MAC Controlled LINC Calibration using Pilot-Aided LSE Channel Estimator for OFDM Systems

Abstract

With the overwhelming adoption of Orthogonal Frequency Division Multiplexing (OFDM) technique in many recent wireless communications standards, there have been extensive approaches to tackle the high Peak-to-Average Power Ratio (PAPR) problem that yields low efficiency in RF power amplifiers, which is the major drawback of OFDM systems. One of the approaches is to replace power amplifiers with the Linear Amplification using Nonlinear Components (LINC) block. However, this produces additional nonlinear distortions caused by amplitude or phase mismatch between two power amplifiers inside the LINC block. In this paper, we introduce a noble LINC calibration technique that utilizes the channel estimator block that is initiated by the Media Access Control (MAC) layer during the Distributed Interframe Space (DIFS) or Short Interframe Space (SIFS). For DIFS or SIFS, pilot symbols are allocated in a payload field and then the outputs of the transmitter are internally forwarded to the receiver to characterize the LINC channel with a pilot-aided Least Square Error (LSE) channel estimator. By applying a reverse distortion onto information symbols after the LINC channel distortion is obtained by channel estimation, we can significantly improve the Symbol Error Rate (SER) and Error Vector Magnitude (EVM) of the OFDM system with the LINC transmitter.