Predistortion-Based Linearization for 5G and Beyond Millimeter-Wave Transceiver Systems: A Comprehensive Survey

Abstract

The next-generation (5G/6G) wireless communication aims to leapfrog the currently occupied sub-6 GHz spectrum to the wideband millimeter-wave (MMW) spectrum. However, MMW spectrums with high-order modulation schemes drive the power amplifier (PA) at significant back-off, causing severe nonlinear distortions, thus deteriorating the transceiver's (TRXs) modulation process. Typically, the TRX efficacy is quantified with standardized linearization matrices, which take advantage of different predistortion (PD) schemes to handle deep compression of the PA. In this regard, TRX baseband signals are mostly linearized in the digital domain, where digitally controlled linearization needs higher sampling rates due to increasing MMW bandwidths to compensate for intermodulation (IMD) products, resulting in increased system cost and power consumption. Alternately, the digitally controlled analog-based linearization, i.e., the hybridization of digital predistortion (DPD) and analog predistortion (APD), is highly productive and cost-effective for fulfilling the linearized energy-efficient design vision of MMW networks. Therefore, this paper puts an extensive spotlight on the progress in PD-based linearization for 5G and beyond communications. It first provides background information on the advancements of PD schemes through recent surveys, then classifies the general roadmap of PD waveform processing across the TRX system models as preliminary. After this, we present three prominent PD architectures and their design approaches with intrinsic performance metrics. Finally, we explore four case studies encompassing PD operation under certain nonlinear constraints of different communication schemes. We examine the suitability of PD-based linearization solutions, both existing and proposed till the first quarter of 2022, and identify the potential prospects in this domain.

Analogue self-interference cancellation of co-frequency co-time unidirectional transponders for low earth orbit satellite systems

“…Due to the imperfection of the PA, the amplified signal will carry nonlinear distortion generated by the power amplifier, namely intermodulation distortion, which can be modelled as a parallel Hammerstein or Wiener-Hammerstein mode 15 in the digital domain. In addition, the digital predistortion (DPD) 16,17 approach is another candidate for dealing with nonlinear distortion.…”

Linearization of the Fifth Generation Power Amplifiers by Injection of the Second Order Digitally Processed Signals

“…A variety of techniques for amplifier linearization such as feedforward, feedback, predistortion [3] and different approaches of digital predistortion [3], [4] can be found in the literature. The authors of this paper anteriorly developed the digital linearization approach (DEB_LIN) [5][6][7][8] that uses the 2nd order digital signals adequately processed in magnitude and phase angles in the baseband, which then modulate the 2nd harmonic of the fundamental carrier.…”

Received Signal Modeling for Millimeter Wave and Terahertz Systems With Practical Impairments

“…Wideband millimeter wave (mm-wave) systems have been envisaged as the viable solutions to realizing high capacity wireless access for the sixth-generation (6G) mobile networks and providing multi-hundred gigabit wireless backhaul for future integrated space and terrestrial networks [1], [2]. With more bandwidth available in terahertz (THz) frequency band, THz systems are also able to provide high-speed space communications between satellites without atmospheric attenuation [3].…”

“…Also, according to the authors' experience, DPD may reduce the Tx power while linearizing the HPA, similar to the effect achieved by the power back-off strategy. Most importantly, even with the state-of-the-art digital technology, no ADC is available or affordable to sample the nonlinear HPA feedback signal with usually 4-5 fold faster speed [2] than the multi-gigahertz signal bandwidth, nor can the digital signal processing be implemented in real-time as the nonlinearity parameter estimation requires inversion of a large matrix with dimension equal to the total number of nonlinearity parameters and the indirect learning used in DPD requires many iterations. Although new techniques such as neural network and artificial intelligence [2], [6], [7] have been exploited recently to significantly improve the HPA linearization performance, the fundamental constraints of existing digital hardware capability make DPD not applicable to low-cost wideband mm-wave and THz systems.…”