Huawei CloudCampus WLAN 802.11ac Wave 2
Technology White Paper
WLAN 802.11ac Wave 2 Technology White Paper
Abstract
Abstract
Since the first-generation 802.11 standards were released in 1997, Wi-Fi has
achieved great developments and has become popular in the past 22 years.
Nowadays, 802.11ac is released, greatly promoting the development of 802.11
standards. 802.11ac is coming to market in two releases: Wave 1 and Wave 2. This
document describes 802.11 Wave 2 and its key features.
WLAN 802.11ac Wave 2 Technology White Paper
Contents
Contents
Abstract ......................................................................................................................................... i
1 Overview..................................................................................................................................... 1
2 Implementation ........................................................................................................................ 1
3 Key Features of 802.11ac Wave 2 .......................................................................................... 5
3.1 Wider Channel Bonding ..................................................................................................................................... 5
3.2 MU-MIMO ............................................................................................................................................................ 7
4 Customer Benefits ................................................................................................................. 10
A Acronyms and Abbreviations ............................................................................................... 12
WLAN 802.11ac Wave 2 Technology White Paper
1 Overview
Background
1 Overview
Since the first-generation 802.11 standards were released in 1997, Wi-Fi has
achieved great developments and has become popular in the past 22 years.
Nowadays, Wi-Fi becomes the first choice for an increasing number of users to
access the Internet, and tends to replace the wired access. To meet requirements
of new service applications and reduce the gap with wired network bandwidth,
each generation of 802.11 standards among four generations of Wi-Fi systems
(801.11, 802.11b, 802.11a/g, and 802.11n) greatly improves the Wi-Fi rate. In the
fifth-generation 802.11 standards, the Wi-Fi rate improvement is undoubtedly a
highlight in the industry.
Figure 1-1 802.11 standard evolution
The wired Ethernet and applications drive 802.11ac development. As wired
Ethernet GE access gradually becomes the mainstream, Wi-Fi needs to provide
good user and service experience. In practice, 802.11n products face the following
challenges:
Large-bandwidth application
Large-bandwidth applications are widely used in the Wi-Fi field:
− Apple iClound service synchronization
− YouTube video services
WLAN 802.11ac Wave 2 Technology White Paper
1 Overview
− Vine (Twitter) video shooting and sharing application services
− Video conference services transferred from fixed devices to mobile
devices
− Video services for product and solution promotion by more and more
enterprises
These applications require higher Wi-Fi bandwidth. As predicted by Ericsson,
video traffic on mobile networks will increase by 60% every year until the end
of 2018. In 2018, video traffic will account for half of global mobile data
traffic.
Access from a large number of STAs
− Facing the BYOD development trend, an employee may have two or more
Wi-Fi STAs, each of which consumes network resources.
− In football fields, new product release conferences, or classrooms,
concurrent access from a large number of users poses a great challenge to
802.11n products.
− As there is more wireless access and fewer wired access, an increasing
number of STAs use Wi-Fi.
3G/4G offload
In the case of an explosive increase of data services in the cellular system,
more traffic is offloaded to Wi-Fi networks to reduce the load of the cellular
system. Wi-Fi shoulders the crossbeam as an "N" network. Wi-Fi networks
are required to provide larger capacity and access for more users.
To meet the preceding requirements, the fifth-generation 802.11 standard
(802.11ac) is developed. 802.11ac is innovated in a large number of technologies.
It will take a long time to release Wi-Fi products using all these technologies to
the market. Therefore, the Wi-Fi Alliance (WFA) defines 802.11ac into two
releases to release it to the market: Wave 1 and Wave 2. This not only facilitates
introduction of 802.11ac technology to the market, meeting the rapidly increasing
traffic requirements, but also supports the evolution of 802.11ac technology,
ensuring Wi-Fi competitiveness.
WLAN 802.11ac Wave 2 Technology White Paper
2 Implementation
Wave 1 and Wave 2 are two phases of the 802.11ac standard that are defined by
Feature
802.11a
802.11n
802.11ac
Channel width
20 MHz
20 MHz
20/40/80 MHz
40 MHz (option)
160 and 80+80 MHz
(option)
OFDM
Y Y Y
SGI N Y
Y
MIMO
Single antenna
SU MMO
Up to 4 antennas
SU and MU MIMO
Up to 8 antennas
Preamble
Legacy
Mixed Format (MF)
Mixed Format (MF) only
Green Field (GF)
Modulation and
coding schemes
Expressed as rates
76 MCS
9 MCS
Beamforming (option)
NA
Staggered and NDP
NDP
Feedback Format
NA
Compressed and
non-Compressed V
Matrix
Compressed V Matrix
Link adaptation
N Y Y
the WFA to release the 802.11ac standard to the market. Before introducing
802.11ac Wave 2, the following describes 802.11ac technology.
