802.11ax：Wi-Fi 6的高效教程：与4G/LTE比较详解

需积分: 9 194 浏览量更新于2024-07-15 收藏 2.11MB PDF 举报

本文是一篇深入探讨IEEE 802.11ax（也称为Wi-Fi 6）高效无线局域网（WLAN）的教程，发表在2018年9月的《IEEE Communications Surveys & Tutorials》期刊上。该文章对比了802.11ax与前一代技术，如4G/LTE，强调了802.11ax在频谱效率、数据传输速率和网络容量方面的显著提升。作者们，包括来自Institute for Information Transmission Problems的Evgeny Khorov、Anton Kiryanov、A. Lyakhov（俄罗斯科学院）以及Giuseppe Bianchi（罗马Tor Vergata大学），共同贡献了他们在量子互联网、物联网（IoT）等领域的专业知识，确保了文章内容的专业性和实用性。 802.11ax标准引入了关键技术，如OFDMA（正交频分多址）和MU-MIMO（多用户MIMO），这些技术允许同时处理多个设备的数据传输，从而显著提高了网络的并发性和吞吐量。此外，它还支持更高效的信道编码和调制方式，减少了信号干扰，并优化了频谱利用率，特别是在密集用户环境中的性能提升尤为明显。文章中可能详细分析了与802.11ac（Wi-Fi 5）相比，802.11ax在以下方面的主要改进： 1. **增强的多址技术**：MU-MIMO和OFDMA技术可以并行处理多个数据流，提高整体网络效率。 2. **更高的数据速率**：通过利用更多的频谱带宽和更先进的调制技术，802.11ax可以实现更快的上传和下载速度。 3. **更低的时延**：短帧技术和快速调度机制有助于减少数据传输的延迟，对于实时应用如VR/AR、远程医疗等具有重要意义。 4. **更好的能效**：通过智能功率管理和更优化的连接管理，802.11ax能够在保持性能的同时降低能耗。 5. **更大的网络容量**：在高密度用户环境中，802.11ax能更好地支持大规模设备接入。阅读这篇文章，读者不仅能了解到802.11ax的具体技术细节，还能了解其对现有网络架构的影响以及与移动通信技术的潜在融合点。如果你对Wi-Fi标准的演进、未来无线网络的发展或者想要深入了解如何部署和优化802.11ax网络有兴趣，这篇文章将提供宝贵的信息和见解。由于该论文已经获得了88次引用和超过11,000次阅读，表明其在学术界和业界受到了广泛的关注和认可。

200 IEEE COMMUNICATIONS SURVEYS & TUTORIALS, VOL. 21, NO. 1, FIRST QUARTER 2019

the decoding of at least some packets in case of short noise

bursts, at the expense of slightly increased overhead.

Since contention-based channel access inevitably leads to

collisions, from the very beginning IEEE 802.11 tried to add

various contention-free channel access mechanisms to the stan-

dard. Both the “historical” Point coordinated function (PCF,

obsolete now) and the subsequent Hybrid Controlled Channel

Access (HCCA) allow an AP to access the channel without

contention. Channel access coordination is accomplished by

introducing an Interframe Space called PIFS (PCF InterFrame

Space) which, being shorter than the DIFS (Distributed coor-

dination function InterFrame Space) used by the remaining

STAs, permits the AP to acquire the channel access with-

out any contention, so as to transmit data or poll the STAs

and grant them channel access. In practice, contention-free

access techniques have seen a very marginal deployment,

especially because of their inefﬁciency in scenarios when sev-

eral APs work in the same area. Indeed, if several APs use

PIFS, their transmissions will start simultaneously and col-

lide. This problem is partially addressed in the HCCA TXOP

Negotiation mechanism introduced in 802.11aa. The mecha-

nism allows various APs to use different time intervals for

transmission. Unfortunately, HCCA TXOP Negotiation can

only avoid collisions between APs which can communicate

with each other. Moreover, it does not reduce the collision

probabilities between an AP and the alien STAs, which still

can use random access.

The IEEE 802.11 Working Group has historically put a sig-

niﬁcant effort to improve the Quality of Service (QoS) in

Wi-Fi networks. Speciﬁcally, the 802.11e amendment intro-

duces Enhanced Distributed Channel Access (EDCA) and

HCCA which distinguish voice, video, best effort and back-

ground trafﬁc and serve them differently. While EDCA just

assigns different priorities to these types of trafﬁc, the sophis-

ticated HCCA allows an AP to schedule transmissions taking

into account speciﬁc QoS requirements, like the delay bound,

the packet loss ratio, or the required bandwidth. However,

determining exact requirements is a non trivial task, and

arguably another key reason behind the scarce deployment of

the contention-free HCCA.

