Nonlinearity Compensation for High Power Amplifiers Based on Look-Up Table Method for OFDM Transmitters Nonlinearity Compensation for High Power Amplifiers Based on Look-Up Table Method

International Journal of Advanced Computer Science and Information Technology (IJACSIT) Vol. 3, No. 4, 2014, Page: 354-367, ISSN: 2296-1739 © Helvetic Editions LTD, Switzerland www.elvedit.com

Nonlinearity Compensation for High Power Amplifiers Based on Look-Up Table Method

for OFDM Transmitters

Authors

Maryam Sajedin Department of Electrical Engineering, Fars Science and Research Branch, Islamic Azad University,

[email protected] Fars, Iran

Ayaz Ghorbani Department of Electrical Engineering, Amirkabir University of Technology

[email protected] Tehran, P.O. Box: 15875-4413,

Iran

Hamid Reza Amin Davar Department of Electrical Engineering, Amirkabir University of Technology

[email protected] Tehran, P.O. Box: 15875-4413, Iran

Abstract The OFDM is generally known as an effective technique for high Bit-rate applications. In OFDM systems, the combination of different signals with different phase and amplitude give a large dynamic range that is used to be characterized by a high PAPR. To obtain maximum efficiency Power Amplifier should be driven near the saturation region, but since the OFDM signal has high PAPR, this power amplifier will cross over to the nonlinear region causing serious in band distortion, and operation in nonlinear mode reduces performances of the output signal. To compensate for this distortion, liberalizers are proposes to utilize a digital pre-distortion of baseband signals, which is efficient and illustrates a high performance for linearization of OFDM transmitters. This paper presents an adaptive digital pre-distortion techniques based on Look Up Table (LUT) method which will result in cancellation of nonlinear distortion appearing in power amplifier through Advanced Design System(ADS) software. It is shown that the new simplified structure exhibits fast convergence and LUT pre-distorter can effectively suppress the spectrum regrowth caused by the dynamic nonlinearity of power amplifier. Key Words

About four key words or phrases in alphabetical order, separated by commas.

Nonlinearity Compensation for High Power Amplifiers Based on Look-Up Table Method for OFDM Transmitters Maryam Maryam Sajedin, Ayaz Ghorbani and Hamid Reza Amin Davar

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I. INTRODUCTION In recent years OFDM has attracted a great deal of attention for digital terrestrial

broadcasting and mainly in 4G technology considered for modulation. The OFDM is a combination of modulation and multiplexing and it is a multicarrier transmission technique too. It uses the spectrum so efficiently by spacing the channels much closer together [1]. Also, it can reduce the frequency selectivity of the channel taking advantage a simple one-tap equalizer [2]. The OFDM signal is robust against multipath fading and impulsive noise [3] and behaves like a Gaussian random process. Furthermore, the inter-symbol interference (ISI) in OFDM can be easily prevented by inserting a guard interval before each transmitted block, longer than the largest delay spread [4]. The OFDM structure requires a summation of a large number of subcarrier for multicarrier modulation and as a result of this summation large signal envelope fluctuations occur.

However, one of the important problems associated with OFDM is its high peak to average power ratio [5] which requires large power back off for linear operation of PA, resulting in a low average efficiency [6]. This nonlinear distortion causes serious in band distortion as well as adjacent channel interference due to spectrum regrowth in the transmitted signal. High Power Amplifier (HPA) working and performance plays the great role in OFDM wireless system [7]. Real PA has a nonlinear response that creates in-band and out-of-band distortion that not only reduces the system performance but also creates interference on adjacent channels (ACI). The nonlinear effects on the transmitted OFDM signal are: spectral-spreading of the subcarriers warping of the signal constellation in each sub channel. Nonlinear amplifiers are characterized by measurement of their AM/AM (amplitude dependent gain) and AM/PM (amplitude dependent phase shift) function in either polar or quadrate form [8]. To obtain maximum efficiency the power amplifier should be driven near the saturation region, but since the OFDM signal has high PAPR these power amplifier will cross over to the nonlinear region causing serious in band distortion. Therefore linearizing techniques should be introduced to minimize the output distortion. The most rapidly developing linearization technique is digital pre-distortion (DPD), this is a popular and reliable technique that allows minimizing output distortion and spectral regrowth [9]. The most developed DPD methods are Look up Table and polynomial [10].

