doc: ieee 802.11-05/0435r0may 2005 submission joe kwak, interdigital 1 support for advanced antennas...

Submission Joe Kwak, InterDigital1

doc: IEEE 802.11-05/0435r0May 2005Support for Advanced Antennas

& Techniques in TGk

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.

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2005-MAY-16Authors:

Name Company Address Phone emailJoe Kwak InterDigital

CommunicationsBolingbrook, IL 630-739-4159 [email protected]


doc: IEEE 802.11-05/0435r0May 2005

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.


doc: IEEE 802.11-05/0435r0May 2005

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%39%

29% 26%

57%

0%

10%

20%

30%

40%

50%

60%

70%

802.11G 802.11A

Th

roughput

Imp

rovem

ent

Dense Office1 Story Home2 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)


doc: IEEE 802.11-05/0435r0May 2005

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.


doc: IEEE 802.11-05/0435r0May 2005

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.

AP BSTA A

AntA1

AntA2

AntA3

AntB3

AntB2

AntB1


doc: IEEE 802.11-05/0435r0May 2005Scenario 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 -95 dBm

(B2-->A2) The Beacon Report is ambiguous without the antenna identifiers.

AP BSTA A

AntA1

AntA2

AntA3

AntB3

AntB2

AntB1


doc: IEEE 802.11-05/0435r0May 2005

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


doc: IEEE 802.11-05/0435r0May 2005

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 for transmission of the beacon or probe response.

Reported Power measurement should be normalized to a reference antenna to permit comparative evaluation of results.


doc: IEEE 802.11-05/0435r0May 2005New Antenna Information for RRM

1. 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 254. The value 0 indicates that the antenna identifier is unknown. The value 255 indicates that this measurement was made with multiple antennas.

2. The Antenna Count field contains the number of antennas available at this STA and may indicate from 1 to 254 antennas. The value 0 indicates that the Antenna Count is unknown. The value 255 is reserved. Each available antenna is unique for the reporting STA and is characterized by a fixed relative position, a fixed relative direction and a peak gain for that position and direction.

ChannelNumber

RegulatoryClass

ActualMeasurement

Start Time

MeasurementDuration

PHY Type RCPI BSSID

Octets: 1 1 8 2 1 1 6

Antenna ID AntennaCount

Parent TSF Target TSF BeaconInterval

CapabilityInformation

ReceivedElements

Octets 1 1 4 8 2 2 variable

Measurement Report field format for a Beacon Report


doc: IEEE 802.11-05/0435r0May 2005

New Antenna Information for RRM (cont)

3. Normalized reported power measurements are to be provided in measurement reports: The reported RCPI value will vary based on the

gain of the particular antenna used for each measurement.

The reported RCPI value needs to be normalized to a 0 db reference antenna so that distinct measurements made with different antennas may be compared.

The normalised reported measurand values apply to both RCPI and RPI values in all defined measurement reports


doc: IEEE 802.11-05/0435r0May 2005

Normative Text Proposal 05/0434r0 contains the proposed normative text to

add support for advanced antennas to TGk draft. Text Changes include:

Antenna ID and Antenna Count info added to Beacon Report, Frame Report and Hidden Station Report.

Antenna ID and Antenna Count info added to Beacon and Probe Response.

Reported RCPI/RPI values are normalized to 0dBm antenna gain when used in Beacon Report, Frame Report, Hidden Station Report, Noise Histogram Report, Received Power Time Histogram Report.

Related MIB Additions.


doc: IEEE 802.11-05/0435r0May 2005

Conclusions 802.11 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.


doc: IEEE 802.11-05/0435r0May 2005

Motion for Improved Normative Text Move to instruct the editor to incorporate text from

document 11-05-0434-00-000k-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 ___%


doc: IEEE 802.11-05/0435r0May 2005

ANNEX A

The following charts are excerpts of additional antenna problem scenarios and suggested solutions which were presented to TGv during the March05 meeting.


doc: IEEE 802.11-05/0435r0May 2005

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.

STA 1

AP

STA 2

Beam 1

Beam 3

Beam 2


doc: IEEE 802.11-05/0435r0May 2005

--- 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.


doc: IEEE 802.11-05/0435r0May 2005

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.


doc: IEEE 802.11-05/0435r0May 2005

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.


doc: IEEE 802.11-05/0435r0May 2005

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 dBmRx from AP B: -65 dBm

STA 1

AP A AP B


doc: IEEE 802.11-05/0435r0May 2005

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 dBmRx from AP B: -80 dBm


doc: IEEE 802.11-05/0435r0May 2005

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.Probe request

Probe response beam 1 of 4




doc: ieee 802.11-05/0435r0may 2005 submission joe kwak, interdigital 1 support for advanced antennas...

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