Overview on IEEE 802.11 standard and new 802.11ax amendment.

1. 802.11ax High Efficiency WLAN
Alice Valentini
alice.valentini7@studio.unibo.it
February 16th 2018
1 / 28

2. Overview
1 802.11
2 802.11ax
2 / 28

3. 802.11
3 / 28

4. 802.11
IEEE 802.11 is a set of media access control (MAC) and physical layer
(PHY) specifications for implementing wireless local area network (WLAN)
computer communication.
The 802.11 committee was set up by IEEE in the early 90s for developing
a reliable, fast, inexpensive wireless solution using the ISM band.
4 / 28

5. 802.11
Many amendments were released over the years.
802.11a, b, g, n, ac regard data transmission.
802.11i regards security.
802.11c, d, e, f, h, j, k, r, s are extensions to the currently available
services.
5 / 28

6. 802.11-1997
The original version of IEEE 802.11 was released in 1997. It is also called
802.11 legacy.
Bitrate from 1 (using BPSK) or 2 Mbps (using QPSK).
Operates in 2.4 GHz ISM band.
Uses CSMA/CA.
Uses DSSS and FHSS transmissions.
Included a MAC-level security protocol WEP.
It also included a specification for infrared wireless communications,
still operating at up to 2 Mbps.
6 / 28

7. 802.11b
Released in 1999.
Operates in 2.4 GHz band.
5.5 Mbps and 11 Mbps bitrates.
Uses only DSSS transmissions which provides higher data rates.
It is probably the most widely-recognized, and widely-used 802.11
standard.
7 / 28

8. Wi-Fi Alliance
In 1999 a group of companies endorsed the IEEE 802.11b specification to
form the Wireless Ethernet Compatibility Alliance (WECA) organization
and branded the new technology Wi-Fi.
WECA (later Wi-Fi Alliance) promotes the Wi-Fi technology and certifies
the interoperability of products.
The logo is applied only on equipment which has passed testing.
8 / 28

9. 802.11a
Released in 1999.
Operates in 5 GHz band which was less used than the 2.4 GHz
spectrum.
54 Mbps bitrate.
Uses OFDM with 52 subcarriers to mitigate interference and achieve
better data rates. Each subcarrier can be a BPSK, QPSK, 16-QAM
or 64-QAM.
Its high operating frequency was readily absorbed by physical
impediments, significantly decreasing its effective range.
Hardware is more expensive.
9 / 28

10. 802.11g
Released in 2003.
Operates in 2.4 GHz band.
54 Mbps bitrate.
Uses OFDM with 52 subcarriers. Each subcarrier can be BPSK,
QPSK, 16-QAM or 64-QAM.
Backward-compatible with the 802.11b.
10 / 28

11. 802.11n
Released in 2009.
Uses multiple-input multiple-output (MIMO) transmitting method
increasing the overall bitrate. 4 streams available.
Uses OFDM with 56 subcarriers which can be BPSK, QPSK,
16-QAM or 64-QAM.
It is backward-compatible with previous 2.4 GHz implementations of
802.11. Could also operate in the 5 GHz band.
It can support data rates up to 600 Mbps.
11 / 28

12. 802.11ac
Published in 2013.
Operates in 5 GHz band.
8 available MIMO streams, which 4 are downlink multi user streams
(MU-MIMO).
Multi-station throughput of at least 1 Gbps and single-link
throughput of at least 500 Mbps.
High-density modulation (up to 256-QAM).
12 / 28

13. 802.11
Bitrate Spectrum MIMO Streams Modulation
802.11-1997 1-2 Mbps 2.4 GHz 0 DSSS, FHSS
802.11b 5.5-11 Mbps 2.4 GHz 0 DSSS
802.11a 54 Mbps 5 GHz 0 OFDM
802.11g 54 Mbps 2.4 GHz 0 OFDM
802.11n 600 Mbps 2.4-5 GHz 4 OFDM
802.11ac 1 Gbps 5 GHz 8 OFDM
13 / 28

14. 802.11ax
14 / 28

15. 802.11ax
802.11ax task group was created in 2013.
The aim is to:
Improve WLAN performance and support multi-user transmission.
Efficient use of spectral resources.
Improve real world performance, especially in dense scenarios.
Improve energy efficiency.
Provide backward compatibility.
This new amendment should be released in 2019.
15 / 28

16. Higher throughput
16 / 28

17. OFDMA
OFDMA is also known as multiuser OFDM.
In OFDMA a channel can be split in several sub-channels and
assigned to different users.
Can be implemented with channel bonding.
Improves throughput.
It is also used in WiMAX (IEEE 802.16) and in LTE standard.
17 / 28

18. MU-MIMO
IEEE 802.11ax will further develop the MU-MIMO capabilities of IEEE
802.11ac by allowing multiple simultaneous transmissions in the uplink.
With UL MU MIMO the AP may simultaneously receive from
multiple transmitters.
UL transmission must be scheduled by the AP using a new control
frame (trigger).
18 / 28

19. Simultaneous Transmit and Receive (STR)
Simultaneous Transmit and Receive (STR) techniques can be used in
addition to OFDMA and MU-MIMO.
They are commonly known as full-duplex transmission.
Using STR a pair of nodes is able to transmit and receive
simultaneously.
Theoretically it doubles the channel capacity.
RTS/CTS packets can be used to start a full-duplex transmission.
19 / 28

20. Better throughput
In addition to the aforementioned techniques, 802.11ax will support
modulation up to 1024-QAM.
All these improvements could allow 802.11ax to reach a top speed of
around 10 Gbps.
20 / 28

21. Dense scenarios
Dense scenarios could be stadiums, apartments or trains.
21 / 28

22. Dense scenarios
Interferences increase the packet error rate reducing the number of
concurrent transmissions.
The presence of many stations in the same area increases the chances
that the backoff counters reach zero simultaneously, which results in a
collision.
22 / 28

23. Dense scenarios
Possible solutions:
Reduce transmit power.
Increasing or dinamically adjust the Clear Channel Assessment (CCA)
level.
Beamforming.
Two NAVs.
23 / 28

24. Target Wakeup Time
TWT permits an AP to define a specific time or set of times for
individual stations to access the medium.
The use of TWT is negotiated between an AP and a STA.
Allows the STA to sleep for periods of time, and wake up in
pre-scheduled (target) times to exchange information with its AP.
24 / 28

25. Backward compatibility
IEEE 802.11ax must support devices using any previous IEEE 802.11
PHY/MAC amendments.
Mandatory transmission of the legacy PHY preamble in all frames.
25 / 28

26. References I
[1] Boris Bellalta.
IEEE 802.11ax: High-efficiency WLANS.
IEEE Wireless Communications, 2016.
[2] Boris Bellalta, Luciano Bononi, Raffaele Bruno, and Andreas Kassler.
Next generation IEEE 802.11 Wireless Local Area Networks: Current status, future
directions and open challenges.
Computer Communications, 75:1–25, 2016.
[3] Der-Jiunn Deng, Kwang-Cheng Chen, and Rung-Shiang Cheng.
IEEE 802.11ax: Next Generation Wireless Local Area Networks.
[4] J Berg.
The IEEE 802.11 Standardization Its History, Specifications, Implementations, and
Future.
Telecom.Gmu.Edu, pages 1–33, 2011.
26 / 28

27. References II
[5] Michelle X Gong, Brian Hart, Cisco Systems, Mao Auburn, and Editor Michelle X
Gong.
Advanced Wireless Lan Technologies :.
18(48), 2014.
27 / 28

28. Thanks for the attention
28 / 28