In this paper we the authors characterize the performance of the OFDM in the presence of a High Power Amplifier .Taking advantage of the Fourier transformation the output correlation function can provide information on the output power spectral density (PSD) .An adaptive digital baseband compensator based on the LUT (Look-Up Table ) method is proposed to overcome the nonlinear distortion .We demonstrate that our simplified scheme exhibits fast convergence. Section 2 briefly describes the concepts of OFDM transceiver, introduces the power amplifier model and the effects of HPA nonlinear distortion on OFDM signal and LUT method. The computer simulations and the experimental results are given in section 3 and finally section 4 concludes the paper.

II. MATERIAL AND METHODS

A. Signal Model

International Journal of Advanced Computer Science and Information Technology Volume 3, Issue 4, 2014, ISSN: 2296-1739

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Figure 1 illustrates a baseband transceiver structure for OFDM using the Fourier transform for modulation and demodulation. Here the serial data stream is mapped to complex data symbols (QAM) with a symbol rate of . The data is then demultiplexed by a serial to parallel converter resulting in a block of N complex symbols, x tox . The parallel samples are then passed through an N point IFFT (in this case no oversampling is assumed) with a rectangular window of length N. T . Resulting in complex samples x to x assuming the incoming complex data is random it follows that the IFFT is a set of N independent random complex sinusoids summed together. The samples, x to x are then converted back into a serial data stream producing a baseband OFDM transmit symbol of length t = N. T .

FIGURE 1: THE BASIC OFDM TRANSMITTER AND RECEIVER PAIR UTILIZING FOURIER TRANSFORM A Cyclic Prefix (CP), which is a copy of the last part of samples is appended to the front of

serial data stream before Radio frequency up conversion and transmission. It combats the disrupting effects of the channel which introduce Inter System Interference. In the receiver the whole process is reversed to recover the transmitter data, the CP is removed prior to the FFT which reverses the effect of the IFFT. The complex symbols at the out of the FFT , y ……y are then decoded and the original bit stream recovered [11].

B. HPA Models

The following equations describe the algorithm used for PA model. The input signal V (t) is represented by its inphase and quadrature components about its carrier frequency.



푉 (푡) = 푅푒{푉 (푡)푒 } ,푉 (푡) = 푉 (푡) + 푗푉 (푡) (1)

The output signal V (t) is then given by the equation

푉 (푡) = 푅푒{푎푔 푉 (푡)푒 } (2)

Where a denotes the gain of the component . {If the input is a baseband timed signal, then only the real part of the Gain is used for a}. g denotes the gain compression factor as determined by the gain compression parameters, ( GCType(Gaincompressiontype) , TOIout(Thirdorderinterceptpower) , dBc1out(1dBgaincompressionpower) , PSat(Saturationpower), GCSat(Gaincompressionatsaturation)) . All gain compression characteristics, are modeled using a polynomial expression up to the saturation point; after this point, output power is held constant for increasing input power. The gain compression expression for nonlinear models is defined with a nonlinear amplitude characteristic. When GCType = PSat + GCSat + TOI, then the g comp factor is due only to the output third-order intercept point TOIout, output saturated power PSat, and the gain compression at saturation GCSat, where (3≤GCSat≤7, and (TOI−10+0.5(GCSat-1)) ≤ PSat≤(TOI−4).

FIGURE 2: ILLUSTRATION OF THE THIRD ORDER INTERCEPTS POINTS

In figure (2), it can be shown that the slope of the linear gain for input and output powers in dBs is unity, likewise the slope of the third gain of the third order IMD component is 3, the point where the third order line intersects with the linear gain line is the third order intercept point. Nonlinear models TOI through PSat + GCSat + TOI + dBc1mathematical gain model,



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푉 (푉 ) = 푎 푉 + 푎 푉 + 푎 푣 + ⋯ (3)

Where V presents input signal voltage, V is output signal voltage, a illustrates small signal gain, a shows third-order gain coefficient and a , presents higher odd-order gain coefficients. The gain compression expression for nonlinear model, in general, has both amplitude and phase changes versus increasing input power. Ref.[12] have shown that only the odd components of the nonlinear model bring distortion to the fundamental signal. When a single carrier input signal, is substituted into above formula (1), the output waveform will contain the original sine wave and harmonic distortion products [12] the harmonics can be eliminated by filtering and do not pose a problem except for wideband communication application requiring wide bandwidth. However, when more than one carrier is present, additional new signals known intermodulation distortion (IMD) are produced in the vicinity of input signals. Filtering cannot easily eliminate IMD products, as these are located on the same frequency or near to the desired input signal [13].

