On Circularity of Receiver Front-end Signals Under RF Impairments

Abstract:
The circularity of receiver front-end signals is analyzed under various link impairments, including transmitter in-phase/quadrature-phase (I/Q) imbalance and local oscillator (LO) leakage, power amplifier nonlinearity, time-varying channel, carrier frequency offset, receiver phase noise, and DC offsets. Expressions are derived for the complementary autocorrelation functions of signals affected by these impairments. The circularity of the received waveform is shown to hold in the presence of transmitter I/Q imbalance and other impairments under certain realistic and non-restrictive conditions, while receiver I/Q imbalance makes the signal non-circular. These findings are important for receiver I/Q imbalance compensation, since many of these algorithms rely on the circularity of the received waveform, either explicitly or implicitly. Receiver DC offsets can potentially make the signal noncircular, but the effect is shown to be insignificant under realistic RF-to-LO isolation values. The results build confidence that low-complexity blind receiver I/Q imbalance compensation is applicable even in the presence of transmitter I/Q imbalances and other system impairments.