1. Support for Advanced Antennas & Techniques in TGk
January 2003
IEEE /100r1
Support for Advanced Antennas & Techniques in TGk
Authors:
2005-JULY-20
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Joe Kwak, InterDigital
Submission

2. January 2003
IEEE /100r1
Introduction
Advanced high-gain, directional antennas for 2-6 GHz have been available for decades.
A few current products offer some advantages using advanced antennas (example on next chart).
Up to now 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
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.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

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
1 Story Home test included fewer points near cell edge
2 Story Home test included more points near cell edge
70%
Dense Office
1 Story Home
2 Story Home
57%
60%
50%
39%
39%
Throughput
Improvement
40%
NOTE:
Throughput improvement compares Advanced Antenna to OEM omni. The Advanced Antenna result is based on Beam Select by Throughput
29%
26%
30%
20%
10% 0%
802.11G
802.11A
Example antenna configuration - Switched Beam (Source: InterDigital)
Joe Kwak, InterDigital
Submission

4. Introduction (cont’d)
January 2003
IEEE /100r1
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 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 standard.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

5. Scenario 1: Ambiguous Beacon Measurement
January 2003
IEEE /100r1
Scenario 1: Ambiguous Beacon Measurement
STA 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.
STA A performs a Beacon Request Measurement and receives beacons from AP B. STA A sends the Beacon Report to the requesting STA indicating the RCPI for the received beacon from AP B.
STA A
AntA3
AntB2
AntA1
AntB1
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
AP B
AntA2
AntB3
Joe Kwak, InterDigital
Submission

6. Scenario 1: Ambiguous Radio Measurement (cont.)
January 2003
IEEE /100r1
Scenario 1: Ambiguous Radio Measurement (cont.)
The STA requesting the measurement cannot interpret the RCPI measured value since it does not know the antenna configuration for STA A and AP B used for the measurement.
RCPI values for received beacons range from -30 dBm (B1-->A1) down to dBm (B2-->A2)
The Beacon Report is ambiguous without the antenna identifiers.
STA A
AntA3
AntB2
AntA1
AntB1
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
AP B
AntA2
AntB3
Joe Kwak, InterDigital
Submission

7. RRM Advanced Antenna Solution
RRM Measurements in which the results depend on the antenna used for the measurement must provide antenna information with the reported measurement results.
Measuring antenna information is needed in
Noise Histogram Report
Beacon Report
Frame Report
Hidden Station Report
Medium Sense Time Histogram
Link Measurement Request/Report
Joe Kwak, InterDigital
Submission

8. RRM Advanced Antenna Solution (cont.)
Accurate beacon measurements are critical to roaming decisions and the measured RCPI depends on the antenna configuration at the transmistting AP.
To support Beacon Measurements Beacons (and Probe Responses) should contain information about the antenna used (Antenna ID) for transmission of the beacon or probe response.
Reported Power measurements will fluctuate at the antenna connector based on gain of selected antenna.
Joe Kwak, InterDigital
Submission

9. New Antenna Information for RRM
The Antenna ID field contains the identifying number for the antenna used for this measurement. The valid range for the Antenna ID is 1 through The value 0 indicates that the antenna identifier is unknown. The value 255 indicates that this measurement was made with multiple antennas. The value 1 is used for a STA with only one antenna. STAs with more than one antenna shall assign Antenna IDs to each antenna as consecutive, ascending numbers. Each Antenna ID number represents a unique antenna characterized by a fixed relative position, a fixed relative direction and a peak gain for that position and direction.
Joe Kwak, InterDigital
Submission

10. Normative Text Proposal
05/0434r0 contains the proposed normative text to add support for advanced antennas to TGk draft.
Text Changes include:
Antenna ID info added to Beacon Report, Frame Report, Hidden Station Report, MedSense Time Histogram and Link Measurement Report
Antenna ID info added to Beacon and Probe Response.
Related MIB Additions.
Joe Kwak, InterDigital
Submission

11. Conclusions
standard lacks support for advanced antennas for measurements, for management and for use to extend range and mitigate interference.
Advanced antenna technology cannot be fully exploited without effective measurements which address both TX and RX STA antenna resources.
Beacon measurement problems and RCPI ambiguities exist in current TGk draft.
Proposed solution includes new antenna info to beacons, probe responses and measurement reports.
11k should modify the spec to permit use of advanced antennas for Radio Measurement.
Joe Kwak, InterDigital
Submission

12. Motion for Improved Normative Text
Move to instruct the editor to incorporate text from document k-NormText Advanced- Antennas.doc into next TGk draft specification document
Moved by Joe Kwak
Seconded by: _______________
Vote YEA _______
Vote NEA _______
ABSTAIN _______
Vote Passes/Fails at ___%
Joe Kwak, InterDigital
Submission

13. ANNEX A
The following charts are excerpts of additional antenna problem scenarios and suggested solutions which were presented to TGv during the March05 meeting.
Joe Kwak, InterDigital
Submission

14. Scenario 2: Uplink Pointing Problem
January 2003
IEEE /100r1
Scenario 2: 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.
Beam 3
STA 1
Beam 1
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1 AP
Beam 2
STA 2
Joe Kwak, InterDigital
Submission

15. --- But for Uplink Frames…
January 2003
IEEE /100r1
--- 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?
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.
Beam 3
STA 1
Beam 1
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1 AP
Beam 2
STA 2
Joe Kwak, InterDigital
Submission

16. Uplink Problem: Many Solution Alternatives
January 2003
IEEE /100r1
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.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

17. New Signaling Solutions for Uplink Problem
January 2003
IEEE /100r1
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.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

18. Scenario 3: Multiple Downlink Beams
January 2003
IEEE /100r1
Scenario 3: 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
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
AP A
AP B
Joe Kwak, InterDigital
Submission

19. Downlink Problem: STA Selects Wrong AP
January 2003
IEEE /100r1
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 A
AP B
STA 1
Rx from AP A: -75 dBm
Rx from AP B: -80 dBm
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission

20. New Signaling Solution for Downlink problem
January 2003
IEEE /100r1
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.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Joe Kwak, InterDigital
Submission