1. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 1 Multipath Testing in a Conducted Environment 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: 2006-09-17 Authors:

2. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 2 Abstract This presentation describes how to augment the TGT conducted environment to measure the performance of WLAN systems in the presence of simulated multipath conditions.

3. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 3 Summary Multipath is an important factor influencing the performance of WLANs However, the current TGT draft does not contain any recommendations on how to make repeatable tests of WLAN devices in the presence of multipath This proposal contains –A recommendation that the TGn channel models be used as the baseline channels –A description of a conducted test environment for measuring multipath performance of two WLAN devices

4. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 4 The TGn Channel Models Before TGn, there was the High Throughput Study Group (HTSG) An ad hoc group within HTSG was formed to develop models for simulating multipath over a range of useful conditions A lot of good work went into developing these models –Various companies engaged in measurement and characterization campaigns –Over a year was spent on the effort Result is a state-of-the-art set of models that everyone agreed on as a basis for comparing PHY proposals –All PHY proposals had to include performance results based on these models

5. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 5 One more fact about the models Channel models existed for the WLAN environment before the HTSG –TGa (802.11a) [2] –HIPERLAN2 [3] However, these models were only appropriate for SISO systems The HTSG (TGn) models were developed explicitly with MIMO considerations in mind –New thinking on creating a Power Delay Profile (cluster model) –A Doppler model appropriate to typical WLAN environments –The need to model multipath correlations between the antenna paths

6. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 6 The TGn models also apply to SISO The models were developed for the MIMO case But multipath for SISO systems is a “special case” of MIMO where the number of antennas on both nodes is one But also, many “SISO” systems are actually “SIMO”: one transmit antenna and two receive antennas The TGn models naturally apply to this situation as well

7. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 7 The TGn models continue to be valuable The original purpose of the models was for simulation in software The models can also be implemented on a channel emulator and used in a conducted environment to test the performance of real WLAN devices in a repeatable fashion

8. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 8 The basic form of the channel models The models are based on tapped delay lines –From 1 to 18 taps There are a maximum of N= 4 inputs and M= 4 outputs –N = number of transmit antennas –M = number of receive antennas The multiple inputs and outputs mean there are a total of NxM paths between transmitter and receiver –I refer to these paths as “MIMO paths” –Each of these paths is modeled as a tapped delay line Each tap is driven by a fading process The fading processes assume a “moving reflector” model –Assumes the transmitter and receiver are stationary, while objects move around in the environment (RMS doppler spread ≈ 3 Hz @ 2.4 GHz, 6 Hz @ 5 GHz) The fading processes are constructed to have a carefully-computed correlation between the MIMO paths –The correlation depends on the spacing between the antennas on the transmit and receive sides

9. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 9 Simplified block diagram of channel models for 2x2 MIMO 2 Tx antennas, max = 4 2 Rx antennas, max = 4 Tapped Delay Line driven by fading processes Fading processes simulating Doppler and correlated according to cluster statistics 4 MIMO Paths Power-Delay Profile determined by cluster statistics Path loss simulated by variable loss at output – allows throughput vs. loss tests

10. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 10 Summary of TGn model parameters Models representing five environments of progressively longer range between endpoints Models also specify several combinations of Tx and Rx antenna spacings – /2, 1, 4

11. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 11 A Unidirectional Channel Emulator Implementation This implementation can be used for SISO testing, and for TGn testing of systems that do not use implicit beamforming

12. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 12 A Bidirectional Channel Emulator When testing implicit beamforming, accurately emulated return path is required Fading between forward and return must be synchronized for so as not to create unrealistic conditions for the protocol

13. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 13 Implementation in the TGT draft Still trying to decide best approach: –Adding a modifier to the conducted environment –Making a new environment Either way, we will need to integrate the TGn channel model document into the draft as an appendix –It only exists as an IEEE submission [1] It may be possible to include the Matlab implementation with the standard –There are copyright issues with this

14. doc.: IEEE 802.11-06/1501r0 Submission September 2006 C. Wright, Azimuth SystemsSlide 14 References [1] IEEE 802.11-03/940r4, “TGn Channel Models”, V. Erceg, et al [2] IEEE 802.11-97/96, “Tentative Criteria for Comparison of Modulation Methods”, N. Chayat [3] 3ERI085B, “Channel models for HIPERLAN/2 in different indoor scenarios”, J. Medbo, et al