Novel Calibration Technique for Wideband Transmitters Using Constellation Mapping

Next generation wireless communication systems such as 5G will feature a step increase in the speed of wireless data transmission. This requires using RF signals of wider bandwidths along with higher order modulation schemes. Such signals are subjected to frequency and power dependent impairments such as gain compression, amplitude ripple and tilt, group-delay and AM-PM conversion as they traverse through the transmitter's hardware blocks. This paper introduces a novel calibration scheme that applies a specially designed wideband 64-QAM modulated stimulus and uses the captured response to evaluate the impairments within the transmitter's RF chain. The needed pre-compensation is applied in a single iteration. This technique is intended for use with Doherty, Outphasing and MIMO type applications. Presented technique was experimentally validated using signal bandwidths up to 100 MHz for both weakly and strongly nonlinear systems.