IMPERFECTION REMOVAL IN SIX PORT BASED MODULATORS

Abstract

The demand for high-speed wireless data communications is increasing day by day. This has led to evolution of new technologies in the wireless domain. One such technology that has the potential to meet the ever increasing demand for high-speed data communications is a technique based on the six-port architecture. The six-port radio not only provides high-speed, but it also has low power consumption and low cost. In this project report, a comprehensive study of the six port technique is done. The construction and working of the six port correlator, six port modulator and six port demodulator had been studied in detail. A brief history of the six port radio was presented. Analysis of six port modulators was carried out and various six port modulator designs were studied. Comparison between the homodyne and heterodyne radio architecture had been done, and the advantages and disadvantages of six port radio over traditional direct conversion radio systems had been stated. The challenges associated with the six port radio had been discussed and proper solutions to mitigate the effect of these problems had also been studied. These solutions include the hardware oriented and digital signal processing based solutions. Though a number of hardware oriented solutions are present to suppress the carrier leakage and I/Q imbalance problem but not many digital signal processing based solutions are present in practice. The use of a digital predistorter to remove the I/Q imbalance, DC Offset and non-linearity problems associated with power amplifiers (PA) and I/Q modulators in broadband direct conversion transmitters [8] had been studied in detail; and the scope of this method has been extended to six port transmitters. A six port modulator was simulated in ADS. A behavioural model which represents this six port system was simulated in MATLAB. Then a digital predistorter was designed using Indirect Learning Architecture (ILA) technique [8] and it was used with the six port model in ADS which resulted in improvements in the overall performance of the six port model. The I/Q Imbalance problem and carrier leakage problem of the six port modulator were effectively minimized by using the digital predistorter.