This document discusses peak-to-average power ratio (PAPR) reduction techniques for orthogonal frequency-division multiplexing (OFDM) signals. It begins with an introduction to PAPR and its causes for OFDM signals. It then outlines various PAPR reduction techniques including clipping, coding, probabilistic/scrambling, predistortion, and DFT-spreading. Each technique has benefits but also cons such as distortion, reduced efficiency, or increased complexity. The document provides analysis of PAPR characteristics for different OFDM parameters and modulation schemes.
Sensitivity or selectivity - How does eLNA impact the receriver performancecriterion123
it describes
1. Why need external LNA ?
2. Why does poor linearity lead to poor sensitivity ?
3. For the eLNA gain, the more the better ?
4. Why can SAW filter improve linearity ?
System(board level) noise figure analysis and optimizationcriterion123
For sensitivity, what a system (board level) RF engineer can improve is only noise figure. This document describes that the noise figure concept you should know, and how to optimize it to improve sensitivity.
Sensitivity or selectivity - How does eLNA impact the receriver performancecriterion123
it describes
1. Why need external LNA ?
2. Why does poor linearity lead to poor sensitivity ?
3. For the eLNA gain, the more the better ?
4. Why can SAW filter improve linearity ?
System(board level) noise figure analysis and optimizationcriterion123
For sensitivity, what a system (board level) RF engineer can improve is only noise figure. This document describes that the noise figure concept you should know, and how to optimize it to improve sensitivity.
desence,sensitivity calculation with and without external LNA, Noise figure calculation with and without external LNA and IIP3 calculation with and without external LNA
Impact of Clipping and Filtering on Peak to Average Power Ratio of OFDM Systemijsrd.com
Orthogonal Frequency Division Multiplexing (OFDM) is an emerging field of research in the field of 4G broadband wireless communications due to its robustness against multipath fading and relatively simple implementation. Peak to Average Power Ratio (PAPR) is the limiting factor for an OFDM system as it consists of large number of independent subcarriers as a result of which the amplitude of such a signal can have high peak values which degrades the system performance. Such a signal when amplified by a Power Amplifier without processing results spectral regrowth and intermodulation among subcarrier. Hence this non linearity destroys the orthogonally of the OFDM signal and introduces out-of-band radiation and in band distortions causing significant performance degradation. The clipping and filtering method is analysed which is an efficient and simple method to reduce the PAPR. We have shown the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate.
desence,sensitivity calculation with and without external LNA, Noise figure calculation with and without external LNA and IIP3 calculation with and without external LNA
Impact of Clipping and Filtering on Peak to Average Power Ratio of OFDM Systemijsrd.com
Orthogonal Frequency Division Multiplexing (OFDM) is an emerging field of research in the field of 4G broadband wireless communications due to its robustness against multipath fading and relatively simple implementation. Peak to Average Power Ratio (PAPR) is the limiting factor for an OFDM system as it consists of large number of independent subcarriers as a result of which the amplitude of such a signal can have high peak values which degrades the system performance. Such a signal when amplified by a Power Amplifier without processing results spectral regrowth and intermodulation among subcarrier. Hence this non linearity destroys the orthogonally of the OFDM signal and introduces out-of-band radiation and in band distortions causing significant performance degradation. The clipping and filtering method is analysed which is an efficient and simple method to reduce the PAPR. We have shown the effects of clipping and filtering on the performance of OFDM, including the power spectral density, the crest factor, and the bit-error rate.
Low Peak to Average Power Ratio and High Spectral Efficiency Using Selective ...theijes
A low complexity peak to average power ratio (PAPR) reduction scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed. All pass filters technique used PAPR is reduction but small amount of reduction, So use Selective Mapping (SLM) technique reduce PAPR and SNR increases.
