1. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 1 Support for Advanced Antennas & Techniques in TGv 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 2005-03-16 Authors :

2. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 2 Introduction Advanced high-gain, directional antennas for 2-6 GHz have been available for decades. A few current 802.11 products offer some advantages using advanced antennas (example on next chart). Up to now 802.11 standards have not addressed advanced antenna capabilities in STA or in AP: Some awareness of diversity antenna (2 omnis with switch to select) No MAC or PHY provisions for configuration and control of antennas No support for advanced antennas in MAC or PHY measurements No support for link level use of advanced, directional antennas. Current advanced antenna products rely on proprietary techniques used within the STA equipped with the advanced antenna 802.11 management functions have no ability to monitor, configure or control antennas within their managed networks. As a result, these advanced antenna technologies cannot be fully exploited at the system or network levels.

3. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 3 Example of Gains with Advanced Antenna Overall throughput improvement ranges from 26% to 57% Greater throughput improvement near cell edge Typically 10% improvement near Access Point Typically >80% improvement near cell edge 39% 29% 26% 57% 0% 10% 20% 30% 40% 50% 60% 70% 802.11G802.11A Throughput Improvement Dense Office 1 Story Home 2 Story Home 2 Story Home test included more points near cell edge 1 Story Home test included fewer points near cell edge NOTE: Throughput improvement compares Advanced Antenna to OEM omni. The Advanced Antenna result is based on Beam Select by Throughput Example antenna configuration - Switched Beam (Source: InterDigital)

4. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 4 Introduction (cont’d) As history has shown, advanced technologies will migrate into use when economics (cost vs performance) permit. Today many vendor-specific solutions on the market implement more than one antenna to achieve performance gains: Improved signal reception quality and net link throughput with simple Rx Diversity antenna architectures in both STAs and APs Multiple, switched beam antenna configurations in APs used to extend coverage area, reduce interference and boost BSS throughput Pre-11n (not officially blessed) MIMO-like solutions are hitting market….. We are likely to see even more advanced antenna techniques in 802.11 in the years to come. Miniature switched beams for mobile applications Steerable, beam-forming antennas for APs Without standardized support, performance gains with advanced antennas can not be fully exploited, interoperability is jeopardized and ROI cannot be fully realized. The following typical problem scenarios indicate limitations of current 802.11 standard.

5. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 5 Scenario 1: Uplink Pointing Problem STA 1 and STA 2 associated to AP Assume that by one way or another, AP knows the best beam to use for STA 1 best is Beam 1 and for STA 2 best is Beam 2. When the AP has a frame to transmit to STA 1, it uses Beam 1 to transmit the frame and receive the ACK; no problem for downlink. STA 1 AP STA 2 Beam 1 Beam 3 Beam 2

6. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 6 --- But for Uplink Frames… After each frame exchange with a particular STA, the AP has to listen to the channel using an omni-directional antenna pattern since it does not know which STA will send the next frame. Even when it starts receiving a frame, the AP does not know the identity of the STA until the frame is entirely received and decoded. How can AP select Beam 1 when STA 1 sends a frame since AP can only read the address of the source after it has decoded the whole frame? STA 1 AP STA 2 Beam 1 Beam 3 Beam 2 AP use of omni for UL and beam for DL leads to asymmetric up/down coverage areas. Same uplink problem typically does not exist in STA equipped with advanced antennas since the STA has only one link to one AP.

7. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 7 Uplink Problem: Many Solution Alternatives  1. AP remains in omni mode when receiving frames.  Forces the STA to set rate lower than would be achievable using directional beams.  No gain from the AP advanced antenna asset for uplink (50% of gain is lost).  2. AP listens on all beams at all times and performs combining (e.g. MRC).  Demands one RF chain per beam  complex/expensive receivers  3. AP can scan among all beams during frame reception.  High probability of not receiving the frame correctly  4. AP could try decoding the MAC address of sender using omni but then switch to appropriate beam for rest of frame.  Requires MAC header to be sent at lower rate to be received correctly in omni  Requires STA to switch to higher rate for frame body (neither currently allowed).  5. STA send RTS to announce it will send the next frame.  High overhead of RTS/CTS which mitigates gain from advanced antennas  6. STA sends special low-overhead signal (RTS+) with info to assist AP selection of beam for UL reception without CTS handshake.  Perhaps very efficient, but would need to modify basic access protocol.

8. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 8 7. New Signaling Solutions for Uplink Problem Upon reception of a frame, the AP needs to know the optimal antenna (beam) as early as possible. That calls for signaling support that should: be in every uplink frame (or one per TXOP) be located at the beginning of the frame be sent at a lower rate than the rest of frame use the smallest number of bits. STA ID Signal (uplink signal ): Add a STA ID in PLCP or between PLCP and rest of frame. Assumes AP has learned best beam for each STA. STA MAC address is longer than needed. Can use a per-BSS STA ID given by AP upon association (≤8 bits). E.g. STAx sets STA ID = x in the frame sent to the AP. AP does table lookup to find that Antenna ID y (Beam y) is best for STA x. AP switches to Antenna y to receive body of frame. Size of STA ID field > the maximum number associated STA per BSS. Antenna ID Signal (uplink and downlink signals): A STA knows which AP antenna (beam) is used for downlink by having the AP signal the Antenna ID (Beam ID) in downlink frames it sends to the STA. STA echoes that Antenna ID in uplink frames in the PLCP or between PLCP and rest of frame. E.g. AP sets Antenna ID=y in downlink frames to STA1; STA 1 sets Antenna ID = y in uplink frames to the AP. AP switches to Antenna y to receive body of frame. Size of beam ID field sets max number of beams (e.g. 3 bits allows 8 beams) Can be generalized to deal with STA-STA links in IBSS or mesh.

9. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 9 Scenario 2: Multiple Downlink Beams AP A and AP B are equipped with advanced antennas that can transmit allowing them to transmit in omni-directional mode or in beam-switching directional mode. When allowed to use the right beams, AP B would offer a better connection to STA 1 than AP A. Rx from AP A: -75 dBm Rx from AP B: -65 dBm STA 1 AP A AP B

10. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 10 Downlink Problem: STA Selects Wrong AP  Because beacons are not aimed at any particular STA but rather to all of them, they tend to use omni antenna even if the AP is equipped with directional antennas. STA will estimate received signal levels from AP A and AP B that are different from the ones actually perceived after association with directional antenna. From the scanning, STA 1 may choose AP A, although AP B is the better choice  sub-optimal throughput at STA and system capacity. AP AAP B STA 1 Rx from AP A: -75 dBm Rx from AP B: -80 dBm

11. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 11 New Signaling Solution for Downlink problem The STA needs to be able to differentiate beacons and probe responses sent using different antennas. AP could send one beacon or probe response per antenna. Beacons/Probe Responses include Antenna ID. The STA further needs to know how many antennas are used in order to know how long it should scan a given channel. Beacons/Probe Responses also include a “number of antennas” field. Example: Can also be generalized for uplink to accommodate STAs with advanced antennas.

12. doc: IEEE 802.11-05/0280r0March 2005 Submission Kwak, Rudolf, InterDigital 12 Conclusions Advanced antennas are increasingly migrating into WLAN networks. 802.11 standard lacks support for advanced antennas for measurements, for management and for use to extend range and mitigate interference. Two antenna problems and straightforward signalling solutions for both have been shown. Advanced antenna technology cannot be fully exploited without effective management and without some basic link level coordination of both TX and RX STA antenna resources. In 11v should make use of the opportunity to address the use and management of advanced antennas in 802.11 networks.