ACCEPTED FROM OPEN CALL IEEE 802.11AX:HIGH-EFFICIENCY WLANS BORIS BELLALTA ABSTRACT um access control (MAC)layer enhancements to further improve the WLAN performance, IEEE 802.11ax-2019 will replace both IEEE with a focus on the throughput and battery 802.11n-2009 and IEEE 802.11ac-2013 as the duration.This article overviews some of those next high-throughput WLAN amendment.In this new enhancements,and describes the potential article,we review the expected future WLAN benefits and drawbacks of each one.We have scenarios and use cases that justify the push for a grouped these enhancements into four main cat- new PHY/MAC IEEE 802.11 amendment.After egories:spatial reuse,temporal efficiency,spec- that,we overview a set of new technical features trum sharing,and multiple-antenna technologies. that may be included in the IEEE 802.11ax-2019 Moreover,we also discuss several key system-lev- amendment.and describe both their advantages el improvements for next-generation WLANs,as and drawbacks.Finally,we discuss some of the in addition to the IEEE 802.11ax-2019 amend- network-level functionalities that are required to ment,they will likely implement other in-prog- fully improve the user experience in next-gener- ress amendments such as IEEE 802.11aq-2016 ation WLANs and note their relation with other (pre-association discovery of services),IEEE ongoing IEEE 802.11 amendments. 802.11ak-2017 (bridged networks),and IEEE 802.11ai-2016(fast initial link setup time)to sat- INTRODUCTION isfy the created expectations. IEEE 802.11 wireless local area networks (WLANs)[1]are a cost-efficient solution for SCENARIOS,USE CASES,AND wireless Internet access that can satisfy most cur- rent communication requirements in domestic, REQUIREMENTS public,and business scenarios. The forecast number of devices and networks. Similar to other wireless technologies.WLANs and traffic characteristics and user demands for have evolved by integrating the latest technolog- the 2020-2030 decade motivate the development ical advances in the field as soon as they have of a new PHY/MAC IEEE 802.11 amendment to become sufficiently mature,aiming to continuous- cope with the new challenges and usages WLANs ly improve spectrum utilization and raw WLAN will face [2]. performance.IEEE 802.11n-2009 adopted sin- One of the most representative characteris- gle-user multiple-input multiple-output (SU-MI- tics of WLANs is the use of carrier sense multiple MO),channel bonding,and packet aggregation. access with collision avoidance (CSMA/CA)as Those mechanisms were further extended in IEEE the MAC protocol.It offers a reasonable trade- 802.11ac-2013,which also introduced downlink off between performance,robustness,and imple- multi-user (MU)MIMO transmissions.In addi- mentation costs.Using CSMA/CA,when a node tion,new amendments such as IEEE 802.11af- has a packet ready for transmission,it listens to 2013 and IEEE 802.11ah-2016 are further the channel.Once the channel has been detect- expanding the application scenarios of WLANs, ed as free (i.e.,the energy level on the channel which include cognitive radio,long-range commu- is lower than the clear channel assessment.CCA nication,advanced power saving mechanisms,and threshold),the node starts the backoff procedure support for machine-to-machine (M2M)devices. by selecting a random initial value for the backoff Partly because of their own success,next-gen- counter.The node then starts decreasing the back- eration WLANs face two main challenges.First. off counter while sensing the channel.Whenever a they must address dense scenarios,which is transmission,either from other nodes within the motivated by the continuous deployment of new same WLAN or belonging to other WLANs,is access points(APs)to cover new areas and pro- detected on the channel,the backoff counter is vide higher transmission rates.Second,the cur- paused until the channel is detected to be free rent evolution of Internet usage toward real-time again,at which point the countdown is resumed. high-definition audio and video content will also When the backoff counter reaches zero,the node significantly increase users'throughput needs in starts transmitting.Figure la shows an example of the coming years. CSMA/CA operation. To address those challenges,the High-Effi- ciency WLAN(HEW)Task Group [2]is current- DENSE WLAN SCENARIOS The author is with Uni- ly working on a new high-throughput amendment Providing high data rates in scenarios where versitat Pompeu Fabra, named IEEE 802.11ax-2019.This new amend- the density of WLAN users is very high (e.g.,1 Barcelona ment will develop new physical(PHY)and medi- user/m2)requires the deployment of many APs 38 1536-1284/16/$25.00©2016IEEE IEEE Wireless Communications.February 201638 1536-1284/16/$25.00 © 2016 