papr reduction in ofdm

Long Paper

2013 ACEEEDOI: 01.IJRTET.9.1.

Int. J. on Recent Trends in Engineering and Technology, Vol. 9, No. 1, July 2013

526

Channel Coding and Clipping in OFDM for WiMAXusing SDR

B. Siva Kumar Reddy 1 and B. Lakshmi 21 Department of Electronics and Communication Engineering,

National Institute of Technology Warangal, Andhra Pradesh-506004, India.Email: [email protected]

2 Department of Electronics and Communication Engineering,National Institute of Technology Warangal, Andhra Pradesh-506004, India.

Email: [email protected]

Abstract Recent developments in broadband wirelesstechnology heightened the need for WiMAX which assureshigh-speed data services. Mobile WiMAX is grounded onorthogonal frequency division multiplexing/orthogonalfrequency division multiplexing Access (OFDM/OFDMA)technology which is an increasing important technique inLTE systems. This paper describes the OFDM transceiverimplementation using software-defined radio system (SDR).A SDR is a radio communication system where elements havebeen generally implemented in hardware are ratherimplemented by software on a personal computer. In this paper,the software part is realized using GNU Radio and thehardware part is implemented using USRP N210. OFDM posesa problem of a Peak to Average Power Ratio (PAPR) or highcrest factor. To stave off this problem either High PowerAmplifiers (HPAs) with large dynamic range or PAPR reductiontechniques are used. The former scheme raises cost of thesystem, while the latter induces redundancy or distortion.This paper presents a novel architecture (which combineschannel coding and clipping) for the PAPR reduction andanalyzes various parameters which effects the performanceof OFDM such as power spectral density, the crest factor andBER. Channel coding part is framed of three stepsrandomization, Forward Error Correction (FEC) andinterleaving. In clipping, certain threshold limits theamplitude of time domain samples. Without filtering, clippingcauses out-of-band radiation. The paper analyzes the out bandradiation value (at 2.395 GHz) and PAPR reduction with respectto clipping threshold value. This scheme is preferred becauseof its lower complexity and hence would be cheaper toimplement than conventional reduction techniques.Experimental results prove that the clipping method reducedPAPR significantly as the number of clip and filtering level isincreased.

Index TermsBER, Clipping, Coding, OFDM, OFDMA, SDR,WIMAX.

I. INTRODUCTION

One of the most significant current discussions in thecommunications is Software Defined Radio (SDR) [1]. SDR ispertained to as a digitally programmable platform that can beprogrammed to realize multiple wireless standards (GSM, W-CDMA, Wi-Fi, WiMAX, etc). SDR has potential to realize thestructure of the device with high mobility, reconfigurabilityand flexibility. In SDR, General-Purpose Processor (GPP), Digi

tal Signal Processor (DSP) and Field Programmable Gate Ar-ray (FPGA) are used to build up the software radio elements.The fundamental architecture of SDR is shown in Fig. 1. Itincludes front-end, processing engine and application. TheRadio Frequency (RF) front-end module digitizes the radiofrequency data from antennas. After the baseband is digi-tized by front-end, the processing engine changes basebanddata and date frames. The application side receives dataframes at last.

Figure 1: Fundamental architecture of Software Defined Radio(SDR)

In recent years, there has been an increasing interest inWiMAX (Worldwide Interoperability for Microwave Access)[2] technology that provides performance similar to Wi-Fi(IEEE 802.11) networks with the coverage and QoS (qualityof service) of mobile networks. WiMAX can providebroadband wireless access (BWA) up to 50 km for fixedstations (called as Fixed WiMAX (IEEE 802.16d)), and 5-15km for mobile stations (called as Mobile WiMAX (IEEE802.16e-2005)). This BWA technology is based on OrthogonalFrequency Division Multiplex (OFDM) technology [3] andconsiders the radio frequency range up to 2-11 GHz and 10-66 GHz. This provides strong performance in multipath andnon-line-of-sight (NLOS) environments. Mobile WiMAXextends the OFDM PHY layer to support efficient multiple-access (known as scalable OFDMA (Orthogonal FrequencyDivision Multiple Access)) [3]. Scalability is carried out byaltering the FFT size from 128 to 512, 1024, and 2048 to supportchannel bandwidths of 1.25 MHz, 5 MHz, 10 MHz and 20MHz respectively.

