Behavioural Modeling of Dynamic Nonlinear Transmitters for LTE-advanced Applications

Abstract

The Long Term Evolution (LTE) and LTE-Advanced (LTE-A) standards for wireless mobile communication are now being commercially available in many countries to increase the capacity and speed of wireless telecommunication networks. They are characterized by wideband signals having a non-constant envelope leading to high peak to-average power ratio (PAPR). Moreover, the base station power amplifier (PA) is an important component of the radio base station as it uses a considerable amount of the power consumed by the entire network. Hence, its efficient performance and linear operation are absolutely essential. Employing signals with high PAPR stimulates the nonlinear behaviour of the PA whereas operating the PA in its linear region results in significant loss of efficiency. Therefore, it is essential to achieve efficient trade-off between linearity and efficiency. Behavioral modeling of radio frequency (RF) PAs has thus attracted the interest of many researchers and has proved to be valuable for digital predistortion which is an important technique to help improve the efficiency of the amplifier while maintaining its linear behavior. An important aspect in behavioral modeling application is selecting an appropriate model that will be able to precisely depict the PA performance. In order to assess the performance and accuracy of a behavioral model various performance evaluation metrics have been studied. A novel technique for identifying the dimensions of the memory polynomial model has been proposed. A new class of behavioral models built on the conventional twin nonlinear two-box models is proposed for power amplifiers driven by wideband LTE-A signals. The conventional forward twin nonlinear two-box (FTNTB) model structure improves the modeling accuracy of the memory polynomial model whereas the hybrid memory polynomial-envelope memory polynomial (HMEM) model gives better modeling performance when the amplifier is driven by wideband signals. The proposed model, labeled hybrid twin nonlinear two-box (HTNTB) model thus combines the advantages of the FTNTB model and the HMEM model. Its performance is benchmarked against the conventional FTNTB model and previously reported augmented twin nonlinear two-box (ATNTB) model. Experimental results validated on 300W Laterally Diffused Metal Oxide Semiconductor (LDMOS) based Doherty amplifier operating at 2140MHz demonstrate the ability of the HTNTB model to considerably outperform the conventional FTNTB model in terms of performance and the ATNTB models in term of complexity reduction.