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60 GHz Impairments Modeling

60 GHz Impairments Modeling. Authors:. Date: 2009-11-17. Outline. PA non-linearities (distortion) modeling PA Output Backoff (OBO) Phase noise modeling Carrier frequency offset and symbol clock modeling I/Q Imbalance modeling. PA Non-Linearities Modeling (1).

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60 GHz Impairments Modeling

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  1. 60 GHz Impairments Modeling Authors: Date: 2009-11-17 Vinko Erceg, Broadcom

  2. Outline • PA non-linearities (distortion) modeling • PA Output Backoff (OBO) • Phase noise modeling • Carrier frequency offset and symbol clock modeling • I/Q Imbalance modeling Vinko Erceg, Broadcom

  3. PA Non-Linearities Modeling (1) • Input signal x(t) to an amplifier produces output singnal y(t): Vinko Erceg, Broadcom

  4. PA Non-Linearities Modeling (2) • Popular approaches to model G and Y are: • Saleh Model [1] • Both amplitude and phase distortion are modeled • This model was originally developed for the Traveling Wave Tube Amplifiers (TWTA) • For some parameter settings output power decreases as input power increases • May be used for some Solid State Power Amplifier (SSPA) applications • Rapp model [2] • Originally developed to model only amplitude distortion • Suitable for SSPA modeling • Modified Rapp Model [3,5] • Phase distortion modeling was added • Suitable for SSPA modeling • Ghorbani model [4] • Both amplitude and phase distortion is modeled • Suitable for SSPA modeling Vinko Erceg, Broadcom

  5. Ghorbani Model • Both amplitude and phase distortions are modeled by 4 parameters: Vinko Erceg, Broadcom

  6. Rapp AM-AM Model • Amplitude distortion (AM-AM) in Rapp model is modeled as: Vinko Erceg, Broadcom

  7. Modified Rapp AM-PM Model • See reference [3] for modified Rapp model that includes also phase distortion modeling • Phase distortion (AM-PM) may be also modeled as: • The above equation is used for our modeling purposes Vinko Erceg, Broadcom

  8. 802.11n PA Distortion Model [7] Example Note: AM-PM is not modeled Vinko Erceg, Broadcom

  9. GaAs PA Model (1) • GaAs PA Model • In [5], a 802.15.3c PA distortion model was proposed based on the GaAs pHEMT 60GHz HPA measurements from NEC • The NEC GaAs PA characteristics seem to have similar trend to other published/measured amplifier characteristics in this class • Characteristic AM-AM and AM-PM curves • Modified Rapp or Ghorbani models may be used for fitting the AM-AM and AM-PM experimental data points • We use modified Rapp model • Least squares fitting function • Voltage is rms • Highest voltage AM-PM point was not included in the modeling (does not follow trend) Vinko Erceg, Broadcom

  10. GaAs PA Model (2) Vinko Erceg, Broadcom

  11. GaAs PA Model (3) Vinko Erceg, Broadcom

  12. GaAs PA Model (4) • Modified Rapp model parameters for NEC GaAs PA • AM-AM parameters • g = 19 • Asat = 1.4 • s = 0.81 • AM-PM parameters • a = - 48000 • b = 0.123 • q1 = 3.8 • q2 = 3.7 Vinko Erceg, Broadcom

  13. CMOS PA Model (1) • We use the measured data from a 65 nm CMOS 60 GHz PA in reference [6] • Modified Rapp or Ghorbani models may be used for fitting the AM-AM and AM-PM experimental data points • We use modified Rapp model • Least squares fitting function • Voltage is rms • AM-PM response was normalized so that the first point has Phase = 0o Vinko Erceg, Broadcom

  14. CMOS PA Model (2) Vinko Erceg, Broadcom

  15. CMOS PA Model (3) Vinko Erceg, Broadcom

  16. CMOS PA Model (4) • Modified Rapp parameters for CMOS PA • AM-AM parameters • g = 5 • Asat = 0.6 • s = 0.71 • AM-PM parameters • a = 2560 • b = 0.114 • q1 = 2.4 • q2 = 2.3 Vinko Erceg, Broadcom

  17. PA Output Backoff (1) • PA Output Backoff (OBO) may be defined as: where P is either PA saturation point or 1 dB PA compression point • OBO is related to: • Meeting spectrum mask requirements • Increasing modulation accuracy (reducing EVM) • Reducing Adjacent Channel Interference (ACI) Vinko Erceg, Broadcom

  18. PA Output Backoff (2) • OBO values for OFDM system reported in [9-11] relative to the 1 dB PA compression point are approximately 6 dB for 64 QAM modulation with R = ¾ coding • OBO value for OFDM system reported in [10] relative to the PA saturation point is approximately 9 dB for 64 QAM modulation with R = ¾ coding • OBO values for OFDM system reported in [11] relative to the 1 dB PA compression point are approximately 4.5 dB for 16 QAM modulation with R = ¾ coding (performance degradation of 1.5 dB) • Theoretical OBO value for Single Carrier (SC) GMSK modulation is 0 dB • OBOSC_GMSK = 0.5 dB may be used Vinko Erceg, Broadcom