Comparative Analysis of PAPR Reduction Techniques in OFDM Using Precoding Tec...IJSRD
In this modern era, Orthogonal Frequency Division Multiplexing (OFDM) has been proved to be an explicit promising technique for wired and wireless systems because of its several advantages like high spectral efficiency, robustness against frequency selective fading, relatively simple receiver implementation etc. Besides having a number of advantages OFDM suffers from few disadvantages like high Peak to Average Power Ratio (PAPR), Intercarrier Interference (ICI), Intersymbol Interference (ISI) etc. These detrimental effects, if not compensated properly and timely, can result in system performance degradation. This paper mainly concentrates on reduction of PAPR.A comparisons have been made between various precoding techniques against conventional OFDM.
Comparative Analysis of PAPR Reduction Techniques in OFDM Using Precoding Tec...IJSRD
In this modern era, Orthogonal Frequency Division Multiplexing (OFDM) has been proved to be an explicit promising technique for wired and wireless systems because of its several advantages like high spectral efficiency, robustness against frequency selective fading, relatively simple receiver implementation etc. Besides having a number of advantages OFDM suffers from few disadvantages like high Peak to Average Power Ratio (PAPR), Intercarrier Interference (ICI), Intersymbol Interference (ISI) etc. These detrimental effects, if not compensated properly and timely, can result in system performance degradation. This paper mainly concentrates on reduction of PAPR.A comparisons have been made between various precoding techniques against conventional OFDM.
The peer-reviewed International Journal of Engineering Inventions (IJEI) is started with a mission to encourage contribution to research in Science and Technology. Encourage and motivate researchers in challenging areas of Sciences and Technology.
A Hybrid PAPR Reduction Scheme for OFDM System ijmnct
Orthogonal frequency division multiplexing (OFDM) i
s considered as most efficient technique for future
wireless communication systems due to its higher sp
ectral bandwidth efficiency, robustness to frequenc
y
selective fading channels, etc. However, the succes
sful implementation of the OFDM system necessitates
several difficulties. The biggest disadvantage to w
ork with OFDM system is its high peak-to-average po
wer
ratio PAPR leadsto severe inter carrier interferenc
e, out-of-band radiation, and poor bit error rate
performance due to the nonlinearity of the high pow
er amplifier. In this paper, a novel hybrid techniq
ue is
proposed to reduce PAPR further and comparison has
been done with conventional techniques as well.
Simulated results are presentedconfirm theoretical
results.MATLAB 7.5 is used to simulate the results
for system parametersconsidered.
Peak-to-Average Power Ratio Reduction in NC-OFDM based Cognitive Radio.CSCJournals
This paper presents a novel technique for reducing the peak-to-average power ratio (PAPR) in non-contiguous bands spectrum of Orthogonal Frequency Division Multiplexing (OFDM) based Cognitive Radio (CR). The proposed system exposed to carry the past channel information and the spectrum sensing to utilize the radio spectrum as well as achieving an appropriate PAPR reduction and maintaining end-to-end throughput performance by using a set of approaches in the current CR environment. The simulation results for PAPR reduction has shown that higher constellation modulation schemes are better compared to lower constellation modulation schemes.
Computationally Efficient Algorithm for Reducing PAPR in OFDM using Null Subc...idescitation
A new algorithm is proposed which is used with
existing null-data subcarrier switching method of Peak to
Average Power Ratio (PAPR) reduction in OFDM to lower the
computational complexity. This proposed algorithm is very
simple and achieves significant reduction in computational
overhead without sacrificing PAPR reduction capability of
null-data subcarrier switching method. The proposed
algorithm is compatible with the current commercial systems
and it can be used with other existing algorithms to reduce
the computational overhead further. The proposed algorithm
is very useful in delay sensitive services. The effectiveness of
the proposed algorithm is demonstrated by presenting
simulation results of PAPR and computational time
requirement.