IEEE IEEE Wireless Communications • February 2016 The author is with Uni￾versitat Pompeu Fabra, Barcelona Abstract IEEE 802.11ax-2019 will replace both IEEE 802.11n-2009 and IEEE 802.11ac-2013 as the next high-throughput WLAN amendment. In this article, we review the expected future WLAN scenarios and use cases that justify the push for a new PHY/MAC IEEE 802.11 amendment. After that, we overview a set of new technical features that may be included in the IEEE 802.11ax-2019 amendment, and describe both their advantages and drawbacks. Finally, we discuss some of the network-level functionalities that are required to fully improve the user experience in next-gener￾ation WLANs and note their relation with other ongoing IEEE 802.11 amendments. Introduction IEEE 802.11 wireless local area networks (WLANs) [1] are a cost-efficient solution for wireless Internet access that can satisfy most cur￾rent communication requirements in domestic, public, and business scenarios. Similar to other wireless technologies, WLANs have evolved by integrating the latest technolog￾ical advances in the field as soon as they have become sufficiently mature, aiming to continuous￾ly improve spectrum utilization and raw WLAN performance. IEEE 802.11n-2009 adopted sin￾gle-user multiple-input multiple-output (SU-MI￾MO), channel bonding, and packet aggregation. Those mechanisms were further extended in IEEE 802.11ac-2013, which also introduced downlink multi-user (MU) MIMO transmissions. In addi￾tion, new amendments such as IEEE 802.11af- 2013 and IEEE 802.11ah-2016 are further expanding the application scenarios of WLANs, which include cognitive radio, long-range commu￾nication, advanced power saving mechanisms, and support for machine-to-machine (M2M) devices. Partly because of their own success, next-gen￾eration WLANs face two main challenges. First, they must address dense scenarios, which is motivated by the continuous deployment of new access points (APs) to cover new areas and pro￾vide higher transmission rates. Second, the cur￾rent evolution of Internet usage toward real-time high-definition audio and video content will also significantly increase users’ throughput needs in the coming years. To address those challenges, the High-Effi￾ciency WLAN (HEW) Task Group [2] is current￾ly working on a new high-throughput amendment named IEEE 802.11ax-2019. This new amend￾ment will develop new physical (PHY) and medi￾um access control (MAC) layer enhancements to further improve the WLAN performance, with a focus on the throughput and battery duration. This article overviews some of those new enhancements, and describes the potential benefits and drawbacks of each one. We have grouped these enhancements into four main cat￾egories: spatial reuse, temporal efficiency, spec￾trum sharing, and multiple-antenna technologies. Moreover, we also discuss several key system-lev￾el improvements for next-generation WLANs, as in addition to the IEEE 802.11ax-2019 amend￾ment, they will likely implement other in-prog￾ress amendments such as IEEE 802.11aq-2016 (pre-association discovery of services), IEEE 802.11ak-2017 (bridged networks), and IEEE 802.11ai-2016 (fast initial link setup time) to sat￾isfy the created expectations. Scenarios, Use Cases, and Requirements The forecast number of devices and networks, and traffic characteristics and user demands for the 2020–2030 decade motivate the development of a new PHY/MAC IEEE 802.11 amendment to cope with the new challenges and usages WLANs will face [2]. One of the most representative characteris￾tics of WLANs is the use of carrier sense multiple access with collision avoidance (CSMA/CA) as the MAC protocol. It offers a reasonable trade￾off between performance, robustness, and imple￾mentation costs. Using CSMA/CA, when a node has a packet ready for transmission, it listens to the channel. Once the channel has been detect￾ed as free (i.e., the energy level on the channel is lower than the clear channel assessment, CCA, threshold), the node starts the backoff procedure by selecting a random initial value for the backoff counter. The node then starts decreasing the back￾off counter while sensing the channel. Whenever a transmission, either from other nodes within the same WLAN or belonging to other WLANs, is detected on the channel, the backoff counter is paused until the channel is detected to be free again, at which point the countdown is resumed. When the backoff counter reaches zero, the node starts transmitting. Figure 1a shows an example of CSMA/CA operation. Dense WLAN Scenarios Providing high data rates in scenarios where the density of WLAN users is very high (e.g., 1 user/m2) requires the deployment of many APs Boris Bellalta IEEE 802.11ax: High-Efficiency WLANs Ac cep te d f r o m Ope n C a ll