  19. PA Output Backoff (3) OBO Requirement Spectrum Mask Requirements OBO (dB) Mod. Accuracy Requirements Modulation Accuracy (dB) EVM Vinko Erceg, Broadcom

  20. Phase Noise Model (1) • Phase noise may be reasonably modeled by a two pole – one zero model • We propose the following parameters of the model: • PSD(0) = -80 dBc/Hz • Pole frequency fp1 = 0.75 MHz • Pole frequency fp2 = 2 MHz • Zero frequency fz = 100 MHz • r1 = 3.7; r2 = 1.65; r3 = 2.05 • PSD(infinity) = -150 dBc/Hz Vinko Erceg, Broadcom

  21. Phase Noise Model (2) Vinko Erceg, Broadcom

  22. Frequency Offset/Symbol Clock Accuracy • Symbol clock frequency tolerance in most systems is specified at +/- 20 ppm • Reasonable cost/performance tradeoff • Frequency offset of –13.675 ppm at the receiver, relative to the transmitter may be used [7] • The symbol clock of the same relative offset as the carrier frequency offset may be used Vinko Erceg, Broadcom

  23. I/Q Imbalance Modeling (1) • Following model may be used for I/Q imbalance modeling [8]: where y(t) is the ideal complex transmit signal, yd(t) is the distorted complex signal, and distortion coefficients are given as where θ and α are phase and gain imbalances, respectively Vinko Erceg, Broadcom

  24. I/Q Imbalance Modeling (2) Vinko Erceg, Broadcom

  25. I/Q Imbalance Modeling (3) • We propose that including I/Q imbalance in the simulations be optional • Slides presented here regarding I/Q imbalance may serve as a reference Vinko Erceg, Broadcom

  26. Conclusion • We propose the following impairments/parameters to be included in the simulations: • PA distortion • OBO • Phase noise • Frequency/Symbol Clock offset • We propose that inclusion of the I/Q imbalance impairment is optional Vinko Erceg, Broadcom

  27. References • [1] A.A.M. Saleh, "Frequency-independent and frequency-dependent nonlinear models of TWT amplifiers," IEEE Trans. Communications, vol. COM-29, November 1981, pp.1715-1720. • [2] C. Rapp, "Effects of HPA-Nonlinearity on a 4-DPSK/OFDM-Signal for a Digital Sound Broadcasting System", in Proceedings of the Second European Conference on Satellite Communications, Liege, Belgium, Oct. 22-24, 1991, pp. 179-184. • [3] M. Honkanen and Sven-Gustav Haggman, “New Aspects on Nonlinear Power Amplifier Modeling in Radio Communication System Simulations”, Proc. IEEE Int. Symp. On Personal, Indoor, and Mobile Comm, PIMRC ’97, Helsinki, Finland, Sep.1-4, 1997, pp. 844-848. • [4] A. Ghorbani, and M. Sheikhan, “The effect of Solid State Power Amplifiers (SSPAs) Nonlinearities on MPSK and M-QAM Signal Transmission”, Sixth Int'l Conference on Digital Processing of Signals in Comm., 1991, pp. 193-197. • [5] IEEE Document 15-06-0477-01-003c-rf-impairment-models-60ghz-band-sysphy-simulation.pdf. • [6] Mikko Varonen, et. al. “Millimeter-Wave Amplifiers in 65-nm CMOS”. ESSCIRC 2007. 11-13 Sep. 2007. pp. 280-283. • [7] IEEE Document 11-03-0814-31-000n-comparison-criteria.doc. • [8] Alireza Tarighat,and Ali H. Sayed, “Joint Compensation of Transmitter and Receiver Impairments in OFDM Systems,” IEEE Transactions on Wireless Communications, VOL. 6, NO. 1, January 2007, pp. 240-247. Vinko Erceg, Broadcom

  28. References • [9] Yongwang Ding and Ramesh Harjani, “A High-Efficiency CMOS +22-dBm Linear Power Amplifier,” IEEE Journal of Solid-State Circuits, VOL. 40, NO. 9, September 2005, pp. 1895-1900. • [10] Mostafa Elmala, Jeyanandh Paramesh, and Krishnamurthy Soumyanath, “A 90-nm CMOS Doherty Power Amplifier With Minimum AM-PM Distortion,” IEEE Journal of Solid-State Circuits, VOL. 41, NO. 6, June 2006, pp. 1323-1332. • [11] Mathias Pauli, Udo Wachsmann, Magnus Sundelin, and Peter Schramm, “Transmitter Impairments in OFDM-Based Wireless LAN,” Vehicular Technology Conference, 53rd VTC 2001 Spring, VOL 1,  6-9 May 2001, pp. 692 – 696. Vinko Erceg, Broadcom

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