Analysis and Power Diversity-Based Cancellation of Nonlinear Distortions in OFDM Systems

Abstract

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR) of the transmitted signals, which can cause the introduction of inter-carrier interference (ICI) due to the presence of nonlinear power amplifiers (PAs). In this paper, a theoretical analysis of the ICI in nonlinear OFDM systems with polynomial PAs is made. Contrary to other works, this analysis provides an exact description of the nonlinear ICI. Moreover, three receivers for channel estimation and ICI cancellation in OFDM systems with polynomial PAs are proposed, based on the concept of power diversity that consists in re-transmitting the information symbols several times with a different transmission power each time. The transmission powers that minimize the sum of the residual mean square errors (MSEs) provided by the proposed receivers are derived in the case of a thirddegree polynomial PA. An important advantage of the proposed receivers is that the optimal transmission powers do not depend on the channel nor the PA coefficients. Index TermsOFDM, power amplifier, nonlinear system, channel estimation, inter-carrier interference cancellation. C. A. R. Fernandes is with the

Baseband Equivalent Volterra Series for Behavioral Modeling and Digital Predistortion of Power Amplifiers Driven With Wideband Carrier Aggregated Signals

“…The LPE Volterra model of (4) has been used extensively in RF research. The model has been applied to develop solutions related to nonlinear communication system modeling and estimation [12], satellite communication [13], digital transmission channel equalization [14], multichannel nonlinear CDMA system equalization [15], analysis, and cancellation of the intercarrier interference in nonlinear orthogonal frequency division multiplexing (OFDM) systems [16], decision feedback equalization [17], nonlinear system and circuit analysis [18], data predistortion [19], PA modeling [20]- [22], and DPD [23]- [25]. Although computationally more efficient than its passband counterpart, the LPE Volterra series in its classical form (4) still suffers from a large number of kernels.…”

“…The convolution form is as follows: (15) Next, the Laplace transformation is applied to the convolution form of the Volterra-series nonlinear-order responses . The Laplace domain representation of (14) and (15) is given by (16) …”

“…The BBE form of (16) and (17) can be derived by applying a frequency translation of to the constituent terms and as follows: (18) where and designate the BBE outputs and and denote the BBE kernels, respectively. Applying the inverse Laplace to (18) yields the continuous-time BBE model as follows: (19) The previous derivations were used to obtain continuous-time BBE expression for the term around in (10); similar derivations can be applied to the conjugate term, i.e., around , to yield an alike expression than (19).…”

Cancelamento de Distorções Não Lineares em Sistemas OFDM Cooperativos AF

“…Há algumas soluções com o objetivo de reduzir os efeitos NL impostos pelo uso de PAs, que são: técnicas de pré-distorção NL do sinal no transmissor e técnicas de cancelamento de distorções NL no receptor. As técnicas de pré-distorção realizam um processamento do sinal no transmissor com o objetivo de reduzir a PAPR para que os picos de amplitude do sinal não atinjam regiões não lineares [7], [8]. Já as técnicas de cancelamento de distorções buscam estimar iterativamente e cancelar as distorções NL no receptor [3], [4], [7]- [14].…”

Análise de Sistemas OFDM com Modulação por Índice e Amplificador de Potência Não Linear

“…C. Alexandre Rolim Fernandesé parcialmente financiado pelo CNPq. estratégia nãoé muito interessante, pois provoca uma baixa SNR (Signal-to-Noise Ratio) no receptor [7].…”