In a single carrier communication system, to avoid inter-symbol interference (ISI), the symbol period must bemaintained greater than the delay time. Having long symbolperiods means low data rate and communication inefficiencybecause data rate is inversely proportional to symbol period.

66

Long Paper



OFDM is a multicarrier multiplexing digital communicationscheme to solve both issues, where data is transmittedthrough several parallel frequency subchannels at a lowerrate. OFDM has become one of the most important buildingblock in the area of modern broadband wireless networks forthe following reasons: i) tolerance to multipath propagationand frequency selective fading ii) high spectral efficiencyand iii) impulse noise rejection. However, a major problemwith this kind of application is high Peak to Average Powerratio (PAPR). To reduce PAPR ratio, Channel coding [4] andclipping [5] have been considered.

Recently, researchers have shown an increased interestin Channel coding [4] which plays a vital role in theperformance of OFDM system. The role of channel coding inconjunctive with frequency and time interleaving is to furnisha link between bits transmitted on separated carriers of thesignal spectrum, in such a way that the data expressed byfaded carriers can be rebuilt in the receiver. Clipping is anonlinear process [5]. Thus, it must be executed in a controlledmanner to prevent any signal distortion. The results ofclipping are in-band distortion and out-of-hand distortion.In-band distortion or the degradation in the wanted signalstrength happens since clipping modifies the signal artificially.Clipping an over sampled signal induces lesser effect ofdistortion to the signal within the original band. This is becauseoversampling shortens the effect of clipping noise in therequired signal by spreading them in a wider bandwidth. Byacting clipping on an oversampled signals also resulted in alesser peak regrowth. The out-of-band radiation can bereduced by performing frequency domain filtering [6]. Thisfiltering results in a lesser peak regrowth and also completelydecimates the out-of-band radiation thus allowing the originalunclipped signal to be retrieved. This paper will focus on thedescription of the proposed novel architecture is shown inFig. 2, which combines Channel coding and Clippingtechniques for PAPR reduction for WiMAX.

526

Figure 2: Novel Architecture composes of channel coding andclipping

The rest of the paper is structured as follows. Section IIand III introduce the software and hardware platformrealizations for for SDR respectively. In Section IV, the systemmodel is presented by focussing the attention on OFDMPHY layer used in WiMAX standords. Section V examine theeffect of clipping and channel coding on PAPR reduction. InSection VI, numerical results evaluating impacts of variousparameters on PAPR, in-band and out-of band distortion,BER. Some literature survey also has done here. Finally, thepaper has concluded in Section VI.

II. GNU RADIO COMPANION

Recent developments in the field of SDR have led to arenewed interest in GNU Radio [7], which is a free and open-source

software development toolkit that offers signal processingblocks to implement Software Defined Radios (SDR). TheUSRP [8] will digitize the incoming data from the air and pass-ing it to the GNU Radio through the USB or Ethernet inter-face. GNU Radio will further process (demodulating and fil-tering) the signal until the signal is translated to a stream ofdata or packet. In GNU Radio, all signal processing is donethrough flow graphs, which consists of blocks. A block doestransforming, decoding, filtering, adding signals, hardwareaccess or many others. Data passes between blocks in vari-ous formats, complex or real integers, floats or basically anykind of data type user can define. Every flow graph demandsat least one sink and source. In GNU Radio, signal process-ing blocks are written in C++ and they are connected byusing Python. SWIG (Simplified Wrapper and Interface Gen-erator) is used as an interface compiler between C++ andPython language [7]. GRC is a signal flow chart generatortool in GNU Radio. Signal flow chart is built through the GUItool and also follow-up the source code to function this flow.Each block has a relative parameter XML file, GRC will auto-matically identify the blocks definition when it is executing.In other words, GRC has the automatic recognition error abil-ity.

