Comparision Between Adaptive Digital Base Band Predistortion Technique And Other Techniques For Power Amplifier

The purpose of the Power Amplifier is to boost the radio signal to a sufficient power level for transmission through the air interface from the transmitter to the receiver. It involves solving several contradicting requirements, which are such as linearity and efficiency. Unfortunately, these requirements tend to be mutually exclusive, so that any improvement in linearity is usually achieved at the expense of efficiency, and vice versa. A lot of studies and reviews on different classes of power amplifiers, their characteristics and distortion parameters have been done. This includes a study on different technique to improve the linearity of power amplifier, where each technique was reviewed to determine its suitability for the proposed applications. In this research, the adaptive digital predistortion technique was been studied and compare with other techniques. The predistortion circuit inversely models the amplifier's gain and phase characteristics and, when combined with the amplifier, produces an overall system that is more linear and reduces the amplifier's distortion. In essence, "inverse distortion" is introduced into the input of the amplifier, thereby canceling any non-linearity that the amplifier might have. This inverse distortion is the data stored in look-up table that is being multiplied into the input signal and then the customized input signal is ready to pass through power amplifier. By analyzing the output signal and the desired signal, the adaptation algorithm will update this data until finding the optimum values. In this thesis, Saleh model was used as a model of power amplifier and been compared with the others results of the model for verification. The Saleh model was used for the adaptive digital predistortion studies to linearize the power amplifier. Simulation and results of this amplifier demonstrate between 15dB to 20dB improvements in output spectrum that means there is 60% to 65% improvement in linearization, maximum 20% improvement in Gain of Power Amplifier, 15% improvement in Power efficiency, and noticeable cancellation in constellations changes

A Physical Layer Security (PLS) approach through Address Fed Mapping Crest Factor Reduction applicable for 5G/6G signals

The privacy and security of 5G/6G infrastructures are receiving great attention together with power consumption and efficiency. Here, Physical Layer Security (PLS) is considered and a technique named Address Fed Mapping (AFM) is proposed which not only enhances the physical layer security, but also reduces the effect of high Peak to Average Power Ratio (PAPR), which results in efficiency improvement in OFDM based signals used in beyond 5G and 6G. The AFM is designed based on the idea of randomly generated signals, modifying the original signal to reduce PAPR. Instead of a typical randomization algorithm, a unique key is generated based on Channel response that is known only transmitter-receiver pairs. This key is used to pick a signal and send it. It is shown that the proposed AFM technique reduces PAPR, which improves the energy efficiency of the system

Peak Shrinking and Interpolating Technique for reducing Peak to Average Power Ratio

This paper discusses topic of high Peak to Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) based signals. An innovative technique is proposed to reduce PAPR without compromising Error Vector Mapping (EVM). The proposed technique is named Peak Shrinking and Interpolating (PSI), and results show no more than 1% EVM when the technique is operated. The hardware resource consumption of PSI technique is analyzed and compared with the simplest Crest Factor Reduction (CFR) technique known as Clipping and Filtering (CF). This analysis, together with EVM performance, and PAPR reduction performance indicates that PSI technique can be an outstanding scheme for existing and future technologies such as Long-Term Evolution (LTE) and 5th Generation of cellular mobile communications (5G), resulting in more efficient Power Amplifier (PA) operation

Performance Investigation of Peak Shrinking and Interpolating the PAPR Reduction Technique for LTE-Advance and 5G Signals