Performance Evaluation of CE-OFDM in PLC ChannelCSCJournals
One major drawback associated with an OFDM system is that the transmitter’s output signal may have a high peak-to-average ratio (PAPR). High levels of PAR may be a limiting factor for power line communication (PLC) where regulatory bodies have fixed the maximum amount of transmit power. To overcome this problem, many approaches have been presented in the literature. One potential solution for reducing the peak-to-average power ratio (PAPR) in an OFDM system is to utilize a constant envelope OFDM (CE-OFDM) system. This paper describes a CE-OFDM based modem for Power Line Communications (PLC) over the low voltage distribution network. The impact of the electrical appliances on the signal transmission is investigated. The good performances of the BER have been checked by the simulation platform of real PLC channel using Matlab. Finally, CE-OFDM-CPM is compared with conventional OFDM under HomePlug AV.
International Journal of Engineering Research and Applications (IJERA) is a team of researchers not publication services or private publications running the journals for monetary benefits, we are association of scientists and academia who focus only on supporting authors who want to publish their work. The articles published in our journal can be accessed online, all the articles will be archived for real time access.
Our journal system primarily aims to bring out the research talent and the works done by sciaentists, academia, engineers, practitioners, scholars, post graduate students of engineering and science. This journal aims to cover the scientific research in a broader sense and not publishing a niche area of research facilitating researchers from various verticals to publish their papers. It is also aimed to provide a platform for the researchers to publish in a shorter of time, enabling them to continue further All articles published are freely available to scientific researchers in the Government agencies,educators and the general public. We are taking serious efforts to promote our journal across the globe in various ways, we are sure that our journal will act as a scientific platform for all researchers to publish their works online.
PAPR REDUCTION OF OFDM SIGNAL BY USING COMBINED HADAMARD AND MODIFIED MEU-LAW...IJCNCJournal
Orthogonal frequency division multiplexing (OFDM) is a technique which gives high quality of service (QOS) to the users by mitigating the fading signals as well as high data rates in multimedia services. However, the peak-to-average power ratio (PAPR) is a technical challenge that reduces the efficiency of RF power amplifiers. In this paper, we propose the combined Hadamard transform and modified meu-law companding transform method in order to lessen the effects of the peak-to-average power ratio of the
OFDM signal. Simulation results show that the proposed scheme reduces PAPR compared to other companding techniques as well as the Hadamard transform technique when used on its own.
A PAPR Reduction for OFDM Signals Based on Self-Adaptive Multipopulation DE a...IJECEIAES
One of major drawbacks of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR). A signal with high PAPR leads to nonlinear distortion caused mainly by power amplifiers in wireless transmitters. Partial transmit sequence (PTS) is one of the most attractive methods to reduce the PAPR in OFDM systems. It achieves considerable PAPR reduction without distortion, but it requires an exhaustive search over all the combinations of the given phase factors, which results in a computational complexity that increases exponentially with the number of partitions. For this optimization problem, we propose in this paper a suboptimal PTS method based on the self-adaptive multipopulation differential evolution algorithm (SAMDE). The self adaptation of control parameters and structured population, is able to obtain high quality solutions with low computational cost by evolving each sub-population of individuals over successive generations.
AN OVERVIEW OF PEAK-TO-AVERAGE POWER RATIO REDUCTION TECHNIQUES FOR OFDM SIGNALSijmnct
OFDM (Orthogonal Frequency Division Multiplexing) has been widely adopted for high data rate wireless
communication systems due to its advantages such as extraordinary spectral efficiency, robustness to
channel fading and better QoS (Quality of Service) performance for multiple users. However, some
challenging issues are still unresolved in OFDM systems. One of the issues is the high PAPR (peak-toaverage
power ratio), which results in nonlinearity in power amplifiers, and causes out of band radiation
and in band distortion. This paper reviews some conventional PAPR reduction techniques and their
modifications to achieve better PAPR performance. Advantages and disadvantages of each technique are
discussed in detail. And comparisons between different techniques are also presented. Finally, this paper
makes a prospect forecast about the direction for further researches in the area of PAPR reduction for
OFDM signals
Distributed Architecture of Subspace Clustering and RelatedPei-Che Chang
Distributed Architecture of Subspace Clustering and Related
Sparse Subspace Clustering
Low-Rank Representation
Least Squares Regression
Multiview Subspace Clustering
Probabilistic Matrix Factorization (PMF)
Bayesian Probabilistic Matrix Factorization (BPMF) using
Markov Chain Monte Carlo (MCMC)
BPMF using MCMC – Overall Model
BPMF using MCMC – Gibbs Sampling
Deterministic MIMO Channel Capacity
• CSI is Known to the Transmitter Side
• CSI is Not Available at the Transmitter Side
Channel Capacity of Random MIMO Channels
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
3. 3
OFDM have high PAPR → many subcarrier components are added via an IFFT operation.
