25 research outputs found
PAPR Reduction Solutions for 5G and Beyond
The latest fifth generation (5G) wireless technology provides improved communication quality compared to earlier generations. The 5G New Radio (NR), specified by the 3rd Generation Partnership Project (3GPP), addresses the modern requirements of the wireless networks and targets improved communication quality in terms of for example peak data rates, latency and reliability. On the other hand, there are still various crucial issues that impact the implementation and energy-efficiency of 5G NR networks and their different deployments.
The power-efficiency of transmitter power amplifiers (PAs) is one of these issues. The PA is an important unit of a communication system, which is responsible from amplifying the transmit signal towards the antenna. Reaching high PA power-efficiency is known to be difficult when the transmit waveform has a high peak-to-average power ratio (PAPR). The cyclic prefix (CP)-orthogonal frequencydivision multiplexing (OFDM) that is the main physical-layer waveform of 5G NR, suffers from such high PAPR challenge. There are generally many PAPR reduction methods proposed in the literature, however, many of these have either very notable computational complexity or impose substantial inband distortion. Moreover, 5G NR has new features that require redesigning the PAPR reduction methods.
In line with these, the first contribution of this thesis is the novel frequencyselective PAPR reduction concept, where clipping noise is shaped in a frequencyselective manner over the active passband. This concept is in line with the 5G NR, where aggressive frequency-domain multiplexing is considered as an important feature. Utilizing the frequency-selective PAPR reduction enables the realization of the heterogeneous resource utilization within one passband.
The second contribution of this thesis is the frequency-selective single-numerology (SN) and mixed-numerology (MN) PAPR reduction methods. The 5G NR targets utilizing different physical resource blocks (PRBs) and bandwidth parts (BWPs) within one passband flexibly. Yet, existing PAPR reduction methods do not exploit these features. Based on this, novel algorithms utilizing PRB and BWP level control of clipping noise are designed to meet error vector magnitude (EVM) limits of the modulations while reducing the PAPR. TheMNallocation has one critical challenge as inter numerology interference (INI) emerges after aggregation of subband signals. Proposed MN PAPR reduction algorithm overcomes this issue by cancelling INI within the PAPR reduction loop, which has not been considered earlier.
The third contribution of this thesis is the proposal of two novel non-iterative PAPR reduction methods. First method utilizes the fast-convolution filteredOFDM (FC-F-OFDM) that has excellent spectral containment, and combines it with clipping. Moreover, clipping noise is also allocated to guard bands by filter passband extension (FPE) and clipping noise in out-of-band (OOB) regions is essentially filtered through FC filtering. The second method is the guard-tone reservation (GTR) which is applied to discrete Fourier transform-spread-OFDM (DFT-s-OFDM). Uniquely, GTR estimates the time domain peaks in data symbol domain before inverse fast Fourier transform (IFFT), and uses guard band tones for PAPR reduction.
The fourth contribution of the thesis is the design of two novel machine learning (ML) algorithms that improve the drawbacks of frequency-selective PAPRreduction. The first ML algorithm, PAPRer, models the nonlinear relation between the PAPR target and the realized PAPR value. Then, it auto-tunes the optimal PAPR target and this way minimizes the realized PAPR. The second ML algorithm, one-shot clipping-and-filtering (OSCF), solves the complexity problem of iterative clipping and filtering (ICF)-like methods by generating proper approximated clipping noise signal after running only one iteration, leading to very efficient PAPR reduction.
Finally, an over-arching contribution of this thesis is the experimental validation of the performance benefits of the proposed methods by considering realistic 5GNR uplink (UL) and downlink (DL) testbeds that include realistic PAs and associated hardware. It is very important to confirm the practical benefits of the proposed methods and, this is realized with the conducted experimental work
PAPR reduction in FBMC using an ACE-based linear programming optimization
This paper presents four novel techniques for peak-to-average power ratio (PAPR) reduction in filter bank multicarrier
(FBMC) modulation systems. The approach extends on current PAPR reduction active constellation extension (ACE)
methods, as used in orthogonal frequency division multiplexing (OFDM), to an FBMC implementation as the main
contribution.
