IEEE 802.11ah is a wireless networking protocol published in 2017[1] called Wi-Fi HaLow[2][3][4] (/ˈheɪˌloʊ/) as an amendment of the IEEE 802.11-2007 wireless networking standard. It uses 900 MHz license-exempt bands to provide extended-range Wi-Fi networks, compared to conventional Wi-Fi networks operating in the 2.4 GHz, 5 GHz and 6 GHz bands. It also benefits from lower energy consumption, allowing the creation of large groups of stations or sensors that cooperate to share signals, supporting the concept of the Internet of things (IoT).[5] The protocol's low power consumption competes with Bluetooth, LoRa, and Zigbee,[6] and has the added benefit of higher data rates and wider coverage range.[2]

Description

A benefit of 802.11ah is extended range, making it useful for rural communications and offloading cell phone tower traffic.[7] The other purpose of the protocol is to allow low rate 802.11 wireless stations to be used in the sub-gigahertz spectrum.[5] The protocol is one of the IEEE 802.11 technologies which is the most different from the LAN model, especially concerning medium contention. A prominent aspect of 802.11ah is the behavior of stations that are grouped to minimize contention on the air media, use relay to extend their reach, use little power thanks to predefined wake/doze periods, are still able to send data at high speed under some negotiated conditions and use sectored antennas. It uses the 802.11a/g specification that is down sampled to provide 26 channels, each of them able to provide 100 kbit/s throughput. It can cover a one-kilometer radius.[8] It aims at providing connectivity to thousands of devices under an access point. The protocol supports machine to machine (M2M) markets, like smart metering.[9]

Data rates

Data rates up to 347 Mbit/s are achieved only with the maximum of four spatial streams using one 16 MHz-wide channel. Various modulation schemes and coding rates are defined by the standard and are represented by a Modulation and Coding Scheme (MCS) index value. The table below shows the relationships between the variables that allow for the maximum data rate. The Guard interval (GI) is defined as the timing between symbols.

2 MHz channel uses an FFT of 64, of which: 56 OFDM subcarriers, 52 are for data and 4 are pilot tones with a carrier separation of 31.25 kHz (2 MHz/64) (32 µs). Each of these subcarriers can be a BPSK, QPSK, 16-QAM, 64-QAM or 256-QAM. The total bandwidth is 2 MHz with an occupied bandwidth of 1.78 MHz. Total symbol duration is 36 or 40 microseconds, which includes a guard interval of 4 or 8 microseconds.[8]

Modulation and coding schemes
MCS
index[lower-alpha 1]		 Spatial
Streams		 Modulation
type		 Coding
rate		 Data rate (Mbit/s)[8]
1 MHz channels2 MHz channels4 MHz channels8 MHz channels16 MHz channels
8 μs GI[lower-alpha 2]4 μs GI8 μs GI4 μs GI8 μs GI4 μs GI8 μs GI4 μs GI8 μs GI4 μs GI
01BPSK1/20.30.330.650.721.351.52.933.255.856.5
11QPSK1/20.60.671.31.442.73.05.856.511.713.0
21QPSK3/40.91.01.952.174.054.58.789.7517.619.5
3116-QAM1/21.21.332.62.895.46.011.713.023.426.0
4116-QAM3/41.82.03.94.338.19.017.619.535.139.0
5164-QAM2/32.42.675.25.7810.812.023.426.046.852.0
6164-QAM3/42.73.05.856.512.213.526.329.352.758.5
7164-QAM5/63.03.346.57.2213.515.029.332.558.565.0
81256-QAM3/43.64.07.88.6716.218.035.139.070.278.0
91256-QAM5/64.04.44——18.020.039.043.378.086.7
101BPSK1/2 x 20.150.17————————
02BPSK1/20.60.671.31.442.73.05.856.511.713.0
12QPSK1/21.21.342.62.895.46.011.713.023.426.0
22QPSK3/41.82.03.94.338.19.017.619.535.139.0
3216-QAM1/22.42.675.25.7810.812.023.426.046.852.0
4216-QAM3/43.64.07.88.6716.218.035.139.070.278.0
5264-QAM2/34.85.3410.411.621.624.046.852.093.6104
6264-QAM3/45.46.011.713.024.327.052.758.5105117
7264-QAM5/66.06.6713.014.427.030.058.565.0117130
82256-QAM3/47.28.015.617.332.436.070.278.0140156
92256-QAM5/68.08.89——36.040.078.086.7156173
03BPSK1/20.91.01.952.174.054.58.789.7517.619.5
13QPSK1/21.82.03.94.338.19.017.619.535.139.0
23QPSK3/42.73.05.856.512.213.526.329.352.758.5
3316-QAM1/23.64.07.88.6716.218.035.139.070.278.0
4316-QAM3/45.46.011.713.024.327.052.758.5105117
5364-QAM2/37.28.015.617.332.436.070.278.0140156
6364-QAM3/48.19.017.619.536.540.5——158176
7364-QAM5/69.010.019.521.740.545.087.897.5176195
83256-QAM3/410.812.023.426.048.654.0105117211234
93256-QAM5/612.013.3426.028.954.060.0117130——

