Title :
Adaptive compensation for imbalance and offset losses in direct conversion transceivers
Author :
Cavers, James K. ; Liao, Maria
Author_Institution :
Sch. of Eng. Sci., Simon Fraser Univ., Burnaby, BC, Canada
Abstract :
It is pointed out that analog implementations of quadrature modulators and demodulators have deficiencies-primarily amplitude and phase imbalances and DC offset-that result in several troublesome problems for digital transceivers. An analysis and quantitative assessment of the losses due to analog implementations are presented. They include spurious tones and intermodulation products at the transmitter and a degraded BER (bit error rate) due to distortion of the signal constellation. The asymptotic degradation in BER performance in 16 QAM (quadrature amplitude modulation) for example is shown to be 1.1 dB for a 5° phase imbalance and 0.65 dB for 5% gain imbalance. An adaptive procedure at the receiver for minimization of the imbalance and offset errors is developed. It is demonstrated that the LMS (least mean square) algorithm can be used to adapt the compensator in a manner similar to an equalizer, and that the computational load is the same as that of a three-tap equalizer
Keywords :
adaptive systems; analogue circuits; demodulators; digital radio systems; mobile radio systems; modulators; signal processing; transceivers; 16 QAM; DC offset; LMS algorithm; adaptive imbalance minimisation; amplitude imbalances; analog demodulators; analog implementations; analog modulators; asymptotic degradation; bit error rate; computational load; degraded BER; digital transceivers; direct conversion transceivers; gain imbalance; intermodulation products; mobile radio; offset errors; phase imbalances; quadrature amplitude modulation; signal processing; spurious tones; Amplitude modulation; Bit error rate; Degradation; Demodulation; Digital modulation; Equalizers; Phase modulation; Quadrature amplitude modulation; Transceivers; Transmitters;
Conference_Titel :
Vehicular Technology Conference, 1991. Gateway to the Future Technology in Motion., 41st IEEE
Conference_Location :
St. Louis, MO
Print_ISBN :
0-87942-582-2
DOI :
10.1109/VETEC.1991.140557