1、An Embedded System to Correct In-Phase and Quadrature-Phase Imbalance for WCDMA Direct Conversion Receiver,Ye Shi Helsinkin University of TechnologySupervisor:Professor Sven-Gustav Hggman11,November 2003,Contents,Motivations Thesis Objectives Direct Conversion Receivers & I/Q imbalances Estimating &
2、 Compensating I/Q Imbalances Tests Conclusions,Motivations,Direct Conversion Receivers (DCR) are used in WCDMA base stations DCR is sensitive to I/Q imbalances Develop an embedded system to estimate and compensate the I/Q imbalances,Thesis Objectives,Study WCDMA base station Study software and hardw
3、are of transceiver ( transmitter and receiver) Develop an embedded system to estimate and compensate I/Q imbalances,DCR,Advantages: Not many components, easier to integrate Low power consumptionDisadvantages: DC-offset High sensitivity not easily available Accurate I/Q phase and amplitude balance re
4、quired,Most Common I/Q Imbalances-1,Amplitude imbalance Since I and Q are two separate signals, each one is created and amplified independently. Inequality of this gain between the I and Q branches results in amplitude imbalance. A perfect signal will have a uniform constellation that is perfectly s
5、ymmetric about the origin. I/Q amplitude imbalance is indicated when the constellation is not “square,“ i.e., when the Q-axis height does not equal the I-axis width, as seen in the Figure.,Most Common I/Q Imbalances-2,Quadrature error If the phase shift between the RF LO signals that mix with the I
6、and Q base band signal at the modulator is not 90 degrees, a quadrature error occurs. The constellation of the signal is distorted, which may cause error in the interpretation of the recovered symbols. The quadrature errors result in a “tipped“ or skewed constellation.,Most Common I/Q Imbalances-3,D
7、elays in the I or Q branches Delays can be caused by the modulator or by the filtersI/Q without dalay Q delayed relative to I,2,Most Common I/Q Imbalances-4,DC-offset DC offsets may be introduced in the I and Q branches. They may be added in the amplifiers in the I and Q branches. DC offset errors r
8、esult in a constellation whose center is offset from the reference center, as seen in the figure.,Estimating & Compensating I/Q Imbalances (1),Developing a mathematical model to estimate Amplitude imbalance Phase imbalance between the I/Q branches Quadrature error Delay Implementing the algorithm in
9、 PowerPC processor Get the inverse values of the estimated I/Q imbalances Caculate the filter tap coefficients based on the estimation,Estimating & Compensating I/Q Imbalances (2),Compensating the I/Q Imbalances Construct an equalizer filter based on the tap coefficients Equalize the signals in the
10、Q branch,Tests,The estimator and equalizer synthesis are implemented and tested The simulation system is tested,Conclusions,This embedded system is specially used in dual-carrier DCR to remove the effects of I/Q imbalances Advantages of the embedded system The compensation method is frequency dependent The pilot signal is not needed Further study is needed,Thank you !,Questions?,