MAC Features

Relay Access Point

A Relay Access Point (AP) is an entity that logically consists of a Relay and a networking station (STA), or client. The relay function allows an AP and stations to exchange frames with one another by the way of a relay. The introduction of a relay allows stations to use higher MCSs (Modulation and Coding Schemes) and reduce the time stations will stay in Active mode. This improves battery life of stations. Relay stations may also provide connectivity for stations located outside the coverage of the AP. There is an overhead cost on overall network efficiency and increased complexity with the use of relay stations. To limit this overhead, the relaying function shall be bi-directional and limited to two hops only.

Power saving

Power-saving stations are divided into two classes: TIM stations and non-TIM stations. TIM stations periodically receive information about traffic buffered for them from the access point in the so-called TIM information element, hence the name. Non-TIM stations use the new Target Wake Time mechanism which enables reducing signaling overhead.[10]

Target Wake Time

Target Wake Time (TWT) is a function that permits an AP to define a specific time or set of times for individual stations to access the medium. The STA (client) and the AP exchange information that includes an expected activity duration to allow the AP to control the amount of contention and overlap among competing STAs. The AP can protect the expected duration of activity with various protection mechanisms. The use of TWT is negotiated between an AP and an STA. Target Wake Time may be used to reduce network energy consumption, as stations that use it can enter a doze state until their TWT arrives.

Restricted Access Window

Restricted Access Window allows partitioning of the stations within a Basic Service Set (BSS) into groups and restricting channel access only to stations belonging to a given group at any given time period. It helps to reduce contention and to avoid simultaneous transmissions from a large number of stations hidden from each other.[11][12]

Bidirectional TXOP

Bidirectional TXOP allows an AP and non-AP (STA or client) to exchange a sequence of uplink and downlink frames during a reserved time (transmit opportunity or TXOP). This operation mode is intended to reduce the number of contention-based channel accesses, improve channel efficiency by minimizing the number of frame exchanges required for uplink and downlink data frames, and enable stations to extend battery lifetime by keeping Awake times short. This continuous frame exchange is done both uplink and downlink between the pair of stations. In earlier versions of the standard Bidirectional TXOP was called Speed Frame Exchange.[13]

Sectorization

The partition of the coverage area of a Basic Service Set (BSS) into sectors, each containing a subset of stations, is called sectorization. This partitioning is achieved through a set of antennas or a set of synthesized antenna beams to cover different sectors of the BSS. The goal of the sectorization is to reduce medium contention or interference by the reduced number of stations within a sector and/or to allow spatial sharing among overlapping BSS (OBSS) APs or stations.

