doc IEEE 802 22 080111 r 4 October

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Spectral Mask Implications IEEE P 802. 22 Wireless RANs Date: 2008 -10 -13 Authors: Notice: This document has been prepared to assist IEEE 802. 22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802. 22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http: //standards. ieee. org/guides/bylaws/sb-bylaws. pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard. " Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair Carl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802. 22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee. org. > Submission 1 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Abstract • This updated presentation gives the results of an updated simulation for estimating the power spectral density (PSD) of the 802. 22 transmission • The previous simulation was a “quick and dirty” simulation. In particular, the previous simulation incorrectly aligned the PSD estimation window with the OFDM symbol edge, which gave an overly optimistic view of the 802. 22 PSD • This presentation describes the new simulator and provides simulation results Submission 2 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Outline 1. Description of the simulator 2. Simulated PSD estimate before the PA 3. Simulated PSD estimates after the PA, for various PA back-off values 4. Discussion on Next Steps Submission 3 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Description of the Simulator • Synthesize a sequence of OFDM symbols • Each OFDM symbol includes – – – Support for both QPSK and 16 QAM (random data) Cyclic prefix 802. 22 null tones Oversampling Eighth-order Butterworth filter • Non-linear PA model • Power Spectral density estimation Submission 4 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Simulator Block Diagram PSD Estimation FFT using Hanning Window OFDM Signal Generator With Oversampling (Baseband) Eighth-order Low-pass Filter fc = 4. 5 MHz Non-linear PA Model PSD Estimation FFT using Hanning Window Submission 5 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Eighth Order Butterworth LPF 3 MHz Submission • Oversampling by 8 x 6 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Non-Linear PA Model • The nonlinearity of the power amplifier (PA) distorts the OFDM spectrum • In this document the 802. 11 nonlinear PA model is used • This model was used in the evaluation of 802. 11 n proposals [3] and was originally used in modeling 802. 11 b [4]. • This same form of non-linearity is specified in the 802. 22 channel models document [5] Submission 7 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Non-Linear PA Model Asat Submission 8 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 1 -d. B Compression Point • The 1 -d. B compression point is the point at which the PA output is 1 d. B less than it would be in a perfectly linear amplifier • To ensure linear operation one must operate well below the 1 -d. B compression point • Back-off of X d. B on the output signal from the 1 d. B compression point Submission 9 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Spectral Estimation • • Capture a window of samples Multiply by a Hanning window Calculate PSD estimate using FFT Average PSD over multiple captured windows Submission 10 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Signal Simulation Parameters • 2 k OFDM symbol – – QPSK (Random data) Null tones (Guard bands and DC) 1/4 Cyclic Prefix Oversampling by 8 x • Signal consists of 100 OFDM symbols • Eighth-order Butterworth Filter with fc = 4. 5 MHz • Initially no PA PSD Estimation • • Window Size = 10 k Hanning window Averaged PSD over more than 50 windows Plot PSD over positive frequencies (symmetric) Submission 11 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 PSD of PA Input Signal Submission 12 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Simulations with PA Back-off • Added non-linear PA model to simulation • Adjusted PA input signal power to find the 1 d. B compression point • Ran simulations for three values of PA backoff, from the 1 -d. B compression point – 8 d. B Back-off – 10 d. B Back-off – 12 d. B Back-off • Plotted PSD of PA Output signal Submission 13 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 PSD of PA Input and PA Output for three values of PA Back-off Submission 14 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Spectral Mask • The draft [1] does not have a spectral mask • The 802. 22 draft [1] requires that the field strength outside the occupied channel is 4. 8 V/m, measured at 3 meters in a 120 k. Hz bandwidth • According to Gerald [2] this equates to a spectral mask of -100 d. Br outside the occupied channel Submission 15 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 Next Steps – Spectral Mask • There are several paths that the working group can take regarding the spectral mask 1. Add a spectral mask to the draft which is consistent with the current 802. 22 signal design 2. Modify the 802. 22 signal design to improve the PSD so that a improved spectral mask can be included in the draft • Which approach does the WG prefer? Submission 16 Steve Shellhammer, Qualcomm

doc. : IEEE 802. 22 -08/0111 r 4 October 2008 References 1. IEEE P 802. 22™/ DRAFTv 1. 0 Draft Standard for Wireless Regional Area Networks Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Policies and procedures for operation in the TV Bands, April 2008 2. Gerald Chouinard, Wireless Microphone Sensing, IEEE 802. 22 -07/530 r 0, November 2007 3. Adrian P Stephens, IEEE 802. 11 TGn Comparison Criteria, IEEE 802. 11 -03/814 r 19, March 2004 4. Mark Webster, Suggested PA Model for 802. 11 HRb, IEEE 802. 11 -00/294 r 0, September 2000 5. Eli Sofer and Gerald Chouinard, WRAN Channel Modeling, IEEE 802. 22 -05/55 r 7, August 2005 Submission 17 Steve Shellhammer, Qualcomm