high performance digital predistortion for wideband rf power amplifiers
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High Performance Digital PredistortionFor Wideband RF Power Amplifiers
High Performance Digital PredistortionFor Wideband RF Power Amplifiers
From Concept to Implementation
Visit To CTVR, Trinity College Dublin, Ireland
Dr. Lei Guan
(lei.guan@ieee.org)
Visit To CTVR, Trinity College Dublin, Ireland
From Concept to Implementation
Verification
ConceptProblem
Digital
Scientific R&D Topic:Specific;Measurable;Achievable;Result-oriented;Time-limited.
/1915th August 2012 2 Dr. Lei Guan (lei.guan@ieee.org)
Simulation
System
Implementation
Digital Predistortion
VHDL
Why need for Power Amplifier (PA) ?
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
Mobile NetworkBase station
/1915th August 2012 3
PA: analogue circuit, converting DC power to added RF powerPA: analogue circuit, converting DC power to added RF power
Mobile Network
TransceiverPower Amplifier
• Wireless communication: communicate with anyone, at anywhere, at anytime;
• To perform long distance wireless transmission, base stations are required for communications signal relay;
• Power amplifiers are used to increase the power of signal.
• Wireless communication: communicate with anyone, at anywhere, at anytime;
• To perform long distance wireless transmission, base stations are required for communications signal relay;
• Power amplifiers are used to increase the power of signal.
Dr. Lei Guan (lei.guan@ieee.org)
Why need for Wideband PA ?
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 4
Wider bandwidth transceiver requiredWider bandwidth transceiver required
Higher data density modulation requiredHigher data density modulation required• To provide faster data transmission (Video call, on-line movie… )
• To provide better service to more users
• To provide faster data transmission (Video call, on-line movie… )
• To provide better service to more users
Dr. Lei Guan (lei.guan@ieee.org)
Why need for High-efficiency PA ?
Typical PA efficiency: 15~30%Typical PA efficiency: 15~30%From Vodafone
PA
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 5
• Economic: reduce wasted cost tosave €€€€;
• Green ICT: reduce wasted powerconsumption to save energy;
• Environmental: reduce CO2 tosave earth;
• Economic: reduce wasted cost tosave €€€€;
• Green ICT: reduce wasted powerconsumption to save energy;
• Environmental: reduce CO2 tosave earth;
High-efficiency PA requiredHigh-efficiency PA requiredFrom NSN
Dr. Lei Guan (lei.guan@ieee.org)
Linearity and Efficiency Compromise
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 6
PA
T-domain
F-domain
How to provide maximum PA efficiency with satisfactory linearity ?
How to provide maximum PA efficiency with satisfactory linearity ?
PA must be operated at linear region !PA must be operated at linear region !
Dr. Lei Guan (lei.guan@ieee.org)
Digital Predistortion (DPD)
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 7
• Extend linear operation region of power amplifiers
• Digital signal processing (Reliable and flexible)
• Standalone unit (Integrated and duplicable)
PA
Dr. Lei Guan (lei.guan@ieee.org)
DPD System Requirement
• Digital Predistorter (DPD):
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 8
• Digital Predistorter (DPD):
– Accurate behavioral models required to describe inverse behavior;
– Real-time processing/High speed hardware implementation required.
• Parameter Extraction / Model Extraction:
– Coefficients value initialization/ adaptation;
– Can be “slowly” updated, not necessarily real-time.
• Data forward and feedback path:
– High speed ADC and DAC required;
– Up-converter and down-converter required.
Dr. Lei Guan (lei.guan@ieee.org)
DPD Simulation System
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 9
• MATLAB/Simulink environment;
• To validate DPD idea/algorithm for genetic RF nonlinear system;
• Simplified system simulation, ideal DAC/ADC, Mod/Demod units;
• Rapid algorithm validation;
• Low cost and flexible;
• But not Physical test for PAs in real wireless systems.
