IEEE 802.11ah is an emerging Wireless LAN (WLAN) standard, operating at sub 1 GHz license-exempt bands and providing improved transmission range compared with the conventional 802.11 WLANs operating at 2.4 GHz and 5 GHz bands. 802.11ah can be used for low speed, low cost, large range data transmission, for various purposes including large scale sensor networks, extended range hotspot, and outdoor Wi-Fi for cellular traffic offloading, whereas the available bandwidth is relatively narrow.
802.11ah Pysical layer is newly designed based on the IEEE 802.11ac PHY.
802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz and 16 MHz channels with a frequency spacing of 31.25 kHz.
The following features are supported —
Three PPDU format: S1G_1M, S1G_SHORT, and S1G_LONG
Three generation modes: S1G, NDP for sounding, NDP for NDP MAC
MCS index: MCSs 0 to 9, and MCS10 (for 1 MHz PPDU only)
Up to 4 spatial streams
Binary convolutional coding
STBC (Space Time Block Coding)
LDPC (Low Density Parity Check)
Short Guard Interval
Single user or up to 4 multiple users
Fixed and Traveling Pilots
Aggregated MPDU
Table 1 Key features of 802.11ah
|
Channel bandwidth |
1 MHz, 2 MHz, 4 MHz, 8 MHz,16 MHz |
|
FFT size |
32, 64, 128, 256, 512 |
|
Data subcarriers / pilots |
24/2, 52/4, 108/6, 234/8, 468/16 |
|
Modulation types |
BPSK, QPSK, 16QAM, 64QAM, 256QAM |
|
MCS supported |
0 to 9 , and 10 (only for 1 MHz PPDU) |
|
Spatial streams |
1 to 4 |
|
MIMO |
up to 4xn |
|
PPDU format |
S1G_1M S1G_SHORT S1G_LONG |
|
Generation modes |
S1G PPDU NDP for sounding NDP for NDP MAC |