802.11ac and 802.11n
2 Implementation
To better understand 802.11ac, 802.11ac is compared with 802.11a that works in
the same frequency bands and 802.11n. The following table compares 802.11a,
802.11n, and 802.11a.
WLAN 802.11ac Wave 2 Technology White Paper
2 Implementation
Feature
802.11a
802.11n
802.11ac
Coding
BCC
BCC/LDPC (option)
BCC/LDPC (option)
Media Access Control
(MAC)
CSMA/CA
CSMA/CA
CSMA/CA
QoS (802.11E)
4 access categories
TXOP support
4 access categories
TXOP support
4 access categories
TXOP support
MAC protection
RTS/CTS
RTS/CTS spoofing
RTS/CTS spoofing
TXOP sharing
NA
NA
Supported for MU-MIMO
Static/Dynamic BA
Operation
NA N Y
MSDU
2304B
2304B or 7920B
2304B or 7920B
MPDU
3895B
3895B or 7991B
3895B, 7991B, or 11454B
A-MSDU
N
3839B or 7396B
3839B or 7396B
A-MPDU
N
65 KB
1 MB
MAC protocol data
unit
MPDU only
MPDU or A-MPDU
A-MPDU only
At the PHY and MAC address layers, 802.11ac optimizes channel bandwidth,
MIMO, and modulation mode, and improves or uses new technologies. 802.11ac
architecture is the same as 802.11n architecture. That is, 802.11ac is evolved
from 802.11n.
802.11ac provides the maximum throughput of 6.93 Gbit/s, which is almost 11
times the maximum throughput of 802.11n. Initially launched 802.11ac Wave 1
products provide the maximum throughput of up to 1.3 Gbit/s, meeting
expectations for Gbit/s Wi-Fi networks. In addition to the great increase of the
maximum throughput, 802.11ac also enhances the concurrent user access
capability. 802.11ac improves channel management when multiple bandwidth
values are used and enhances compatibility with 802.11a and 802.11n.
Wave 1 and Wave 2
802.11ac Wave 1 products start to enter the market in 2013. 802.11ac Wave 1 is
supported and used widely by USB terminals, household wireless routers, APs
used by enterprises and carriers, as well as smart STAs. Various types of STAs
and devices supporting 802.11ac Wave 2 have come into the markets since 2015.
The following table lists differences between 802.11ac Wave 1 and Wave 2 defined
by WFA and the IEEE 802.11ac standard.
WLAN 802.11ac Wave 2 Technology White Paper
2 Implementation
802.11ac Wave 1
(WFA)
802.11ac Wave 2 (WFA)
802.11ac (IEEE)
Band
5 GHz
5 GHz
5 GHz
MIMO
Single User (SU)
Multi User (MU)
MU
Channel width
20, 40, and 80
MHz
20, 40, 80, 80-80, and 160
MHz
20, 40, 80, 80-80, and
160 MHz
Modulation
256QAM
256QAM
256QAM
Spatial streams
3 4 8
PHY rate
1.3 Gbps
3.47 Gbps
6.9 Gbps
MAC throughout*
845 MHz
2.26 Gbps
4.49 Gbps
Note: The MAC throughput value is provided assuming that the MAC layer
efficiency is 65%.
Compared with 802.11ac Wave 1, 802.11ac Wave 2 supports MU-MIMO that
provides higher channel bandwidth and more MIMO streams. Therefore, 802.11ac
Wave 2 provides higher user access capabilities, a more flexible bandwidth
combination, and a higher throughput.
Supports MU-MIMO.
802.11ac Wave 1 supports only SU-MIMO, that is, an AP can communicate
with only one user at a time. 802.11ac Wave 2 supports MU-MIMO, that is, an
AP can concurrently communicate with multiple users. MU-MIMO increases
the number of access STAs, meeting requirements for the access of a large
number of STAs in the all Wi-Fi and Internet of Things (IoT) era when one user
has multiple STAs.
Supports up to 160 MHz channel bandwidth (a combination of adjacent
channels or two non-adjacent 80 MHz channels).
