Multicarrier Successive Predistortion for Nonlinear Satellite Systems

Abstract

To satisfy the aggressive demand for higher satellite throughput, industry trend is moving toward sharing the transponder amplifier by multiple carriers, each employing high-order modulations that are spectrally compact. This trend, in conjunction with the inherently nonlinear nature of the amplifier when driven efficiently closer to saturation, creates significant intermodulation distortion that needs to be appropriately compensated. This paper presents a powerful compensation technique that is capable of mitigating the nonlinear intermodulation distortion and is placed at the transmitter or gateway. It is a novel multicarrier data predistortion technique that successively modifies the transmitted symbols to drive multicarrier distortion vector toward zero. This distortion vector results from passing the transmitted symbols from the multiple carriers, intrinsically accessible at the gateway, through the nonlinear satellite channel model. The novel successive predistortion technique and methods of estimating the distortion are described in detail. It is demonstrated using extensive computer simulations that the proposed multicarrier predistortion technique is capable of achieving near-optimum performance, even when only a simple linear receiver is employed and no exchange of data is assumed between receivers.