a CDMA system coupled with multi-carrier modulation offers many potential benefits but it alsosuffers from a major drawback due to multicarrier transmis-sion that is high PAPR Depending on the user data thesummation of subcarriers may result in a signal with largeamplitude or small amplitude And as a result the peak powerof signal is much greater than the average power The highPAPR causes out-of-band radiations due to nonlinear poweramplifier Therefore the transmit power amplifier must beoperated in linear region but it results in poor power conver-sion efficiency The multicarrier modulation (OFDMA) hasnow been replaced with SC-FDMA which provides furtherreduction in PAPR value of the transmit signal
A number of approaches have been proposed in theliterature [7] for reducing high value of PAPR in OFDMsystems Broadly speaking these PAPR reduction techniquescan be divided into two categories namely distortion-basedand distortionless techniques The distortion-based tech-niques achieve significant PAPR reduction but at the cost ofincreased BER high computational complexity data rate lossand so forth On the other hand distortionless techniquesachieve PAPR reduction without any degradation in BERand spectral efficiency The distortionless techniques mainlyrely on hybrid structures without introducing any deliber-ate distortion in the transmit signal Keeping in view this
Journal of Computer Networks and Communications 3
advantage of distortionless techniques we have proposed amodified hybrid technique that is SC-FDMA-DSCDMAwhich is a combination of SC-FDMA and DS-CDMA Asimilar technique has also been considered earlier by Luo andXiong [5] But in this paper we have explored an idea thatPAPR can be reduced further by proper placement of spread-ingdespreading block in hybrid OFDM-CDMA systems Inthe technique proposed by us CDMA spreading operationis performed before interleaving and modulation operation(Figure 1) However Luo and Xiong [5] have used the spread-ing process after modulation
Thus the main focus of this paper is on the reduction inPAPR value without any BER degradation through the use ofmodified hybrid SC-FDMA-DSCDMA technique Further itis aimed at establishing the proposed technique as a suitablealternative to the technique proposed by Luo and Xiong [5]and other existing techniques like SC-FDMA MC-DS-CDMA and OFDMA by comparing the PAPR and BER per-formance under different channel conditions Firstly it will beensured that no degradation in BER performance takes placedue to the modified systemThen the extent of improvementin PAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique will be analyzed
3 Overview of Proposed SC-FDMA-DSCDMA
Figure 1 shows the modified SC-FDMA-DSCDMA systemstructure Unlike OFDMA or OFDM-CDMA SC-FDMA-DSCDMA is a single-carrier spread spectrum technique Inthis technique the signal is generated by serial concatenationof DS-CDMA and SC-FDMA The key model of this systemis SC-FDMAmodelTheprinciple of SC-FDMA-DSCDMA isfirstly to map the chips of a spread data symbol in frequencydomain
The transmitter of this system groups the modulationsymbols into blocks each containing 119873 symbols The SC-FDMA system involves an119873-point FFT operation and thenit maps each of the 119873-FFT outputs to one of the 119872 (gt 119873)
orthogonal subcarriers that can be transmitted Then an119872-point IFFT transforms the subcarrier amplitudes to a complextime domain signal After that it inserts cyclic prefix to pro-vide guard time [8 9]
Therefore transmitted data propagating through the cha-nnel can be modelled as a circular convolution between thechannel impulse response and the transmitted data blockthrough the use of cyclic prefix At receiver side the receivedsignal is converted into frequency domain via DFT and thenfrequency domain equalization is performed after demappingthe subcarriers The equalized symbols are transformed backto the time domain via IDFT and decoding takes place inthe time domain At last despreading is done by multiplyingeach symbol with the same pseudorandom code and thendetection takes place [8]
4 PAPR of SC-FDMA-DSCDMA Signals
In this section we analyze the PAPR of the SC-FDMA-DSC-DMA signal for localized FDMA The information symbolsare represented by 119887119896 = 119887119896(119899) 119899 = 1 2 119873 for user 119896
where 119896 = 1 2 119870 The random data 119887119896 is first multipliedwith the spreading code yielding 119910119896 It is Kronecker productof 119887119896 and 119862119896radic119871 as shown in
119910119896 = 119887119896 ⊙119862119896
radic119871
(1)
Each data symbol is mapped into complex-valued data sym-bol that is 119889119896 In the process of spreading the spreading codewill be normalized We call the elements in 119910119896 ldquochipsrdquo Then119910119896 is passed to SC-FDMA modulation after DFT precodedoperation yielding 119884119896 [5] Let 119884119896 119896 = 0 1 119873 minus 1 denotethe frequency domain samples after DFT of 119910119896 Define 119896 119896 = 0 1 119872 minus 1 as the frequency domain samples aftersubcarrier mapping which can be described as follows
119896 = 119884119896 0 le 119896 le 119873 minus 1
0 119873 le 119896 le 119872 minus 1(2)
Define 119910119898 119898 = 0 1 119872minus1 as the time domain symbolsafter IDFT of 119896 Then let119898 = 119876119899 + 119902 where 0 le 119902 le 119876minus 1
and 0 le 119899 le 119873 minus 1 Then 119910119898 can be expressed as follows[10]
119910119898 = 119910119876119899+119902
=
119910119899
119876 119902 = 0
1 minus 1198901198952120587(119902119876)
119876119873sdot
119873minus1
sum
119901=0
119910119901
1 minus 1198901198952120587((119899minus119901)119873+119902119876119873) 119902 = 0
(3)
As expressed in (3) 119910119898 has 1119876 weighed copies from theinitial sequence 119910119898 in positions where 119902 = 0 However inthose positions where 119902 = 0 119910119898 is the linear combination of119910119898 which can be regarded as the interpolation process thatleads to PAPR Hence the PAPR of LFDMA can be definedas [10]
PAPR =max0le119905le119872119879
1003816100381610038161003816119910 (119905)1003816100381610038161003816
2
(1119872119879) int119872119879
0
1003816100381610038161003816119910 (119905)1003816100381610038161003816
2119889119905
(4)
where 119910(119905) represents the analog time domain signal of SC-FDMA-DSCDMA data block after considering the effect ofbaseband pulse shaping filter and 119879 is the period
5 Simulation Results
To evaluate the BER and PAPR performance of the proposedSC-FDMA-DSCDMA system theMATLAB Simulinkmodelhas been developed for uplink over different fading channels(AWGN Rayleigh fading and Rician fading) and withrespect to different size of FFT Table 1 shows the various par-ameters considered in the Simulink model for performanceevaluation
