IEEE 802.11ah
IEEE 802.11ah is a standard for wireless networks (WLANs). The industry association Wi-Fi Alliance promoted the standard with Wi-Fi HaLow in early 2016. Areas of application are in smart homes and machine-to-machine communication.
Technical details
IEEE 802.11ah is implemented in the frequency band around 900 MHz , which means that, compared to a standard 2.4 GHz WLAN and other IEEE 802.11 transmission methods, with otherwise comparable parameters, a range is achieved that is roughly double (distance 1 km). The network has a wireless access point ( English Relay Access Point , RAP ) and so-called network stations (STAs) to transfer data from device to device using a frame .
With IEEE 802.11ah, the bit transmission layer ( English Physical Layer ) and the Media Access Control (MAC) of the security layer (English Data Link Layer ) must be considered:
Physical Layer (PHY)
When designing the PHY layer, IEEE 802.11ac was used . The new standard is a variant of this that has been clocked down by a factor of 10 and therefore works with 2 MHz, 4 MHz, 8 MHz and 16 MHz channel bandwidths. There is also an additional 1 MHz channel to improve area coverage. Transfers using multi-user MIMO (MU-MIMO) are possible; this one has to IEEE 802.11a oriented.
The standard supports 2 MHz, 4 MHz, 8 MHz and 16 MHz when transmitting, while the STAs are suitable for receiving 1 MHz and 2 MHz.
The ISM band is handled differently in different countries. The following applies to channelization (frequency):
- USA: 902-928 MHz
- EU: 863 - 868 MHz
- Japan: 916.5-927.5 MHz
- Korea: 917.5-923.5 MHz
- China: 755 - 787 MHz
- Singapore: 866 - 869 MHz and 920 - 925 MHz
The following applies to the number of radio channels and bandwidth :
| region | 1 MHz | 2 MHz | 4 MHz | 8 MHz | 16 MHz |
|---|---|---|---|---|---|
| China | 32 | 4th | 2 | 1 | - |
| United States | 26th | 13 | 6th | 3 | 1 |
| Singapore | 8th | 3 | 1 | - | - |
| Korea | 6th | 3 | 1 | - | - |
| EU | 5 | 2 | - | - | - |
| Japan | 11 | - | - | - | - |
An orthogonal frequency division multiplexing process (OFDM) consisting of a total of 64 carrier frequencies with a spacing of 31.25 kHz is used. As modulation is phase-shift keying (BPSK), Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM) with 16 to 256 symbols in the constellation diagram used.
IEEE 802.11ah MCS 2 MHz bandwidth channels:
| MCS index | modulation | Code rate | Mbit / s at
Normal GI |
Mbit / s at
Short GI |
|---|---|---|---|---|
| MCS0 | BPSK | 1/2 | 0.65 | 0.72 |
| MCS1 | QPSK | 1/2 | 1.3 | 1.44 |
| MCS2 | QPSK | 3/4 | 1.95 | 2.17 |
| MCS3 | 16QAM | 1/2 | 2.6 | 2.89 |
| MCS4 | 16QAM | 3/4 | 3.9 | 4.33 |
| MCS5 | 64QAM | 2/3 | 5.2 | 5.78 |
| MCS6 | 64QAM | 3/4 | 5.85 | 6.5 |
| MCS7 | 64QAM | 5/6 | 6.5 | 7.22 |
| MCS8 | 256QAM | 3/4 | 7.8 | 8.67 |
| MCS9 | 256QAM | 5/6 | --- | --- |
Media Access Control (MAC)
When designing the MAC layer, a large number of stations (STAs) were targeted. When looking at the number, these can run into the thousands, since you are dealing with an extremely large number of sensors . In addition, power consumption should be kept low.
If you look at a MAC frame , it is made up of fields. The first three fields and the last field represent a minimum frame. The first three are: Frame Control, Duration / ID and address. The last field is: FCS. The other fields are used or not used. With sensors you have little data. That is why IEEE 802.11ah has been simplified. The basic problem is that small amounts of data produce a high overhead. IEEE 802.11 uses a 28-byte MAC header, IEEE 802.11ah reduces this to 18 bytes.
Null data packet frames (NDP) are also defined, which consist of a single PHY header in order to shorten the current IEEE 802.11 signaling frames such as ACKs, block ACKs, CTSs and PS polls. In addition, a speed frame exchange mechanism, i.e. Bi Directional TXOP, is used. In WLANs according to 802.11 the transmission opportunity (TXOP) is the transmission right.
literature
- Khorov, Evgeny; Lyakhov, Andrey; Krotov, Alexander; Guschin, Andrey (2014). "A survey on IEEE 802.11 ah: an Enabling Networking Technology for Smart Cities," (PDF). Computer Communications (Elsevier).
- Sun, Weiping; Choi, Munhwan; Choi, Sunghyun (2013). "IEEE 802.11 ah: A Long Range 802.11 WLAN at Sub 1 GHz" (PDF). Journal of ICT Standardization 1 (1): 83-108.
- Zhou, Yuan; Wang, Haiguang; Zheng, Shoukang; Lei, Zander Zhongding (2013). "Advances in IEEE 802.11 ah standardization for machine-type communications in sub-1GHz WLAN". Communications Workshops (ICC), 2013 IEEE International Conference on. IEEE. pp. 1269-1273.
- Aust, Stefan; Prasad, R Venkatesha; Niemegeers, Ignas GMM (2012). "IEEE 802.11 ah: Advantages in standards and further challenges for sub 1 GHz Wi-Fi,". Communications (ICC), 2012 IEEE International Conference on. IEEE. pp. 6885-6889.
Web links
Individual evidence
- ↑ Press release of the Wi-Fi Alliance of January 4, 2016 (English) , accessed on January 7, 2016.
- ↑ Weiping Sun, Munhwan Choi, Sunghyun Choi: IEEE 802.11ah: A Long Range 802.11 WLAN at Sub 1 GHz (pdf, 379 kB), from the website of Seoul National University , May 14, 2013, accessed on June 28, 2016
- ↑ IEEE P802.11 - Wireless LANs (Proposed Specification Framework for TGah) (doc, 2 MB), on IEEE.org from January 2013, accessed on June 28, 2016
- ↑ IEEE 802.11ah - sub GHz Wi-Fi
- ↑ http://riverpublishers.com/journal/journal_articles/RP_Journal_2245-800X_115.pdf IEEE 802.11ah: A Long Range 802.11 WLAN at Sub 1 GHz, page 99
- ↑ Enabling Wi-Fi Internet of Things with 802.11ah Technology, page 9