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Doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 1 TGT Power and EVM measurements Notice: This document has been prepared to.

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Presentation on theme: "Doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 1 TGT Power and EVM measurements Notice: This document has been prepared to."— Presentation transcript:

1 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 1 TGT Power and EVM measurements Notice: This document has been prepared to assist IEEE 802.11. 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 802.11. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures, 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 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 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: Sept 20, 2005 Authors:

2 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 2 Abstract This document introduces the description of transmit power measurement and Transmit EVM measurements in Conductive Test Environment as a part of Recommended Practice for the Evaluation of 802.11 Wireless Performance. We are seeking to get feedback from TGT group on “work under progress” in this direction.

3 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 3 Summary Purpose Test Equipment Transmit power measurement Transmit EVM measurement Conclusion

4 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 4 Purpose of Power and EVM measurements Provide calibrated Tx level which is required for many tests. –for example, TPT vs. Attenuation requires the knowledge of Tx power to correctly correlate the TPT to the Rx signal level. Provide TX EVM which can effect TPT performance tests. –for example, TPT can degrade when TX EVM is low.

5 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 5 Main Test Equipment DUT – any wireless 802.11 device (AP or Client) that includes relevant SW running on the specific platform WLCP (WireLess CounterPart) - reference AP or a reference Client. Optional Shielded enclosure for DUTs and WLCPs in order to isolate from extraneous signals –Usually not required since the measured signal is much stronger than any possible interferer. It is commonly used with other tests that requires shielding. Cables –RF-cables – connected to antenna connectors. –Wired LAN cables –Control cables Attenuators – to close the RF link.

6 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 6 Main Test Equipment (cont.) Power Meter Device – to measure RF signal power per packet. Alternative options will be presented in this document. Calibrated combiners, splitters and couplers – to handle different RF path, including antennas entries. Wired Traffic Generator to generate data traffic from DUT to WLCP on top of layer 2. Optional - Wired Traffic Analyzer to gather delivered data payload over time through wired interface on top of layer 2.

7 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 7 Main Test Equipment (cont.) Test controller Includes the following capabilities, likely automated and controlled by dedicated SW: –The ability to control TX rates and TX power of DUT –The ability to control power meter. –The ability to control Wired Traffic Generator. –Optional - The ability to control Wired Traffic Analyzer –Optional - The ability to control attenuators

8 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 8 Important Notes The power measurement and EVM can be performed on any output port of any 802.11 component in the network. It is not required to have continuous transmission. The power measuring techniques presented later should have triggering mechanism that starts measuring the power only when the signal ramps and stops when there is no signal, so that duty cycle averaging won’t effect the measurement.

9 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 9 TX Power measurement techniques for WLAN

10 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 10 TX Power measurement techniques for WLAN Power meter approach Spectrum Analyzer approach extracted from doc doc.: IEEE 802.11-04/0935r4 VSA (Receiver) approach

11 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 11 Spectrum Analyzer approach extracted from doc doc.: IEEE 802.11-04/0935r4 -

12 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 12 VSA approach

13 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 13 TX Power Test setup

14 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 14 VSA approach What is measured. How it is measured. Freq domain measurement –Integration of spectral density over BW– recommended. Time domain measurement – not recommended, sensitive to window size errors.

15 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 15 Test procedure example Set the spectrum window in the VSA at the center of the channel. With span wider than the channel BW. Set the power measurement boundaries +/-BW/2 around the center. Set the Receiver range to be linear (for the expected TX power). Coupling AC 50ohm Trigger on IF pos slop Resolution Bandwidth = 23.87kHz Windowing type Flat top. Time 90% overlap with average off. Synchronize on channel estimation Sequence Demodulation (DSSS/CCK/OFDM) Subcarrier select all, spacing 312.5Khz, Symbol timing adjust -3.125%

16 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 16 Calibration TBD

17 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 17 EVM measurements techniques for WLAN

18 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 18 EVM Overview Background EVM IEEE minimal performance specification – OFDM example. EVM Test setup Block diagram EVM test definition from IEEE 802.11 clause 17.3.9.7 EVM Test EVM test procedure Calibration Results Example

19 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 19 EVM (OFDM) 17.3.9.6.3 Transmitter constellation error The relative constellation RMS error, averaged over subcarriers, OFDM frames, and packets, shall not exceed a data-rate dependent value according to Table 90. Table 90—Allowed relative constellation error versus data rate

20 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 20 TX EVM Test setup

21 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 21 17.3.9.7 Transmit modulation accuracy test The sampled signal shall be processed in a manner similar to an actual receiver, according to the following steps, or an equivalent procedure: a) Start of frame shall be detected. b) Transition from short sequences to channel estimation sequences shall be detected, and fine timing (with one sample resolution) shall be established. c) Coarse and fine frequency offsets shall be estimated. d) The packet shall be derotated according to estimated frequency offset. e) The complex channel response coefficients shall be estimated for each of the subcarriers. f) For each of the data OFDM symbols: transform the symbol into subcarrier received values, estimate the phase from the pilot subcarriers, derotate the subcarrier values according to estimated phase, and divide each subcarrier value with a complex estimated channel response coefficient. g) For each data-carrying subcarrier, find the closest constellation point and compute the Euclidean distance from it. h) Compute the RMS average of all errors in a packet. It is given by: (28) where LP is the length of the packet; Nf is the number of frames for the measurement; (I0(i,j,k), Q0(i,j,k)) denotes the ideal symbol point of the ith frame, jth OFDM symbol of the frame, kth subcarrier of the OFDM symbol in the complex plane; (I(i,j,k), Q(i,j,k)) denotes the observed point of the ith frame, jth OFDM symbol of the frame, kth subcarrier of the OFDM symbol in the complex plane (see Figure 121); P0 is the average power of the constellation. The vector error on a phase plane is shown in Figure 121. The test shall be performed over at least 20 frames (Nf), and the RMS average shall be taken. The packets under test shall be at least 16 OFDM symbols long. Random data shall be used for the symbols.

22 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 22 Equation 28 and figure 121

23 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 23 EVM test procedure example Set the spectrum window in the VSA at the center of the channel. With span wider than the channel BW. Set the power measurement boundaries +/-BW/2 around the center. Set the Receiver range to be linear (for the expected TX power). Coupling AC 50ohm Trigger on IF positive slop Resolution Bandwidth = 23.87kHz Windowing type Flat top. Time 90% overlap with average off. Synchronize on channel estimation Sequence Demodulation (DSSS/CCK/OFDM) I/Q normalize Pilot Track Phase & Timing Equalizer training on channel estimation sequence only Subcarrier select all, Spacing 312.5Khz, Symbol timing adjust -3.125%

24 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 24 Calibration TBD

25 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 25 VSA Approach Results Example

26 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 26 Conclusions These are Important secondary metrics. Tx power is required in most tests in order to get correct Signal strength in different location in the Link. EVM results can help analyze TPT anomalies. –It is important to verify good TX EVM when testing RX performance of the counterpart. The proposed methodology is applicable for testing in a full system.

27 doc.: IEEE 802.11-05/1198r0 Submission Nov 2005 Uriel Lemberger, IntelSlide 27 References [1] IEEE 802.11-1999, P802.11a -1999, P802.11b -1999 [2] IEEE 802.11-05/0661r0 TGT Conductive Test Environment and Metrics. Alexander Tolpin. [3]P802.11.2-D0.4 - Draft Recommended Practice for the Evaluation of 802.11 Wireless Performance

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