On the effects of memoryless nonlinearities on M-QAM and DQPSK OFDM signals

In the design of RF up-conversion and down-conversion communication links, an issue of special interest is presented by the nonlinear characteristic of analog devices. In this paper, we deal with the effect of memoryless nonlinear distortion on orthogonal frequency-division multiplexing (OFDM) transceivers. We tackle the issue of calculation of the number of intermodulation products with methods from combinatorics theory and derive closed-form expressions for the signal-to-noise ratio (SNR). We deal with third-order nonlinearities alone though the methodology used can be extended to cover higher order nonlinear phenomena. We then proceed to deriving SNR expressions in the presence of a high adjacent channel of the same service and predict the generation of in-band tonal interference. Finally, we generalize to the case of a multichannel OFDM transceiver. In each case, bit-error-rate estimations for differential quadrature phase-shift keying and symbol-error-rate estimations for M-quadrature amplitude-modulation constellations are presented and a mapping between circuit characteristics and OFDM performance is outlined.