Nonlinear channel estimation based on multi-level PN sequences in OFDM systems

Nonlinear distortion of power amplifier is one of the major factor that degrades the performance of OFDM systems Instead of estimating the nonlinearity at transmitter such as ordinary pre-distortion (PD), this paper estimates the nonlinearity of amplifier at the receiver. The problem is that nonlinear and multipath dispersion mix together at receiver end. And their parameters are generally unknown, so conventional method doesn't work well. In this paper, an algorithm that estimates both the nonlinear parameters of the power amplifier and the impulse response of the wireless channel is proposed. Multi-level PN sequences are transmitted to construct a Vandermonde matrix, which separates the nonlinearity and linearity into different subspaces. The separation makes it easy to estimate the nonlinearity and linearity independently.