Effect of Constellation-shaping-based PAPR Reduction Methods Over the Capacity of OFDM Systems

Abstract

This paper studies the effect of two Peak to Average Power Ratio (PAPR) reduction methods over the capacity of Orthogonal Frequency Division Multiplexing (OFDM) systems. These two methods are the Active Constellation Extension-Projection Onto Convex Sets (ACE-POCS) and Branch-and-Bound Constellation Extension (BBCE). Both methods modify the constellation points of some transmitted symbols to reduce the PAPR, so the channel capacity could be affected due to the unequal power allocation. In this work, the capacity is obtained through simulations of an uncoded OFDM system over a Rayleigh fading channel. Our results show that the ACE-POCS method obtains a capacity similar to the ergodic capacity of the Rayleigh fading channel. On the other hand, the capacity using the BBCE method is less than the ACE-POCS but with a higher reduction in the PAPR. Additionally, we compare the channel capacity using these two PAPR reduction schemes with an upper bound obtained with the water-filling algorithm, which maximizes the capacity by changing the power of the sub-carriers. Finally, we found that the PAPR of the OFDM signal obtained when the water-filling algorithm is applied shows a small variation compared to the OFDM signal without PAPR reduction.