1. Support for Load Balancing in 802.11v
January 2003
IEEE /100r1
May 2005
doc: IEEE /xxx5r0
Support for Load Balancing in v
Joe Kwak, Marian Rudolf (InterDigital)
Submission
Kwak, Rudolf

2. Agenda Introduction Load balancing illustration 802.11 today
STA-centric
802.11v opportunities
Decision taken by network
AP-centric with support from STA
Hybrid scheme
Split of load balancing responsibilities between AP and STA
Kwak, Rudolf
Submission

3. Introduction What do we mean by load balancing? Why is this needed?
Handover of one or multiple STA from one AP to another AP
Triggered by load considerations; not by mobility
Why is this needed?
Indoor or dense deployments tend to be characterized by geographically non-uniformly distributed traffic
This can translate into having a congested BSS while other neighbor BSS’s have spare capacity
Sub-optimal use of system resources (e.g. achieved system throughput much lower than it actually could be)
Sub-optimal throughput and/or QoS experienced by users
Kwak, Rudolf
Submission

4. Load balancing illustration
Non-uniform load
Kwak, Rudolf
Submission

5. Load balancing illustration
Spare
Capacity
Congestion
Load
Non-uniform load
Kwak, Rudolf
Submission

6. Load balancing illustration
No more congestion
More uniform and predictable service
Load
Kwak, Rudolf
Submission

7. today (STA-centric)
Each STA has its own criteria to determine its handover triggers
Many or most STA do not try to select BSS based on network load balancing considerations
Pros
STAs are in a good position to evaluate the different candidates RF-wise and decide at which instant they should handover
Cons
STAs do not have a view of the whole system, particularly not network-wide traffic distribution
Unless all STAs come from the same vendor and are configured the same, load balancing is not performed in a cohesive fashion today
Kwak, Rudolf
Submission

8. Possible Load Balancing approach for 802.11v (1/2)
Decision could be taken by the network (AP-centric approach)
Pros
APs (or network) have broader view of system and are in better position to perform actions that will optimize system performance
For a network operator, it is easier to implement a given load balancing policy through the APs (O&M) than through the STAs
APs can capitalize on robustness and bandwidth of Distribution System for facilitating handover
Signalling for Handover execution is (almost) in place, r
Cons
Proper timing of the handover and load balancing performance trade-offs could require the AP to monitor the quality perceived by STA
Outline for one possible way for TGv to support load balancing
Signaling for AP to initiate STA handover to another AP in the ESS
Signaling for AP to suggest a STA to handover to an AP in the ESS
STA supporting AP by sending candidate AP lists
Rely on TGr for handover execution by STA
Kwak, Rudolf
Submission

9. Possible Load Balancing approach for 802.11v (2/2)
Or, load balancing responsibilities shared between STA and AP (as alternative to AP-centric, some sort of hybrid approach)
AP’s (or network) responsible for determining the load balancing policy in the BSS that will optimize system-wide throughput
Broadcast in the BSS or sent to STAs during (re-)association
STA is responsible for implementing/executing the load balancing policy
Monitoring of load-balancing motivated handover conditions and actual handover execution (as by 11r for example)
One possible approach for the AP
Serving AP sends the BSS load balancing policy to STA
Triggers, for example metric X BSS1 - metric X BSS2 > Margin for 10 sec
In addition, serving AP supporting STA by – for example -
Sending neighboring AP lists accompanied by observed load metrics and timing of beacons (11k)
APs supporting STA by sending advertisement packets on channels other than their own to allow STA to scan without changing channels
Kwak, Rudolf
Submission