Cons:
• Peak signal fall in the nonlinear region of power amplifier (PA) cause distortion.
• Degrading the efficiency of the PA in the transmitter.
• Decreases the SQNR (Signal-to-Quantization Noise Ratio) of ADC and DAC.
• Destroy the orthogonality of the different subcarriers and generate power leakage among the
subcarriers → ICI.
The PAPR problem is more important in the uplink since the efficiency of PA is critical due to the
limited battery power in a mobile terminal.
Root Cause Analysis
5. 5
Introduction to PAPR
nonlinear region can be described by IBO (Input Back-Off) or OBO (Output Back-Off).
nonlinear characteristic of HPA (High Power Amplifier), excited by a large input, causes the
out-of-band radiation that affects signals in adjacent bands, and in-band distortions that
result in rotation, attenuation, and offset on the received signal.
Input-output characteristic of an HPA.
8. 0 50 100 150 200 250 300 350
0
20
40
60
80
100
50
Class C
Class B
Class AB
Conduction angle (degree)
PADrainefficiency(%)
180
78.5
Class A
0Θ
0 0
0 0
0
sin
2 2sin cos
2 2
η
Θ − Θ
=
Θ Θ
− Θ
8
9. 假設, 傳遞到PA的總功率, Pdc+Pin 中的一部分被
消耗了, 產生了熱耗散+諧波(harmonic distortion)
或互調失真(IMD)形式所表現出來的Pdis.
( )
1
1
in dc out dis
out dc dis
in in
out in in
dc dc
P P P P
P P P
G
P P
P P P
PAE G
P P
+ = +
−
≡ = +
−
≡ = −
www.STADTAUS.com_C55_Lavrador_Efficiency_Linearity
9
如果要依賴於有限的電源, 沒有任何電子器件可以保持恒定的增益, 因而無法保持恒定的線
性度.
為了使PAE更高, 在同樣的輸出功率條件下, 系統需要從電源吸收較少的功率. 這便不可避免
地導致了更高的增益壓縮, 而這又會使得系統的頻譜效益降低.
這便是線性度-效率之間矛盾關係的基本原理, 同樣也可稱作為功率-頻譜效率的折衷.
10. Linearity technology - feedforward
1τ∆
2τ∆
/ /
A in err
B A in err
C B err
out A C in
V V G V
V V G V V G
V V G V
V V V V G
= +
= − =
= =
= − =
10
Pros: good stability.
Cons: Amplitude and phase should be exacted
matching so need delay line not easy to integrate.
