Simplified polynomial digital predistortion for multimode software defined radios

Abstract

Increasing the efficiency of mobile communication networks while keeping operational and maintenance cost at reasonable level is a major task for operators. Multimode radios capable of operating according to various mobile broadband standards, such as WCDMA, WiMAX and LTE, represent the new trend for resolving these challenges. A transparent radio solution, agnostic to wireless standards, with high capacity and low power consumption is the overall target. Regulating power consumption for radio modules can be achieved by introducing linearization methods for power amplifiers. This paper presents a simplified approach using polynomial digital predistortion in the intermediated frequency (IF) domain. It is fully implementable in software and no hardware changes are required on the digital or analog platform. The adaptation algorithm selected was Least Mean Squares because of its relevant simplicity compared to more sophisticated adaptation algorithms, which are expensive in FPGA hardware resources. Simulation results show improvement of Adjacent Channel Power Ratio (ACPR) over 20dB by reducing the 3rd and 5th order intermodulation products providing compliance to the strict spectrum mask requirements. In the mean time, the Error Vector Magnitude (EVM) is maintained below 2% meeting the requirements for WiMAX and LTE wireless standards.