1. Support for Advance Antennas & Techniques in WNM
January 2003
IEEE /100r1
September 2004
doc: IEEE /xxxr0
Support for Advance Antennas & Techniques in WNM
Joe Kwak, Marian Rudolf
InterDigital Communcations
Submission
Kwak, Rudolf

2. January 2003
IEEE /100r1
Introduction
Advanced antenna products have been available for the unlicensed WLAN bands for several 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
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
Submission

3. Example of Gains with Advanced Antenna
Overall throughput improvement ranges from 26% to 57%
Greater 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%
802.11G
802.11A
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 Smart Antenna to OEM omni. The Smart Antenna result is based on Steer by Throughput
Test Antenna == Switched Beam with Proprietary Control
Kwak, Rudolf
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
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
802.11n incorporation of MIMO techniques into antenna system
Without standardized support, performance gains with advanced antennas can not be fully exploited 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
Submission

5. 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 with STA 1 is Beam 1 and Beam 2 with STA 2.
When the AP has a packet to transmit to STA 1, it uses Beam 1 to transmit the packet 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
Submission

6. But for uplink packets…
January 2003
IEEE /100r1
But for uplink packets…
After each frame exchange with a particular STA, the AP has to go back listening to the channel using an omni-directional antenna pattern since it does not know which STA will send the next packet
Even when it starts receiving a packet, the AP does not know the identity of the STA until the frame is entirely received.
How can AP select Beam 1 when STA 1 sends a packet since AP can only read the address of the source after it has decoded the whole packet?
Beam 3
STA 1
Beam 1
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1 AP
Beam 2
STA 2
Kwak, Rudolf
Submission

7. Scenario 2 - Measurement Coordination Problems
January 2003
IEEE /100r1
Scenario 2 - Measurement Coordination Problems
Both STA and AP have implemented advanced antenna capabilities
STA 1 AP
Beam 1
Beam 3
Beam 2
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Kwak, Rudolf
Submission

8. Need to Coordinate Antennas for Measurements
January 2003
IEEE /100r1
Need to Coordinate Antennas for Measurements
Measurements for antenna selection is performed locally at each STA without any antenna co-ordination from the other STA. Measurements may vary widely due to antenna configurations, and so may not be useful.
To use advanced antennas, more is needed:
the information on the antenna capability of the STA and the AP should be exchanged.
Possible Coordination during optimization of advanced antenna features such as beam selection etc.
Measurement support for antenna selection: parameters for antenna ID, direction and gain so that measurements made with different antennas may be compared.
SMI – Structure of Management Information
ASN.1 – Abstract Syntax Notation 1
Kwak, Rudolf
Submission

9. Scenario 3 - Association Error with Omnis
January 2003
IEEE /100r1
Scenario 3 - Association Error with Omnis
AP A and AP B are equipped with omni antennas for beacons but use beam-switching directional antennas for all unicast traffic.
When allowed to use the right beams, AP B would offer a better connection to STA 1 than AP A would
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
Submission

10. January 2003
IEEE /100r1
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
Submission

11. Conclusions
Advanced antennas are increasingly migrating into WLAN networks.
standards lack support for measurements and management of advanced antennas.
Advanced antenna technology cannot be fully exploited without effective management.
Future location-based services will depend on managing advanced antennas in WLAN networks.
WNM Task Group will need to address the use and management of advanced antennas in a practical way and within the time constraints of the project.
Kwak, Rudolf
Submission