For many devices which use Wi-Fi (e.g., laptops and smart-

phones) power consumption is an important issue. In 802.11

networks, power management is based on alternating between

two states: awake and doze. In the awake state, a STA can

transmit and receive frames, while in the doze state, its radio

is switched off. An active STA is always awake, while a

power-saving (PS) STA alternates between these states. The

AP buffers data destined for PS STAs until the STA wakes

up and retrieves it. Many amendments introduce new power-

saving features, but most of them are related to switching off

the radio for a rather long time, i.e., for hundreds of mil-

liseconds or even for seconds. Some of them require a PS

STA to contend for the channel if it wants to retrieve data

from the AP. Such methods are inefﬁcient in dense environ-

ments because of collisions, huge overhead and large delays.

Some other methods allow an AP and a PS STA to schedule

a series of times when the STA retrieves data from the AP.

The period of the series depends on the QoS requirements.

The tight dependence of these methods with HCCA function-

ality — speciﬁcally with the Trafﬁc Speciﬁcation (TSPEC)

information element which parametrizes QoS requirements —

prevents their usage in consumer electronics.

Finally, the 802.11ac amendment [17]–[19] was introduced

mainly with the purpose of signiﬁcantly increasing the data

rate of a 10x factor with respect to 802.11n. Besides increas-

ing the number of spatial streams up to 8, 802.11ac addresses

the problem of how to cope with terminals that, for obvious

manufacturing reasons, could not deploy more than 1 or 2

antennas. To this purpose, the 802.11ac ﬁrst introduces the

DL MU-MIMO, which allows an AP to assign various DL

spatial streams to different STAs — the UL MU transmis-

sion was postponed to subsequent standards owing to the tight

synchronization requirements which would have required a

signiﬁcant re-design. Additionally, 802.11ac widens the trans-

mission bands up to 160 MHz (also exploting non-contiguous

80+80Mhz channels) and increases the constellation order to

256-QAM, which raises data rates up to 7 Gbps. To reduce

the header-induced overhead at such high data rates, the

amendment increases the maximal length of a frame from

65 535 (802.11n) to 4 692 480 octets. Nevertheless, for

short packets, such as instant messages, Web requests, TCP

acknowledgments, etc. the channel is still used inefﬁciently.

B. Main Features of 802.11ax

Similarly to the previous amendments that improve the

nominal bit rates, 802.11ax contains a new PHY protocol

with higher modulation and coding schemes. In contrast to

802.11ac, 802.11ax does not increase the number of the

MIMO spatial streams and does not widen the channel. Thus

the nominal data rates are increased up to 9.6 Gbps, which is

just 37% higher than that of 802.11ac (rather small compared

to the 10x growth of 802.11n or 802.11ac!) [20]. The desired

increase of the user throughput is achieved by more efﬁcient

spectrum usage.

The key feature of 802.11ax is the adoption of an OFDMA

approach, an approach widely used in cellular networks, but

brand new in Wi-Fi. The rationale is that the very wide chan-

nels (80 MHz, 80+80 MHz and 160 MHz) introduced by

802.11ac suffer from frequency selective interference, which

signiﬁcantly impairs the practically achievable rates. With

OFDMA, adjacent subcarriers (tones) are grouped together

into a resource unit (RU) and a sender can choose the best RU

for each particular receiver, which actually results in higher

Signal-to-Interference-plus-Noise Ratio (SINR), Modulation

and Coding Scheme (MCS) and throughput. Moreover, since

the efﬁciency of high data rates degrades when a STA has

only few data to transmit, advanced aggregation techniques

aimed to reduce channel access, acknowledgment (ACK) and

preamble-induced overhead become useless. Allocating nar-

row RUs for such STAs is an efﬁcient remedy. According to

the latest TGax investigations, OFDMA provides a 6 times

higher throughput than legacy DCF [21], see Fig. 1.

OFDMA makes Wi-Fi radio access closer to the LTE one.

However in contrast to LTE, OFDMA works on top of the

legacy DCF and is coordinated by the AP. It means that having

剩余20页未读，继续阅读

zql2003

粉丝: 0
资源: 18

802.11ax：Wi-Fi 6的高效教程：与4G/LTE比较详解

2019-A Tutorial on IEEE 802.11ax High Efficiency WLANs.pdf

BROADCOM_WLAN_win7_6205551.exe

ieee 802.11 tutorial

[4]Shlens J. A Tutorial on Principal Component Analysis[J]. arXiv preprint arXiv:1404.1100, 2014.的标准文献参考名

metal.programming.guide.tutorial.and.reference.via.swift

A Machine Learning Tutorial for Operational Meteorology. Part I: Traditional Machine Learning改为引用文献格式

How To Simulate It – A Tutorial on the Simulation Proof Technique

用自动化编码器实现低剂量CT重建pytorch代码

tutorial_nn.py，这是什么意思

最新资源