Figure 2 shows the BER performance of modified SC-FDMA-DSCDMA obtained for fixed number of users withQPSK modulation over AWGN channel
4 Journal of Computer Networks and Communications
Table 1 Simulation parameters
Parameter ValueModulation scheme QPSKNormalization factor 1radic2
FFT size 64Spreading code Pseudorandom codesCoding mode (rate) Convolutional (12)Cyclic prefix 14
Channel AWGN Rayleigh and RicianChannel estimation IdealChannel equalization Zero-forcing equalizer
0 2 4 6 8 10 12
Multicarrier transmission with QPSK modulation over AWGN channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 2 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overAWGN channel) BER performance of the proposed technique isbest and very close to that of SC-FDMA and Luo and Xiong [5] Nodegradation in BER
Simultaneously it is compared with BER performanceof other multicarrier techniques such as SC-FDMA MC-DS-CDMA and OFDMA The figure shows that the BERperformance is improved with increase in SNR value It canbe very clearly observed from Figure 2 that at BER of 10minus3over AWGN channel the SNR requirement of SC-FDMAsystem and SC-FDMA-DSCDMAsystem is 92 dB and 96 dBrespectively Further MC-DS-CDMA system requires SNRvalue around 105 dB whereas the OFDMA systemrsquos require-ment is 117 dBThus it can be concluded from this figure thatBER vs SNR performance of the proposed SC-FDMA-DSC-DMA system is best when compared to MC-CDMA as wellas OFDMA and very close to that of SC-FDMA system Ithas also been observed that the BER performance of the pro-posed technique does not show any degradation in BER with
0 2 4 6 8 10 12 14 16 18 20
Multicarrier transmission with QPSK modulation over Rayleigh channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 3 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overRayleigh channel) BER performance of the proposed technique isagain best and very close to that of SC-FDMA No degradation dueto modified technique
respect to technique described in [5] Figure 3 shows the com-parative BER curves for the different systems that is SC-FDMA-DSCDMA SC-FDMA MC-CDMA and OFDMAover Rayleigh fading channel
The comparative BER curves in Figure 3 depict similarbehaviour to that of Figure 2 under AWGN It can beobserved from Figure 3 that to achieve a BER of 10minus3 overRayleigh channel the SC-FDMA SC-FDMA-DSCDMAMC-DS-CDMA and OFDMA systems require SNR valueof 168 dB 175 dB 20 dB and 21 dB respectively The BERperformance of SC-FDMA-DSCDMA is again found to bevery close to that of SC-FDMA and no degradation inBER has taken place due to the use of proposed techniqueFigure 4 also shows a similar BER performance of differentmulticarrier systems over Rician channel
The different relevant parameters are clearly marked inFigure 4 We have used localized subcarrier mapping forSC-FDMA-DSCDMA Thus it can be concluded that BERvs SNR performance of the proposed SC-FDMA-DSCDMAsystem shows no degradation in the BER due to change inthe placement of CDMA spreading blockThe proposed tech-nique is best when compared to MC-CDMA as well as OFD-MAand very close to that of SC-FDMAsystem Further theseresults are clearly in line with earlier reported research workby Luo and Xiong [5]
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique now it is imperative to determine the extent ofimprovement in PAPR performance offered by the proposedtechnique PAPR is a performance measurement that is
Journal of Computer Networks and Communications 5
0 2 4 6 8 10 12 14 16 18
Multicarrier transmission with QPSK modulation over Rician channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 4 BER performance of the proposed SC-FDMA-DSCDMAtechnique comparedwith othermulticarrier techniques (over Ricianchannel) BER performance of the proposed technique is again bestand very close to that of SC-FDMANo degradation due tomodifiedtechnique
indicative of the power efficiency of the transmitter A posi-tive PAPR in dBmeans that we need a power backoff to oper-ate in the linear region of the power amplifier and high PAPRdegrades the transmit power efficiency performance Wecalculate the CCDF (complementary cumulative distributionfunction) of PAPR which is the probability that PAPR ishigher than a certain PAPR value PAPR0 (PrPAPR gt
PAPR0) Figure 5 shows the PAPR performance of SC-FDMA-DSCDMAwith respect to different119873-point FFTwithQPSK modulation
It has been observed that as the FFT size increases thePAPR value is also increased For example in Figure 5 64-point FFT has PAPR of 64 dB 128-point FFT has PAPR of755 dB whereas 256-point FFT has PAPR of 86 dB Next thePAPR performance of the proposed SC-FDMA-DSCDMAtechnique is being illustrated in Figure 6
Figure 6 shows the CCDF curves of PAPR for differentmulticarrier systems while modulation technique is QPSKand FFT size is 256This plot clearly shows that the proposedmodified technique that is SC-FDMA-DSCDMA providesbest PAPR performance among all multicarrier systemsconsidered in this paper From the figure it is observed thatOFDMAhas the highest PAPRof 112 dB followed byMC-DS-CDMA (98 dB) SC-FDMA (95 dB) and the proposed SC-FDMA-DSCDMA (86 dB) respectively SC-FDMA-DSC-DMA thus provides the best PAPR performance around 1 dBbetter than SC-FDMA Further an improvement of around2 dB has also been obtained by the proposed modified tech-nique as compared to the technique by Luo and Xiong [5]
0 1 2 3 4 5 6 7 8 9 10
SC-FDMA-DSCDMA system with N-point FFT with QPSK modulation
z (dB)
CCD
F
N 64N 128N 256
10minus2
10minus1
100
Figure 5 PAPR performance of the proposed SC-FDMA-DSCDMA technique for different FFT size with QPSK modulationFFT size 119873 indicates the number of subcarriers PAPR increaseswith increase in FFT size
Therefore we can say that the modified SC-FDMA-DSCD-MA technique is best suited for uplink in next generationwireless communication
6 Conclusion
The main objective of this paper was to propose such a tech-nique which could provide improved PAPR performancewithout any degradation in the system BER In view of thiswe proposed amodified hybrid technique that is SC-FDMA-DSCDMA which is a combination of SC-FDMA and DS-CDMA In this paper we have explored an idea that PAPRcan be reduced further by proper placement of spread-ingdespreading block in hybridOFDM-CDMA systemsTheproposed technique has been obtained by modifying thetechnique considered by Luo and Xiong [5]
In order to justify the relevance of the proposed tech-nique firstly it was ensured that no degradation in BERperformance takes place due to the modified technique whensimulated under different fading channel conditions (AWGNRayleigh and Rician) Then the extent of improvement inPAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique has been analyzed