Orthogonal frequency division multiplexing (OFDM) has become an indispensable part of waveform generation in wideband digital communication since its first appearance in digital audio broadcasting (DAB) in Europe in 1980s, and it is indeed in use. As has been seen, the OFDM based waveforms work well with time division duplex operation in new radio (NR) systems in 5G systems, supporting delay-sensitive applications, high spectral efficiency, massive multiple input multiple output (MIMO) compatibility, and ever-larger bandwidth signals, which has demonstrated successful commercial implementation for 5G downlinks and uplinks up to 256-QAM modulation schemes. However, the OFDM waveforms suffer from high peak to average power ratio (PAPR), which is not desired by system designers as they want RF power amplifiers (PAs) to operate with high efficiency. Although NR offers some options for maintaining the efficiency and spectral demand, such as cyclic prefix based (CP-OFDM), and discrete Fourier transform spread based (DFT-S-OFDM) schemes, which have limiting effects on PAPR, the PAPR is still as high as 13 dB. This value increases when the bandwidth is increased. Moreover, in LTE-Advance and 5G systems, in order to increase the bandwidth, and data-rate, carrier aggregation technology is used which increases the PAPR the same way that bandwidth increment does; therefore, it is essential to employ PAPR reduction in signal processing stage before passing the signal to PA. In this paper, we investigate the performance of an innovative peak shrinking and interpolation (PSI) technique for reducing peak to average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) based signals at waveform generation stage. The main idea behind the PSI technique is to extract high peaks, scale them down, and interpolate them back into the signal. It is shown that PSI technique is a possible candidate for reducing PAPR without compromising on computational complexity, compatible for existing and future telecommunication systems such as 4G, 5G, and beyond. In this paper, the PSI technique is tested with variety of signals in terms of inverse fast Fourier transform (IFFT) length, type of the signal modulation, and applications. Additional work has been carried out to compare the proposed technique with other promising PAPR reduction techniques. This paper further validates the PSI technique through experimental measurement with a power amplifier (PA) test bench and achieves an adjacent channel power ratio (ACPR) of less than –55 dBc. Results showed improvement in output power of PA versus given input power, and furthermore, the error vector magnitude (EVM) of less than 1% was achieved when comparing of the signal after and before modification by the PSI techniqu

A low complexity PAPR reduction scheme based on radix-II IFFT

Due to no feedback process and simplicity in searching algorithm, conventional selected mapping (CSLM) is an efficient crest factor reduction (CFR) technique in orthogonal frequency division multiplexing (OFDM) systems. However high number of inverse fast Fourier transform (IFFT) block is required to achieve the desired PAPR reduction performance. In this paper a PAPR reduction method based on N point radix-2 IFFT is proposed in which the number of IFFTs is reduced to one. The gist of the proposed method is based on storing a part of calculations and using them for the next searching operation results in elimination of the redundant calculations. Simulation results show at least 46.8% complexity reduction compared to CSLM by comparable PAPR performance

A low complexity selected mapping scheme for peak to average power ratio reduction with digital predistortion in OFDM systems

One of the effective methods used for reducing peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems is selected mapping (SLM). In this paper, a new SLM scheme called DSI-SLM, which is a combination of dummy sequence insertion (DSI) and conventional selected mapping (C-SLM) is proposed. Previous techniques have had some drawbacks. In DSI, increasing the number of dummy sequences to have better PAPR degrades transmission efficiency, and in C-SLM, the complexity rises dramatically when the number of sub-blocks increases. The proposed DSI-SLM scheme significantly reduces the complexity because of the reduction in the number of sub-blocks compared with the C-SLM technique while its PAPR performance is even better. To enhance the efficiency of the OFDM system and suppress the out-of-band distortion from the power amplifier nonlinearity, a digital predistortion technique is applied to the DSI-SLM scheme. Simulations are carried out with the actual power amplifier model and the OFDM signal based on the worldwide interoperability for microwave access standard and quadrature phase-shift keying modulation. The simulation results show improvement in PAPR reduction and complexity, whereas the BER performance is slightly worse

An improvement method for reducing power amplifiers memory effects based on complex gain predistortion

Efficient RF power amplifiers used in third generation systems require linearization in order to reduce adjacent channel inter-modulation distortion, without sacrificing efficiency. Digital baseband predistortion is a highly cost-effective way to linearize power amplifiers (PAs), but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA) or wideband orthogonal frequency-division multiplexing (W-OFDM), PA memory effects can no longer be ignored. In this paper we proposed a technique for adaptation of digital predistorter that considers memory effects in power amplifiers