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Power Amplifier for Wireless Links: System Level Models

Power Amplifier for Wireless Links: System Level Models. Daniel Bustos Marco Pirola Giovanni Ghione Simona Donati Dipartimento di Elettronica Politecnico di Torino Microwave & RF Electronics Group. Outline. Behavioral nonlinear model motivations; The implemented models:

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Power Amplifier for Wireless Links: System Level Models

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  1. Power Amplifier for Wireless Links:System Level Models Daniel Bustos Marco Pirola Giovanni Ghione Simona Donati Dipartimento di Elettronica Politecnico di Torino Microwave & RF Electronics Group

  2. Outline • Behavioral nonlinear model motivations; • The implemented models: • The cooperation between Polito and Chalmers Units; • Simulatotion Tools; • Model and extraction procedure description; • Some simulation examples: (IM3, BER, …); • A case study: a 812.11a WLAN Power amplifier: • Model the PHEMT ATF-54143 Transistor; • Circuit level and system level simulations; • Model behaviour comparison (VSS VS IT++); • Conclusions and future works;

  3. Envelope or base-band model I • Oriented to high level (system) simulations (eye diagram, BER) rather than circuit ones; • Identified through input/output system observation-> intrinsically behavioural (black-box); • System level modelling is oriented to the prediction of the system envelope behaviour; • System evaluation through RF simulation possible but: • simulation circuit level far from the system level layer; • system level model identification directly focused on system; • system level simulation unbearably slow.

  4. Envelope or base-band model II y(t) x(t)

  5. Motivations I • The models used to simulate the PA at circuit level are capable to represent nonlinearities with a high degree of accuracy • Memory effects in principle included, although difficulties are related to the model extraction (from measured data or physics-based simulations) and to the simulation techniques used (HB); • System level simulation unsuitable for fast simulation in presence of complex modulation scheme-; • Classical system level models include nonlinearities in a too simplistic way -> lost of accuracy for complex modulation schemes; • More sofisticated models: • need complex identification procedures; • increase the computation time; Find a model trade off between accuracy, simple model parameter identification, reasonable computation time

  6. Motivation II • Chalmers unit develops and maintains a system level simulator (IT++) adopted within the NEWCOM network; • IT++ is able to implement a complete communication links at system level; • IT++ did not account for the effects of PA non idealities on the system level performances; • Polito units has a consolidated activities on the PA field at circuit and system level (e.g. activities within TARGET network). Implement within IT++ the Polito NL models

  7. Circuit Level – System Level Link

  8. Simulation framework • Circuit level simulations carried out with AWR MWOFFICE, used as the reference model virtual; • System level identification through practicable non-linear experimental data • Automated extraction implemented at the moment within Matlab; • System level simulation: • AWR VSS automatically extracted from MWO; • Classical AM-AM AM-PM model implemented in IT++; • Advanced model with memory implemented in IT++; • Comparisons on a case study power amplifier for WLAN 802.11a application;

  9. AM -AM AM -AM AM - PM AM - PM W(k) y(k) Linear Part with Memory Static Nonlinear Part The implemented models Classical AM-AM, AM-PM y(k) U(k) Static Nonlinear Part Advanced Wiener Scheme Model U(k)

  10. Memory Model Extraction • The linear part of the model extracted from two tone excitation varying the tone spacing; • FIR filter implemented through ARX approach; • Static nonlinear part, extracted for single and two tones excitation as a function of tone power; • Non linear static behaviour approximated with a suitable degree polynomial

  11. Case of study: A 802.11a WLAN Driver Amplifier using PHEMT ATF-54143 Transistor • The frequency range includes USA U-NII lower band 5.125 – 5.250 GHz. • MWO tools used to simulate a circuit implementation. • For the nonlinear analysis, a harmonic – balanced (HB) simulation was used • The Non-linear transistor model used in the simulation is based on the work of Curtice (Advanced Curtice2 Model)

  12. MWO Diagram of Driver Amplifier

  13. Example: WLAN 802.11a Driver Amplifier Single Tone AM/AM at 5 GHz

  14. Single Tone AM/PM at 5 GHz

  15. Two-tone simulation at 0 dBm input power

  16. Two-tone simulation at 0 dBm input power

  17. Two-tone simulation at 0 dBm input power

  18. Two-tone simulation at 0 dBm input power

  19. , dB OFDM Mod. scheme: BER simulation at several PA compression levels

  20. Conclusions • Collaboration with Chalmers Univeristy through PhD student exchange (maybe to be renewed); • Methodology for extraction of system oriented models from measured data or standard HB (multitone) circuit simulations; • Model validation on virtual experimental data; • Extractor implemented in Matlab; • Model implemented within IT++; • Future possible developments: • model validation on true experimental non linear data; • further model refinements and improvements (e.g. three box model) • testing and implementation of other models (e.g. neural, volterra/wiener series appproach, …)

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