Comparison with 802.11af

Another WLAN standard for sub-1 GHz bands is IEEE 802.11af which, unlike 802.11ah, operates in licensed bands. More specifically, 802.11af operates in the TV white space spectrum in the VHF and UHF bands between 54 and 790 MHz using cognitive radio technology.[14]

IEEE 802.11 network standards

802.11 network standards
Frequency
range,
or type		 PHY Protocol Release
date [15]		 Frequency Bandwidth Stream
data rate [16]		 Allowable
MIMO streams		 Modulation Approximate
range
Indoor Outdoor
(GHz) (MHz) (Mbit/s)
1–7⅛ GHz DSSS[17], FHSS[upper-alpha 1] 802.11-1997 June 1997 2.4 22 1, 2 — DSSS, FHSS[upper-alpha 1] 20 m (66 ft) 100 m (330 ft)
HR/DSSS [17] 802.11b September 1999 2.4 22 1, 2, 5.5, 11 — CCK, DSSS 35 m (115 ft) 140 m (460 ft)
OFDM 802.11a September 1999 5 5, 10, 20 6, 9, 12, 18, 24, 36, 48, 54
(for 20 MHz bandwidth,
divide by 2 and 4 for 10 and 5 MHz)		 — OFDM 35 m (115 ft) 120 m (390 ft)
802.11j November 2004 4.9, 5.0
[upper-alpha 2][18]		 ? ?
802.11y November 2008 3.7 [upper-alpha 3] ? 5,000 m (16,000 ft)[upper-alpha 3]
802.11p July 2010 5.9 200 m 1,000 m (3,300 ft)[19]
802.11bd December 2022 5.9, 60 500 m 1,000 m (3,300 ft)
ERP-OFDM 802.11g June 2003 2.4 38 m (125 ft) 140 m (460 ft)
HT-OFDM [20] 802.11n
(Wi-Fi 4)		 October 2009 2.4, 5 20 Up to 288.8[upper-alpha 4] 4 MIMO-OFDM
(64-QAM)		 70 m (230 ft) 250 m (820 ft)[21]
40 Up to 600[upper-alpha 4]
VHT-OFDM [20] 802.11ac
(Wi-Fi 5)		 December 2013 5 20 Up to 693[upper-alpha 4] 8 DL
MU-MIMO OFDM
(256-QAM)		 35 m (115 ft)[22] ?
40 Up to 1600[upper-alpha 4]
80 Up to 3467[upper-alpha 4]
160 Up to 6933[upper-alpha 4]
HE-OFDMA 802.11ax
(Wi-Fi 6,
Wi-Fi 6E)		 May 2021 2.4, 5, 6 20 Up to 1147[upper-alpha 5] 8 UL/DL
MU-MIMO OFDMA
(1024-QAM)		 30 m (98 ft) 120 m (390 ft) [upper-alpha 6]
40 Up to 2294[upper-alpha 5]
80 Up to 4804[upper-alpha 5]
80+80 Up to 9608[upper-alpha 5]
EHT-OFDMA 802.11be
(Wi-Fi 7)		 Dec 2024
(est.)		 2.4, 5, 6 80 Up to 11.5 Gbit/s[upper-alpha 5] 16 UL/DL
MU-MIMO OFDMA
(4096-QAM)		 30 m (98 ft) 120 m (390 ft) [upper-alpha 6]
160
(80+80)		 Up to 23 Gbit/s[upper-alpha 5]
240
(160+80)		 Up to 35 Gbit/s[upper-alpha 5]
320
(160+160)		 Up to 46.1 Gbit/s[upper-alpha 5]
WUR [upper-alpha 7] 802.11ba October 2021 2.4, 5 4, 20 0.0625, 0.25
(62.5 kbit/s, 250 kbit/s)		 — OOK (multi-carrier OOK) ? ?
mmWave
(WiGig)		 DMG [23] 802.11ad December 2012 60 2160
(2.16 GHz)		 Up to 8085[24]
(8 Gbit/s)		 — OFDM[upper-alpha 1], single carrier, low-power single carrier[upper-alpha 1] 3.3 m (11 ft)[25] ?
