1. 60 GHz Impairments Modeling
Month Year
doc.: IEEE /xxxxr0
November 2009
60 GHz Impairments Modeling
Date:
Authors:
Name
Affiliations
Address
Phone
Vinko Erceg
Broadcom
San Diego
Murat Messe
Alireza Tarighat
Michael Boers
Jason Trachewsky
Changsoon Choi
IHP
Vinko Erceg, Broadcom
Vinko Erceg, Broadcom

2. November 2009
Revision History
Rev1: Phase Noise and CMOS PA AM-AM model parameters were updated
Vinko Erceg, Broadcom

3. Outline PA non-linearities (distortion) modeling
November 2009
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

4. PA Non-Linearities Modeling (1)
November 2009
PA Non-Linearities Modeling (1)
Input signal x(t) to an amplifier produces output signal y(t):
Vinko Erceg, Broadcom

5. PA Non-Linearities Modeling (2)
November 2009
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
Ghorbani model [4]
Both amplitude and phase distortion is modeled
Vinko Erceg, Broadcom

6. November 2009
Ghorbani Model
Both amplitude and phase distortions are modeled by 4 parameters:
Vinko Erceg, Broadcom

7. November 2009
Rapp AM-AM Model
Amplitude distortion (AM-AM) in Rapp model is modeled as:
Vinko Erceg, Broadcom

8. Modified Rapp AM-PM Model
November 2009
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

9. 802.11n PA Distortion Model [7] Example
November 2009
802.11n PA Distortion Model [7] Example
IM1
PA non-linearity
Simulation should be run at an oversampling rate of at least 4x. Use RAPP power amplifier model as specified in document 00/294 with p = 3. Calculate backoff as the output power backoff from full saturation:
PA Backoff = ­10 log10(Average TX Power/Psat).
Total TX power shall be limited to no more than 17 dBm.
Disclose: (a) EIRP and how it was calculated, (b) PA Backoff, and (c) Psat per PA.
Note: the intent of this IM is to allow different proposals to choose different output power operating points.
Note: the value Psat = 25dBm is recommended.
Note: AM-PM is not modeled
Vinko Erceg, Broadcom

10. GaAs PA Model (1) GaAs PA Model
November 2009
GaAs PA Model (1)
GaAs PA Model
In [5], a c 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

11. November 2009
GaAs PA Model (2)
Vinko Erceg, Broadcom

12. November 2009
GaAs PA Model (3)
Vinko Erceg, Broadcom

13. GaAs PA Model (4) Modified Rapp model parameters for NEC GaAs PA
November 2009
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 =
b = 0.123
q1 = 3.8
q2 = 3.7
Vinko Erceg, Broadcom

14. November 2009
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

15. November 2009
CMOS PA Model (2)
Vinko Erceg, Broadcom

16. November 2009
CMOS PA Model (3)
Vinko Erceg, Broadcom

17. CMOS PA Model (4) Modified Rapp parameters for CMOS PA
November 2009
CMOS PA Model (4)
Modified Rapp parameters for CMOS PA
AM-AM parameters
g = 4.65
Asat = 0.58
s = 0.81
AM-PM parameters
a = 2560
b = 0.114
q1 = 2.4
q2 = 2.3
Vinko Erceg, Broadcom

18. PA Output Backoff (1) PA Output Backoff (OBO) may be defined as:
November 2009
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

19. November 2009
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

20. Modulation Accuracy (dB)
November 2009
PA Output Backoff (3)
OBO Requirement
Spectrum Mask
Requirements
OBO (dB)
Mod. Accuracy
Requirements
Modulation Accuracy (dB)
EVM
Vinko Erceg, Broadcom

21. November 2009
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) = -90 dBc/Hz
Pole frequency fp = 1 MHz
Zero frequency fz = 100 MHz
PSD(infinity) = -130 dBc/Hz
Vinko Erceg, Broadcom

22. November 2009
Phase Noise Model (2)
Vinko Erceg, Broadcom

23. Frequency Offset/Symbol Clock Accuracy
November 2009
Frequency Offset/Symbol Clock Accuracy
Symbol clock frequency tolerance in most systems is specified at +/- 20 ppm
Reasonable cost/performance tradeoff
Frequency offset of – 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

24. I/Q Imbalance Modeling (1)
November 2009
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

25. I/Q Imbalance Modeling (2)
November 2009
I/Q Imbalance Modeling (2)
Tx EVM (-dB)
Vinko Erceg, Broadcom

26. I/Q Imbalance Modeling (3)
November 2009
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

27. November 2009
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

28. November 2009
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
[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 , 1991, pp
[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
[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
[5] IEEE Document c-rf-impairment-models-60ghz-band-sysphy-simulation.pdf.
[6] Mikko Varonen, et. al. “Millimeter-Wave Amplifiers in 65-nm CMOS”. ESSCIRC Sep pp
[7] IEEE Document n-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
Vinko Erceg, Broadcom

29. November 2009
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
[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
[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