Predistortion performance considering Peak to Average Power ratio reduction in OFDM context

International audienceSome recent communication systems like DVB-T2 standard set up a PAPR reduction technique followed by a linearization's one. So in such a scenario, the performance of the linearization is influenced undoubtedly by the PAPR reduction method. In this paper, we revisit the EVM metric and evaluate a closed form regarding the performance of both the PAPR reduction technique and the linearization's one. We choose the predistortion as a linearization technique and define a predistortion error. Assuming that the baseband OFDM signal is characterized as a complex Gaussian process, we consider the three top categories of PAPR reduction methods presented in [2] and we first study the distribution of the resulted signal. Then, we derive some theoretical expressions of the first and second order moments of the predistortion error and show that the error depends mainly on the PAPR of the signal after PAPR reduction method and on the predistortion quality. Some simulations compared to our proposed model confirm our results

Theoretical analysis of the trade-off between efficiency and linearity of the High Power Amplifier in OFDM context

International audiencePower efficiency and linearity are key parameters of amplification systems but they cannot be achieved simultaneously. A perfect linearity is observed when the power efficiency is low and vice versa. In this paper, we first analyze through some theoretical expressions, the power efficiency and the linearity measured by the Error Vector Magnitude (EVM) metric. Then we propose an analytical trade-off that ensures a good linearity with reasonable efficiency by combining Peak-to-Average Power Ratio (PAPR) reduction and linearization. This analysis is carried out based on Solid State Power Amplifiers (SSPA) and Predistortion (PD) as linearization technique. We show that a trade-off can be achieved for a high distortionless PAPR reduction gain followed by an effective predistortion. Last but not least the most important is to avoid the amplifier saturation by setting the PAPR of the signal after PAPR reduction technique identical to the input back-off (IBO)

Adding signal for peak-to-average power reduction and predistortion in an orthogonal frequency division multiplexing context

International audienceIn this study, the authors look into digital predistortion and its combination with the peak-to-average power ratio (PAPR) reduction technique in the case of orthogonal frequency division multiplexing (OFDM)-based systems. First of all, the authors propose a new predistortion methodology which uses the addition of signals. Two different algorithms are investigated for the predistortion signals generation. The first one is based on the traditional predistortion method, where an estimation of the power amplifiers (PAs) characteristics is needed in the first place. The second algorithm to generate the predistortion signal does not need a priori PA estimation. It is based on an iterative compensation of the error between the amplified signal and the OFDM signal. Then, the authors combine this latter algorithm with the tone reservation PAPR reduction method in order to have a global adding signal expression. Two combination scenarios of PAPR reduction and predistortion obtained by means of adding a signal are proposed. The first one combines both of them in series while the second one is parallel. Performances of the proposed predistortion algorithms and the combination scenarios are compared thanks to simulations based on IEEE802.il a/g standards for a memoryless solid state PA

Joint study of PAPR reduction and digital predistortion

International audienceWithin the issue of transmission of signals with no constant envelope as Orthogonal Frequency Division Multiplexing (OFDM) for example, the Peak-to-Average Power Ratio (PAPR) reduction and the linearization are nowadays the two solutions proposed to deal the effects of the nonlinearities of the power amplifiers. In spite of their interdependence, these two solutions are separately studied and optimized.This can degrade seriously their common performance once stakes together because of opposite effects. In this paper, based on Rapp's memoryless amplifier, we demonstrate that predistortion increase the signal's PAPR and then proposed a joint combination scheme of "clipping & filtering" and polynomial predistortion. Computer simulations and analysis show that signal keeps a good level of linearity improvement measured with Modulation Error Ration (MER) while decreasing the predistortion's complexity

A joint approach for PAPR reduction and predistortion by adding signal in Cognitive Radio

International audienceMulti-carrier and multi-standard systems are prone to high Peak-to-Average Power Ratio (PAPR). Due to the non-linearity of the high Power Amplifier (PA), this results in interferences and/or low power efficiency. In this paper, we propose to use a joint approach for PAPR reduction and memoryless predistortion by adding signal in order to improve PA linearity and efficiency performances depending on the radio environment. First, the radio environment is sensed and informations such as signal's PAPR, channel estimation, Signal-to-Noise Ratio (SNR) and battery level are collected. Accordingly, a decision engine updates additional signals for PAPR reduction and predistortion in order to meet targeted linearity and power efficiency requirements. Ideally suited for Cognitive Radio (CR) systems, this dynamic joint approach by adding signal is simulated and validated through two scenarios represented on two examples of radio environment. The PAPR reduction performance is evaluated by the Complementary Cumulative Density Function (CCDF) and the PA linearity by Error Vector Magnitude (EVM) criteria

Digital Predistortion Expressed As an Adding Signal Technique in OFDM Context

International audienceIn this paper, we propose to model the digital predistortion as an adding signal technique in the Orthogonal Frequency Division Multiplexing (OFDM) context. The additional signal is then the predistortion signal for the Power Amplifier's (PA) non-linearity compensation. Two different algorithms are investigated for this signal generation. The first one is based on the Bussgang theorem for a memoryless predistortion where a preliminary step of PA's characteristic estimation is needed. The second algorithm doesn't need a priori PA's characteristic estimation; it is based on an iterative compensation of the error between the amplified signal and the OFDM signal. Thanks to the well known performance of Peak-to Average Power Ratio (PAPR) reduction methods based on the adding signal technique, this new formulation of predistortion by adding signal will allow us to have a common vision of both PAPR reduction and predistortion and by the way an optimal compromise between PA's efficiency and linearity. Simulations results in terms of Error Vector Magnitude (EVM), Adjacent Channel Power Ratio (ACPR) and Power Spectral Density (PSD) criteria show that both algorithms have close performances. Moreover, the second algorithm has a fast convergence; after 2 iterations, its performance is almost identical to that of the traditional predistortion