Simulation results prove that BER vs SNR performanceof the proposed SC-FDMA-DSCDMA system shows nodegradation in the BER due to change in the placementof CDMA spreading block The proposed technique is bestwhen compared to MC-CDMA as well as OFDMA and veryclose to that of SC-FDMA system Further these results are
6 Journal of Computer Networks and Communications
1 2 3 4 5 6 7 8 9 10 11
Different multicarrier systems with QPSK modulation
SC-FDMA-DSCDMASC-FDMA
MC-DS-CDMAOFDMA
10minus2
10minus1
100
Pr (P
APRgt
PAPR
0)
PAPR0 (dB)
Figure 6 PAPR performance of the proposed SC-FDMA-DSCDMA technique compared with other multicarrier techniquesQPSK modulation with FFT size being 256 PAPR performance ofthe proposed technique is best 1 dB better than SC-FDMA and 2 dBbetter than Luo and Xiong [5]
clearly in line with earlier reported research work by Luo andXiong [5] without any degradation
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique the main objective of determining the extent ofimprovement in PAPR performance offered by the proposedtechnique has been realized Simulation results showed thatthe proposed modified technique that is SC-FDMA-DSCD-MA provides an improvement of around 1 dB over SC-FDMA technique and 2 dB over the technique reported byLuo and Xiong [5]
Thus it can be concluded that the proposedmodified SC-FDMA-DSCDMA technique provides improved PAPR per-formancewith no degradation in the systemBER It performsbetter than any other existing OFDM-CDMA based systemfor next generation wireless communication and thus couldprove to be a good alternative technique However the BERand PAPR performance could further be improved throughvarious equalization techniques and by implementing othercodingspreadingPAPR reduction techniques
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] S C YangOFDMA System Analysis and Design Artech House2010
[2] H GMyung J Lim andD J Goodman ldquoSingle carrier FDMAfor uplink wireless transmissionrdquo IEEE Vehicular TechnologyMagazine vol 1 no 3 pp 30ndash38 2006
[3] D Falconer S L Ariyavisitakul A Benyamin-Seeyar andB Eidson ldquoFrequency domain equalization for single-carrierbroadband wireless systemsrdquo IEEE Communications Magazinevol 40 no 4 pp 58ndash66 2002
[4] S Hara and R Prasad ldquoOverview of multicarrier CDMArdquo IEEECommunications Magazine vol 35 no 12 pp 126ndash133 1997
[5] Z Luo and X Xiong ldquoPerformance comparison of SC-FDMA-CDMA and OFDM-CDMA systems for uplinkrdquo in Proceedingsof the International Conference on Consumer Electronics Com-munications and Networks (CECNet rsquo11) pp 1475ndash1479 April2011
[6] A C McCormick and E A Al-Susa ldquoMulticarrier CDMAfor future generation mobile communicationrdquo Electronics andCommunication Engineering Journal vol 14 no 2 pp 52ndash602002
[7] S H Han and J H Lee ldquoAn overview of peak-to-average powerratio reduction techniques for multicarrier transmissionrdquo IEEEWireless Communications vol 12 no 2 pp 56ndash65 2005
[8] H G Myung ldquoIntroduction to single carrier FDMArdquo in Pro-ceedings of the 15th European Signal Processing Conference(EUSIPCO rsquo07) pp 2144ndash2148 Poznan Poland September2007
[9] H G Myung and D J Goodman Single Carrier FDMA ANew Air Interface for Long Term Evolution John Wiley amp SonsLondon UK 2008
[10] P Li Y Zhu Z Wang and N Wang ldquoPeak-to-average powerratio of SC-FDMA systems with localized subcarrier mappingrdquoin Proceedings of the Global Mobile Congress (GMC rsquo2010) pp1ndash6 Shanghai China October 2010
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International Journal of
Journal of Computer Networks and Communications 3
advantage of distortionless techniques we have proposed amodified hybrid technique that is SC-FDMA-DSCDMAwhich is a combination of SC-FDMA and DS-CDMA Asimilar technique has also been considered earlier by Luo andXiong [5] But in this paper we have explored an idea thatPAPR can be reduced further by proper placement of spread-ingdespreading block in hybrid OFDM-CDMA systems Inthe technique proposed by us CDMA spreading operationis performed before interleaving and modulation operation(Figure 1) However Luo and Xiong [5] have used the spread-ing process after modulation
Thus the main focus of this paper is on the reduction inPAPR value without any BER degradation through the use ofmodified hybrid SC-FDMA-DSCDMA technique Further itis aimed at establishing the proposed technique as a suitablealternative to the technique proposed by Luo and Xiong [5]and other existing techniques like SC-FDMA MC-DS-CDMA and OFDMA by comparing the PAPR and BER per-formance under different channel conditions Firstly it will beensured that no degradation in BER performance takes placedue to the modified systemThen the extent of improvementin PAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique will be analyzed
3 Overview of Proposed SC-FDMA-DSCDMA
Figure 1 shows the modified SC-FDMA-DSCDMA systemstructure Unlike OFDMA or OFDM-CDMA SC-FDMA-DSCDMA is a single-carrier spread spectrum technique Inthis technique the signal is generated by serial concatenationof DS-CDMA and SC-FDMA The key model of this systemis SC-FDMAmodelTheprinciple of SC-FDMA-DSCDMA isfirstly to map the chips of a spread data symbol in frequencydomain
The transmitter of this system groups the modulationsymbols into blocks each containing 119873 symbols The SC-FDMA system involves an119873-point FFT operation and thenit maps each of the 119873-FFT outputs to one of the 119872 (gt 119873)
orthogonal subcarriers that can be transmitted Then an119872-point IFFT transforms the subcarrier amplitudes to a complextime domain signal After that it inserts cyclic prefix to pro-vide guard time [8 9]
Therefore transmitted data propagating through the cha-nnel can be modelled as a circular convolution between thechannel impulse response and the transmitted data blockthrough the use of cyclic prefix At receiver side the receivedsignal is converted into frequency domain via DFT and thenfrequency domain equalization is performed after demappingthe subcarriers The equalized symbols are transformed backto the time domain via IDFT and decoding takes place inthe time domain At last despreading is done by multiplyingeach symbol with the same pseudorandom code and thendetection takes place [8]
4 PAPR of SC-FDMA-DSCDMA Signals
In this section we analyze the PAPR of the SC-FDMA-DSC-DMA signal for localized FDMA The information symbolsare represented by 119887119896 = 119887119896(119899) 119899 = 1 2 119873 for user 119896
where 119896 = 1 2 119870 The random data 119887119896 is first multipliedwith the spreading code yielding 119910119896 It is Kronecker productof 119887119896 and 119862119896radic119871 as shown in
119910119896 = 119887119896 ⊙119862119896
radic119871
(1)