(a) (b)

FIGURE 3: (A) AM/AM AND (B) AM/PM TRANSFER CURVES

Figure (3) presents the distortion characteristics of power, use of a exact approximation of these nonlinearities allows a linearization good enough. The accuracy and efficiency of the pre-distortion rely strongly on modeling of the true nonlinearities.

C. The Effects of HPA Nonlinear Distortion on OFDM Signals

HPA nonlinearity may have bad influence on OFDM signal mainly on two aspects: a out of band distortion, which will cause the OFDM power spectrum distortion i.e. the spectral spreading of the amplified signal and introduce ACI, as is shown in figure 4 right, requirements on ACI for RF systems are very strict especially with large number of subscribers, therefore, it is of great importance to distortion, which may disturb the OFDM constellations and result in BER performance degradation. Figure 4 left; show that the spectrums of OFDM signals through HPA



have spectrum re-growth distortion.

Regulatory bodies specify power spectral density masks which define the maximum allowable adjacent channel interference (ACI) levels. In order to meet the regulatory mask, at least a 20 dB improvement in the intermodulation products is required.to satisfy these requirements, linearizing techniques should be introduced to minimize the output distortion. the Digital Pre-distortion (DPD) is one of the promising linearization techniques ,since it allows the use of well

developed digital signal processing techniques in the Baseband [14, 15].

FIGURE 4: LEFT: THE POWER SPECTRUM DENSITY (PSD) REFERENCE OFDM SIGNAL SPECTRUM , RIGHT:

DISTORTED OFDM SIGNAL SPECTRUM

D. The Adaptive Digital Predistortion System

Pre-distortion techniques have proposed as a potential solution to overcome the nonlinear effects [15], it is equivalent to a nonlinear circuit with gain expansion response that is the inverse of the PA gain compression (AM/AM) response and a phase rotation that is the negative of the PA phase rotation (AM/PM), when combining the pre-distortion with the PA that can compensate the distortion generated by the nonlinear amplifier. Pre-distortion is widely used as a method in which signal processing is applied to the time signal before it is input to the amplifier [16]. A predistorter can successfully correct distortion up to the full saturation level of the amplifier. Alternative LUT adaption techniques with low complexity and low memory requirement proposed in the literature. Building a LUT predistorter from a set of stored input and output complex envelope samples is a trivial process. A block diagram of an adaptive digital predistortion system is shown in figure 5. The predistorter consists of a complex gain adjuster which controls the amplitude and phase of the input signal. The amount of predistortion is



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controlled by the entries of a Look-up Table that interpolate the AM/AM and AM/PM nonlinearities of the power amplifier. The feedback path samples the distorted signal for which the DSP adjusts the Look-up Table entries so as to minimize the level of distortion.

FIGURE 5: DIGITAL PREDISTORTION BLOCK DIAGRAM

Notably, the nonlinear distortion is determines by the signal envelope [17]. Thus, using the input signal envelope would be much more efficient way to addressing of the predistortion Look Up Table. The LUT coefficients implement the predisotion function. The adaptation algorithm determines the values of the coefficients by comparing the feedback signal and a delay version of the input signal. The size of the LUT employed determines the number of points at which the predistortion function is calculated [18]. The LUT is in fact implemented by two RAMs of which the first determines the magnitude of the complex gain, whereas the second one determines the phase shift. It has been shown that if the input signal is Gaussian the best Look Up Table address spacing is linear [19]. It’s mentioned that the OFDM signal being the sum of a large number of QAM or QPS modulated carriers is approximately Gaussian.



FIGURE 6: THE ALGORITHM OF LUT

Figure 6 describes the basic algorithm implemented in the LUT design. The incoming complex samples in I and Q, have correction factors applied from the LUT and sent to module. The addresses for the LUT are derived from the input power. The LUT must contain two values for each location the real part and the imaginary part Q. in the module ,samples are unconverted and sent to the PA . In the feedback loop, the output of the PA is downconverted—transformed to polar form—and compared with the delayed version of the input to the predistorter in polar form. This error is then used to update the values currently stored in the LUT. The LUT address is derived from the input power. Hence this algorithm is only able to correct for phase and magnitude error that are purely a function of the current input power. The LUT coefficient is fed into the predistorter, which reads an appropriate correction value (LUT value) from the LUT and uses it to modify the input data .the resultant modified coefficient is referred to as predistorted data.

