Design of Improved Coding Schemes with Low Peak to Average Power Ratio for OFDM System

Abstract

Orthogonal frequency division multiplexing (OFDM) is an exceptionally attractive practice in the field of wireless communications because of the spectrum efficiency and channel robustness. It is modulation technique in which a high-rate bit stream is split into a large number of parallel low rate data sub-streams and the sub-streams are utilized for modulating the number of orthogonal sub-carriers with the help of Fourier transform processing. OFDM attains robustness against multipath fading due to extended symbol interval for every sub-carrier and against the inter-symbol interference (ISI) due to introduction of a guard interval in each OFDM symbol. Therefore, OFDM has been accepted in many modern communication applications, like wireless local area networks (WLANs) and digital video and audio broadcast. In spite of numerous plus points, a foremost disadvantage of OFDM is the high peak to average power ratio (PAPR). In view of the fact that OFDM signal consists of numerous independently modulated sub-carriers, which results in high PAPR when summed-up coherently. This necessitates the use of power amplifier (linear) with the huge dynamic range. High PAPR increases the dynamic range of analog-to-digital converter (ADC), also it reduces the efficiency of linear power amplifier. Consequently, discovering methods to reduce transmitted signal s PAPR in the OFDM systems is becoming an extremely active field of research in the communication communities. Numerous procedures have been suggested in the literature for reducing the PAPR. These procedures may be classified into the signal mixing methods and signal distortion methods. Signal mixing methods are the various techniques which suggest how to mix up the codes for reducing the PAPR. Scrambling of signals is achieved by various available coding techniques.