What are common RF impairments and how are they compensated?

RF impairments degrade signal quality and must be compensated. Phase noise: VCO/PLL instability causes constellation rotation and ICI in OFDM; improved PLL design, common phase error estimation, and CPE correction. I/Q imbalance: Gain/phase mismatch between I and Q paths creates image interference; compensated by calibration or digital pre/post-compensation. DC offset: Mixer LO leakage creates DC component; removed by DC blocking or digital subtraction. PA nonlinearity: Causes spectral regrowth and EVM degradation; DPD (Digital Pre-Distortion) linearizes PA, memory polynomial models popular. Carrier frequency offset: Due to oscillator mismatch; compensated by frequency synchronization algorithms. Sample timing offset: Causes ISI; compensated by timing recovery and interpolation. ADC/DAC quantization: Causes noise floor increase.