The four techniques introduced can be split up into two: linear programming optimization ACE-based techniques
and smart gradient-project (SGP) ACE techniques. The linear programming (LP)-based techniques compensate for
the symbol overlaps by utilizing a frame-based approach and provide a theoretical upper bound on achievable
performance for the overlapping ACE techniques. The overlapping ACE techniques on the other hand can handle
symbol by symbol processing. Furthermore, as a result of FBMC properties, the proposed techniques do not require
side information transmission. The PAPR performance of the techniques is shown to match, or in some cases improve,
on current PAPR techniques for FBMC. Initial analysis of the computational complexity of the SGP techniques indicates
that the complexity issues with PAPR reduction in FBMC implementations can be addressed.
The out-of-band interference introduced by the techniques is investigated. As a result, it is shown that the
interference can be compensated for, whilst still maintaining decent PAPR performance. Additional results are also
provided by means of a study of the PAPR reduction of the proposed techniques at a fixed clipping probability. The bit
error rate (BER) degradation is investigated to ensure that the trade-off in terms of BER degradation is not too severe.
As illustrated by exhaustive simulations, the SGP ACE-based technique proposed are ideal candidates for practical
implementation in systems employing the low-complexity polyphase implementation of FBMC modulators. The
methods are shown to offer significant PAPR reduction and increase the feasibility of FBMC as a replacement
modulation system for OFDM.http://asp.eurasipjournals.com/hb201
Recommended from our members
Design and Linearization of Energy Efficiency Power Amplifier in Nonlinear OFDM Transmitter for LTE-5G Applications. Simulation and measurements of energy efficiency power amplifier in the presence of nonlinear OFDM transmitter system and digital predistortion based on Hammerstein-Wiener method
This research work has made an effort to understand a novel line of radio frequency
power amplifiers (RFPAs) that address initiatives for efficiency enhancement and
linearity compensation to harmonize the fifth generation (5G) campaign. The objective
is to enhance the performance of an orthogonal frequency division multiplexing-long
term evolution (OFDM-LTE) transmitter by reducing the nonlinear distortion of the
RFPA.
The first part of this work explores the design and implementation of 15.5 W class AB
RF power amplifier, adopting a balanced technique to stimulate efficiency enhancement
and redeeming exhibition of excessive power in the transmitter. Consequently, this work
goes beyond improving efficiency over a linear RF power amplifier design; in which a
comprehensive investigation on the fundamental and harmonic components of class F
RF power amplifier using a load-pull approach to realise an optimum load impedance
and the matching network is presented. The frequency bandwidth for both amplifiers was
allocated to operate in the 2.620-2.690 GHz of mobile LTE applications.
The second part explores the development of the behavioural model for the class AB
power amplifier. A particular novel, Hammerstein-Wiener based model is proposed to
describe the dynamic nonlinear behaviour of the power amplifier. The RF power amplifier
nonlinear distortion is approximated using a new linear parameter approximation
approach. The first and second-order Hammerstein-Wiener using the Normalised Least
Mean Square Error (NLMSE) algorithm is used with the aim of easing the complexity of
filtering process during linear memory cancellation. Moreover, an enhanced adaptive
Wiener model is proposed to explore the nonlinear memory effect in the system. The
proposed approach is able to balance between convergence speed and high-level
accuracy when compared with behavioural modelling algorithms that are more complex
in computation.
Finally, the adaptive predistorter technique is implemented and verified in the OFDM
transceiver test-bed. The results were compared against the computed one from
MATLAB simulation for OFDM and 5G modulation transmitters. The results have
confirmed the reliability of the model and the effectiveness of the proposed predistorter.FundacĂŁo para a CiĂŞncia e a Tecnologia, Portugal, under
European Union’s Horizon 2020 research and innovation programme ... grant agreement H2020-MSCA-ITN- 2016 SECRET-722424
I also acknowledge the role of the National Space Research and Development Agency (NASRDA)
Sokoto State Government
Petroleum Technology Trust Fund (PTDF
A digital polar transmitter for multi-band OFDM Ultra-WideBand
Linear power amplifiers used to implement the Ultra-Wideband standard must be
backed off from optimum power efficiency to meet the standard specifications and
the power efficiency suffers. The problem of low efficiency can be mitigated by polar
modulation. Digital polar architectures have been employed on numerous wireless
standards like GSM, EDGE, and WLAN, where the fractional bandwidths achieved
are only about 1%, and the power levels achieved are often in the vicinity of 20 dBm.
