Student Conference on Research and Development (SCOReD) 2003 Proceedings, Puhajaya, Malaysia zyxw PAPR Reduction in WLAN-OFDM System Using Code Repetition Technique NNgajikin, N.Fisal and S.K. Yusof Faculty of Electrical Engineehg Universiti Teknologi Malaysia zyxwv 81310 Skudai, Johor e-mail zyxwvut : n hafizah@s~ii.ia. Re. ut n1.1~ Abstract- Orthogonal Frequency Division Multiplexing (OFDM) is the best choice to achieve high data rate transmission in wireless environment. OFDM system shows many favorable property such as high spectral efficiency, robustness to channel fading and immunity to impulse interference. However, there are some obstacles in using OFDM in transmission system, which is in contrast to its advantages. One of the major drawbacks is a very high peak to average power ratio (PAPR) of the zyxwvu OFDM signals. Therefore this paper analyzes the capability of Code Repetition (CR) to reduce PAPR in WLAN/OFDM system. The analysis is on a network model designed by WLAN 802.11a standard using Madab, a mathematical simulation software tool. Thc network model has been simulated in AWGN channel environment to investigate the behavior of PAPR and BER performance. The proposed technique to reduce PAPR in the WLAWOFDM channel coding consists of two part; convolutional code and CR. SimuIation model with different number of. repetition has been anaIyzed and the results were compared with the conventional coded OFDM (COFDM). The simulation results show that the proposed technique based on CR reduces PAPR down to zyxwvutsrq 5 zyxwvutsrqp dB compared to COFDM model. Keywords OFDM, PAPR, Wireless LANS02.1 la, Code Repetition, Convolutional Code. I. INTRODUCTION orthogonal Frequency Division Multiplexing (OFDM) is one of the multi-carrier modulation (MCM) techniques that can reduce the Intersymbol Interference (ISI), delay spread of signal and increase the spectral efficiency of system. Due to the nymerous advantages of this system, it has been successfully applied in wide variety of digital communications over the past several years and has been adapted to the wireless LAN standards [ 11. However, an OFDM system dynamic range is typically two or four times larger than a single carrier system Increasing value of the dynamic range will lead to an increased the cost, power consumption of transmitter amplifier and also lead to high peak to 0-7803-8 173-4/03/$17.00 02003 IEEE. average power ratio (PAPR). This is one of the major drawbacks of OFDM system. A serious problem of large PAPR presents when cheap and energy-efficient nonlinear power amplifiers are used. Frequent excursions into the nonlinear operating region contribute to the increment of BER and spectral regrowth outside the intended frequencies of operation. Therefore PAPR reduction techniques are required to overconie this problem. There are several techniques have been proposed to reduce PAPR in OFDM system. From the literature, clipping is the simplest approach to reduce PAPR. However it results a significant in-band distortion and this technique requires filtering to overcome the weakness. Besides of using clipping and filtering, coding scheme get attention since it can handling both reducing PAPR and error correction at the same time. Therefore, this paper investigate the effectiveness of coding technique in reducing PAPR for OFDM system. In this method a combination of convolutional code and Code Repetition was developed. This paper is divided into 6 sections. Section 11, gives a brief overview of the hndamentals of PAPR in WLAN/OFDM system. In section 111, Channel coding that had been used in this thesis are presented. This section briefly explains the encoding and decoding process of code repetition, which is the coding that had been proposed to reduce PAPR. Section IV gives the methodologies used for reducing PAPR. Section V discusses the results obtained in this research and an analysis and discussion of these results are carried out, Lastly, Section VI gives the conclusions of this research followed by possible extensions and addition as fhre work. 11. PEAK TO AVERAGE POWER RATIO (PAPR) An OFDM signal is the sum of Ci complex random variables, each of it can be considered as a complex modulated signal at a different frequency. In some cases, all signal components can add up in phase and produce a large output and in some cases, they may cancel each other, producing zero output. Thus, the peak-to-average ratio (PAPR) of an OFDM system is very large. 85