Carrier-oriented WIFI for cellular offload

1. Carrier-oriented WIFIfor cellular offload Date: 2012-07-17 Authors: Laurent Cariou, Orange

2. Abstract Presentation for WNG SC July 2012 Laurent Cariou, Orange

3. Background • Wi-Fi is increasingly becoming an integral component in the delivery of broadband wireless services by fixed and mobile network operators around the globe • Hotspot deployments will increase strongly in the next few years • to support the capacity crunch, cellular operators will need to densify their networks and the small cells deployments will be inevitable, for indoor but also outdoor. • 3GPP integrated solutions exist (micro, pico, femtocells) but WIFI has a role to play in such deployments assuming the fact that it fulfills the requirements • 3GPP small cells should arrive in the market in 2014, WIFI should be competitive at this time Laurent Cariou, Orange

4. Background • We believe that hotspot requirements are different from home and entreprise requirements • higher number of users with lower throughputs • strong performance requirements in instable environments with interferers • different market performance evaluation: average throughput and cell-edge throughput more important than peak throughput • Following 802.11n, 802.11ac have focused its energy on very high throughput scenarios and provided technical solutions accordingly • home network and entreprise markets will largely benefit from this WIFI generation • in the meanwhile, the hotspot market, especially for cellular offload, will not benefit as much from the evolution of 802.11ac, while it is a major growing market Laurent Cariou, Orange

5. Different hotspot deployment scenarios • Classical hotspots • using a fixed network interconnected to the cellular core network (high layer interconnection) • sometimes (not always) deployed with a controller • Hotspots deployed within LTE small cells • WIFI directly connected to the cellular core network (low layer interconnection) • Home private APs used as hotspots • Private SSID for home users and public SSID for cellular offload Laurent Cariou, Orange

6. Different hotspot deployment scenarios • Classical hotspots • using a fixed network interconnected to the cellular core network (high layer interconnection) • stand-alone APs • cluster APs with a controller 3GPP gateway WIFI controller Light AP Proprietary coordination through WIFI controller No coordination with other APs Laurent Cariou, Orange

7. Different hotspot deployment scenarios • Hotspots deployed within LTE small cells (candidate for LTE-A rel12) • Better integration of WIFI in the RAN • Eventually, WIFI directly connected to the cellular core network (low layer interconnection controlled by LTE) Macro-cell 3G/4G Small cell WIFI Laurent Cariou, Orange

8. Different hotspot deployment scenarios • Home private APs used as hotspots • Private SSID for home users and public SSID for cellular offload Public Private Home APs used as Hotspots 3GPP gateway WIFI gateway/controler Coffee shop with many public APs available at the cell edge Laurent Cariou, Orange

9. Major requirements • Improve average throughputs • requires the improvement of cell-edge (BSS-edge) throughput • requires the reduction of the degrading impact of cell-edge STA on other STA • Improve the scheduling capabilities of the AP to apply fairness strategies • note that this will also improve the average throughput • our objective: building a consensus to ensure that such solutions will reach the market • Improve robustness to interference (mostly OBSS management) • better coordination is needed between co-located BSSs for spectrum sharing, interference management and QoS • better robustness to band saturation • Ensure the adaptation to outdoor deployments • potential range extension, support for longer delay spreads Laurent Cariou, Orange

10. Improve average throughput by improving cell-edgestand-alone APs • Operators will deploy many stand-alone APs as small cells. • the objective of small cells is to offload as much traffic as possible from the overlaying macrocell • the strategy is therefore that all STAs in the coverage of the small cells connect to it (small cell range extension in LTE-A) • if cell-edge users have a too strong impact on the performance of the whole WIFI cell, this strategy is not applicable. We therefore need to find solutions for this. Macro-cell Small cell Cell range-extension Slide 10 Laurent Cariou, Orange