802.11ac Wave 1 supports a maximum of 80 MHz channel bandwidth, while
802.11ac Wave 2 supports up to 160 MHz channel bandwidth. The 160 MHz
bandwidth can be the total bandwidth of a combination of adjacent channels
or two non-adjacent 80 MHz channels. This increases the peak throughput
and channel combination flexibility. When larger-bandwidth channels are
configured, the usage of channels on the 5 GHz frequency band can also be
improved.
Supports up to four MIMO spatial streams.
802.11 Wave 1 supports three MIMO spatial streams, while 802.11ac Wave 2
supports up to four MIMO spatial streams. The increase of MIMO spatial
streams improves users' peak throughput or expands the coverage scope of a
Wi-Fi network. The increases of channel bandwidth and MIMO spatial
streams improve the throughput of 802.11ac Wave 2 products. The peak
throughput provided by 802.11ac Wave 2 products increases to 3.47 Gbit/s (4
WLAN 802.11ac Wave 2 Technology White Paper
2 Implementation
MIMO spatial streams) from 1.3 Gbit/s (3 MIMO spatial streams) provided by
802.11ac Wave 1 products.
The preceding table also demonstrates that 802.11ac Wave 2 defined by the WFA
is different from the 802.11ac standard defined by IEEE in the number of spatial
streams. This is because costs (complexity) need to be considered when the
standards are applied to products.
WLAN 802.11ac Wave 2 Technology White Paper
3 Key Features of 802.11ac Wave 2
3 Key Features of 802.11ac Wave 2
802.11ac Wave 2 introduces two features: wider channel bonding and MU-MIMO.
3.1 Wider Channel Bonding
IEEE 802.11n supports only two bandwidth modes: 20 MHz and 40 MHz. The 20
MHz mode is mandatory while the 40 MHz mode is optional. IEEE 802.11ac
supports 20 MHz, 40 MHz, 80 MHz, 80+80 MHz (non-adjacent), and 160 MHz
channel bandwidth. The 20 MHz, 40 MHz, and 80 MHz modes are mandatory while
the 80+80 MHz and 160 MHz modes are optional. 802.11ac Wave 1 defined by the
WFA supports 20 MHz, 40 MHz, and 80 MHz channel bandwidth. 802.11ac Wave 2
defined by the WFA supports adjacent and non-adjacent 160 MHz channel
bonding. Figure 3-1 uses the frequency spectrum in North America as an example
to compare channel bonding in 802.11ac Wave 1, 802.11ac Wave 2, 802.11n, and
802.11a.
Figure 3-1 Channel bandwidth in 802.11ac Wave 2
As shown in Figure 3-1, if the channel bandwidth is 20 MHz, 40 MHz, or 80 MHz,
there are 25, 12, or 6 channels respectively. If the channel bandwidth is 160 MHz,
WLAN 802.11ac Wave 2 Technology White Paper
3 Key Features of 802.11ac Wave 2
there are two adjacent channels. The 160 MHz channel can be a combination of
two non-overlapping 80 MHz channels. Channel bonding allows a flexible
combination of channels. For example, to avoid the use of DFS channels, users
can bind two non-DFS 80 MHz channels into a 160 MHz channel. In 80+80 MHz
channel bonding mode, up to 13 bonding methods are supported.
Figure 3-2 80+80 MHz channel combination in 802.11ac Wave 2
Wider channel bonding can provide wider channel bandwidth. Channel bonding
helps avoid some interference and can improve the utilization of scattered
channels.
Similar to HT20, HT40, and HT80 channels, an HT160 channel consists of one
primary 80 MHz channel and one secondary 80 MHz channel. As shown in the
following figure, an 80 MHz channel consists of one primary 40 MHz channel and
one secondary 40 MHz channel, and a 40 MHz channel consists of one primary 20
MHz channel and one secondary 20 MHz channel.
WLAN 802.11ac Wave 2 Technology White Paper
3 Key Features of 802.11ac Wave 2
Figure 3-3 HT160 channel in 802.11ac Wave 2
3.2 MU-MIMO
SU-MIMO can increase the throughput of a single user significantly. However,
most STAs, especially mobile smart STAs, on live networks support one stream
only. Compared with multi-stream STAs, single-stream STAs occupy air
interfaces for a longer period when they transmit data of the same size.
