Active-set based PAR reduction under PSD constraints

Common to all DMT/OFDM systems is a large peak-to-average power ratio (PAR), which can lead to low power efficiency and nonlinear distortion. Tone reservation uses unavailable or reserved tones to design a peak-cancelling signal to lower the PAR of a transmit block. In real-baseband DMT ADSL systems, the power allocated to these tones may be limited due to crosstalk issues with many users in one twisted-pair bundle. This PSD limitation not only limits PAR reduction ability, but also makes the optimization problem more challenging to solve. Extending the recently proposed active-set tone reservation method, an efficient algorithm is developed, with performance close to the optimal solution.