Dr. Lei Guan (lei.guan@ieee.org)
DPD Simulation Results
AM/AM
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
Volterra model
Coefficients are linear with respect to input
/1915th August 2012 10
DPD model extraction
PSD
LS/LMS
Linear System ID
Dr. Lei Guan (lei.guan@ieee.org)
Direct DPD Implementation
Direct structure: A large number of complex multipliers are required, and this number increases dramatically when nonlinear order P and memory length M increase
Direct structure: A large number of complex multipliers are required, and this number increases dramatically when nonlinear order P and memory length M increase
1 1
2 22 2( 1) 2 *
2 1,1 2 1,20 0 1 1
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
P P
M Mk k
k kk i k i
u n g i x n x n i g i x n x n x n i
Volterra model:
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 11
Hardware Multiplier (HM) occupies a large area of silicon; dedicated signal processing units with limited number on chip, e.g., Xilinx Virtex-4 XC4SX35 ( Only 192 DSP48 units)
Hardware Multiplier (HM) occupies a large area of silicon; dedicated signal processing units with limited number on chip, e.g., Xilinx Virtex-4 XC4SX35 ( Only 192 DSP48 units)
Dr. Lei Guan (lei.guan@ieee.org)
Low-cost DPD Implementation
1. LUT-assisted Gain Indexing:Memory is much cheaper than hardware multipliers
2. TDM-based Multiplier Sharing:FPGA clock is faster than required data rate
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
1 1
2 22 2( 1) 2 *
2 1,1 2 1,20 0 1 1
( ) ( ) ( ) ( ) ( ) ( ) ( ) ( )
P P
M Mk k
k kk i k i
u n g i x n x n i g i x n x n x n i
Volterra model:
/1915th August 2012 12
[L. Guan, WO 2010/136114 A1]
Dr. Lei Guan (lei.guan@ieee.org)
DPD Validation Platform Design
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
• Practicability: Focus on Fundamental units• Flexibility: 2-Mode DPD (soft & Hard)Hardware (e.g., FPGA) + Software (e.g., Matlab)
• Expandability: Design each function independently
• Practicability: Focus on Fundamental units• Flexibility: 2-Mode DPD (soft & Hard)Hardware (e.g., FPGA) + Software (e.g., Matlab)
• Expandability: Design each function independently
/1915th August 2012 13
[L. Guan, et al., EI project report]
Dr. Lei Guan (lei.guan@ieee.org)
Matlab-based Graphic User Control Panel (PC)
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
Other necessary functions are required to get the whole system running properly, as shown in the diagram
/1915th August 2012 14
Graphic User Control Panel Background Layer of Control Panel
Dr. Lei Guan (lei.guan@ieee.org)
FPGA-based Core Logics (Baseband)
Clock Management Logics (Multi -region clocks)
Clock Management Logics (Multi -region clocks)
Data Interface Logics (UART, LVDS)
Data Interface Logics (UART, LVDS) Xilinx Virtex 5
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 15
User Defined Logics (DPD,…)User Defined Logics (DPD,…)
External ICs ConfigurationLogic (DAC,…)
External ICs ConfigurationLogic (DAC,…)
Mode:1. Soft-DPD2. Hard-DPD
Mode:1. Soft-DPD2. Hard-DPD
Dr. Lei Guan (lei.guan@ieee.org)
Typical Analog Front-end (RF)
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 16 Dr. Lei Guan (lei.guan@ieee.org)
Picture of the DPD Test Platform
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
Robust Validation Procedure:
1. FPGA -> EXP -> FPGA (Chip Loop);
2. PC -> FPGA ->PC (Digital Loop);
/1915th August 2012 17
3. ESG -> RF -> FPGA -> PC (RX);
4. PC -> FPGA -> RF ->PSA (TX);
5. PC -> FPGA -> RF -> FPGA -> PC (System loop);
Step1: Physical link validation;Step2: Core function validation;
Dr. Lei Guan (lei.guan@ieee.org)
DPD Linearization Performance
Problem -> Concept -> System -> Simulation -> Implementation -> Verification
/1915th August 2012 18
PA: Doherty PA;
Fc: 2.14 GHz;
Sig: 8-carrier UMTS (40 MHz);
ACPR (± 5MHz): (Required spectral mask: -45 dB)W/O DPD -25 dB;With DPD -57 dB;
EVM (%):W/O DPD 10.77%;With DPD 0.39%;
Dr. Lei Guan (lei.guan@ieee.org)
Q and A
• Basic introduction of Digital Predistortion;
• Include all the fundamental development procedure (From concept to implementation);
• Can be used to compensate for nonlinear distortion in other electronic systems (ADC, Echo
/19
distortion in other electronic systems (ADC, Echo cancellation…)
• Thanks for your attention !!
15th August 2012 19 Dr. Lei Guan (lei.guan@ieee.org)
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