III. UNIVERSAL SOFTWARE RADIO PERIPHERAL

USRP is a flexible hardware platform for the developmentof SDRs [8]. Any USRP board consists of a motherboard anddaughterboard. In this paper, a network series USRP N210 issuggested, because of its high-bandwidth, high-dynamicrange processing capability. This board includes a XilinxSpartan 3A-DSP 3400 FPGA, 100 MS/s dual ADC (Analog toDigital Converter), 400 MS/s dual DAC (Digital to AnalogConverter) and Gigabit Ethernet connectivity to stream datato and from host processors. The USRP N210 can stream upto 50 MS/s to and from host applications. The FPGA (FieldProgrammable Gate Array) also offers the potential to processup to 100 MS/s in both transmit and receive directions. TheUSRP N210 operates from DC to 6 GHz and an expansion portallows using in MIMO configuration.

IV. OFDM TRNSEIVER MODEL

OFDM is one of the most widely used technique in LTE(Long Term Evaluation) system. In OFDM, spectrally coin-cided sub-carriers can be used and since they are orthogo-nal, they do not interfere with each other. This causes OFDMa bandwidth efficient modulation scheme [3]. OFDM is a tech-nique as shown in Fig. 3, where the input data is converted toparallel bits and mapped according to predefined standard.Inverse Fast Fourier Transform (IFFT) is a part to convertsignal from frequency domain to time domain. After IFFT theparallel data is again converted to serial data. Before it getsconverted from digital to analog data, Cyclic prefix is alsoadded. The input data should be prepared preserving spe-cific standard. In the IFFT mapping, the total subcarriers infrequency domain are converted to time domain. In order topreserve the orthogonally of OFDM signal, preamble bits are

67

Long Paper



526

added. Also the cyclic prefix enables synchronization as thebits are used to detect the beginning and end of each frameand it appends the OFDM symbols one after another. At thereceiver side, do reverse processes to demodulate the re-ceived sequences of data bits.

Figure 3: OFDM Transciever block diagram

OFDM symbol consists of N subcarriers which haveconstant spacing f. Bandwidth of the signal is B= f.N andsymbol time T=1/ f. This conducts to sum of N sinsoids inthe time domain, that have exactly an integer number of cyclesin the intervel T. Each subcarrier is regulated by complexvalue Xm,n , where m refers symbol index and n subcarrierindex.M-th OFDM symbol can be defined as [5]:

(1)

where gn(t) = exp(j2nft), for 0 d t dT and gn(t) = 0, for other t.

Time domain signal is defined as sum of symbols [5]:

(2)

The complex value Xm,n based on partial modulation(Usually M-PSK or M-QAM is used).

V. CHANNEL CODING AND CLIPPING

The novel architecture combines the use of channelcoding and Clipping method as shown in Fig. 2. Thesechannel codes improve the bit error rate performance byappending redundant bits in the conveyed bit stream thatare used by the receiver to correct errors introduced by thechannel [4]. OFDM contains of lots of independent modulatedsubcarriers (without considering coding). That causes toproblem with peak to average power ratio. If N subcarriersare in phase with same symbols regulated on all subcarriers,the peak power is N times average power. For sampled signal,PAPR can be defined [9]:

(3)