Can the architecture be employed on wireless standards with low-power and high
fractional bandwidth requirements and yet achieve good power efficiency?
To answer these question, this thesis studies the application of a digital polar transmitter
architecture with parallel amplifier stages for UWB. The concept of the digital
transmitter is motivated and inspired by three factors. First, unrelenting advances
in the CMOS technology in deep-submicron process and the prevalence of low-cost
Digital Signal processing have resulted in the realization of higher level of integration
using digitally intensive approaches. Furthermore, the architecture is an evolution
of polar modulation, which is known for high power efficiency in other wireless applications.
Finally, the architecture is operated as a digital-to-analog converter which
circumvents the use of converters in conventional transmitters.
Modeling and simulation of the system architecture is performed on the Agilent Advanced
Design System Ptolemy simulation platform. First, by studying the envelope
signal, we found that envelope clipping results in a reduction in the peak-to-average
power ratio which in turn improves the error vector magnitude performance (figure
of merit for the study). In addition, we have demonstrated that a resolution of three
bits suffices for the digital polar transmitter when envelope clipping is performed.
Next, this thesis covers a theoretical derivation for the estimate of the error vector
magnitude based on the resolution, quantization and phase noise errors. An analysis
on the process variations - which result in gain and delay mismatches - for a
digital transmitter architecture with four bits ensues. The above studies allow RF
designers to estimate the number of bits required and the amount of distortion that
can be tolerated in the system.
Next, a study on the circuit implementation was conducted. A DPA that comprises
7 parallel RF amplifiers driven by a constant RF phase-modulated signal and 7
cascode transistors (individually connected in series with the bottom amplifiers)
digitally controlled by a 3-bit digitized envelope signal to reconstruct the UWB
signal at the output. Through the use of NFET models from the IBM 130-nm
technology, our simulation reveals that our DPA is able to achieve an EVM of -
22 dB. The DPA simulations have been performed at 3.432 GHz centre frequency
with a channel bandwidth of 528 MHz, which translates to a fractional bandwidth
of 15.4%. Drain efficiencies of 13.2/19.5/21.0% have been obtained while delivering
-1.9/2.5/5.5 dBm of output power and consuming 5/9/17 mW of power.
In addition, we performed a yield analysis on the digital polar amplifier, based
on unit-weighted and binary-weighted architecture, when gain variations are introduced
in all the individual stages. The dynamic element matching method is also
introduced for the unit-weighted digital polar transmitter. Monte Carlo simulations
reveal that when the gain of the amplifiers are allowed to vary at a mean of 1 with a
standard deviation of 0.2, the binary-weighted architecture obtained a yield of 79%,
while the yields of the unit-weighted architectures are in the neighbourhood of 95%.
Moreover, the dynamic element matching technique demonstrates an improvement
in the yield by approximately 3%.
Finally, a hardware implementation for this architecture based on software-defined
arbitrary waveform generators is studied. In this section, we demonstrate that the error vector magnitude results obtained with a four-stage binary-weighted digital polar
transmitter under ideal combining conditions fulfill the European Computer Manufacturers
Association requirements. The proposed experimental setup, believed to
be the first ever attempted, confirm the feasibility of a digital polar transmitter architecture
for Ultra-Wideband. In addition, we propose a number of power combining
techniques suitable for the hardware implementation. Spatial power combining, in
particular, shows a high potential for the digital polar transmitter architecture.
