RF Analog Impairments Modeling for Communication Systems Simulation: Application to OFDM-based Transceivers

4.6 Summary

With the strong demand to provide low-cost and low-power integrated transceivers for high data-rate mobile applications, RF analog front-end imperfections became a serious concern during system design. However, recent advances in embedded digital signal processing techniques allow now “living” with impaired RF analog front-end by compensating in baseband its impact on system performance.

In this chapter we presented and studied some DBB techniques used to correct RF analog impairments in communication transceivers, particularly those using OFDM modulation, which are carrier and SFOs, I and Q mismatch, and PA nonlinearity.

For carrier and frequency offsets, we focused on their estimation with an analytical description of the algorithms based on training sequences used, either in the time or frequency domain, in order to extract the deterministic phase shift introduced by both frequency errors. In addition, we described a joint estimation scheme allowing one to derive the CFO from the sampling frequency one. We simulated their sensitivity to AWGN and we saw that the estimation of SFO is much more sensitive to noise than that of the carrier frequency.

For IQ mismatch we presented an algorithm which estimates the ISR coefficients in the frequency domain, that is, after the receiver FFT, using at least two known subcarriers (pilots). For a better accuracy, several pairs of subcarriers can be used in order to obtain an average value of the estimate. Afterwards, these coefficients ...