Performance comparisons of power loaded OFDM systems over peak power limited channels

Orthogonal Frequency Division Multiplexing (OFDM) has been widely adopted in many applications and standards for a number of benefits including high efficiency and immunity against the frequency-selective channel. Power loading, which is a technique that allocates different amount of power for each subcarrier, further enhances the system performance by maximizing mutual information, reducing Bit Error Rate (BER) or improving other aspects of the communication system. OFDM, however, suffers from high Peak-to-Average Power Ratio (PAR) due to its wide dynamic range of time-domain waveforms. This makes OFDM symbols be affected by nonlinearity resides at the power amplifier (PA), causing the power efficiency to decrease and symbols to be distorted. The effect of power loading techniques over peak power limited OFDM systems has not been well studied. In this paper, some existing power loading techniques are applied to OFDM system, and performance is compared from four different aspects: PAR, Error Vector Magnitude (EVM), spectral characteristics, and Symbol Error Rate (SER). The paper concludes with the answer to the question of whether power loading hurts or helps if it is available for OFDM system.