11. Linearity technology - feedback
cos
cos( )
LO
LO
t
t
ω
ω θ+
1
1
out
f
in
V A
A
V AF F
= = ≈
+
if 1AF >>
Cons: Phase shift control
Stability
11
13. Linear amplification with Nonlinear Components (LINC)
1 2
1 0
2 0
1
0
( ) ( )cos[ ( )] ( ) ( )
1
( ) sin[ ( ) ( )]
2
1
( ) sin[ ( ) ( )]
2
( )
( ) sin
in c
c
c
v t a t t t v t v t
v t V t t t
v t V t t t
a t
t
V
ω ϕ
ω ϕ θ
ω ϕ θ
θ −
= + = +
= + +
= − + −
=
1 2
1
2
2 2
0
( ) ( )cos[ ( )] ( ) ( )
( ) ( )cos( ) ( )sin( )
( ) ( )cos( ) ( )sin( )
( ) ( ) / 2
( ) ( ) / 2
in c
I c Q c
I c Q c
I
Q
v t a t t t v t v t
v t v t t v t t
v t v t t v t t
v t a t
v t V a t
ω ϕ
ω ϕ ω ϕ
ω ϕ ω ϕ
= + = +
= + + +
= − + + +
=
= −
13
14. Envelope Elimination and Restoration (EE&R)
( ) ( )cos[ ( )]
envelope : ( )
phase : ( )
in cv t a t t t
a t
t
ω ϕ
ϕ
= + non-linear PA
a(t)
linear
PA
b(t)
0( ) cos[ ( )]
phase modulation
cb t b t tω ϕ= +
http://ww.radioliberty.org/document23.pdf14
17. 17
Peak-to-Mean Envelope Power Ratio (PMEPR)
PMEPR is the ratio between the maximum power and the average power for
the envelope of a baseband complex signal ( )s tɶ
Peak Envelope Power (PEP)
PEP represents the maximum power of a complex baseband signal ( )s tɶ
Peak-to-Average Power Ratio (PAPR)
PAPR is the ratio between the maximum power and the average power of the complex passband signal ( )s t
The above power characteristics can also be described in terms of their
magnitudes (not power) by defining the crest factor (CF) as
We are interested in finding
the probability that the signal
power is out of the linear
range of the HPA!!
18. OFDM PAPR ?
2
Crest factor peak
rms
x
C
x
PAPR C
= =
=
( )
/2 2
0
/2
0
1 1
sin 0.707
/ 2 2
1 2
sin 0.636
/ 2
rms peak peak peak
avg peak peak peak
V V d V V
V V d V V
π
π
θ θ
π
θ θ
π π
= = =
= = =
∫
∫
For sin wave:
18
19. 19
Fig. Block diagram of transmitter and receiver in an OFDM system.
(S/P)
Pulse
shaping
(S/P)
20. 20
Central limit theorem:
Input signals of N-point IFFT have the independent and finite magnitudes which are uniformly distributed for QPSK
and QAM, we can assume that the real and imaginary parts of the time-domain complex OFDM signal s(t) (after IFFT
at the transmitter) have asymptotically Gaussian distributions for a sufficiently large number of subcarriers.
→ amplitude of the OFDM signal s(t) follows a Rayleigh distribution.
we consider the following complementary CDF (CCDF):
• assumption that N samples are independent
and N is sufficiently large.
• assumption that N samples are independent
and N is sufficiently large.
Real, Imag follow (0, 1/2) Gaussian distributions
(均值均值均值均值, 方差方差方差方差σ2 )
21. 21
Sampled signal does not necessarily contain the maximum point of the original continuous-time signal.
It is difficult to derive the exact CDF for the oversampled signals and therefore, the following simplified CDF will
be used:
CCDFs of OFDM signals with N = 64, 128, 256, 512, and 1024.
N = 1024
N = 64
https://github.com/oklachumi/octave-in-communications/blob/master/plot_OFDM_CCDF.m
23. 23
Distribution of OFDM Signal
Characteristics of time-domain QPSK/OFDM signals: N = 8 and 16.
24. 24
Characteristics of time-domain QPSK/OFDM signals: N = 8 and 16.
Time-domain OFDM signals Magnitude distribution of OFDM signal
Probabilistic Analysis of Time-Domain OFDM Signals
https://github.com/oklachumi/octave-in-communications/blob/master/OFDM_signal_distribution.m
25. 25
PAPR and Oversampling
PAPR for x[n] is lower than that for x(t), because x[n] may not have all the peaks of x(t).
In practice, the PAPR for the continuous-time baseband signal can be measured only after implementing the
actual hardware, including digital-to-analog convertor (DAC).
Measurement of the PAPR for the continuous-time baseband signal is not straightforward.
x[n] can show almost the same PAPR as x(t) if it is L-times interpolated (oversampled) where L ≥ 4.
Block diagram of L-times interpolator.