E[|Sn|2] is average power of transmitted symbol. Oversampling

is necessary to get right values of PAPR and it can beperformed by plodding IFFT source data with zeros. The timedomain signal is normally oversampled by factor of four orgreater. The channel encoder includes three stages: data scrambling,convolution coding, and data interleaving [4]. The datascrambler uses generator polynomial S(x) = x7 + x4 + 1 withall ones (1111111) as the initial state. The 127-bit binarysequence is employed repeatedly to be XORed with the databit sequence. The output of the scrambler is shipped to a rate1/2, K = 7 convolutional encoder with generator polynomialsg0 = 1338 (1011011) and g1 = 1718 (1111001) the encoded databits are then handed to an interleaver with the block sizerepresenting to the number of bits in a single OFDM symbol.The interleaver is defined by a two-step permutation. Thefirst permutation insures that the adjacent coded bits aremapped onto nonadjacent subcarriers, while the secondpermutation insures that the adjacent coded bits are mappedalternately onto less and more significant bits of theconstellation and, thereby, long runs of low reliability (LSB)bits are avoided. If the code rate is k/n, then k bits per secondinput to the convolutional encoder and the output is n bitsper second.QAM64 data symbols are passed through an inverse fastFourier transform (IFFT) module to realize the OFDMmodulation. If the digital OFDM signals are clipped instantly,the resulting clipping noise will be fall in-band and may notbe reduced by filtering. Data symbols are sent through aninverse fast Fourier transform (IFFT) module to realize theOFDM modulation. In addition, the complex-valued basebandOFDM signal is regulated up to a carrier frequency equal to1/4 of the sampling frequency to descend the implementationcomplexity. Then, the real-valued bandpass samples x, areclipped at an amplitude A as follows [6]:

(4)

In the following discussion, we will use a normalized clippinglevel, which we call the clipping ratio (CR = A/, where isthe rms level of the OFDM signal). It is easy to show that, for

an OFDM signal with N subchannels, = N for a

baseband signal = 2/N and for a bandpass signal. Inthe following discussion, we will use a normalized clippinglevel, which we call the clipping ratio (CR = A/, where isthe rms level of the OFDM signal). A CR of 1.4 denotes thatthe clipping level is about 3 dB higher than the rms level.Filtering after clipping is required to reduce the out-of-band

68

Long Paper



clipping noise. Filtering after clipping is required to reducethe out-of-band clipping noise [5].

VI. EXPERIMENTAL RESULTS

WiMAX confirms a various modulation and Forward ErrorCorrection (FEC) coding schemes and grants the scheme pera user based on channel conditions accordingly. This causesto Adaptive modulation and coding [10] which is an effectivemechanism to maximize throughput, fairness and BERperformance in a continuously time-varying channel. Figs 4,5 and 6 present the effectiveness of encoding on AWGN,SUI-1 and SUI-2 channel models. Simulation results showthe advantage of convolutional coding and for the QPSKdigital modulation scheme [11]. The Table 1 depicts the BERunder QPSK modulation technique over AWGN, SUI-1 andSUI-2 fading channel with encoder for a SNR value of 5dBbut in the case of without encoder is found SNR value of9dB, 10dB and 8dB respectively [11]. As shown in Fig. 7, theBER performance has been improved for coded signal (dueto channel coding) than uncoded signal [12].

526

Figure 4. BER performance under AWGN channel for QPSK [11]

Figure 5. BER performance under SUI 1 channel for QPSK

Figure 6. BER performance under SUI 2 channel for QPSK

TABLE I. SNR IN DB WITH AND WITHOUT ENCODER FOR QPSK

SNR (in dB)

AWGN SUI-1 SUI-2

With Encoder 5 5 5 Without Encoder 9 10 8

Figure. 7. BER performance for coded and uncoded signal [12]

One of the simple and effective PAPR reductiontechniques is clipping, which cancels the signal compo-nents that outperform some unchanging amplitude calledclip level [5]. However, clipping affords distortion power,which called clipping noise, and elaborates the transmittedsignal spectrum, which causes interfering. The technique ofiterative clipping and filtering reduces the PAPR withoutspectrum expansion. However, the iterative signal carrieslong time and it will gain the computational complexity ofan OFDM transmitter. But without performing interpolationbefore clipping causes it out-of-band. To avoid out-of band,signal should be clipped after interpolation. However, thisinduces significant peak re-growth. So, it can employ itera-tive clipping and frequency domain filtering to avoid peak re-growth. Fig. 8 depicts the power spectral density (PSD) ofthe Mobile WiMAX MC-OFDMA-256-QAM clipped signal.The in-band signal attenuation as well as the out-of bandinduced by clipping is apparent. In Normal OFDMA the out-of band noise emission power is only 30 dB lower than thesignal power. But With hard clipping ratio CR= 0.5 and afterapplying the filtering, it is observed that the spectralsidelobes after filtering are at least 25 dB lower than the sig-nal mainlobe [13]. Fig. 9 shows the effect of clipping level onPAPR reduction. As clipping level increases, the PAPR re-duction increases [14].