802.11aj April 2018 60 [upper-alpha 8] 1080[26] Up to 3754
(3.75 Gbit/s)		 — single carrier, low-power single carrier[upper-alpha 1] ? ?
CMMG 802.11aj April 2018 45 [upper-alpha 8] 540,
1080		 Up to 15015[27]
(15 Gbit/s)		 4[28] OFDM, single carrier ? ?
EDMG [29] 802.11ay July 2021 60 Up to 8640
(8.64 GHz)		 Up to 303336[30]
(303 Gbit/s)		 8 OFDM, single carrier 10 m (33 ft) 100 m (328 ft)
Sub 1 GHz (IoT) TVHT [31] 802.11af February 2014 0.054–
0.79		 6, 7, 8 Up to 568.9[32] 4 MIMO-OFDM ? ?
S1G [31] 802.11ah May 2017 0.7, 0.8,
0.9		 1–16 Up to 8.67[33]
(@2 MHz)		 4 ? ?
Light
(Li-Fi)		 LC
(VLC/OWC)		 802.11bb December 2023
(est.)		 800–1000 nm 20 Up to 9.6 Gbit/s — O-OFDM ? ?
IR[upper-alpha 1]
(IrDA)		 802.11-1997 June 1997 850–900 nm ? 1, 2 — PPM[upper-alpha 1] ? ?
802.11 Standard rollups
  802.11-2007 (802.11ma) March 2007 2.4, 5 Up to 54 DSSS, OFDM
802.11-2012 (802.11mb) March 2012 2.4, 5 Up to 150[upper-alpha 4] DSSS, OFDM
802.11-2016 (802.11mc) December 2016 2.4, 5, 60 Up to 866.7 or 6757[upper-alpha 4] DSSS, OFDM
802.11-2020 (802.11md) December 2020 2.4, 5, 60 Up to 866.7 or 6757[upper-alpha 4] DSSS, OFDM
802.11me September 2024
(est.)		 2.4, 5, 6, 60 Up to 9608 or 303336 DSSS, OFDM
  1. 1 2 3 4 5 6 7 This is obsolete, and support for this might be subject to removal in a future revision of the standard
  2. ↑ For Japanese regulation.
  3. 1 2 IEEE 802.11y-2008 extended operation of 802.11a to the licensed 3.7 GHz band. Increased power limits allow a range up to 5,000 m. As of 2009, it is only being licensed in the United States by the FCC.
  4. 1 2 3 4 5 6 7 8 9 Based on short guard interval; standard guard interval is ~10% slower. Rates vary widely based on distance, obstructions, and interference.
  5. 1 2 3 4 5 6 7 8 For single-user cases only, based on default guard interval which is 0.8 microseconds. Since multi-user via OFDMA has become available for 802.11ax, these may decrease. Also, these theoretical values depend on the link distance, whether the link is line-of-sight or not, interferences and the multi-path components in the environment.
  6. 1 2 The default guard interval is 0.8 microseconds. However, 802.11ax extended the maximum available guard interval to 3.2 microseconds, in order to support Outdoor communications, where the maximum possible propagation delay is larger compared to Indoor environments.
  7. ↑ Wake-up Radio (WUR) Operation.
  8. 1 2 For Chinese regulation.

