Digital Pre-distortion for Multiple Antenna Transmitters

This paper proposes a novel cross-talk cancelling pre-distorter (CTC-DPD), which accurately models the cross- talk and nonlinearity in multiple-input multiple-output (MIMO) radio systems, and compensates for these effects. The cross-talk introduced before the power amplifier (PA) in a multi-antenna transmitter, which is termed as non-linear cross-talk degrades the performance of digital pre-distortion (DPD). A cross-over pre-distortion (CO-DPD) that compensates for the cross-talk and non-linearity in multi-antenna transmitters was proposed in [2]. However, CO-DPD ignores the higher order cross-terms between the input signals. As a result, the performance of CO-DPD degrades, as the crosstalk between the branches of the multi-antenna transmitter becomes stronger. In the CTC-DPD structure, linearization and cross-talk compensation are done separately by pre-distorters for the PAs and a cross-talk pre-cancellation block. The performances of pre-distortion techniques for a two-antenna transmitter are evaluated through measurements. It is observed that CTC-DPD achieves an error vector magnitude (EVM) improvement of 1.5% at -15 dB non-linear cross-talk and 0.8% at -20 dB non-linear crosstalk, compared to CO-DPD, for an universal mobile telecommunications system (UMTS) signal.