1. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 1 The Need for TRP and TIS in 802.11.2 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: 2006-9-20 Authors:

2. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 2 Abstract This presentation discusses the need for the test capabilities provided by the TRP and TIS test metrics in document 11-06-0906-00-000t, “TRP and TIS Performance Metrics Proposed Text”. It also shows how the measurements possible with the COAT methodology relate to TRP/TIS testing.

3. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 3 Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) are industry standard methods for determining the RF performance of wireless devices. They represent traceable quantitative metrics that completely represent the RF performance of a device at the PHY layer, including the antenna(s), the DUT body, and the effect of objects typically found in the near field of the DUT. These metrics provide critical link budget information necessary for good network design. Introduction

4. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 4 Several industry organizations (CTIA, Wi-Fi Alliance) already use TRP/TIS metrics. Wireless service providers use this information to qualify products before they’re allowed on their network. The test plans used by these organizations can only be used by members of those organizations. We need a public IEEE document that provides the same type of test metrics without the burden of joining an industry organization. Introduction

5. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 5 An error of a dB or two is costly to network layout. In free-space propagation, losing 1 dB of signal in a link budget increases the number of required APs by 25%! Propagation over ground tends to reinforce the direct path, so in that case a 2 dB reduction in the link budget will cause the same 25% increase. Indoor LOS/NLOS environments will have more complicated field distributions, but similar network guidelines apply. Network Design Issues

6. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 6 An understanding of the RF performance of the APs, as well as that of the target clients, is critical to good network design. Once a network is designed, it’s even more costly to add APs to try to fill in gaps caused by poorly performing clients. Thus, it’s critical that a certain level of RF performance can be guaranteed. We need test techniques that give useful quantitative RF performance metrics. Network Design Issues

7. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 7 A common assumption in the wireless industry is that the radiation pattern of a device is defined by the antenna pattern. –i.e. Dipole antenna = dipole radiation pattern –OTA performance = conducted DUT + antenna gain The Antenna Assumption + ? =

8. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 8 While this may hold for remote antennas or for electrically small devices, electrically large devices (laptops, etc.) generate radiation patterns that rarely match that of the antenna by itself. The Antenna Assumption =/

9. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 9 Even if the antenna is tested passively within the body of the DUT so that the effect of the rest of the DUT on the pattern is accounted for, there are other issues: The Antenna Assumption –Cabled testing of DUT assumes antenna has a 50  impedance. Mismatches between radio circuitry and actual antenna impedance can cause non-linear behavior in radio circuitry. –Near field coupling to objects typically found near DUT (tables, walls, hands, heads) can change both antenna impedance and radiation pattern. –Platform noise from electronics can interfere with the receiver through the antenna (and vice-versa). –Cable effects can still distort pattern.

10. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 10 The current COAT methodology is essentially a substitution measurement. –The gain of a reference antenna is used to determine RF path loss. –DUT is substituted for the reference antenna and path loss While the method can produce highly repeatable results, there are inherent assumptions made about the radiation pattern of the DUT. COAT methodology requires orienting DUT with antenna in exact position and polarization of reference antenna. COAT Methodology

11. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 11 Assumes that orientation/position of antenna is known. Even if it is known, that may not be enough to achieve the intended results. Testing in only one orientation does not represent the expected behavior of the DUT if the pattern varies as a function of orientation. The antenna pattern information is required to be able to determine relationship to actual device performance. COAT Methodology

12. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 12 Comparing two NICs in same laptop: Testing four different orientations: COAT Example + InternalExternal 0°90°180°270°

13. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 13 Evaluating two possible measurement polarizations COAT Example Vertically Polarized Total Field Vector

14. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 14 Fixing the orientation and/or polarization direction between measurements of DUTs doesn’t help. Differences in the deltas between the two NIC configurations are much larger than the expected error from the calibration process. COAT Example Vertically PolarizedTotal Field Vector

15. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 15 The reason for these issues is simple. The DUTs don’t have simple radiation patterns. These patterns definitely aren’t dipole-like! Analysis Internal NICExternal NIC

16. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 16 An ideal dipole produces an omnidirectional pattern. –It radiates symmetrically about one axis of rotation, but not the same in all directions. Analysis

17. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 17 Assume for the moment that we have a DUT that does have a perfect dipole pattern. Wireless networks are commonly considered as a two dimensional problem (floor plan). Results in two dimensional analysis of the pattern effects. Analysis

18. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 18 If an ideal dipole is vertically polarized, we get the same signal in all directions. Analysis Average Gain = Peak Gain This is of course the ideal condition.

19. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 19 If the antenna were horizontally polarized, the performance becomes a function of angle with respect to the DUT. Analysis One common solution is to take the average performance as a function of angle. Peak Gain = 2.15 dBi Average Gain = -1.35 dBi

20. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 20 Comparing cuts through the two patterns shows that on average the external NIC performs better. Analysis Comparing the average power gives: Internal NIC = 8.85 dBm External NIC = 13.76 dBm Difference = 4.91 dB.

21. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 21 AP and Client unlikely to be at the same height. –Performance at angles other than horizontal is required. Analysis Comparing the average power for this cut gives: Internal NIC = 8.32 dBm External NIC = 13.24 dBm Difference = 4.92 dB. Considerably different pattern, but similar results.

22. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 22 TRP is nothing more than the average transmit performance over an entire spherical surface (i.e. in all directions) rather than just a single cut. Analysis Comparing the TRPs shows results similar to that for the individual cuts: Internal NIC = 8.44 dBm External NIC = 12.22 dBm Difference = 3.78 dB. Principal cuts tend to overestimate actual performance.

23. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 23 The proposed TRP and TIS methods are simply methods for performing radiation pattern measurements on active devices. While the basic methodology for TRP and TIS involves measuring the entire transmit power and sensitivity radiation patterns, the relationship between these quantities can be used to simplify the total amount of testing required. Once the “real” radiation pattern information is known, it is possible to use single point COAT type tests to determine equivalent total pattern quantities. Analysis

24. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 24 Analysis Point measured as part of pattern measurement. Same point measured for a different quantity and normalized to available pattern information.

25. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 25 Conclusion There is a real need for TRP/TIS testing for 802.11 devices. Effective network design and operation utilizes link budgets that rely on TRP/TIS values. Without this type of measurement, too many assumptions are made about the DUT RF performance. TRP/TIS complements the COAT concept and provides ways to determine/verify those quantities that are assumed.

26. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 26 Conclusion Failure to incorporate these methods into the TGT draft will be doing a disservice to users of the Recommended Practice who do not have access to industry organization test plans. By adding these metrics, the TGT draft becomes harmonized with industry test requirements.

27. Doc.: IEEE 802.11-06/1490r0 Submission September 2006 Dr. Michael D. Foegelle, ETS-LindgrenSlide 27 References 1. IEEE 802.11-06/0906r0, “ TRP and TIS Performance Metrics Proposed Text,” M.D. Foegelle. 2. IEEE 802.11-06/0760r0, “Calibrated Over the Air Test Environment Proposed Draft Text,” M.D. Foegelle.