Each data symbol is mapped into complex-valued data sym-bol that is 119889119896 In the process of spreading the spreading codewill be normalized We call the elements in 119910119896 ldquochipsrdquo Then119910119896 is passed to SC-FDMA modulation after DFT precodedoperation yielding 119884119896 [5] Let 119884119896 119896 = 0 1 119873 minus 1 denotethe frequency domain samples after DFT of 119910119896 Define 119896 119896 = 0 1 119872 minus 1 as the frequency domain samples aftersubcarrier mapping which can be described as follows
119896 = 119884119896 0 le 119896 le 119873 minus 1
0 119873 le 119896 le 119872 minus 1(2)
Define 119910119898 119898 = 0 1 119872minus1 as the time domain symbolsafter IDFT of 119896 Then let119898 = 119876119899 + 119902 where 0 le 119902 le 119876minus 1
and 0 le 119899 le 119873 minus 1 Then 119910119898 can be expressed as follows[10]
119910119898 = 119910119876119899+119902
=
119910119899
119876 119902 = 0
1 minus 1198901198952120587(119902119876)
119876119873sdot
119873minus1
sum
119901=0
119910119901
1 minus 1198901198952120587((119899minus119901)119873+119902119876119873) 119902 = 0
(3)
As expressed in (3) 119910119898 has 1119876 weighed copies from theinitial sequence 119910119898 in positions where 119902 = 0 However inthose positions where 119902 = 0 119910119898 is the linear combination of119910119898 which can be regarded as the interpolation process thatleads to PAPR Hence the PAPR of LFDMA can be definedas [10]
PAPR =max0le119905le119872119879
1003816100381610038161003816119910 (119905)1003816100381610038161003816
2
(1119872119879) int119872119879
0
1003816100381610038161003816119910 (119905)1003816100381610038161003816
2119889119905
(4)
where 119910(119905) represents the analog time domain signal of SC-FDMA-DSCDMA data block after considering the effect ofbaseband pulse shaping filter and 119879 is the period
5 Simulation Results
To evaluate the BER and PAPR performance of the proposedSC-FDMA-DSCDMA system theMATLAB Simulinkmodelhas been developed for uplink over different fading channels(AWGN Rayleigh fading and Rician fading) and withrespect to different size of FFT Table 1 shows the various par-ameters considered in the Simulink model for performanceevaluation
Figure 2 shows the BER performance of modified SC-FDMA-DSCDMA obtained for fixed number of users withQPSK modulation over AWGN channel
4 Journal of Computer Networks and Communications
Table 1 Simulation parameters
Parameter ValueModulation scheme QPSKNormalization factor 1radic2
FFT size 64Spreading code Pseudorandom codesCoding mode (rate) Convolutional (12)Cyclic prefix 14
Channel AWGN Rayleigh and RicianChannel estimation IdealChannel equalization Zero-forcing equalizer
0 2 4 6 8 10 12
Multicarrier transmission with QPSK modulation over AWGN channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 2 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overAWGN channel) BER performance of the proposed technique isbest and very close to that of SC-FDMA and Luo and Xiong [5] Nodegradation in BER
Simultaneously it is compared with BER performanceof other multicarrier techniques such as SC-FDMA MC-DS-CDMA and OFDMA The figure shows that the BERperformance is improved with increase in SNR value It canbe very clearly observed from Figure 2 that at BER of 10minus3over AWGN channel the SNR requirement of SC-FDMAsystem and SC-FDMA-DSCDMAsystem is 92 dB and 96 dBrespectively Further MC-DS-CDMA system requires SNRvalue around 105 dB whereas the OFDMA systemrsquos require-ment is 117 dBThus it can be concluded from this figure thatBER vs SNR performance of the proposed SC-FDMA-DSC-DMA system is best when compared to MC-CDMA as wellas OFDMA and very close to that of SC-FDMA system Ithas also been observed that the BER performance of the pro-posed technique does not show any degradation in BER with
0 2 4 6 8 10 12 14 16 18 20
Multicarrier transmission with QPSK modulation over Rayleigh channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 3 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overRayleigh channel) BER performance of the proposed technique isagain best and very close to that of SC-FDMA No degradation dueto modified technique
respect to technique described in [5] Figure 3 shows the com-parative BER curves for the different systems that is SC-FDMA-DSCDMA SC-FDMA MC-CDMA and OFDMAover Rayleigh fading channel
The comparative BER curves in Figure 3 depict similarbehaviour to that of Figure 2 under AWGN It can beobserved from Figure 3 that to achieve a BER of 10minus3 overRayleigh channel the SC-FDMA SC-FDMA-DSCDMAMC-DS-CDMA and OFDMA systems require SNR valueof 168 dB 175 dB 20 dB and 21 dB respectively The BERperformance of SC-FDMA-DSCDMA is again found to bevery close to that of SC-FDMA and no degradation inBER has taken place due to the use of proposed techniqueFigure 4 also shows a similar BER performance of differentmulticarrier systems over Rician channel
The different relevant parameters are clearly marked inFigure 4 We have used localized subcarrier mapping forSC-FDMA-DSCDMA Thus it can be concluded that BERvs SNR performance of the proposed SC-FDMA-DSCDMAsystem shows no degradation in the BER due to change inthe placement of CDMA spreading blockThe proposed tech-nique is best when compared to MC-CDMA as well as OFD-MAand very close to that of SC-FDMAsystem Further theseresults are clearly in line with earlier reported research workby Luo and Xiong [5]
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique now it is imperative to determine the extent ofimprovement in PAPR performance offered by the proposedtechnique PAPR is a performance measurement that is
Journal of Computer Networks and Communications 5
0 2 4 6 8 10 12 14 16 18
Multicarrier transmission with QPSK modulation over Rician channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 4 BER performance of the proposed SC-FDMA-DSCDMAtechnique comparedwith othermulticarrier techniques (over Ricianchannel) BER performance of the proposed technique is again bestand very close to that of SC-FDMANo degradation due tomodifiedtechnique
indicative of the power efficiency of the transmitter A posi-tive PAPR in dBmeans that we need a power backoff to oper-ate in the linear region of the power amplifier and high PAPRdegrades the transmit power efficiency performance Wecalculate the CCDF (complementary cumulative distributionfunction) of PAPR which is the probability that PAPR ishigher than a certain PAPR value PAPR0 (PrPAPR gt
PAPR0) Figure 5 shows the PAPR performance of SC-FDMA-DSCDMAwith respect to different119873-point FFTwithQPSK modulation
It has been observed that as the FFT size increases thePAPR value is also increased For example in Figure 5 64-point FFT has PAPR of 64 dB 128-point FFT has PAPR of755 dB whereas 256-point FFT has PAPR of 86 dB Next thePAPR performance of the proposed SC-FDMA-DSCDMAtechnique is being illustrated in Figure 6
