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High-efficiency Wi-Fi

High-efficiency Wi-Fi. Authors:. Date: 2013-03-19. Outline. We propose to start a new study group to enhance 802.11 PHY and MAC in 2.4/5 GHz bands

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High-efficiency Wi-Fi

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  1. High-efficiency Wi-Fi Authors: Date: 2013-03-19 Laurent Cariou, Orange

  2. xxx, Orange

  3. Outline • We propose to start a new study group to enhance 802.11 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 802.11 across a broad range of market segments Laurent Cariou, Orange

  4. Status • In July 2012 meeting, Orange presented some requirements for 802.11 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 802.11 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 802.11 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 802.11. • We believe the current proposal has sufficient maturity to move to Study Group creation Laurent Cariou, Orange

  5. 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 • The key point is the increasing usage of 802.11 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 802.11 • Resulting in enhanced Quality of Experience for a broad spectrum of 802.11 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 Laurent Cariou, Orange

  8. 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 802.11 • 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. 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 802.11 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

  10. Straw Poll • Should IEEE 802.11 consider the creation of a study group to further discuss the topic of “High efficiency Wi-Fi” ? • Yes • No • Abstain Laurent Cariou, Orange

  11. Motion to create a Study Group • Request approval by IEEE 802 LMSC to form an 802.11 Study Group to consider High-efficiency Wi-Fi [as described in doc 11-13-xxxx] with the intent of creating a PAR and five criteria. • Moved: <name>, Seconded: <name>, Result: y-n-a Laurent Cariou, Orange

  12. 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, 802.11: 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. Annexes Laurent Cariou, Orange

  14. Annex 1 Hotspot deployment scenarios MCS0 range AP AP • Hostpot deployments will scale between: • Street deployment for a blanket coverage of a neighborhood (typical cellular network pico-cell deployment) • 50 APs per km², 150-200m distance between hotspots • Very high density deployments (stadiums, train stations, …) • 6400 APs per km², 12-20m distance between APs • 0.5 users per m² STA 160-200m MCS6 range MCS0 range MCS6 range Laurent Cariou, Orange

  15. Annex 1 Pico-cell street scenario AP AP • 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 150-200 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 STA 160-200m Laurent Cariou, Orange

  16. Annex 1 Stadium / train station scenario MCS0 range • 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 willoverlap largely) – around 12-20 meters • AP Tx Power is usually reduced (6-12dBm) • high AP density: high constraints on frequency reuse: multi-BSS spatial capacity improvements MCS6 range • 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 MCS6 range Laurent Cariou, Orange

  17. Annex 2 What are the main problems? • High number of STAs per AP • 802.11 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 theavailable airtime Laurent Cariou, Orange

  18. 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 802.11 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. 126-134, 2004 •  AP sum throughput collapses Laurent Cariou, Orange

  19. 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. 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 15-20 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 150-200m • 500Mbps on 20000m² (80m-radius BSS) Laurent Cariou, Orange

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