The basic idea of determine the LUT coefficients fairly straightforward. By considering the scenario depicted in Figure 7, let r be the amplitude of the input signal. The desired output is known from the linear response. This value is used to search through the output characteristic of the amplifier. The value r is the desired output amplitude; from which the proper input amplitude to the amplifier is determinedr . The original input r ,amplitude is adjusted to produce r [20]. Thenr should produce the correct output amplitude to give the overall predistorter-power amplifier chain a linear response. Although not shownr , is also used to determine Φ to predistort the phase. Phase is not always corrected, but if it is, it can also compensate for any quadrature modulation errors in addition to the amplifier errors [21]. Note that if the desired output amplitude is beyond the saturation limit of the amplifier, the corresponding r will not be able to fully correct for the nonlinearity.



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FIGURE7. THE CONCEPTUAL MODEL OF PREDISTORTION.

Values of rversus A(r) and r versus ∆Φ(r) are stored in Look Up Tables. For every complex input r, the pre-distorter Look up the desired output level in A(r) and applies a correction factor based upon A(r ) to produce r , next r is compared to the closet value of r in the phase table and the predistorter applies the correction −∆Φ(r). The resulting output (and thus the input to the amplifier), is a pre-distorted sample [22]. The delay in the feedback path is estimated by calculating the correlation between the magnitude of the input signal and the magnitude of the feedback signal. The benefit of using the signal magnitude is that it does not require phase synchronization in the feedback path.

III. THE EXPERIMENTS AND RESULT In this section the authors simulate a real digital predistorter based on the complex gain lookup

table technique. In order to demonstrate linearizing performance of the baseband predistorter ,Advanced Design System (ADS) simulator were carried out with a OFDM signal. We also used the Linearization Design Guide, which provides a complete tool kit to interactively explore dynamic linearization systems at the top level as part of an integrated design process. Adaptation using the digital predistorter is very rapid. Figure 8 shows the schematic of the digital predistorter wherein all subsystems have been implemented in the ADS Agilent Ptolemy simulation. The main ADS digital circuit uses a data flow simulation controller in order to execute simulations.



FIGURE 8: PROPOSED LUT-BASED ADAPTIVE DIGITAL PREDISTORTER

This platform has been implemented using Agilent ADS software. Because of each block has been implemented at component level, so details of each component have not being given deliberately. The LUT address generation component translates the magnitude of the baseband input signal into a LUT address using power addressing schemes [23]. The LUT is implemented using the LUT_RAM and the number of entries in the LUT is taken as 256.

The simulations have been performed in the baseband domain. In figure 9, the simulated output spectra of the linearly amplified input signal, with the PA output, with and without predistortion are reported. Without predistortion a visible spectral re-growth is present, while using the proposed baseband predistortion the input and output spectra appropriately scale by a constant factor. The PA has been driven near the saturation. The spectral densities have been normalized with the maximum power of the desired output signal; we can appreciate the significance of the cancellation of PA memory in reducing in-band distortion.

Finally, we can determine the performance of our digital predistortion circuit. Figure 10 shows the output from the digital baseband predistorter once the LUT entries have adapted. We can observe the spectral growth that occurs using a predistorter. The adjacent channel power is spread over a wider bandwidth but the mask requirements can be meet. Approximately 20 dB of distortion correction is achieved.



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FIGURE 9: PA OUTPUT WITH AND WITHOUT DP OF THE MODELED PA IN ADS (RED: WITHOUT PREDISTORTION,

BLUE: WITH PREDISTORTION).

FIGURE 10: AM/AM CHARACTERIZATION; AND AM/PM CHARACTERIZATION

-10 -5 0 5 10-15 15

-120

-100

-80

-60

-40

-20

-140

0

Frequency (MHz)

Pow

er (d

Bm

)

PA Output

Final Coefficients (iteration 6)

0.90

0.95

1.00

1.05

1.10

1.15

0.85

1.20

Mag

nitu

de

MagMarker

MagMarkerindep(MagMarker)=mag(LUTFinal)=1.813995

255

32 64 96 128 160 192 2240 256

-0.02

-0.01

0.00

0.01

0.02

-0.03

0.03

LUT Entry

Phas

e (d

egre

es)



The AM/AM and AM/PM transfer characteristic simulation curves derived from the polynomial HPA model are present in figure 10, which confirms the removal of the nonlinear distortion with memory effects by the LUT PD.

