A Fast Converging Adaptive Pre-Distorter for Multi-Carrier Transmitters

Digital pre-distortion is a powerful technique for combating nonlinearity in power amplifiers. Nonlinear response identification of the amplifier is one of the primary objectives in all pre-distortion schemes. If the estimation performance of the adaptive algorithm is not fast and accurate enough, the system will not be able to satisfy the stringent timing and spectral requirements of modern standards. This problem is exacerbated in modern communication systems which are rapidly converging towards a multi-carrier scheme. In such schemes, due to high peak to average power ratios, the convergence of pre-distorters worsens significantly. This paper highlights the problem of slow convergence in multi-carrier systems, and proposes a novel solution, which consists of implementing a twin feedback loop, one including the power amplifier and the other including the pre- distortion system itself. The goal is to leverage the learning curve of the pre-distorter itself and build on what is already known from the partially converged characteristics. Simulations with standard multi-carrier schemes indicate that such a method can deliver vastly improved performance over conventional systems.