Support for Load Balancing in 802.11v

1. doc: IEEE 802.11-05/xxx5r0 May 2005 Support for Load Balancingin 802.11v Joe Kwak, Marian Rudolf (InterDigital) 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

3. Introduction • What do we mean by load balancing? • 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

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

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

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

7. 802.11 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

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, 802.11r • 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

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