OFDM subcarrier interference cancellation for non-linear PA distortion

Abstract

P 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 ofOFDM is that it exhibits high peak-toaverage 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 backoffofthe PA, using our OFDM design with SCIC. We conclude that robust channel estimation, using optimized pilot designfor OFDM with null edge subcarriers, and SCIC are jointly critical for improving OFDM's robustness when transmitted through nonlinear PA devices.

Adaptive schemes and analysis for blind beamforming with insufficient cyclic prefix in single carrier‐frequency division multiple access systems

“…In Fig. 8, the output SINRs defined in (24) are plotted to show the convergence characteristics of the proposed scheme in a stationary environment at input SNR = 3 dB and 23 dB, respectively. It shows convergence and is very close to the optimal value.…”

“…By considering the effect of CFOs, the blind scheme utilises the least squares (LS) criteria [23] to deal with frequency synchronisation errors in calculating the beamforming weight vector. In [24], the paper proposes a power amplifier subcarrier interference cancellation method to overcome the distortion because of high peak-to-average power ratio (PAPR) characteristic in OFDM-based systems.…”