11. Improve average throughput by improving cell-edgeAPs cluster • Operator will also deploy clusters of APs with efficient coverage/capacity. • current WIFI strategy is to densify the number of APs, with strong coverage overlap. In these cases, the use of low MCSs can even be forbidden • This allows to avoid bad performance at cell-edge and the throughput degradation impact of cell-edge user on all other users • Compared to enterprise deployments, outdoor hotspot deployments will have strong positioning constraints • On top of that, many WIFI hotspots will be deployed as a small cell which incorporates a WIFI AP and an LTE pico/femtocell • The deployment strategy of such small cells will mostly be based on LTE pico/femto • which will usually have a slightly higher coverage • which don’t push for densifying as it creates interference 3G/4G Small cell WIFI • Finding technical solutions to improve cell-edge performance can not be avoided in hotspot deployments as it is in enterprise deployments •  Efficient SON mechanisms are required for capacity/coverage optimisation, handover optimization Slide 11 Laurent Cariou, Orange

12. Improve average throughput by improving cell-edgeHome APs • In many cases, especially in the home APs hotspots case, STAs will be far from APs but will see many APs. • The throughput of ths cell-edge STA will be limited to reduce the impact on private SSID • such a STA should be able to associate on multiple APs/hotspots in order to aggregate the throughputs offered by all APs • this could also facilitate handovers Home APs used as Hotspots 3GPP gateway WIFI gateway/controler Coffee shop with many public APs available at the cell edge Laurent Cariou, Orange

13. Improve average throughput by improving cell-edge • Potential technical solutions: • Beam selection mechanisms at AP side, especially for the weaker UL signal • Longer range lower throughput transmission scheme, associated with a multiple access scheme to keep a low occupation of the channel and a good MAC efficiency: OFDMA is a good candidate • Coordination between neighboring APs • adaptation of CoMP mechanisms defined in LTE-A: multi-cell high-level scheduling • Multiple MAC (MMAC) association • … Slide 13 Laurent Cariou, Orange

14. Improve the scheduling capabilities of the AP to apply fairness strategies • Currently, EDCA leads to throughput fairness • leads to bad average throughput, high airtime occupation by cell-edge users, … • We are looking for ONE realistic solution to enable different fairness strategies. Bringing scheduling capabilities to the AP is a solution for this. • Some technical solutions have already been proposed, none of them have reached the market. We are not pushing for a particular technical solution but want to reach a consensus to ensure it will reach the market. It can be • based on EDCA with parameterization improvement • based on EDCA with the use of a multiple access scheme like OFDMA or simple multi-user aggregation, following the example of 802.11ac MU-MIMO (scheduling capabilities for the AP) • based on EDCA with protocol modifications adapting strategies proposed in 802.11ah • … or based on modifications of HCCA Laurent Cariou, Orange

15. Improve robustness to interference • Self organizing networks (SON) is a very important feature of LTE, in order to save OPEX and improve capacity/coverage • It enables self-configuration of new cells, automatic neighbor relation (ANR), load balancing, mobility robustness/handover optimization, Energy savings, Capacity and coverage optimisation (Radio ressource management (RRM) to detect dead spots, reduce interference between cells, select channels/bandwidth, adjust tilt and MIMO antenna configurations, adjust transmission power, …) • For WIFI, SON mechanisms (especially RRM) can easily be done with proprietary solutions on an area if all APs are managed by a controller (entreprise scenario). Products already exists. • But WIFI Hotspots deployments will be done by using • multiple stand-alone APs potentially from different vendors (example of home APs hotspots) • hotspots clusters deployed by the operator, by other operators or by a tier who deployed first with a roaming license • In such cases (multi-controller, multi-operator, multi-vendor), SON mechanisms require standardized features like exchange of information between neighboring APs • 802.11ah can be a good candidate for AP-to-AP coordination exchange: we need to define these information exchange Slide 15 Laurent Cariou, Orange