IV. CONCLUSION In this paper, the effects of nonlinearities in the power amplifier over OFDM systems were

investigated, it is noticed that the effects of nonlinearity of the high power amplifier depends upon the type of modulation used in OFDM system. This study has proposed a baseband digital compensation method for nonlinear distortions in digital transmitters. Performances of the digital predistortion circuit have been investigated. The implemented predistorter uses two LUTs containing the real and imaginary part of the adaptive predistortion function. LUT size, indexing, interpolation and update are important factors in the design of a digital predistorter. the LUT configuration reduces complexity in the implementation and permits in order to meet the tradeoff between complexity scalability and PD accuracy. The proposed design shows better performance in terms of improving ACPR, and easy to implement.

REFERENCES [1] F. H. Gregorio and T. I. Laakso.(2005). The performance of OFDM-SDMA systems with power

amplifier nonlinearities. Proceedings of the 2005 finnish signal symposium , Kuopio ,Finland.

[2] M. Alard and R. Lassale .(1987) . Principles of modulation and channel coding for digital broadcasting for mobile recivers . EBU Tech.Rev.,no224 , 3-25

[3] L. J. Cimini . (1985). Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing. IEEE Trans, Commun , Com-33 , 665-667

[4] Vivek Ashok Bohara, See Ho Ting. (2008). Analysis of OFDM signals in nonlinear high power amplifier with memory .IEEE Communication in the ICC 2008 preceeding , 3653-3657

[5] Dytro Bonder, Djuradj Budmir and Boris Shelkovnikor. (2008) . Linearization of power amplifier by baseband digital predistortion for OFDM transmitter. INT.Crimean Conference Microwave & Telecommunication Technology , 270-272

[6] Jinho Jeong .(2012). New digital predistortion technique of RF power amplifier for wideband OFDM signal .IEICE Electronics Express ,Vol 9.No.5, 326-332

[7] Tushar Kanti and Monir Morshed.(2013). High power amplifier effects analysis for OFDM system. International Journal of Science , Engineering and Technology Research ,(IJSETR) ,Vol.2 , Issue 5 , 1119-1121

[8] Amanjot Singh ,Hardeep Kaur. (2012). nonlinearity analysis of power amplifier in OFDM system. International Journal of Computer Applications ,Vol .37 , 37-41



www.elvedit.com 366

[9] Bo Ai , Member, IEEE , Zhi –Xing Yang , Chang – Yong Pan, Shi –Gang Tang and Tao –Tao Zhang . (2007). Analysis on LUT based predistortion method for HPA with memory .IEEE Transaction on Broadcasting , Vol.53 , No.1 , 127-129

[10] Dmytro Bondar, Djuradj Budimir and Boris shelkonvniko. (2008). Linearization of power amplifiers by basedband digital predistortion for OFDM transmitters. IEEE Microwave & Telecommunication Technology,270-271

[11] Gavin Hill. (2011). Peak power reduction in orthogonal frequency division multiplexing transmitters. Victoria University of Technology ,Thesis submitted in fulfilment of the requirement for the degree of doctor of philosophy .

[12] Stevens Creek Blvd., Santa Clara. (2011). Advanced Design System 2011.01 - Timed Components. Agilent Technologies.

[13] Sangeeta Bawa ,Maninder Pal ,Jyoti Gupta. (2013). Predistortion based linearization technique for power amplifiers of wideband communication systems. International Journal of Science & Engineering Reserch ,Vol4 ,Issue 5

[14] ]AIBO , YAG , ZHI –XING, PAN CHANG –YONG, ZHANG TAO –TAO , WANG YONG and GE JIAN HUA. (2006). Improve LUT Technique for HPA Nonlinear predistortion in OFDM System. Wireless personal Communication , No 38 , 495-507

[15] Amanjot Singh ,Hardeep Kaur. (2012). Non Linearity Analysis of High Power Amplifier in OFDM system. International Journal of Computer Aplication ,Vol 37, NO.2

[16] Won Gi Jeon ,Kyung Hi Chang and Yong Soo Cho. (1997). An Apaptive Data Predistortion for Compensation of Nonlinear Distortion in OFDM System. IEEE Transaction on communications , Vol 45 ,No .10.

