1. Support for Advanced Antennas & Techniques in TGv
January 2003
IEEE /100r1
Support for Advanced Antennas & Techniques in TGv
Authors:
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Kwak, Rudolf, InterDigital
Submission

2. Kwak, Rudolf, InterDigital
Outline
Introduction: Need for Change and Benefits (review)
Uplink Pointing Problem (review)
MAC layer solution: New RFA
Downlink Selection Problem (review)
MAC layer solution: Modified Probe Request/Response
Antenna Tracking Suggestions (review)
Conclusions
Kwak, Rudolf, InterDigital
Submission

3. Kwak, Rudolf, InterDigital
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
Kwak, Rudolf, InterDigital
Submission

4. 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)
Kwak, Rudolf, InterDigital
Submission

5. 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
Kwak, Rudolf, InterDigital
Submission

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

7. --- 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
Kwak, Rudolf, InterDigital
Submission

8. 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. (Too costly)
3. AP can scan among all beams during frame reception.
High probability of not receiving the frame correctly. (Inefficient)
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. (PHY change)
5. STA send RTS to announce it will send the next frame.
High overhead of RTS/CTS which mitigates gain from advanced antennas. (Inefficient)
6. STA sends special low-overhead signal Request for Antenna (RFA) with info to request AP selection of beam for UL reception without CTS handshake.
Simple, effective and implemented in MAC with modified access protocol.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Kwak, Rudolf, InterDigital
Submission

9. New Request for Antenna for Uplink Solution
January 2003
IEEE /100r1
New Request for Antenna for Uplink Solution
STA decides which uplink transmission needs advanced antenna, e.g. any large uplink burst, any uplink burst requiring high data rate or low latency, etc.
STA transmits RFA frame which contains a requested AP antenna ID (one which provides this STA with the best downlink signal). NAV is set to cover time period for the data transmission or first fragment.
AP receives RFA frame and switches to the requested antenna.
STA sends the uplink frame with updated NAV timer set to cover the ACK for the next fragment.
RFA is a Management Action Frame which is used to define a new frame exchange sequence similar to use of CTS for NAV distribution purposes.
NAV
RFA
STA
NAV
SIFS AP
ACK
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
ACK
AP selects
requested antenna
Kwak, Rudolf, InterDigital
Submission

10. Scenario 2: Multiple Downlink Beams
January 2003
IEEE /100r1
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
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
AP A
AP B
Kwak, Rudolf, InterDigital
Submission

11. 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
Kwak, Rudolf, InterDigital
Submission

12. Modified Active Probe for Downlink problem
January 2003
IEEE /100r1
Modified Active Probe for Downlink problem
The STA discovers neighbor AP information including number of configured antennas.
STA sends Probe Request frame to AP including new request information element for “Antenna Information”.
AP sends one probe response per antenna, each Probe Response contains Antenna ID.
Example:
Can also be generalized to Beacons to help all associated STAs track best AP antenna.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Kwak, Rudolf, InterDigital
Submission

13. Modified Link Measurement to Track Best Antenna
January 2003
IEEE /100r1
Modified Link Measurement to Track Best Antenna
STA send modified Link Measurement Request to discover/confirm best AP antenna for its current location.
AP sends one Link Measurement Report per antenna, each Link Measurement Report contains Antenna ID.
Example:
When STA is equipped with advanced antenna, AP may also use this same modified Link Measurement protocol to track best STA antenna for the STAs current location/orientation.
Link Meas Request
Link Meas Report beam1 of 4
Link Meas Report beam2 of 4
Link Meas Report beam3 of 4
Link Meas Report beam4 of 4
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Kwak, Rudolf, InterDigital
Submission

14. Kwak, Rudolf, InterDigital
Conclusions
Advanced antennas are increasingly migrating into WLAN networks.
standard lacks support for advanced antennas for measurements, for management and for use to extend range and mitigate interference.
Two antenna problems and straightforward MAC layer 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.
Comments for improvement are welcome.
Kwak, Rudolf, InterDigital
Submission

15. Strawpoll for Support as Work Item
Advanced Antenna Work Item:
YES_______
No________
Kwak, Rudolf, InterDigital
Submission