Transmitter IQ Imbalance Mitigation and PA Linearization in Software Defined Radios

Radio frequency (RF) power amplifiers (PA) are efficiently linearized by adaptive digital predistortion (DPD). However, performance of DPD is severely degraded in presence of transmitter’s frequency-selective in-phase/quadrature (I/Q) imbalance. We propose DPD/IQ method that compensates the effects of transmitter I/Q imbalance and PA nonlinearity, which is dedicated for implementation in low-cost software radio defined (SDR) cellular base stations. The advantage of DPD/IQ is low complexity in terms of reduced number of DPD coefficients which provides significant savings of FPGA resources. The DPD/IQ has been evaluated after method has been implemented in SDR board. Measured results clearly demonstrate efficient compensation of PA and transceiver impairments enabling transmission of wide bandwidth waveforms and realization of sophisticated modulation schemes. Improvement in image rejection ratio of 10-15dB is achieved. Considering compensation of PA nonlinearities, the ACPR at PA output is decreased by 15dBc.