The discussed above two techniques ([11], [12] and [13])are combined to get both the advantages in terms of BER andPAPR reduction in novel approach. The experimental setuphas a USRP N210 platform and a General Purpose Processor(laptop) is shown in Fig. 10. The required OFDM parametersfor WiMAX specifications have been shown in Table 2. Theflow graph of novel architecture is Source>Scrambling>Convolutional Coding>Interleaving>OFDM block>Rail Clipping>Multiply Const>Channel Model>Sink,shown in Fig. 11. OFDM modulator modulates an OFDM

69

Long Paper



526

Figure 8. PSD of Normal-OFDMA and MC-OFDMA for WiMAX-256QAM

Figure 9. Clipping level effect on PAPR in OFDM [14]

stream based on the configurability such as FFT length, oc-cupied tones, and cyclic prefix length. This block createsOFDM symbols using specified modulation scheme (here in64-QAM) shown in Fig. 11. The USRP N210 is connected assource and captured a signal at 2.46 GHz from the environ-ment using VERT 2450 antenna and the processing has doneusing XCVR 2450 daughterboard in USRP. WiMAX PHY layerprocessing has done in GNU Radio [7], shown in Fig. 11.

Figure 10. Experimental setup for the development of SoftwareDefined Radio (SDR)

TABLE II. EXPERIMENTAL PARAMETERS DEFINED

Parameters Values FFT size (NFFT) 1024 Occupied Tones 840 Sampling rate 10.66667M Center Frequency 2.48 GHz Convolutional Code 1/2

Cyclic Prefix length 184

Useful symbol duration 91.43 s

Carrier spacing (1/Tu) 10.94 KHz

Guard time (Tg=(1/4)* Tu) 11.43 s

OFDM symbol duration 102.86 s Mapping Schemes BPSK, 4QAM, 16QAM

and 256QAM

From the experimental results, it can be observed thatOFDM signal is has higher PAPR (Shown in Figs. 12 and 13)and after applying the proposed method, PAPR has beenreduced significantly (Shown in Figs. 14 and 15). Theamplitude clipping is simple method with minimal computingcomplexity. The clipping is followed by filtering to reduceout of band power. Figs 16, 17, 18 and 19 show the average64QAM-OFDM signals with Clipping Thresholds (CT) 0.2,0.6, 3 and 5 respectively. It can be concluded that thedifference between out-of band and in-band radiation hasbeen increased as clipping level increased. So, the selectionof clipping threshold value is carefully taken. The clipping isthe easiest technique to reduce the power by setting amaximum level for the transmitted signal [5]. Though, thistechnique has several disadvantages:i) The performance of BER could be affected negatively dueto the in-band distortion caused by the clipping.ii) Also out-of-band radiation usually appears with clippingtechnique that could disturb the adjacent channels. However,we can use filtering operation to decrease the appearance ofthe out-of-band radiation but the signal may exceed themaximum level of the clipping operation.

On the other hand, the BER performance is worsen badlyat it gets better when the CR get higher as shown in Fig. 20.It is clear that the performance of the BER get worse as theCR gets lower [15].

70

Long Paper


2013 ACEEEDOI: 01.IJRTET.9.1.526

Figure 11. GNU Schematic for the implementation of Channel coding and clipping for mobile WiMAX

TABLE III. OBTAINED RESULTS FOR MOBILE WIMAX WITH CHANNEL CODING AND CLIPPING USING SDR

Clipping Threshold

Value (CT)

Scope Sink FFT sink PAPR (in db)

(in db) Peak to peak Amp

(in counts) Average Amp

(in counts) Peak to peak Amp

(in db) Average Amp

(in db) 5 -900 to +900 -200 to +200 4 to 32 16 to 28 20.25 -13 37 3 -850 to +850 -200 to +200 5 to 32 19 to 26 18.06 -10 35 2 -800 to +800 -200 to +200 5 to 31 18 to 26 16 -5 28 1 -500 to +500 -200 to +200 5 to 29 18 to 24 6.25 2 18

