OFDM subcarrier interference cancellation for non-linear PA distortion

OFDM offers high bandwidth efficiency and low receiver equalization complexity; consequently OFDM is growing in popularity for adoption into robust high data rate services in wireless multipath channels. While these advantages have been proven for many wireless applications (including numerous IEEE wireless standards), one potential disadvantage of OFDM is that it exhibits high peak-to-average power ratios (PAPR). The high PAPR characteristic of OFDM can induce in-band and out-of-band distortions when the peaks of the OFDM waveform enter the compression region of the transmitter power amplifier (PA). Several techniques exist to reduce the PAPR and, in addition, signal pre-distortion can be applied prior to the PA to linearize the signal; however, significant distortion can still reach the receiver. We introduce a PA subcarrier interference cancellation (SCIC) method that improves upon previous receive-side non-linear interference cancellation (NLIC) techniques and show the resulting improvement using actual PA devices. Initially we derive theoretical performance analysis that enables us to predict the performance analytically and confirm the improvements via simulation of our SCIC technique. We demonstrate at least a 5 dB SNR improvement, at 0 dB input backoff of the PA, using our OFDM design with SCIC. We conclude that robust channel estimation, using optimized pilot design for OFDM with null edge subcarriers, and SCIC are jointly critical for improving OFDM´s robustness when transmitted through nonlinear PA devices.