[17] F. ZAVOSH, MTHOMAS, C. THRON, THALL, D. ARTUSI, D. ANDERSON, D. N. AND DAVID R. (1999). DIGITAL PREDISTORTION TECHNIQUES FOR RF POWER AMPLIFIERS WITH CDMA APPLICATIONS. TECHNICAL FEATURE, MICROWAVE JOURNAL.

[18] B. Abdulrahman, G.Baudoin. (2002). Applying Digital Predistortion To Power Amplifiers Used in Third Generation Systems. ESIEE, Signal Processing and Telecommunications Department. BP-99, 93162

[19] By Kelly M., Wan-Jong Kim, Shawn P. Stapleton, Simon Fraser University Jong Heon Kim, K. University . (2004). Linearizing Power Amplifiers Using Digital Predistortion, EDA Tools and Test Hardware. High Frequency Design, High Frequency Electronics. AMPLIFIER LINEARIZATION

[20] J. de Mingo and A. Valdovinos. (1997). Amplifier linearization using a new digital predistorter for digital mobile radio systems. IEEE 47th Vehicular Technology Conf., vol. 2, 671–75

[21] A. Mansell and A. Bateman. (1994). Practical implementation issues for adaptive predistortion transmitter linearization. IEE, London, U.K., WC2R 0BL.

[22] Kathleen J. M., Mohsen K., Fellow, IEEE, and Rajeev K. (2000). Look-Up Table Techniques for Adaptive Digital Predistortion: A Development and Comparison. IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, VOL. 49, NO. 5



[23] R Singla and SK Sharma. (2012). Low complexity look up table based adaptive digital predistorter with low memory requirements. nication and Networking , EURASIP Journal on Wireless Commu Singla and Sharma EURASIP Journal on Wireless Communications and Networking

AUTHORS’ BIOGRAPHY

Maryam Sajedin was born in Tehran, Iran, on April 4, 1986. She received the B.Sc. degree in Electrical Engineering in 2008, She is currently working toward the M.Sc degree in communication engineering at Islamic Azad University, fars, Iran since 2014. Her working experiences are digital communication, nonlinear power amplifier and application of signal processing in multimedia communication system. her research interests include nonlinear modeling of HPA and compensation techniques for nonlinear distortion in OFDM system.

Ayaz Ghorbani received Postgraduate Diploma, M.Phil., and Ph.D. degrees in electrical and communication engineering as well as postdoctoral degree from the University of Bradford, UK, in 1984, 1985, 1987, and 2004, respectively. Since 1987 up to now he has been teaching various courses in the Department of Electrical and Electrical Engineering, AmirKabir University of Technology (Tehran Polytechnic), Tehran, Iran. Also from 2004 to 2005, he was with Bradford University for sabbatical leave. He has authored or coauthored more than 120 papers in various national and international conferences as well as refereed journals. In 1987, Dr. Ghorbani received John Roberts haw Travel Award to visit

USA. In 1990, he received the URSI Young Scientists Award at the General Assembly of URSI, Prague, Czech Republic. He also received the Seventh and Tenth Kharazmi International Festival Prize in 1993 and 1995 for designing and implementation of anti-echo chamber and microwave subsystems, respectively. His research areas include Radio wave propagation, antennas bandwidth, nonlinear modeling of HPA, antecho chambers modeling and design, electromagnetic shielding as well as EMI/EMC analysis and modeling. He has authored one book in Microwave circuit and devices.

Hamidreza Amindavar received B.Sc., M.Sc., M.Sc.AMATH, and Ph.D. degree from the University of Washington in Seattle, in 1985, 1987,and 1991, respectively, all in electrical engineering. He is currently a Professor in the Department of Electrical Engineering, Amirkabir University of Technology, Tehran, Iran. His research interests include signal and image processing, array processing, and multiuser detection. Prof. Amindavar is a member of Tau Beta Pi and Eta Kappa Nu.

Nonlinearity Compensation for High Power Amplifiers Based on Look-Up Table Method for OFDM Transmitters Nonlinearity Compensation for High Power Amplifiers Based on Look-Up Table Method

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