0.8 -400 to +400 -200 to +200 10 to 28 16 to 23 4 3 14 0.6 -300 to +300 -200 to +200 5 to 24 16 to 23 2.25 5 10 0.4 -200 to +200 -180 to +180 5 to 21 15 to 20 1.11 6 5 0.2 -100 to +100 -100 to +100 -5 to 15 8 to 15 1 8 2

Table 3 shows (Where = Out of band radiation at2.395GHz, = Difference between out-ofband and in bandradiation), as clipping threshold value (CT) decreases, out ofband value is increased and the difference between in bandradiation to out of band radiation is decreased. So it can beconcluded that there is a tradeoff between clipping thresholdand out of band radiation. In FFT sink peak to peak amplitudevalue and average amplitude values are increased as CT valueincreases. Out of band radiation value has been controlledby filtering [5]. Fig. 21 shows, particularly fast way ofcalculating auto-correlations [16]. Table 4 shows thecomparison of various PAPR reduction techniques, each

technique has its own advantages and disadvantages. Aproper PAPR reduction technique selection is based on theapplication.

Through our SDR platform consists of GNU Radiosoftware [7] and USRP hardware device [8], we candynamically adjust the central frequency of the digital datacommunication service and choose the unlicensed band aslong as we want. Because GNU Radio provides highinstantaneous and accurate spectrum sensing ability, we canefficiently utilize SDR to achieve digital data communicationunder the current limited spectrum resource. Due to simplecomplexity, clipping technique is preferred more.

71

Long Paper



526

Figure 12. Without clipping, 64QAM-OFDM signal on Scope sink

Figure 13. Without clipping, 64QAM-OFDM signal on FFT sink

Figure 14. Clipped signal at CT=0.6 on scope plot

Figure 15. Peak to Peak OFDM signal at CT=0.8 on FFT sink

Figure 16. Average OFDM signal at CT=0.2 for 64-QAM modscheme

Figure 17. Average OFDM signal at CT=0.6 for 64-QAM modscheme

72

Long Paper


2013 ACEEEDOI: 01.IJRTET.9.1.526

Figure 18. Average OFDM signal at CT=3 for 64-QAM modscheme

Figure 19. Average OFDM signal at CT=5 for 64-QAM mod scheme

Figure 20. BER for clipped and unclipped signal [15]

Figure 21. Fast Autocorrelation for OFDM at CT=5

TABLE IV. COMPARISON OF VARIOUS PAPR REDUCTION TECHNIQUES

Reduction Technique

Parameters Operation required at Transmitter

(TX)/Receiver (RX)

Decrease distortion

Power Raise

Defeat Data rate

Clipping and

Filtering

NO No No TX: Clipping RX: None

Selective Mapping (SLM)

Yes No Yes TX:M times IFFTs

operation RX: Side

information extraction,

inverse SLM Block

Coding Yes No Yes TX: Coding

or table searching

RX: Decoding or table

searching Partial

Transmit Sequence

(PTS)

Yes No Yes TX: V times IFFTs

operation RX: Side

information extraction,

inverse PTS Interleavin

g Yes No Yes TX: D times

IFFTs operation, D-

1 times interleaving

RX: Side information extraction,

deinterleaving Tone

Reservation (TR)

Yes Yes Yes

Tone Injection

(TI)

Yes Yes No

CONCLUSIONS

Though, there is a major drawback for using OFDM, whichis the high PAPR, recently OFDM became a compulsory in allLTE systems for higher data rates. This problem can be

73

Long Paper



526

reduced by using channel coding and clipping as a powerreduction technique. We proposed and implemented areconfigurable SDR platform by combing USRP N210 andGNU Radio. The selected technique allows for us with agood range in performance to reduce PAPR problem. Thepaper concludes that as SNR increases, BER will decreases.And higher order PSK requires a larger SNR to minimize BER.QAM constitutes of amplitude as well as phase, but QPSKonly have phase, so QAM is widely used instead QPSK .The obtained results prove that PAPR reduces more at lowerCR and there is a tradeoff between the clipping thresholdvalue (CT) and out-of-band radiation. This out-of-bandradiation can be controlled by frequency domain filtering.The results show how clipping and filtering affect the BER ofan OFDM signal and it is clear that the BER is increased afterthis process. Filter is used to decrease the distortion thatresult from clipping. This research will extend in directionsFirstly, PAPR reduction concepts will be expanded fordistortion less transmission and identifying the bestalternatives in terms of performance increase Secondly,PAPR reduction technique will be develop for low datarate loss and efficient use of channel.