Interpolation with L = 4 in the time domain. Interpolation with L = 4 in the frequency domain.
27. 27
PAPRs of Chu Sequence and IEEE 802.16e Preambles
PAPR characteristics of Chu sequence in the time domain.
https://github.com/oklachumi/octave-in-communications/blob/master/PAPR_of_Chu.m
28. 28
PAPRs of Chu Sequence and IEEE 802.16e Preambles
The values of PAPR with oversampling are just about 0.4 dB greater than those without oversampling.
These preambles are originally designed to have the low PAPR, since they are subject to power boosting in
practice.
PAPR characteristics of IEEE 802.11e preamble in the time domain.
https://github.com/oklachumi/octave-in-communications/blob/master/PAPR_of_preamble.m
29. 29
PAPR of the passband signal in front of HPA is generally larger than that of the
baseband signal after the RF filtering and other processing.
30. 30
Clipping and SQNR
Probabilistic distribution of the real part of a time-domain OFDM signal.
One simplest approach of reducing the PAPR is to
clip the amplitude of the signal to a fixed level.
The pseudo-maximum amplitude in this approach is
referred to as the clipping level and denoted by μ.
Reducing PAPR, the clipping approach helps improve
the signal-to-quantization noise ratio (SQNR) in
analog-to-digital conversion (ADC).
If the clipping level is low, the signal will suffer from
a clipping distortion while the PAPR and
quantization noise will decrease.
If the clipping level is high, a clipping distortion
decreases while it suffers from the PAPR and
quantization noise.
• This trade-off relationship between the clipping distortion and quantization noise
should be taken into consideration in selecting the clipping level and the number
of bits for quantization.
32. 32
PAPR Reduction Techniques
Classified into the different approaches: clipping technique, coding technique, probabilistic (scrambling) technique, adaptive
predistortion technique, and DFT-spreading technique.
1. The clipping technique employs clipping or nonlinear saturation around the peaks to reduce the PAPR.
Cons:
• in-band and out-of-band interferences while destroying the orthogonality among the subcarriers.
2. The coding technique is to select such codewords that minimize or reduce the PAPR.
Cons:
• bandwidth efficiency as the code rate is reduced.
• complexity to find the best codes and to store large lookup tables for encoding and decoding.
3. The probabilistic (scrambling) technique is to scramble an input data block of the OFDM symbols and transmit one of them with
the minimum PAPR so that the probability of incurring high PAPR can be reduced.
Cons:
• spectral efficiency decreases and the complexity increases as the number of subcarriers increases.
4. The adaptive predistortion technique can compensate the nonlinear effect of a high power amplifier (HPA) in OFDM systems.
Pons:
• cope with time variations of nonlinear HPA by automatically modifying the input constellation with the least hardware
requirement (RAM and memory lookup encoder).
5. The DFT-spreading technique is to spread the input signal with DFT, which can be subsequently taken into IFFT.
Pons:
• can reduce the PAPR of OFDM signal to the level of single-carrier transmission.
• particularly useful for mobile terminals in uplink transmission, and is known as the Single Carrier-FDMA (SC-FDMA), which
is adopted for uplink transmission in the 3GPP LTE.
34. ET Overview & Principle
• Maximizes the PA efficiency by operating the PA in compression for most envelope amplitudes.
• Envelope amplifier (for example, QET4100/QFE1100) provides a dynamic supply voltage.
Env amp
provides a dynamic
supply voltage
• CW sweeps of PA PAE versus Pout.
• Each colored line represents a different PA Vcc,
from 0.5 V to 3.7 V, in 0.2 V steps.
34
• Vcc track the envelope of RF signal.
Review…
35. PA Compression and PAE
CW PAE and Pout vs. Pin
PA PAE maximum occurs in the
compressed region.
(PAE drops rapidly with back-off)
35
This plot shows the CW PAE and Pout vs. Pin.
The PA PAE maximum occurs in the compressed region.
The PAE drops rapidly with back-off.
The PAE for high PAR waveforms drop.