Therefore, single-stream STAs become a bottleneck for increasing the number of
access users. MU-MIMO is a good solution to this problem. With the user
bandwidth and frequency unchanged, an AP can concurrently transmit different
data to four users at most. Figure 3-4 compares the SU-MIMO and MU-MIMO
transmission modes of a 4x4 MIMO AP. In the SU-MIMO transmission mode, all
antennas of the AP send the same data. Although this transmission mode
provides diversity gains, the gains are limited. In the MU-MIMO transmission
mode, antennas of the AP transmit different data to different users. A single AP
can send four different data packets, increasing the efficiency by four times than
that in single-MIMO transmission mode.
Figure 3-4 Comparison between SU-MIMO and MU-MIMO
WLAN 802.11ac Wave 2 Technology White Paper
3 Key Features of 802.11ac Wave 2
MU-MIMO is also applicable to scenarios where both multi-stream and singlestream STAs exist. For example, Figure 3-5 shows two application scenarios: one
dual-stream STA + two single-stream STAs and two dual-stream STAs.
Figure 3-5 Application scenarios where both multi-stream and single-stream STAs
exist
MU-MIMO is an outstanding feature of 802.11ac Wave 2, which depends on
explicit transmit beamforming (TxBF). This feature requires that STAs support
explicit TxBF. The reason is that when an AP concurrently transmits data to
multiple users over the same frequency, signals are interference to users who are
not target receivers of the signals. MU-MIMO uses TxBF to detect channels and
uses precoding technology based on the feedback to mitigate such interference.
Figure 3-6 Comparison between SU-MIMO and MU-MIMO
Figure 3-6 shows a MU-MIMO application scenario with one 3x3 MIMO AP and
three 1x1 MIMO STAs. To obtain channel information about each STA, the AP
sends a sounding frame to each STA. The STAs reply the AP with channel
information. The AP uses precoding technology to implement beamforming to
WLAN 802.11ac Wave 2 Technology White Paper
3 Key Features of 802.11ac Wave 2
generate strong signals in the respective direction to each STA but weak signals
in other directions (including directions to other STAs). In this way, the AP ensures
good wireless coverage and mitigates interference to other users.
MU-MIMO applies to downlink transmission only and can concurrently transmit
data to four users at most. In the uplink, data frames of a single user are
transmitted one by one. If lengths of concurrently-transmitted frames are
different, frame padding is used to adjust the frame lengths. The scheduled BA
mechanism is used to schedule ACK responses from each user so that ACK
responses are sent one by one.
MU-MIMO increases the number of concurrent users on a single AP, enhancing
the concurrent user access capability. In single-stream STA scenarios especially,
MU-MIMO improves the downlink throughput of APs significantly. In multi-user
transmission, interference between streams limits the usage of higher-order
modulation modes, for example, 256QAM.
WLAN 802.11ac Wave 2 Technology White Paper
4 Customer Benefits
4 Customer Benefits
Standard
Channel
Size
Max.
Modulation
Max. Spatial
Streams
Max Data
Rate
802.11
20 MHz
DQPSK
1
2 Mbps
802.11b
20 MHz
CCK
1
11 Mbps
802.11g
20 MHz
64QAM
1
54 Mbps
802.11a
20 MHz
64QAM
1
54 Mbps
802.11n
40 MHz
64QAM
4
600 Mbps
802.11ac Wave 1
80 MHz
256QAM
3
1.3 Gbps
802.11ac Wave 2
160 MHz
256QAM
4
3.47 Gbps
1. Higher throughput
High throughput has always been the goal of Wi-Fi standards. The throughput
is being improved from the first-generation Wi-Fi standards to the latestgeneration standards, as listed in the following table.
Higher throughput can meet the requirements of rapidly growing video
services and data services. Moreover, higher throughput provides Wi-Fi
networks with more advantages in competition with wired networks. This is a
step toward achieving the goal of making Wi-Fi become the first choice for
wireless access.
2. More access users
Although 802.11ac Wave 2 does not change the multiple access modes on WiFi networks, it provides higher throughput and MU-MIMO, improving the user
access capability. Higher rates lead to shorter air interface occupation
duration of each user. In the same time period, an AP can allow access of
more users. MU-MIMO also provides stronger concurrent access capability.
An AP can concurrently transmit data to multiple users. In the all Wi-Fi and
IoT era when one user has multiple STAs, stronger access capabilities can
better meet the access requirements of a large number of STAs.
WLAN 802.11ac Wave 2 Technology White Paper
4 Customer Benefits
Figure 4-1 One user with multiple STAs
WLAN 802.11ac Wave 2 Technology White Paper
A Acronyms and Abbreviations
A Acronyms and Abbreviations
M
MIMO
Multiple-input multiple-output
S STA
Station
T TxBF
Transmit beamforming
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