Mobile transmitter digital predistortion: Feasibility analysis, algorithms and design exploration

Abstract

This article addresses intermodulation challenges in carrier aggregation (CA) and multicluster type transmission scenarios in mobile transmitters. In such transmission schemes, emerging in 3GPP LTE-Advanced mobile cellular radio evolution, the spectrum of the signal entering the transmit power amplifier (PA) is of non-contiguous nature and thus severe intermodulation is created which may violate the spurious emission mask. To satisfy the stringent emission requirements and limits, devices may need to considerably back off their transmit power, compared to nominal value of ;23dBm, but this will reduce the uplink coverage. As an alternative, feasibility of digital predistortion (DPD) is explored in this article. A DPD solution is developed to control the most critical intermodulation components from terminal emission mask perspective with reduced complexity compared to conventional DPD solutions. The DPD is based on the Augmented Parallel Hammerstein (APH) architecture which can handle IQ imbalance and local oscillator leakage in addition to the PA nonlinearity while using simple digital linear estimation techniques. Furthermore, digital design exploration is carried out for the predistortion algorithm, implying that the needed computational resources are close to what is already available in most advanced mobile platforms and chipsets in the market.