1. High-efficiency Wi-Fi
November 2011
doc.: IEEE /1507r1
March 2013
High-efficiency Wi-Fi
Date:
Authors:
Laurent Cariou, Orange
Stephen McCann, RIM

2. November 2011
xxx, Orange

3. November 2011
doc.: IEEE /1507r1
March 2013
Outline
We propose to start a new study group to enhance PHY and MAC in 2.4/5 GHz bands
“High-efficiency Wi-Fi” targets the key issues that should be addressed to support continued growth and competitiveness of across a broad range of market segments
Laurent Cariou, Orange
Stephen McCann, RIM

4. November 2011
doc.: IEEE /1507r1
March 2013
Status
In July 2012 meeting, Orange presented some requirements for to improve the Wi-Fi experience for mobile devices, emphasizing cellular offload as a strong use case [1].
A strawpoll proposing the creation of a study group was largely positive.
We received strong support and interest from many actors, interested in this topic and willing to contribute.
In September 2012, Orange, Huawei, Samsung, NTT and others presented further arguments [2, 5, 3, 4, 8]. Since then, we continued our work to:
clearly identify the main problems to solve in IEEE and clarify the scope
be confident that technical approaches exist that would allow these objectives to be met
During this period, it became clear that many of the key issues that should be addressed for cellular offload are common with many other market segments.
“High-efficiency Wi-Fi” enhancements have broad market appeal in multiple market segments to form a next-generation of
We believe the current proposal has sufficient maturity to move to Study Group creation
Laurent Cariou, Orange
Stephen McCann, RIM

5. The mobile data explosion
March 2013
The mobile data explosion
The mobile data explosion is a combination of three components:
increased number of mobile devices (absolute, and per area)
increased requirements for per-device data throughput
increased usage of these mobile devices
Per-device data throughput
Today, a (reliable) 1 – 5 Mbps connection is adequate for a reasonable user experience with most mobile web applications, including video [6]
This minimum satisfactory throughput will grow 50% per year in the coming years [7]
due to increased cloud services, higher resolution video, …
Increased usage of mobile devices
The most significant contributor to the data explosion: predicted 45x growth in next 5 years
55 MB/month in 2011  2.5 GB/month in 2016 for smartphones [7]
Operators will need to deploy Wi-Fi hotspots everywhere, including outdoors
Most of the environments – residential, enterprise, public spaces – will become high density scenarios
Laurent Cariou, Orange

6. High-Efficiency Wi-Fi
March 2013
High-Efficiency Wi-Fi
The key point is the increasing usage of in high density scenarios
This relates not only to operator hotspots, but equally to enterprise, residential, retail and ad-hoc scenarios
We propose “High-efficiency Wi-Fi” as a theme to drive the next generation of
Resulting in enhanced Quality of Experience for a broad spectrum of users in everyday scenarios
Three key focus points:
(1) To improve efficiency in dense networks with large no. of STAs
(2) To improve efficiency in dense heterogeneous networks with large no. of APs
(3) To improve efficiency in outdoor deployments
Laurent Cariou, Orange

7. The main issues for enhancement
March 2013
The main issues for enhancement
Topic
Scenarios
(see details in Annex 1)
Issues
(see details in Annex 2-3)
1. Large no. of STAs
hotspots in dense areas
enterprise (BYOD)
weak flexibility in use of resources (time, frequency, space) to multiplex users efficiently
high collisions and weak MAC efficiency with many STAs, especially with mixed traffic and legacy devices
2. Large no. of APs
APs deployed by operators, businesses and consumers in the same neighborhood
Wi-Fi Direct devices (Miracast, sync-and-go, etc) and personal Wi-Fi routers
limited spatial capacity with OBSS due to spatial protection, interference and lack of coordination with neighboring APs
lack of framework for consistent and flexible admission control, load balancing and fairness
weak airtime occupation ratio for management vs data
3. Outdoor
hotspots in open areas
small-cell deployments
weak uplink and high interference, weak non-LOS reliability
weak robustness to higher delay spreads and Doppler
Laurent Cariou, Orange

