IEEE 802.11ax：下一代高效率WLAN技术概述

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"这篇文章主要探讨了IEEE 802.11ax标准，该标准将替代802.11n和802.11ac，成为新一代高吞吐量无线局域网（WLAN）的修正案。文章审查了推动新标准实施的未来WLAN场景和应用案例，并详述了可能包含在802.11ax修正案中的技术特性，以及它们的优缺点。最后，讨论了提升下一代WLAN用户体验所需的网络级功能，并指出这些功能与其他正在进行的IEEE 802.11修正案的关系。" 在介绍部分，文章指出IEEE 802.11无线局域网标准是满足当前各种环境（家庭、公共和商业）无线互联网接入需求的经济有效解决方案。与其它无线技术一样，WLANs通过整合领域的最新技术进步不断演进。 802.11ax标准，也被称为WiFi6，旨在解决不断增长的数据需求和密集用户环境下的性能挑战。相比于之前的802.11n和802.11ac标准，802.11ax提供了更高的效率和更大的容量。这个新标准引入了一系列关键技术改进，包括： 1. **高密度接入**：802.11ax利用了多用户MIMO（MU-MIMO）技术，允许路由器同时与多个设备通信，显著提高了网络的效率和容量。 2. **OFDMA（正交频分多址）**：与802.11ac使用的OFDM不同，OFDMA允许在单个信道上分配资源给多个设备，减少了调度开销，提高了频谱效率。 3. **目标唤醒时间（TWT）**：设备可以协商与接入点的通信时间，从而降低了功耗，对电池寿命敏感的设备尤为有利。 4. **1024-QAM调制**：比802.11ac的256-QAM提供更多数据编码位，提高了每个符号传输的信息量，从而提升了数据速率。 5. **频道绑定和更宽的带宽**：支持更宽的频道宽度，如160MHz，进一步提高了传输速率。文章还讨论了这些技术的特点和局限性，例如，虽然OFDMA提高了效率，但其对同步要求更高，可能会增加复杂性。此外，1024-QAM对信号质量有较高要求，可能导致在弱信号环境下的性能下降。在提升用户体验方面，802.11ax引入的网络级功能包括更好的服务质量（QoS）管理、增强的漫游能力以及更高效的资源调度。这些改进与正在进行的其他IEEE 802.11修正案（如802.11be，旨在超越802.11ax的性能）相辅相成，共同构建更加先进和适应未来的无线网络环境。 IEEE 802.11ax标准，即WiFi6，旨在通过引入一系列创新技术来应对高密度无线环境的挑战，提高网络效率、容量和用户体验。随着物联网和5G的快速发展，802.11ax为无线通信设定了新的标准，为未来网络的扩展和优化打下了坚实基础。

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

equIrements

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/m

) requires the deployment of many APs

Boris Bellalta

IEEE 802.11ax: HIgH-EffIcIEncy WLans

a c c E p t E d f r o m o p E n c a L L

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