DSP Based Transmitter I/Q Imbalance Calibration: Implementation and Performance Measurements
Tutkimustuotos: Diplomityö tai pro gradu -työ ›
|Kustantaja||Tampere University of Technology|
|Tila||Julkaistu - 4 marraskuuta 2011|
|OKM-julkaisutyyppi||G2 Pro gradu, diplomityö, ylempi amk-opinnäytetyö|
In this thesis, some recently developed algorithms for I/Q imbalance estimation and compensation are studied on the transmitter side. The calibration algorithms use a baseband test signal combined with a feedback loop from I/Q modulator output back to transmitter digital parts to efficiently estimate the modulator I/Q mismatch. In the feedback loop, the RF signal is demodulated and compared with the original test signal to estimate the I/Q imbalance and the needed pre-distortion parameters. The actual digital transmit signal is then properly pre-distorted with the obtained I/Q imbalance knowledge, in order to cancel the effects of modulator I/Q imbalance at the data transmission phase. The performance of the compensation algorithms is first evaluated with computer simulations. A prototype system using laboratory instruments is also developed to illustrate the effects of I/Q imbalance in direct conversion and low-IF transmitters and is used to prove the usability of algorithms in real life front-ends. The results of computer simulations and laboratory measurements prove that the compensation algorithms yield a good calibration performance by suppressing the image signal interference close to or even below the noise floor.