PAPR Reduction using DFT Spreading with FEC for OFDM Systems
Abstract: The next generation of mobile communication is based on OFDM technology. It is an efficient method of data transmission for high speed communication system. Orthogonal frequency division multiplexing (OFDM) systems have been proposed in the recent past years for providing high spectral efficiency, less vulnerability to echoes, low implementation complexity and resistance to non linear distortion .However the main drawback of OFDM system is high peak to average power ratio (PAPR) of transmitted signals due to inter-symbol interference between the subcarriers as a result the amplitude of such a signal can have high peak values. Thus a power amplifier must be carefully manufactured to have a linear input output characteristics or to have large input output back-off. Drawback of high PAPR is that dynamic range of power amplifier and Digital to Analog (D/A) converter during the transmission and reception of the signal is higher. As a result total cost of transceiver increases with reduced efficiency. Discrete Fourier Transform (DFT) Spreading is one of the schemes to reduce the PAPR problem in OFDM system by using different subcarrier mapping schemes. In this paper we proposed combination of DFT spreading technique with FEC coding to reduce PAPR in OFDM system. Performance evaluation carried out in terms of SNR (signal to noise ratio) BER (bit error rate).
Keywords: MIMO OFDM, Peak to average power ratio (PAPR), Discrete Fourier Transform (DFT), IFDMA, DFDMA, LFDMA, FEC, Viterbi decoding.
I. INTRODUCTION
Nowadays, the demand for multimedia data services has grown up rapidly. One of the most promising multicarrier systems, Orthogonal Frequency Division Multiplexing (OFDM) is basis for all 4G wireless communication systems due to its large capacity to allow the number of subcarriers, high data rate and ubiquitous coverage with high mobility [1]. It effectively combats the multipath fading channel and improves the bandwidth efficiency. At the same time, it also increases system capacity so as to provide a reliable transmission. OFDM uses the principles of Frequency Division Multiplexing (FDM) [2]. The basic principle of OFDM is to split a high-rate data stream into a number of lower rate streams that are transmitted simultaneously over a number of subcarriers [3]. These subcarriers are overlapped with each other. Inter-symbol interference (ISI) is eliminated almost completely by introducing a guard time in every OFDM symbol [3]. An OFDM signal consists of a number of independently modulated subcarriers, which can give a large peak to average power ratio and these subcarriers are mutually orthogonal that’s why its name occur as orthogonal frequency division multiplexing[4].
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