16. Ensure the adaptation to outdoor deployments • WIFI has been designed for indoor environments. • OFDM parameters has been set to cope with small delay spreads • When used in a outdoor environment, the performance can be severly degraded • OFDM is not well parametrized (some papers show that performance of 11g is worth than 11b) • delay spread excess cyclic prefix which cause interference, • errors due to too short preambles lead to packet loss. • Outdoor WIFI hotspots (especially within 3G-4G small cells) will be heavily deployed in the incoming years if the performance is preserved • we can modify OFDM parameters or apply downsampling techniques as in 11af or 11ah. Slide 16 Laurent Cariou, Orange

17. Proposal • IEEE 802.11 should provide solutions to address this growing market. • What sort of thing are we looking for? • A new study group, perhaps “Carrier-oriented WIFI - Cellular offload”, with the objective to: • improve cellular offload WIFI performance for hotspot deployments • We envision PHY and MAC light modifications in order to improve current WIFI generation for hotspots requirements (not a new generation) • 802.11n/ac as the basis of such improvement (2.4 and 5GHz) • 802.11ah as a good candidate for AP-to-AP coordination exchange • Different levels of improvements: • depending on the targeted deployment scenario: home APs, hotpots deployed by operators and WIFI hotspots aggregated with LTE • and on the WIFI technologies integrated in chipsets: - 11n/ac in STAs and APs - 11n/ac in STAs and 11n/11ac/11ah in APs - 11n/ac/ah in STAs and 11n/11ac/11ah in APs Laurent Cariou, Orange

18. Straw Poll • Should IEEE 802.11 consider the creation of a study group to further discuss the topic of “cellular offload WIFI” ? • Yes • No • Need more information • Abstain/Don’t care Laurent Cariou, Orange

19. Motion to create a Study Group • Request approval by IEEE 802 LMSC to form an 802.11 Study Group to consider the cellular offload WIFI / Carrier-oriented WIFI [as described in doc 11-12-0910] with the intent of creating a PAR and five criteria. • Moved: <name>, Seconded: <name>, Result: y-n-a Laurent Cariou, Orange

20. Annexes Laurent Cariou, Orange

21. Small cell performance evaluation • Evaluation methodology for an improved fairness • inspired from 3GPP evaluation methodology: peak throughput, average throughput and cell-edge thoughput (5%) • The cell edge user throughput is defined as the 5% point of CDF of the user throughput normalized with the overall cell bandwidth. • Average spectrum efficiencyis defined as the aggregate throughput of all users (the number of correctly received bits over a certain period of time) normalized by the overall cell bandwidth divided by the number of cells. The average spectrum efficiency is measured in b/s/Hz/cell. Laurent Cariou, Orange

22. Efficient share of spectral resources between BSSs • Each AP signals its occupation and load at 5GHz • enables dynamic channel selection without scanning • benefit from 11ah range for a better knowledge of channel occupation • Potential negociation between APs using signaling band for channel occupancy • dynamic channel occupancy to satisfy the needs from all APs AP need: 80MHz 60% load  co-channel with AP2 • AP need: 80MHz 90% load • co-channel with AP2 not possible • channel switch request to AP2 Slide 22 Laurent Cariou, Orange

23. Efficient share of spectral resources within a BSS • STAs far from AP (cell-edge STA) can strongly impact the performance of other APs • transmit with low MCS and low bandwidth for a long time • One solution is to enable to simultaneously transmit on the primary 20MHz channel towards this cell-edge STA and on secondary channel towards other STA (simple multi-band DL-OFDMA) toward STA1 Primary channel Secondary channel toward STA2 Slide 23 Laurent Cariou, Orange

24. Use of 802.11ah as a signaling band for improved cooperation • Use 802.11ah for signaling and 802.11ac/ad/af for data transmissions • Information sharing between APs to improve cooperation/coordination between neighboring cells • interference management, frequency planning, power control, … • Information sharing between AP and STAs to improve quality of service, energy efficiency, interference management Laurent Cariou, Orange