Séminaire général COMELEC : Germain Pham (PhD, C2S RnD Eng.)

Digital predistortion for wideband 5G transmitters

For the last decades, the exchange rates in telecommunication standards have exponentially increased thanks to major innovations at many levels in radio-transceivers.
The 5th generation of mobile standards (5G) targets even higher data rates than previous cellular standards. The increase of data rates is made possible by using larger transmission bandwidths (up to several hundred of MHz) and by using modulation schemes with high spectral efficiency such as OFDM-based modulations. One drawback of these waveforms is that they are very sensitive to any non-linearity in the transceiver and require highly linear transmitters to maintain signal quality and spectral purity. In parallel, one of the other major goals of 5G is to reduce energy consumption or maintain equal energy consumption while providing more services.

In radio-transceivers, there is one component for which these two constraints are in complete opposite design directions: the power amplifier (PA). In the last few years, the digital predistortion technique (DPD) has been developed to improve the PA linearity/efficiency trade-off. This technique consists in distorting the signal before amplification with the inverse characteristic of the PA in order to correct the distortions caused by the PA during amplification. Although this technique has proven itself over the past generations of mobile telephony, it reaches its limits for the 5G because of the very wide bandwidths.

In this talk we will review the main recent and promising solutions to implement efficient predistortion techniques for future wideband transceivers. We will cover the most common approaches for PA modeling and for computing predistorter models and discuss the implementation of the predistortion for RF transmitter highlighting the advantages and drawbacks of different approaches. We will elaborate on promising solutions addressing the bandwidth limitations of digital predistortion.