8. March 2013
Summary
“High-efficiency Wi-Fi” aims to achieve a very substantial increase in the real-world throughput achieved by each user in such scenarios
Creating an instantly recognizable improvement in Quality of Experience of the major use cases
Generating spatial capacity increase (area throughput)
PHY-MAC enhancements for carrier-oriented Wi-Fi are also applicable to broad market segments (residential, enterprise, retail, …)
We propose a single SG to integrate these requirements in the overall evolution of
avoid interdependencies between SGs; timelines may not be much different in practice
We believe such evolution will create a broad market appeal for multiple market segments and ecosystem players
Consumers, enterprise, operators, Wi-Fi Direct service providers, device vendors, TV/video, medical, …
Laurent Cariou, Orange

9. Month Year
doc.: IEEE yy/xxxxr0
March 2013
Proposal and timeline
We propose to start a new study group to add new PHY and MAC enhancements focused on “High-efficiency WLAN”
The scope and duration should be kept focused
Focus on the primary spectrum of in 2.4 and 5GHz, preserving backward compatibility
Main objectives of the study group will be:
Prepare use case documents, detail the list of problems and requirements
Develop performance metrics to address use cases and quantify objectives
Prepare PAR & 5C documents
Laurent Cariou, Orange
John Doe, Some Company

10. November 2011
doc.: IEEE /1507r1
March 2013
Straw Poll
Should IEEE consider the creation of a study group to further discuss the topic of “High efficiency Wi-Fi” ?
Yes No
Abstain
Laurent Cariou, Orange
Stephen McCann, RIM

11. Motion to create a Study Group
November 2011
doc.: IEEE /1507r1
March 2013
Motion to create a Study Group
Request approval by IEEE 802 LMSC to form an Study Group to consider High-efficiency Wi-Fi [as described in doc xxxx] with the intent of creating a PAR and five criteria.
Moved: <name>, Seconded: <name>, Result: y-n-a
Laurent Cariou, Orange
Stephen McCann, RIM

12. March 2013
References
[1] 12/0910r0, Carrier oriented WIFI for cellular offload, Orange
[2] 12/1123r0, Carrier oriented WIFI for cellular offload, Orange
[3] 12/1126r0, Wi-Fi techniques for hotspot deployment and cellular offload, Samsung
[4] 12/1063r0, Requirements for WLAN Cellular Offload, NTT
[5] 13/0098r0, : Looking Ahead to the Future – Part II, Huawei
[6] Cisco WLAN design guide for High Density
[7] Cisco VNI mobile 2012
[8] 13/0113r0, Application and Requirements for Next Generation WLAN, Samsung
Laurent Cariou, Orange

13. March 2013
Annexes
Laurent Cariou, Orange

14. Hotspot deployment scenarios
Annex 1
Hotspot deployment scenarios
Hostpot deployments will scale between:
Street deployment for a blanket coverage of a neighborhood (typical cellular network pico-cell deployment)
50 APs per km², m distance between hotspots
Very high density deployments (stadiums, train stations, …)
6400 APs per km², 12-20m distance between APs
0.5 users per m² AP
STA m
MCS0 range
MCS0 range
MCS6 range
MCS6 range
Laurent Cariou, Orange

15. Pico-cell street scenario
Annex 1
Pico-cell street scenario
Characteristics of outdoor street deployments:
most deployments will be made with placement below rooftop (3 - 10m): lamp poles, hanged on cables, stuck to walls…
mostly side coverage (omni or directional)
ITU Micro (UMI) model could be a good fit
deployment is costly (backhaul, site rental…). As a consequence:
the distance between APs must be as high as possible (2 neighbor deployed APs will overlap close to the minimum sensitivity) – around meters
AP Tx Power is high (23-30dBm)
less constraints on frequency reuse
high density of STAs, spread over the whole BSS coverage
heterogeneous dense deployment: potential high proportion of interfering APs in the coverage of hotspots
indoor home or shop private APs leaking outdoors (usually in hidden node situation)
at 2.4GHz, between 15 to 20 APs in all 3 channels (beacons already occupy 20% of channel)
other public hotspots
coordination is feasible if they belong to the same operator,
is very difficult with other APs m AP
STA
Laurent Cariou, Orange