REFERENCES

[1] J.Mitola, Software radios-survey, critical evaluation andfuture directions, IEEE National Telesystems Conference,pages 13/15-13/23, 19-20 May 1992.

[2] Bo Li; Yang Qin; Chor Ping Low; Choon Lim Gwee; , ASurveyon Mobile WiMAX [Wireless Broadband Access],Communications Magazine, IEEE , vol.45, no.12, pp.70-75,December 2007.

[3] Chen, H.M. and Chen, W.C. and Chung, C.D. Spectrallyprecoded OFDM and OFDMA with cyclic pre x andunconstrained guard ratios, Wireless Communications, IEEETransactions on, vol 10, no. 5, pp. 416-1427, 2011.

[4] Sonagi, Rupa and Chaudhary, Shubhangi and Patil, AJPerformance Analysis of an OFDM system using ChannelCoding Techniques, IJCA Proceedings on InternationalConference and workshop on Emerging Trends in Technology(ICWET 2012)}, page 7, 2012.

[5] Albdran, Saleh and Alshammari, Ahmed and Matin, Mohammad,Clipping and Filtering Technique for reducing PAPR inOFDM, IOSR Journal of Engineering (IOSRJEN), vol2, pp91-97, 2012.

[6] Li, Xiaodong and Cimini Jr, Leonard J, Effects of clippingand filtering on the performance of OFDM, CommunicationsLetters, IEEE, pages 131133, vol 2, 1998.

[7] GNU Radio Trac, http://gnuradio.org/trac/wiki.[8] Matt Ettus, Universal software radio peripheral. http://

www.ettus.com.[9] J.Mitola, Analysis and comparison of clipping techniques for

OFDM Peak-to-Average Power Ratio reduction, Digital SignalProcessing, 2009 16th International Conference on, pages 16, 2009.

[10] Reddy, B Siva Kumar and Lakshmi, B, Adaptive Modulationand Coding in COFDM for WiMAX Using LMS ChannelEstimator,2013.

[11] Sekar, Venkatesh and Palanisamy, V and Baskaran, K,Performance Analysis of IEEE 802.16 d using Forward ErrorCorrection, Journal of Computer Science,vol 7, num 3, pp431433, 2011.

[12] Kaiser, Stefan, OFDM code-division multiplexing in fadingchannels, Communications, IEEE Transactions on, vol 50,num 8, pp 12661273, 2002.

[13] Al-kebsi, Ibrahim Ismail and Ismail, Mahamod and Jumari,Kasmiran and Rahman, TA, Mobile WiMaX performanceimprovement using a novel algorithm with a new form ofadaptive modulation, IJCSNS International Journal ofComputer Science and Network Security, vol 9, num 2, 7682, 2009.

[14] Rana, MM and Naseer, A and Hussain, S and Siddiq, Shahidand Ali, Aasim and Malik, Clipping Based PAPR ReductionMethod for LTE OFDMA Systems, IEEE IJECS-IJENS,vol10, num 05, 2000.

[15] Albdran, Saleh and Alshammari, Ahmed and Matin,Mohammad, Clipping and Filtering Technique for reducingPAPR in OFDM,2012.

[16] Ren, Yu, Analysis and Implementation of ReinforcementLearning on a GNU Radio Cognitive Radio Platform, IEEENational Telesystems Conference, 2010.

74

papr reduction in ofdm

Documents

software defined radio

software radio elements

radio communication

communication engineering

performanceof ofdm

ofdm transceiverimplementation

gnu radio

long paper