Nonlinear and Decision-Oriented Signal Processing for OFDM-Based Wireless Communications

Orthogonal frequency division multiplexing (OFDM) modulation has several attributes which favor it for high speed wireless communications. But its high peak-to-average-power ratio (PAPR) seriously limits the linear range, and hence the power efficiency, of the transmitter´s high power amplifier (HPA). The authors present two complementary approaches to the solution of this problem. The first approach uses an adaptive nonlinear predistorter (PD) to compensate for the nonlinearity in the HPA. The analytical expressions used, for the HPA and the corresponding PD, lead to satisfactory overall system operation up to the saturation region of the HPA, under rapidly time-varying conditions. The second approach reduces the PAPR to an acceptable range by means of a decision-oriented modification of the partial transmit sequence (PTS) technique. It uses a decision tree in seeking the best trade-off between the high-performance/high-complexity behavior of the ordinary PTS algorithm and the low-performance/low-complexity behavior of the iterative flipping PTS (IF-PTS) algorithm