The above studies demonstrate the feasibility of the digital polar architecture with
good power efficiency for a wideband wireless standard with low-power and high
fractional bandwidth requirements
Systèmes OFDM optiques à détection directe à complexité réduite pour les communications à haut débit
A possible approach to maximize the data rate per wavelength, is to employ the high spectral efficiency discrete multitone (DMT) modulation. The work presented in this thesis mainly focuses on optimizing the power consumption and cost of DMT, that are the major obstacles to its market development. Within this context, we have first developed novel techniques permitting to discard the use of Hermitian symmetry in DMT modulations, thus significantly reducing the power consumption and the system cost. We have next proposed an asymmetric linear companding algorithm permitting to reduce the optical power of conventional DCO-OFDM modulation with a moderate complexity. A new VCSEL behavioural model based on the use of the VCSEL quasi-static characteristic was also developed to accurately evaluate the VCSEL impact on DMT modulations. Finally, we have built an experimental system to experimentally validate our proposed techniques. Several simulations and measurement results are then provided.Une approche pour augmenter le débit par longueur d'onde, est d'utiliser la modulation DMT (Discrete Multitone) à haute efficacité spectrale. Le travail présenté dans cette thèse se focalise principalement sur l'optimisation de la consommation en puissance et le coût de la DMT, qui présentent des obstacles majeurs à son industrialisation. Dans ce cadre, nous avons tout d'abord développé des nouvelles techniques permettant d'exclure la symétrie Hermitienne des modulations DMT, réduisant ainsi considérablement la consommation en puissance et le coût du système. Nous avons ensuite proposé un algorithme de compression linéaire asymétrique permettant de réduire la puissance optique de la modulation DMT avec une complexité modérée. Un nouveau modèle comportemental du VCSEL basé sur la caractéristique quasi-statique a été également développé. Nous avons enfin validé expérimentalement les techniques que nous avons proposées. Plusieurs résultats de simulations et de mesures sont ainsi présentés
Recommended from our members
Design and implementation of adaptive baseband predistorter for OFDM nonlinear transmitter. Simulation and measurement of OFDM transmitter in presence of RF high power amplifier nonlinear distortion and the development of adaptive digital predistorters based on Hammerstein approach.
The objective of this research work is to investigate, design and measurement of a digital
predistortion linearizer that is able to compensate the dynamic nonlinear distortion of a High
Power Amplifier (PA). The effectiveness of the proposed baseband predistorter (PD) on the
performance of a WLAN OFDM transmitter utilizing a nonlinear PA with memory effect is
observed and discussed. For this purpose, a 10W Class-A/B power amplifier with a gain of 22
dB, operated over the 3.5 GHz frequency band was designed and implemented.
The proposed baseband PD is independent of the operating RF frequency and can be used in
multiband applications. Its operation is based on the Hammerstein system, taking into account
PA memory effect compensation, and demonstrates a noticeable improvement compared to
memoryless predistorters.
Different types of modelling procedures and linearizers were introduced and investigated, in
which accurate behavioural models of Radio Frequency (RF) PAs exhibiting linear and
nonlinear memory effects were presented and considered, based on the Wiener approach
employing a linear parametric estimation technique. Three new linear methods of parameter
estimation were investigated, with the aim of reducing the complexity of the required filtering
process in linear memory compensation. Moreover, an improved wiener model is represented to
include the nonlinear memory effect in the system. The validity of the PA modelling approaches
and predistortion techniques for compensation of nonlinearities of a PA were verified by several
tests and measurements. The approaches presented, based on the Wiener system, have the
capacity to deal with the existing trade-off between accuracy and convergence speed compared
to more computationally complex behavioural modelling algorithms considering memory
effects, such as those based on Volterra series and Neural Networks.
In addition, nonlinear and linear crosstalks introduced by the power amplifier nonlinear
behaviour and antennas mutual coupling due to the compact size of a MIMO OFDM transmitter
have been investigated
Cognitive Radio Systems
Cognitive radio is a hot research area for future wireless communications in the recent years. In order to increase the spectrum utilization, cognitive radio makes it possible for unlicensed users to access the spectrum unoccupied by licensed users. Cognitive radio let the equipments more intelligent to communicate with each other in a spectrum-aware manner and provide a new approach for the co-existence of multiple wireless systems. The goal of this book is to provide highlights of the current research topics in the field of cognitive radio systems. The book consists of 17 chapters, addressing various problems in cognitive radio systems