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IEEE 802.11ah is a wireless networking protocol that is an amendment of the IEEE 802.11-2007 wireless networking standard. It utilizes sub 1 GHz license-exempt bands to provide extended range Wi-Fi networks, compared to conventional Wi-Fi networks operating in the 2.4 GHz and 5 GHz bands. It also benefits from lower energy consumption, allowing the creation of large groups of stations or sensors that cooperate to share the signal, supporting the concept of the Internet of Things (IoT).
The standard is expected to be finalized and arrive in 2016, with chips and systems based on 802.11ah hitting the market as early as 2015.
A benefit of 802.11ah is extended range, making it useful for rural communications and offloading cell phone tower traffic. The other purpose of the protocol is to allow low rate 802.11 wireless stations to be used in the sub-gigahertz spectrum. 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 behaviour 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 area. It aims at providing connectivity to thousands of devices under an access point. The protocol supports machine to machine (M2M) markets, like smart metering.
Relay Access Point (AP)
A Relay is an entity that logically consists of an Relay AP 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.
Grouping of stations
Grouping 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. Grouping can also reduce the signaling overhead where stations receive management frames that are meaningless to them. Grouping of stations may be used to reduce network energy consumption, as stations that are not in the group assigned to the current slot can enter a doze state until their slot time or assigned Target Wait Time (TWT) arrives.
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 STA. The AP can protect the expected duration of activity with various protection mechanisms. The use of TWT is negotiated between an AP and a STA.
Speed Frame Exchange
Speed frame exchange 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.
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.
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IEEE 802.11 network standards
|802.11 network PHY standards|
|Stream data rate||Allowable
|—||Jun 1997||2.4||22||1, 2||N/A||DSSS, FHSS||20||66||100||330|
|a||Sep 1999||5||20||6, 9, 12, 18, 24, 36, 48, 54||N/A||OFDM||35||115||120||390|
|b||Sep 1999||2.4||22||1, 2, 5.5, 11||N/A||DSSS||35||115||140||460|
|g||Jun 2003||2.4||20||6, 9, 12, 18, 24, 36, 48, 54||N/A||OFDM, DSSS||38||125||140||460|
|n||Oct 2009||2.4/5||20||7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2 [B]
(6.5, 13, 19.5, 26, 39, 52, 58.5, 65) [C]
|40||15, 30, 45, 60, 90, 120, 135, 150 [B]
(13.5, 27, 40.5, 54, 81, 108, 121.5, 135) [C]
|ac||Dec 2013||5||20||7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2, 86.7, 96.3 [B]
(6.5, 13, 19.5, 26, 39, 52, 58.5, 65, 78, 86.7) [C]
|40||15, 30, 45, 60, 90, 120, 135, 150, 180, 200 [B]
(13.5, 27, 40.5, 54, 81, 108, 121.5, 135, 162, 180) [C]
|80||32.5, 65, 97.5, 130, 195, 260, 292.5, 325, 390, 433.3 [B]
(29.2, 58.5, 87.8, 117, 175.5, 234, 263.2, 292.5, 351, 390) [C]
|160||65, 130, 195, 260, 390, 520, 585, 650, 780, 866.7 [B]
(58.5, 117, 175.5, 234, 351, 468, 702, 780) [C]
|ad||Dec 2012||60||2,160||Up to 6,912 (6.75 Gbit/s) ||N/A||OFDM, single carrier,
low-power single carrier
- A1 A2 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[update], it is only being licensed in the United States by the FCC.
- B1 B2 B3 B4 B5 B6 Assumes short guard interval (SGI) enabled.
- "Wi-Fi Advanced 802.11ah". Qualcomm.com. Retrieved 2014-06-25.
- "Wi-Fi preps for 900 Mhz with 802.11ah". FierceWirelessTech.com. 2013-09-02. Retrieved 2014-06-25.
- "Official IEEE 802.11 working group project timelines". June 2, 2014. Retrieved 2014-06-03.
- "Wi-Fi CERTIFIED n: Longer-Range, Faster-Throughput, Multimedia-Grade Wi-Fi® Networks" (registration required). Wi-Fi Alliance. September 2009.
- "802.11n Delivers Better Range". Wi-Fi Planet. 2007-05-31.
- "IEEE 802.11ac: What Does it Mean for Test?". LitePoint. October 2013.
- "WiGig and IEEE 802.11ad For Multi-Gigabyte-Per-Second WPAN and WLAN". Tensorcom Inc.
Resources (White papers, technical papers, application notes)