Figure 6 shows the CCDF curves of PAPR for differentmulticarrier systems while modulation technique is QPSKand FFT size is 256This plot clearly shows that the proposedmodified technique that is SC-FDMA-DSCDMA providesbest PAPR performance among all multicarrier systemsconsidered in this paper From the figure it is observed thatOFDMAhas the highest PAPRof 112 dB followed byMC-DS-CDMA (98 dB) SC-FDMA (95 dB) and the proposed SC-FDMA-DSCDMA (86 dB) respectively SC-FDMA-DSC-DMA thus provides the best PAPR performance around 1 dBbetter than SC-FDMA Further an improvement of around2 dB has also been obtained by the proposed modified tech-nique as compared to the technique by Luo and Xiong [5]
0 1 2 3 4 5 6 7 8 9 10
SC-FDMA-DSCDMA system with N-point FFT with QPSK modulation
z (dB)
CCD
F
N 64N 128N 256
10minus2
10minus1
100
Figure 5 PAPR performance of the proposed SC-FDMA-DSCDMA technique for different FFT size with QPSK modulationFFT size 119873 indicates the number of subcarriers PAPR increaseswith increase in FFT size
Therefore we can say that the modified SC-FDMA-DSCD-MA technique is best suited for uplink in next generationwireless communication
6 Conclusion
The main objective of this paper was to propose such a tech-nique which could provide improved PAPR performancewithout any degradation in the system BER In view of thiswe proposed amodified hybrid technique that is SC-FDMA-DSCDMA which is a combination of SC-FDMA and DS-CDMA In this paper we have explored an idea that PAPRcan be reduced further by proper placement of spread-ingdespreading block in hybridOFDM-CDMA systemsTheproposed technique has been obtained by modifying thetechnique considered by Luo and Xiong [5]
In order to justify the relevance of the proposed tech-nique firstly it was ensured that no degradation in BERperformance takes place due to the modified technique whensimulated under different fading channel conditions (AWGNRayleigh and Rician) Then the extent of improvement inPAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique has been analyzed
Simulation results prove that BER vs SNR performanceof the proposed SC-FDMA-DSCDMA system shows nodegradation in the BER due to change in the placementof CDMA spreading block The proposed technique is bestwhen compared to MC-CDMA as well as OFDMA and veryclose to that of SC-FDMA system Further these results are
6 Journal of Computer Networks and Communications
1 2 3 4 5 6 7 8 9 10 11
Different multicarrier systems with QPSK modulation
SC-FDMA-DSCDMASC-FDMA
MC-DS-CDMAOFDMA
10minus2
10minus1
100
Pr (P
APRgt
PAPR
0)
PAPR0 (dB)
Figure 6 PAPR performance of the proposed SC-FDMA-DSCDMA technique compared with other multicarrier techniquesQPSK modulation with FFT size being 256 PAPR performance ofthe proposed technique is best 1 dB better than SC-FDMA and 2 dBbetter than Luo and Xiong [5]
clearly in line with earlier reported research work by Luo andXiong [5] without any degradation
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique the main objective of determining the extent ofimprovement in PAPR performance offered by the proposedtechnique has been realized Simulation results showed thatthe proposed modified technique that is SC-FDMA-DSCD-MA provides an improvement of around 1 dB over SC-FDMA technique and 2 dB over the technique reported byLuo and Xiong [5]
Thus it can be concluded that the proposedmodified SC-FDMA-DSCDMA technique provides improved PAPR per-formancewith no degradation in the systemBER It performsbetter than any other existing OFDM-CDMA based systemfor next generation wireless communication and thus couldprove to be a good alternative technique However the BERand PAPR performance could further be improved throughvarious equalization techniques and by implementing othercodingspreadingPAPR reduction techniques
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] S C YangOFDMA System Analysis and Design Artech House2010
[2] H GMyung J Lim andD J Goodman ldquoSingle carrier FDMAfor uplink wireless transmissionrdquo IEEE Vehicular TechnologyMagazine vol 1 no 3 pp 30ndash38 2006
[3] D Falconer S L Ariyavisitakul A Benyamin-Seeyar andB Eidson ldquoFrequency domain equalization for single-carrierbroadband wireless systemsrdquo IEEE Communications Magazinevol 40 no 4 pp 58ndash66 2002
[4] S Hara and R Prasad ldquoOverview of multicarrier CDMArdquo IEEECommunications Magazine vol 35 no 12 pp 126ndash133 1997
[5] Z Luo and X Xiong ldquoPerformance comparison of SC-FDMA-CDMA and OFDM-CDMA systems for uplinkrdquo in Proceedingsof the International Conference on Consumer Electronics Com-munications and Networks (CECNet rsquo11) pp 1475ndash1479 April2011
[6] A C McCormick and E A Al-Susa ldquoMulticarrier CDMAfor future generation mobile communicationrdquo Electronics andCommunication Engineering Journal vol 14 no 2 pp 52ndash602002
[7] S H Han and J H Lee ldquoAn overview of peak-to-average powerratio reduction techniques for multicarrier transmissionrdquo IEEEWireless Communications vol 12 no 2 pp 56ndash65 2005
[8] H G Myung ldquoIntroduction to single carrier FDMArdquo in Pro-ceedings of the 15th European Signal Processing Conference(EUSIPCO rsquo07) pp 2144ndash2148 Poznan Poland September2007
[9] H G Myung and D J Goodman Single Carrier FDMA ANew Air Interface for Long Term Evolution John Wiley amp SonsLondon UK 2008
[10] P Li Y Zhu Z Wang and N Wang ldquoPeak-to-average powerratio of SC-FDMA systems with localized subcarrier mappingrdquoin Proceedings of the Global Mobile Congress (GMC rsquo2010) pp1ndash6 Shanghai China October 2010
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
4 Journal of Computer Networks and Communications
Table 1 Simulation parameters
Parameter ValueModulation scheme QPSKNormalization factor 1radic2
FFT size 64Spreading code Pseudorandom codesCoding mode (rate) Convolutional (12)Cyclic prefix 14
Channel AWGN Rayleigh and RicianChannel estimation IdealChannel equalization Zero-forcing equalizer
0 2 4 6 8 10 12
Multicarrier transmission with QPSK modulation over AWGN channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 2 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overAWGN channel) BER performance of the proposed technique isbest and very close to that of SC-FDMA and Luo and Xiong [5] Nodegradation in BER
Simultaneously it is compared with BER performanceof other multicarrier techniques such as SC-FDMA MC-DS-CDMA and OFDMA The figure shows that the BERperformance is improved with increase in SNR value It canbe very clearly observed from Figure 2 that at BER of 10minus3over AWGN channel the SNR requirement of SC-FDMAsystem and SC-FDMA-DSCDMAsystem is 92 dB and 96 dBrespectively Further MC-DS-CDMA system requires SNRvalue around 105 dB whereas the OFDMA systemrsquos require-ment is 117 dBThus it can be concluded from this figure thatBER vs SNR performance of the proposed SC-FDMA-DSC-DMA system is best when compared to MC-CDMA as wellas OFDMA and very close to that of SC-FDMA system Ithas also been observed that the BER performance of the pro-posed technique does not show any degradation in BER with