See also

Notes

  1. ↑ MCS 9 is not applicable to all channel width/spatial stream combinations.
  2. ↑ GI stands for the guard interval.

References

  1. ↑ IEEE Standard for Information technology--Telecommunications and information exchange between systems - Local and metropolitan area networks--Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 2: Sub 1 GHZ License Exempt Operation. doi:10.1109/IEEESTD.2017.7920364. ISBN 978-1-5044-3911-4.
  2. 1 2 "There's a new type of Wi-Fi, and it's designed to connect your smart home". theverge.com. 2016-01-04. Retrieved 2015-01-04.
  3. ↑ Wi-Fi Alliance introduces low power, long range Wi-Fi HaLow; wi-fi.org; January 4, 2016.
  4. ↑ Low power, long range Wi-Fi® for IoT; wi-fi.org; May 21, 2020.
  5. 1 2 "Wi-Fi Advanced 802.11ah". Qualcomm.com. Archived from the original on 2014-09-24. Retrieved 2014-06-25.
  6. ↑ "Which Technologies Does Wi-Fi HaLow Have The Best Potential To Disrupt". Newracom. 30 August 2022. Retrieved 1 March 2023.
  7. ↑ Tammy Parker (2013-09-02). "Wi-Fi preps for 900 MHz with 802.11ah". FierceWirelessTech.com. Retrieved 2014-06-25.
  8. 1 2 3 Sun, Choi & Choi 2013.
  9. ↑ Aust, Prasad & Niemegeers 2012.
  10. ↑ Sun, Choi & Choi 2013, p. 94, 5.2 Power Saving.
  11. ↑ Khorov et al. 2014, 4.3.2. Restricted Access Window.
  12. ↑ ZhouWang & ZhengLei 2013, 4. Channel Access.
  13. ↑ Khorov et al. 2014, 4.3.1. Virtual carrier sense.
  14. ↑ Flores, Adriana B.; Guerra, Ryan E.; Knightly, Edward W.; Ecclesine, Peter; Pandey, Santosh (October 2013). "IEEE 802.11af: A Standard for TV White Space Spectrum Sharing" (PDF). IEEE. Retrieved 2013-12-29.
  15. ↑ "Official IEEE 802.11 working group project timelines". January 26, 2017. Retrieved 2017-02-12.
  16. ↑ "Wi-Fi CERTIFIED n: Longer-Range, Faster-Throughput, Multimedia-Grade Wi-Fi Networks" (PDF). Wi-Fi Alliance. September 2009.
  17. 1 2 Banerji, Sourangsu; Chowdhury, Rahul Singha. "On IEEE 802.11: Wireless LAN Technology". arXiv:1307.2661.
  18. ↑ "The complete family of wireless LAN standards: 802.11 a, b, g, j, n" (PDF).
  19. ↑ The Physical Layer of the IEEE 802.11p WAVE Communication Standard: The Specifications and Challenges (PDF). World Congress on Engineering and Computer Science. 2014.
  20. 1 2 "Wi-Fi Capacity Analysis for 802.11ac and 802.11n: Theory & Practice" (PDF).
  21. ↑ Belanger, Phil; Biba, Ken (2007-05-31). "802.11n Delivers Better Range". Wi-Fi Planet. Archived from the original on 2008-11-24.
  22. ↑ "IEEE 802.11ac: What Does it Mean for Test?" (PDF). LitePoint. October 2013. Archived from the original (PDF) on 2014-08-16.
  23. ↑ "IEEE Standard for Information Technology". IEEE Std 802.11aj-2018. April 2018. doi:10.1109/IEEESTD.2018.8345727.
  24. ↑ "802.11ad - WLAN at 60 GHz: A Technology Introduction" (PDF). Rohde & Schwarz GmbH. November 21, 2013. p. 14.
  25. ↑ "Connect802 - 802.11ac Discussion". www.connect802.com.
  26. ↑ "Understanding IEEE 802.11ad Physical Layer and Measurement Challenges" (PDF).
  27. ↑ "802.11aj Press Release".
  28. ↑ "An Overview of China Millimeter-Wave Multiple Gigabit Wireless Local Area Network System". IEICE Transactions on Communications. E101.B (2): 262–276. 2018. doi:10.1587/transcom.2017ISI0004.
  29. ↑ "IEEE 802.11ay: 1st real standard for Broadband Wireless Access (BWA) via mmWave – Technology Blog". techblog.comsoc.org.
  30. ↑ "P802.11 Wireless LANs". IEEE. pp. 2, 3. Archived from the original on 2017-12-06. Retrieved Dec 6, 2017.
  31. 1 2 "802.11 Alternate PHYs A whitepaper by Ayman Mukaddam" (PDF).
  32. ↑ "TGaf PHY proposal". IEEE P802.11. 2012-07-10. Retrieved 2013-12-29.
  33. ↑ "IEEE 802.11ah: A Long Range 802.11 WLAN at Sub 1 GHz" (PDF). Journal of ICT Standardization. 1 (1): 83–108. July 2013. doi:10.13052/jicts2245-800X.115.

Bibliography

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