A Review of PAPR Reduction Techniques in OFDM Systems

Authors: Shankar Kumar, Asst. Prof. Sneha , Jain

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Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is an efficient multicarrier modulation scheme in wireless communication. It is used in applications like 4G (fourth generation) mobile Communications, wireless networks, digital television, power line networks and audio Broadcasting. It offers both advantages and disadvantages for multicarrier transmission. The main advantages are the elimination of Inter Carrier Interference (ICI) and Inter Symbol Interference (ISI) in the signal. But OFDM’s one of the main detrimental aspects are high Peak-to-Average Power Ratio (PAPR) value of the transmitted signal which highly affects the power amplifiers complexity. Several techniques to overcome and reduce PAPR such as Tone Reservation (TR), selective mapping (SLM), clipping and filtering, partial transmit sequence (PTS), etc. are proposed and implemented. Detailed description and comparisons of all techniques are discussed in this paper. Keywords - Peak-to-Average Power Ratio (PAPR), PTS, OFDM, Inter Carrier Interference

Introduction

With increased demand for high quality communication services in 4G and 5G, it’s been a great challenge to improve the Quality of Service (QoS) and reduces the delay time. To overcome and fulfill this requirement, a technique called Orthogonal Frequency Division Multiplexing (OFDM) is encountered. It over several outfalls like maintaining high data rate, high bandwidth efficiency, low computational complexity and eliminating multipath fading [1]. OFDM is a special case of the frequency division multiplexing (FDM), which is used by the American National Defense Department for military communications. Compared with the conventional FDM, OFDM allows the spectrums from different subcarriers that are orthogonal to be overlapped with each other, which improves the spectral efficiency of the system. The concept of OFDM techniques was first proposed by RW Chang in 1965. In 1967, Saltzberg analyzed the performance of OFDM systems. In 1970, OFDM technology was patented at the USPD and then after it was used in military communication systems. In 1971, SB Weinstern and PM Ebert employed the Discrete Fourier Transform (DFT) into the MCM. in practice, the Fast Fourier Transform (FFT) implementation of the DFT has made OFDM modulation and demodulation feasible and very successful. In the 1980s, ISI was decreased when Peled and Ruiz added cyclic prefix (CP) into the basic OFDM signals to have the orthogonality maintenance among subcarriers [1-2]. OFDM transceiver- The fundamental principle of OFDM is to split the available bandwidth into multiple subcarriers. As the number of subcarriers increases, it gets more immune to frequency selective fading, and data rates are also increasing. However, number of sub-carriers cannot be increased arbitrarily because it increases the complex architecture of the system and symbol durations that make transmission more sensitive to the time incoherence of the channel. The problem of the intricate design of the system was handled by Weinstein and Ebert with the implementation of OFDM modulation OFDM system transmitter The incoming serial data is the information that needs to be transmitted through the channel using OFDM system. The serial data is converted into N different parallel data streams by using serial to parallel converter. These symbols can be modulated by using different modulation techniques and given to the IFFT block as an input [3]. IFFT block gives the digital time domain signal for the given input, and this parallel data is converted into serial data by using parallel to serial converter. The cyclic prefix is introduced between two OFDM symbols to cancel the effect of ISI due to channel dispersion. Now this digital time signal is converted into real time waveform with the use of digital to analog converters. The available baseband signal is up converted to an RF pass band signal with the use of a mixer or modulators.

Conclusion

In this paper, we have analyzed and compared eight PAPR reduction techniques. Among above analyzed techniques, it was found out that from present techniques no technique is fully effective in reduction of PAPR and is the best for the OFDM system. As before choosing the appropriate PAPR technique, various other factors like maintaining data rate, computational complexity, BER, signal power should also be taken into acknowledgement. So, it is suggested to propose peak to average power ratio (PAPR) reduction scheme and design a network/model supporting it for OFDM systems after comparing existing conventional methods..