0 2 4 6 8 10 12 14 16 18 20
Multicarrier transmission with QPSK modulation over Rayleigh channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 3 BER performance of the proposed SC-FDMA-DSCDMAtechnique compared with other multicarrier techniques (overRayleigh channel) BER performance of the proposed technique isagain best and very close to that of SC-FDMA No degradation dueto modified technique
respect to technique described in [5] Figure 3 shows the com-parative BER curves for the different systems that is SC-FDMA-DSCDMA SC-FDMA MC-CDMA and OFDMAover Rayleigh fading channel
The comparative BER curves in Figure 3 depict similarbehaviour to that of Figure 2 under AWGN It can beobserved from Figure 3 that to achieve a BER of 10minus3 overRayleigh channel the SC-FDMA SC-FDMA-DSCDMAMC-DS-CDMA and OFDMA systems require SNR valueof 168 dB 175 dB 20 dB and 21 dB respectively The BERperformance of SC-FDMA-DSCDMA is again found to bevery close to that of SC-FDMA and no degradation inBER has taken place due to the use of proposed techniqueFigure 4 also shows a similar BER performance of differentmulticarrier systems over Rician channel
The different relevant parameters are clearly marked inFigure 4 We have used localized subcarrier mapping forSC-FDMA-DSCDMA Thus it can be concluded that BERvs SNR performance of the proposed SC-FDMA-DSCDMAsystem shows no degradation in the BER due to change inthe placement of CDMA spreading blockThe proposed tech-nique is best when compared to MC-CDMA as well as OFD-MAand very close to that of SC-FDMAsystem Further theseresults are clearly in line with earlier reported research workby Luo and Xiong [5]
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique now it is imperative to determine the extent ofimprovement in PAPR performance offered by the proposedtechnique PAPR is a performance measurement that is
Journal of Computer Networks and Communications 5
0 2 4 6 8 10 12 14 16 18
Multicarrier transmission with QPSK modulation over Rician channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 4 BER performance of the proposed SC-FDMA-DSCDMAtechnique comparedwith othermulticarrier techniques (over Ricianchannel) BER performance of the proposed technique is again bestand very close to that of SC-FDMANo degradation due tomodifiedtechnique
indicative of the power efficiency of the transmitter A posi-tive PAPR in dBmeans that we need a power backoff to oper-ate in the linear region of the power amplifier and high PAPRdegrades the transmit power efficiency performance Wecalculate the CCDF (complementary cumulative distributionfunction) of PAPR which is the probability that PAPR ishigher than a certain PAPR value PAPR0 (PrPAPR gt
PAPR0) Figure 5 shows the PAPR performance of SC-FDMA-DSCDMAwith respect to different119873-point FFTwithQPSK modulation
It has been observed that as the FFT size increases thePAPR value is also increased For example in Figure 5 64-point FFT has PAPR of 64 dB 128-point FFT has PAPR of755 dB whereas 256-point FFT has PAPR of 86 dB Next thePAPR performance of the proposed SC-FDMA-DSCDMAtechnique is being illustrated in Figure 6
Figure 6 shows the CCDF curves of PAPR for differentmulticarrier systems while modulation technique is QPSKand FFT size is 256This plot clearly shows that the proposedmodified technique that is SC-FDMA-DSCDMA providesbest PAPR performance among all multicarrier systemsconsidered in this paper From the figure it is observed thatOFDMAhas the highest PAPRof 112 dB followed byMC-DS-CDMA (98 dB) SC-FDMA (95 dB) and the proposed SC-FDMA-DSCDMA (86 dB) respectively SC-FDMA-DSC-DMA thus provides the best PAPR performance around 1 dBbetter than SC-FDMA Further an improvement of around2 dB has also been obtained by the proposed modified tech-nique as compared to the technique by Luo and Xiong [5]
0 1 2 3 4 5 6 7 8 9 10
SC-FDMA-DSCDMA system with N-point FFT with QPSK modulation
z (dB)
CCD
F
N 64N 128N 256
10minus2
10minus1
100
Figure 5 PAPR performance of the proposed SC-FDMA-DSCDMA technique for different FFT size with QPSK modulationFFT size 119873 indicates the number of subcarriers PAPR increaseswith increase in FFT size
Therefore we can say that the modified SC-FDMA-DSCD-MA technique is best suited for uplink in next generationwireless communication
6 Conclusion
The main objective of this paper was to propose such a tech-nique which could provide improved PAPR performancewithout any degradation in the system BER In view of thiswe proposed amodified hybrid technique that is SC-FDMA-DSCDMA which is a combination of SC-FDMA and DS-CDMA In this paper we have explored an idea that PAPRcan be reduced further by proper placement of spread-ingdespreading block in hybridOFDM-CDMA systemsTheproposed technique has been obtained by modifying thetechnique considered by Luo and Xiong [5]
In order to justify the relevance of the proposed tech-nique firstly it was ensured that no degradation in BERperformance takes place due to the modified technique whensimulated under different fading channel conditions (AWGNRayleigh and Rician) Then the extent of improvement inPAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique has been analyzed
Simulation results prove that BER vs SNR performanceof the proposed SC-FDMA-DSCDMA system shows nodegradation in the BER due to change in the placementof CDMA spreading block The proposed technique is bestwhen compared to MC-CDMA as well as OFDMA and veryclose to that of SC-FDMA system Further these results are
6 Journal of Computer Networks and Communications
1 2 3 4 5 6 7 8 9 10 11
Different multicarrier systems with QPSK modulation
SC-FDMA-DSCDMASC-FDMA
MC-DS-CDMAOFDMA
10minus2
10minus1
100
Pr (P
APRgt
PAPR
0)
PAPR0 (dB)
Figure 6 PAPR performance of the proposed SC-FDMA-DSCDMA technique compared with other multicarrier techniquesQPSK modulation with FFT size being 256 PAPR performance ofthe proposed technique is best 1 dB better than SC-FDMA and 2 dBbetter than Luo and Xiong [5]
clearly in line with earlier reported research work by Luo andXiong [5] without any degradation
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique the main objective of determining the extent ofimprovement in PAPR performance offered by the proposedtechnique has been realized Simulation results showed thatthe proposed modified technique that is SC-FDMA-DSCD-MA provides an improvement of around 1 dB over SC-FDMA technique and 2 dB over the technique reported byLuo and Xiong [5]
Thus it can be concluded that the proposedmodified SC-FDMA-DSCDMA technique provides improved PAPR per-formancewith no degradation in the systemBER It performsbetter than any other existing OFDM-CDMA based systemfor next generation wireless communication and thus couldprove to be a good alternative technique However the BERand PAPR performance could further be improved throughvarious equalization techniques and by implementing othercodingspreadingPAPR reduction techniques