16. Stadium / train station scenario
Annex 1
Stadium / train station scenario
Characteristics of stadium/train station deployments:
side or overhead coverage (omni or directional)
very high user density (ex: hypothesis of 0.5 users/m²). As a consequence,
the distance between APs is reduced as much as possible (2 neighbor deployed APs will overlap largely) – around meters
AP Tx Power is usually reduced (6-12dBm)
high AP density: high constraints on frequency reuse: multi-BSS spatial capacity improvements
high density of STAs, regrouped over a limited range (higher MCSs) and not on the whole AP coverage (MCS0 range)
high co-channel interference coming from neighboring APs reusing the same frequencies
coordination is possible via the controller
potential interference coming from soft APs
more difficult to coordinate
MCS0 range
MCS0 range
MCS6 range
MCS6 range
Laurent Cariou, Orange

17. What are the main problems?
Annex 2
What are the main problems?
High number of STAs per AP
channel access has been designed for and is effective with a limited number of users. However, with a high density of STAs:
limitations of CSMA-CA: inefficient after a certain density of STAs due to increased collisions
MAC efficiency/airtime use limitations:
- much less efficient for a high number of users, each with limited throughput applications
- airtime use can be very inefficient with a traffic mix (small and big packets)
- a significant proportion of packets are very small
- e.g. web browsing: <100B packets represent 90% UL packets and 25% DL packets
airtime use can be also very inefficient with a mix of legacy devices
management frames (e.g. probe requests/responses) consume a large fraction of the available airtime
Laurent Cariou, Orange

18. Illustration: collision issues with high STA density per BSS
Annex 2
Illustration: collision issues with high STA density per BSS
Average PER increases rapidly with the number of STAs, approaching 50% for 25 STAs
Throughput and latency and power consumption is strongly impacted
Most rate prediction algorithms in devices lower MCS when PER increases, leading to a spiraling down of throughput.
Example with a rate prediction AARF (PER based)
AARF reference: IEEE rate adaptation: a practical approach Mathieu Lacage, Mohammad Hossein Manshaei, Thierry Turletti International Workshop on Modeling Analysis and Simulation of Wireless and Mobile Systems - MSWiM , pp , 2004
 AP sum throughput collapses
Laurent Cariou, Orange

19. What are the main problems?
Annex 2
What are the main problems?
In very high density deployment scenarios (large no. of APs)
saturation with high number of STAs per AP
channel reuse is almost impossible
co-channel interference strongly limits spatial capacity
problem is harder in environments without walls where propagation is very good
other interferences (adjacent-channel interference, non Wi-Fi interference)
inefficient cohabitation with tethering devices (soft APs) and Wi-Fi Direct devices
difficult to achieve consistent admission control, load balancing and fairness behavior to optimize networks even when APs deployed together
CCA protection zone
Typical scenario:
e.g. user density: 0.5 user/m²
cellular-like APs planning (with frequency reuse pattern)
AP density: 6400 AP/km² (distance between neighboring APs: 14m)
Channel reuse 3
Laurent Cariou, Orange

20. What are the main problems?
Annex 2
What are the main problems?
In outdoor deployment scenarios
delay spread issue in typical outdoor ITU UMI channels
links can hardly be maintained
in non-LOS, even with good received SNR (with Rx power below -70/75 dBm)
uplink is the limiting factor - especially with smartphones (10-12dBm Tx power)
high levels of interference
home gateways leaking outdoors
minimum of uncoordinated APs per channel (2.4GHz) under coverage (with rather small Rx power – but sufficient to cause interference, especially at BSS-edge)
saturation with a high number of STAs per AP
Typical scenario:
Pico-cell/AP deployment
50 to 60 APs per km²: inter-AP distance of m
500Mbps on 20000m² (80m-radius BSS)
Laurent Cariou, Orange