An effective scheme for PAPR reduction of OFDM signal using time-varying subcarrier

Abstract

One of the challenges of Orthogonal Frequency Division Multiplexing (OFDM) is its high Peak-To-Average Power Ratio (PAPR) which may lead to system performance degradation due to low power efficiency in the presence of nonlinear power amplification. All existed PAPR reduction methods in the literature such as clipping, phase shift and compand transform are based on the conventional OFDM scheme, which means that the modulation system usually has a fixed symbol block length or fixed subcarrier number. In this paper we introduce a new concept, namely time-varying symbol block length or time-varying subcarrier number, into the OFDM system to reduce the PAPR values. We call the new modulation system Time-varying OFDM (TV-OFDM). Here, the PAPR is used as a criterion to adjust the symbol block length or subcarrier number accordingly. The algorithm for finding out the symbol block length or subcarrier number is present, and the comparison results with other classical PAPR reduction methods in the literature are given by numerous experiment. The simulation results show that the time-varying modulation schemes can clearly reduce the PAPR values of the OFDM system, while the Symbol Error Rate (SER) of time-invariant OFDM and TV-OFDM modulation remains almost constant.