Effectiveness of tone-reservation using null subcarriers (TR-NS) in WiMAX systems

In this paper, we propose a modified tone reservation method to reduce peak-to-average power ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) system by using null subcarriers (TR-NS), and evaluate its performance under physical layer model of IEEE standard 802.16d-2004, i.e., WiMAX systems. We first verified that the spectrum of transmitted OFDM signals processed by TR-NS method with a small number of null subcarriers do not violate the spectrum mask specified in ETSI standard. Furthermore, we explored that the gain from TR-NS method increase slightly with the number of null subcarriers, but the TR-NS method is efficient in certain extent in terms of both complementary cumulative probability function and total degradation. Additionally we found that an efficient PAPR [1] definitively exist for the proposed TR-NS method, where a lower predefined PAPR threshold can not promise a better peak-power reduction gain. It is worthy noting that this result differs from that of TR using arbitrary reserved tones in the literature. Finally, we compared proposed TR-NS method with clipping-like methods in terms of total degradation to show the effectiveness of the TR-NS method by simulation, in which nonlinearity distortion due to high-power amplifiers is introduced.