PEAK-TO-AVERAGE POWER RATIO REDUCTION IN OFDM SYSTEMS

Abstract

OFDM (Orthogonal Frequency Division Multiplexing) is a promising technique for achieving high data rate and combating multipath fading in wideband data communications. OFDM can be thought as a hybrid of multi-carrier modulation (MCM) and frequency shift keying (FSK) modulation The transmitted data by dividing into several parallel bit streams and modulating each of these data streams onto individual carriers or subcarriers. OFDM was exploited for wideband data communications over wireless LAN(IEEE802.1laIg), WIMAX(IEEE802.16a) , High-bit-rate Digital Subscriber Lines (HDSL; 1.6 Mbps),.Asymmetric Digital Subscriber Lines (ADSL; up to 6 Mbps), Very-high-speed Digital Subscriber Lines (VDSL; 100 Mbps), Digital Audio Broadcasting (DAB), and High-Definition Television (HDTV) terrestrial broadcasting. OFDM has many well-known advantages, such as the robustness to the intersymbol interference (ISI) and multi-path fading, high bandwidth efficiency, and so on. But it has suffered from the high Peak-to-Average Power Ratio (PAPR). The PAPR reduces the power efficiency of the RF high power amplifier in the transmitter and the complexities of analog-to-digital converter (ADC) and digital-to-analog converter (DAC).This issue is especially important for mobile terminals to sustain longer battery life time. Therefore, reducing the PAPR can be regarded as an important issue to realize efficient and affordable mobile communication services. In current techniques, Partial Transmitted Sequences (PTS) has been proved efficient and distortion less, in which multiple candidate signals are generated to reduce the PAPR but with side effect of high complexity. In general, the complexity of PTS proportional to the number of candidate signals. However, in individual candidate signal, the complexity for combining the phase factor and computing the PAPR still remains high. The focus of this dissertation is mainly to reduce the complexity of phase factor combining and PAPR computation for an individual candidate signal in Partial Transmit Sequence technique. In this dissertation, a class of PTS techniques with low complexity are studied and simulated. Complementary Cumulative Distribution Function (CCDF) of the peak-to-average power of an OFDM signal are plotted to measure the PAPR reduction performance of all these techniques. The PAPR reduction performances of each of these suboptimal PTS techniques are compared with the OFDM system without any PAPR reduction technique and also conventional PTS technique