Detection and evaluation of I/Q impairments in RF digital transmitters

Troubleshooting of radio-frequency (RF) digital transmitters is considered. A new digital signal-processing method is developed, which is capable of both detecting and evaluating the most recurrent impairments in the I and Q paths of the transmitter. Only the acquisition of either the intermediate-frequency (IF) or RF output signal is needed, thus avoiding any difficulty connected with the inaccessibility of the baseband and/or IF section in a fully assembled transmitter. Moreover, the method has the required features of automation and effectiveness, granted by the use of RLS-based algorithms and proved by the results obtained in many experiments on actual IF and RF output signals. Even though the experiments presented in the paper refer to wideband code-division multiple-access technology, the method shows itself suitable for troubleshooting any digital transmitter implementing quadrature-amplitude modulation.