Abstract—Orthogonal Frequency Division Multiplexing (OFDM) technique has some drawbacks. One of them is high peak-to-average power ratio (PAPR). This paper proposes a technique to reduce the PAPR using Huffman coding combined with clipping and filtering (CF). The simulation results show that using the combination of Huffman and CF methods is more effective than using each method separately. By using 52 subcarriers and QPSK modulation, about 7 dB PAPR reduction is achieved. I. INTRODUCTION HE communication technology, nowadays, have moved into IP-centric platform based and the need of information grows exponentially. Thus, the need of broadband communications, including voice, data, and multimedia, increases rapidly through Internet and mobile devices [1] – [3]. OFDM technique can be used to transmit the broadband data over wireless channel. OFDM is a special case of multicarrier transmission where a single datastream is transmitted over a number of lower rate subcarriers [1]. The advantage of OFDM is that it can handle multipath interference by increasing the robustness against frequency selective fading or narrowband interference that may cause intersymbol interference (ISI). In addition, OFDM is more efficient in bandwidth than conventional multicarrier transmission. OFDM is used in digital audio broadcasting (DAB), digital video broadcasting terrestrial–TV (DVB-T), asymmetric digital subscriber lines (ADSL), wireless local area networks (WLAN), broadband wireless access (BWA) networks, ultra wideband (UWB) systems, and expected to be standard for 4G cellular systems [4]. There are two drawbacks in OFDM system namely frequency offset and large peak-to-average power ratio (PAPR). Large PAPR may cause nonlinear distortion in the high power amplifier (HPA) because HPA limits the output with certain value (the output will be saturated) and reduces the power efficiency of the amplifier. Also, it increases complexity of the analog-to-digital and digital-to-analog converters [1], [4], [5]. The objective of this paper is to Manuscript received March, 30, 2009. Filbert H. Juwono is with Electrical Engineering Department, University of Indonesia. He is now taking Master Degree programs in Telecommunication Engineering (e-mail: filberthilmanjuwono@yahoo.com) Dadang Gunawan is Professor in Digital Signal Processing. He is with Electrical Engineering Department, University of Indonesia. (e-mail: guna@eng.ui.ac.id) reduce the PAPR. The methods of reducing PAPR are divided into three categories [4], [5], [6]: 1) Distortion method such as clipping and filtering (CF), active constellation extension, peak windowing, peak cancellation, and peak power suppression; 2) Distortionless or probabilistic method such as multiple signal representation (MSR), selective mapping (SLM), and partial transmit sequences (PTS); 3) Coding or signal scrambling method such as Golay complementary sequences, Shapiro-Rudin sequences, M-sequences, and Barker Codes. Distortion method such as CF is very simple in practice. It has less complexity but at the expense of degraded BER performance. Coding method has good BER performance but it has less bandwidth efficiency [5]. This paper proposes PAPR reduction method by using combination of Huffman coding and CF. This paper is organized as follows. Section II discusses about OFDM, PAPR, and HPA theory. The proposed method is explained in section III and the simulation results in section IV. Finally, conclusion is presented in section V. II. OFDM, PAPR AND HPA OVERVIEW A. OFDM and PAPR OFDM signal in baseband notation for interval ( ) 1 u u mT t m T ≤ ≤ + can be expressed as [7] () () ( ) ( ) 1 1 0 0 exp 2 C C N N m k k k k xt x t a j k ft - - = = = = πΔ ∑ ∑ (1) where () k x t is k-th modulated subcarrier with frequency k f k f = ⋅Δ and () m k a is modulation symbol in k-th subcarrier during m-th OFDM symbol interval. Invers Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT) are very helpful in OFDM implementation because they can replace complex subchannel modems. IFFT is used at the transmitter and FFT is used at the receiver. If the number of subchannel is denoted by N c and N-point IFFT is used, then the ratio of N / N c is called oversampling factor. Cyclic prefix (CP) is required to avoid ISI. CP copies the last part of the OFDM symbol then place it in front of the symbol. CP length is usually about 25% [8]. The PAPR is defined by [8] PAPR Reduction Using Huffman Coding Combined with Clipping and Filtering for OFDM Transmitter Filbert H. Juwono and Dadang Gunawan, Member, IEEE T 2009 Conference on Innovative Technologies in Intelligent Systems and Industrial Applications (CITISIA 2009) Monash University, Sunway campus, Malaysia, 25th & 26th July 2009. 978-1-4244-2887-8/09/$25.00 ©2009 IEEE 344