Efficient Compensation of RF Impairments for OFDM Systems

OFDM based systems are very sensitive to radio frequency (RF) impairments such as in-phase/quadrature-phase (IQ) imbalance and carrier frequency offset (CFO). In this paper, a generally applicable joint transmitter (Tx) and receiver (Rx) RF impairment compensation scheme is proposed. It is composed of a time domain equalizer (TEQ) and two frequency domain equalizers (FEQ). The TEQ utilizes the short training symbols (STS) to estimate and compensate the frequency selective Rx IQ imbalance along with the CFO. The two FEQs then work on the specially induced phase rotated long training symbols (LTS) in order to compensate the remaining Tx or the combined Tx and Rx IQ imbalance along with the channel. A frequency-domain smoothing technique is also utilized in order to further speed up the convergence of the equalizers. The resulting cascade of equalizers provide an efficient compensation scheme in terms of both computational complexity as well as faster convergence.