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] S C YangOFDMA System Analysis and Design Artech House2010
[2] H GMyung J Lim andD J Goodman ldquoSingle carrier FDMAfor uplink wireless transmissionrdquo IEEE Vehicular TechnologyMagazine vol 1 no 3 pp 30ndash38 2006
[3] D Falconer S L Ariyavisitakul A Benyamin-Seeyar andB Eidson ldquoFrequency domain equalization for single-carrierbroadband wireless systemsrdquo IEEE Communications Magazinevol 40 no 4 pp 58ndash66 2002
[4] S Hara and R Prasad ldquoOverview of multicarrier CDMArdquo IEEECommunications Magazine vol 35 no 12 pp 126ndash133 1997
[5] Z Luo and X Xiong ldquoPerformance comparison of SC-FDMA-CDMA and OFDM-CDMA systems for uplinkrdquo in Proceedingsof the International Conference on Consumer Electronics Com-munications and Networks (CECNet rsquo11) pp 1475ndash1479 April2011
[6] A C McCormick and E A Al-Susa ldquoMulticarrier CDMAfor future generation mobile communicationrdquo Electronics andCommunication Engineering Journal vol 14 no 2 pp 52ndash602002
[7] S H Han and J H Lee ldquoAn overview of peak-to-average powerratio reduction techniques for multicarrier transmissionrdquo IEEEWireless Communications vol 12 no 2 pp 56ndash65 2005
[8] H G Myung ldquoIntroduction to single carrier FDMArdquo in Pro-ceedings of the 15th European Signal Processing Conference(EUSIPCO rsquo07) pp 2144ndash2148 Poznan Poland September2007
[9] H G Myung and D J Goodman Single Carrier FDMA ANew Air Interface for Long Term Evolution John Wiley amp SonsLondon UK 2008
[10] P Li Y Zhu Z Wang and N Wang ldquoPeak-to-average powerratio of SC-FDMA systems with localized subcarrier mappingrdquoin Proceedings of the Global Mobile Congress (GMC rsquo2010) pp1ndash6 Shanghai China October 2010
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
Journal of Computer Networks and Communications 5
0 2 4 6 8 10 12 14 16 18
Multicarrier transmission with QPSK modulation over Rician channel
Signal to noise ratio (SNR) (dB)
Bit e
rror
rate
(BER
)
SC-FDMASC-FDMA-DSCDMA
MC-DS-CDMAOFDMA
10minus4
10minus3
10minus2
10minus1
100
Figure 4 BER performance of the proposed SC-FDMA-DSCDMAtechnique comparedwith othermulticarrier techniques (over Ricianchannel) BER performance of the proposed technique is again bestand very close to that of SC-FDMANo degradation due tomodifiedtechnique
indicative of the power efficiency of the transmitter A posi-tive PAPR in dBmeans that we need a power backoff to oper-ate in the linear region of the power amplifier and high PAPRdegrades the transmit power efficiency performance Wecalculate the CCDF (complementary cumulative distributionfunction) of PAPR which is the probability that PAPR ishigher than a certain PAPR value PAPR0 (PrPAPR gt
PAPR0) Figure 5 shows the PAPR performance of SC-FDMA-DSCDMAwith respect to different119873-point FFTwithQPSK modulation
It has been observed that as the FFT size increases thePAPR value is also increased For example in Figure 5 64-point FFT has PAPR of 64 dB 128-point FFT has PAPR of755 dB whereas 256-point FFT has PAPR of 86 dB Next thePAPR performance of the proposed SC-FDMA-DSCDMAtechnique is being illustrated in Figure 6
Figure 6 shows the CCDF curves of PAPR for differentmulticarrier systems while modulation technique is QPSKand FFT size is 256This plot clearly shows that the proposedmodified technique that is SC-FDMA-DSCDMA providesbest PAPR performance among all multicarrier systemsconsidered in this paper From the figure it is observed thatOFDMAhas the highest PAPRof 112 dB followed byMC-DS-CDMA (98 dB) SC-FDMA (95 dB) and the proposed SC-FDMA-DSCDMA (86 dB) respectively SC-FDMA-DSC-DMA thus provides the best PAPR performance around 1 dBbetter than SC-FDMA Further an improvement of around2 dB has also been obtained by the proposed modified tech-nique as compared to the technique by Luo and Xiong [5]
0 1 2 3 4 5 6 7 8 9 10
SC-FDMA-DSCDMA system with N-point FFT with QPSK modulation
z (dB)
CCD
F
N 64N 128N 256
10minus2
10minus1
100
Figure 5 PAPR performance of the proposed SC-FDMA-DSCDMA technique for different FFT size with QPSK modulationFFT size 119873 indicates the number of subcarriers PAPR increaseswith increase in FFT size
Therefore we can say that the modified SC-FDMA-DSCD-MA technique is best suited for uplink in next generationwireless communication
6 Conclusion
The main objective of this paper was to propose such a tech-nique which could provide improved PAPR performancewithout any degradation in the system BER In view of thiswe proposed amodified hybrid technique that is SC-FDMA-DSCDMA which is a combination of SC-FDMA and DS-CDMA In this paper we have explored an idea that PAPRcan be reduced further by proper placement of spread-ingdespreading block in hybridOFDM-CDMA systemsTheproposed technique has been obtained by modifying thetechnique considered by Luo and Xiong [5]
In order to justify the relevance of the proposed tech-nique firstly it was ensured that no degradation in BERperformance takes place due to the modified technique whensimulated under different fading channel conditions (AWGNRayleigh and Rician) Then the extent of improvement inPAPR performance offered by the proposed modified SC-FDMA-DSCDMA technique has been analyzed
Simulation results prove that BER vs SNR performanceof the proposed SC-FDMA-DSCDMA system shows nodegradation in the BER due to change in the placementof CDMA spreading block The proposed technique is bestwhen compared to MC-CDMA as well as OFDMA and veryclose to that of SC-FDMA system Further these results are
6 Journal of Computer Networks and Communications
1 2 3 4 5 6 7 8 9 10 11
Different multicarrier systems with QPSK modulation
SC-FDMA-DSCDMASC-FDMA
MC-DS-CDMAOFDMA
10minus2
10minus1
100
Pr (P
APRgt
PAPR
0)
PAPR0 (dB)
Figure 6 PAPR performance of the proposed SC-FDMA-DSCDMA technique compared with other multicarrier techniquesQPSK modulation with FFT size being 256 PAPR performance ofthe proposed technique is best 1 dB better than SC-FDMA and 2 dBbetter than Luo and Xiong [5]
clearly in line with earlier reported research work by Luo andXiong [5] without any degradation
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique the main objective of determining the extent ofimprovement in PAPR performance offered by the proposedtechnique has been realized Simulation results showed thatthe proposed modified technique that is SC-FDMA-DSCD-MA provides an improvement of around 1 dB over SC-FDMA technique and 2 dB over the technique reported byLuo and Xiong [5]