Review…
36. ET Mode – (1) Digital Predistortion (DPD)
DPD compensates for RF chain nonlinearities.
• RF nonlinearity is dominated by the PA.
• Corrects for AM/AM and AM/PM nonlinear distortion.
Tx baseband signal has wider bandwidth due to DPD.
• Legacy SAW filters limit the systems ability for predistortion due to the sharp roll off at the band edges.
• Wideband SAW filters are being developed to cope with this issue.
Tx BB signal has
wider BW due to DPD
improve the close-in
linearity of a system
36
Review…
37. ET Mode – (2) Detroughing
Most Tx waveforms result in I-Q origin crossings.
• Cause ET envelope signal BW expansion and low PA supply voltages.
The solution is detroughing (envelope shaping).
• Detroughing of the envelope waveform reduces the envelope signal bandwidth, and also eliminates the
issue of low PA supply voltages.
After detroughing
• low PA supply voltages
• Sharp V cause BW expansion
I-Q origin crossings
Envelope signal BW expansion
Modem detroughing LUT:
• Enables flexible control over the detroughing (envelope shaping) function.
• Allows for precise Vcc versus VRF_IN trajectory control.
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After detroughing
reduces the envelope signal BW
就是用一種detroughing的技術, 讓他PA Vcc電壓限制在某點以上
Review…
38. ET Mode – (3) Time Alignment
The time alignment adjusts the envelope path delay to match the RF Tx path delay.
• The two paths are separated from modem and combined at PA.
• RF Tx path: modem → WTR → (Tx SAW) → PA.
• Envelope (Vcc) path: modem → QET4100 → PA.
modem → QET4100 → PA
modem → WTR → (Tx SAW) → PA
delay
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Review…
39. ET Mode – (4) Rx-band Noise into PRx LNA
ET system uses DPD to linearize the PA.
• Meet ACLR emissions.
• Predistortion BW limited by Tx system filters (Tx BB BW increased due to DPD).
• Outside predistortion BW, emissions met by inherent linearity of PA in the ET mode.
ET introduces new noise sources that can degrade LNA performance.
• There is potential Rx desense in ET mode due to additional noise sources.
1. Typical desense is ~ 0.25 dB (50 dB isolation duplexers).
2. Improved duplexers, recommendation is 55 dB isolation in the Rx band, Tx port to Rx port.
3. Good layout of buck/boost bypass capacitors placement and routing; isolate the Rx trace from the Tx trace as much as possible;
ground plane below QFE1100; DPx layout/grounding is critical; ground vias, etc can suppress RxBN.
4. Buck inductor selection is critical for the QET4100 ET RxBN performance. 5. ET PA matching, Rx band impedance short circuit.
solutions
delay
ACLR emission
experiments
39
Review…
40. 40
Clipping and Filtering
Limits the maximum of transmit signal to a pre-specified level.
Drawbacks:
• Clipping causes in-band distortion, resulting in BER performance degradation.
• Clipping causes out-of-band radiation, which imposes out-of-band interference
signals to adjacent channels.
• Filtering the clipped signal can reduce out-of-band radiation at the cost of peak
regrowth. The signal after filtering operation may exceed the clipping level
specified for the clipping operation.
Block diagram of a PAPR reduction scheme using clipping and filtering.
Define the clipping ratio (CR) as the clipping level
normalized by the RMS value σ of OFDM signal
or
in-band distorƟon ↓
out-of-band radiation ↓
Better BER
performance
41. 41
The performance of PAPR reduction schemes can be evaluated in the following three aspects:
• In-band ripple and out-of-band radiation that can be observed via the power spectral density (PSD).
• Distribution of the crest factor (CF) or PAPR, which is given by the corresponding CCDF.
• Coded and uncoded BER performance.
Parameters used for simulation of clipping and filtering.
42. 42
[ ]x m′ [ ]p
x m
https://github.com/oklachumi/octave-in-communications/blob/master/PDF_of_clipped_and_filtered_OFDM_signal.m