Thus it can be concluded that the proposedmodified SC-FDMA-DSCDMA technique provides improved PAPR per-formancewith no degradation in the systemBER It performsbetter than any other existing OFDM-CDMA based systemfor next generation wireless communication and thus couldprove to be a good alternative technique However the BERand PAPR performance could further be improved throughvarious equalization techniques and by implementing othercodingspreadingPAPR reduction techniques
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] S C YangOFDMA System Analysis and Design Artech House2010
[2] H GMyung J Lim andD J Goodman ldquoSingle carrier FDMAfor uplink wireless transmissionrdquo IEEE Vehicular TechnologyMagazine vol 1 no 3 pp 30ndash38 2006
[3] D Falconer S L Ariyavisitakul A Benyamin-Seeyar andB Eidson ldquoFrequency domain equalization for single-carrierbroadband wireless systemsrdquo IEEE Communications Magazinevol 40 no 4 pp 58ndash66 2002
[4] S Hara and R Prasad ldquoOverview of multicarrier CDMArdquo IEEECommunications Magazine vol 35 no 12 pp 126ndash133 1997
[5] Z Luo and X Xiong ldquoPerformance comparison of SC-FDMA-CDMA and OFDM-CDMA systems for uplinkrdquo in Proceedingsof the International Conference on Consumer Electronics Com-munications and Networks (CECNet rsquo11) pp 1475ndash1479 April2011
[6] A C McCormick and E A Al-Susa ldquoMulticarrier CDMAfor future generation mobile communicationrdquo Electronics andCommunication Engineering Journal vol 14 no 2 pp 52ndash602002
[7] S H Han and J H Lee ldquoAn overview of peak-to-average powerratio reduction techniques for multicarrier transmissionrdquo IEEEWireless Communications vol 12 no 2 pp 56ndash65 2005
[8] H G Myung ldquoIntroduction to single carrier FDMArdquo in Pro-ceedings of the 15th European Signal Processing Conference(EUSIPCO rsquo07) pp 2144ndash2148 Poznan Poland September2007
[9] H G Myung and D J Goodman Single Carrier FDMA ANew Air Interface for Long Term Evolution John Wiley amp SonsLondon UK 2008
[10] P Li Y Zhu Z Wang and N Wang ldquoPeak-to-average powerratio of SC-FDMA systems with localized subcarrier mappingrdquoin Proceedings of the Global Mobile Congress (GMC rsquo2010) pp1ndash6 Shanghai China October 2010
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
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DistributedSensor Networks
International Journal of
6 Journal of Computer Networks and Communications
1 2 3 4 5 6 7 8 9 10 11
Different multicarrier systems with QPSK modulation
SC-FDMA-DSCDMASC-FDMA
MC-DS-CDMAOFDMA
10minus2
10minus1
100
Pr (P
APRgt
PAPR
0)
PAPR0 (dB)
Figure 6 PAPR performance of the proposed SC-FDMA-DSCDMA technique compared with other multicarrier techniquesQPSK modulation with FFT size being 256 PAPR performance ofthe proposed technique is best 1 dB better than SC-FDMA and 2 dBbetter than Luo and Xiong [5]
clearly in line with earlier reported research work by Luo andXiong [5] without any degradation
After ensuring that no degradation in BER performancetakes place due to the use of proposed SC-FDMA-DSCDMAtechnique the main objective of determining the extent ofimprovement in PAPR performance offered by the proposedtechnique has been realized Simulation results showed thatthe proposed modified technique that is SC-FDMA-DSCD-MA provides an improvement of around 1 dB over SC-FDMA technique and 2 dB over the technique reported byLuo and Xiong [5]
Thus it can be concluded that the proposedmodified SC-FDMA-DSCDMA technique provides improved PAPR per-formancewith no degradation in the systemBER It performsbetter than any other existing OFDM-CDMA based systemfor next generation wireless communication and thus couldprove to be a good alternative technique However the BERand PAPR performance could further be improved throughvarious equalization techniques and by implementing othercodingspreadingPAPR reduction techniques
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper
References
[1] S C YangOFDMA System Analysis and Design Artech House2010
[2] H GMyung J Lim andD J Goodman ldquoSingle carrier FDMAfor uplink wireless transmissionrdquo IEEE Vehicular TechnologyMagazine vol 1 no 3 pp 30ndash38 2006
[3] D Falconer S L Ariyavisitakul A Benyamin-Seeyar andB Eidson ldquoFrequency domain equalization for single-carrierbroadband wireless systemsrdquo IEEE Communications Magazinevol 40 no 4 pp 58ndash66 2002
[4] S Hara and R Prasad ldquoOverview of multicarrier CDMArdquo IEEECommunications Magazine vol 35 no 12 pp 126ndash133 1997
[5] Z Luo and X Xiong ldquoPerformance comparison of SC-FDMA-CDMA and OFDM-CDMA systems for uplinkrdquo in Proceedingsof the International Conference on Consumer Electronics Com-munications and Networks (CECNet rsquo11) pp 1475ndash1479 April2011
[6] A C McCormick and E A Al-Susa ldquoMulticarrier CDMAfor future generation mobile communicationrdquo Electronics andCommunication Engineering Journal vol 14 no 2 pp 52ndash602002
[7] S H Han and J H Lee ldquoAn overview of peak-to-average powerratio reduction techniques for multicarrier transmissionrdquo IEEEWireless Communications vol 12 no 2 pp 56ndash65 2005
[8] H G Myung ldquoIntroduction to single carrier FDMArdquo in Pro-ceedings of the 15th European Signal Processing Conference(EUSIPCO rsquo07) pp 2144ndash2148 Poznan Poland September2007
[9] H G Myung and D J Goodman Single Carrier FDMA ANew Air Interface for Long Term Evolution John Wiley amp SonsLondon UK 2008
[10] P Li Y Zhu Z Wang and N Wang ldquoPeak-to-average powerratio of SC-FDMA systems with localized subcarrier mappingrdquoin Proceedings of the Global Mobile Congress (GMC rsquo2010) pp1ndash6 Shanghai China October 2010
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
International Journal of
AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
RoboticsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Active and Passive Electronic Components
Control Scienceand Engineering
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
International Journal of
RotatingMachinery
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporation httpwwwhindawicom
Journal ofEngineeringVolume 2014
Submit your manuscripts athttpwwwhindawicom
VLSI Design
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Shock and Vibration
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Civil EngineeringAdvances in
Acoustics and VibrationAdvances in
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Electrical and Computer Engineering
Journal of
Advances inOptoElectronics
Hindawi Publishing Corporation httpwwwhindawicom
Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
SensorsJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chemical EngineeringInternational Journal of Antennas and
Propagation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Navigation and Observation
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
DistributedSensor Networks
International Journal of
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