Similar 1 MHz channel, the standard defines a
Similar to .11ac, .11ah uses Orthogonal Frequency DivisionMultiplexing (OFDM), Multiple Input Multiple Output (MIMO)and Downlink Multi-User MIMO (DL MU-MIMO).For the channels P2 MHz, the PHY layer is just 10 times downclockingof the .11ac’s PHY, i.e., the duration of OFDM symbols in.11ah is 10 times longer than in .11ac, while the numbers of sub-carriers in .11ah channels are the same as those in the corresponding.11ac channels. E.g., both 2 MHz channel in .11ah and20 MHz channel in .11ac have 64 sub-carriers including pilot andguard, and only 52 of them transmit data.For the 1 MHz channel the total number of sub-carriers is twicelower, but only 24 (which is less than 52/2) transmit data becausethe number of guard sub-carriers cannot be reduced..11ah inherits 10 MCSs (referred to as MCS0, . . ., MCS9) with differentreliability properties and transmission rates from the .11acstandard. Since MCS9 is not available in 20 MHz .11ac channel, itis not valid in 2 MHz .11ah channel, too. To extend transmissionrange of 1 MHz channel, the standard defines a novel MCS10,which is nothing but a modification of MCS0 with 2″ repetition,increasing transmission reliability.Authors of 5 model .11ah channel and prove that in outdoorscenarios with 200 mW transmission power and 1 MHz channel,the transmission range indeed exceeds 1 km if MCS 10 is used,while MCS 0 provides 850 m, and MCS 10 gives about 200 m. Withthe default Wi-Fi frequencies of 2.4 GHz and 5 GHz, the transmissionrange is 3–9 times lower.The regular data rates for various bandwidths and MCSs arelisted in Table 2. They can be improved by reducing the durationof OFDM symbol and using several spatial streams.The duration of a normal OFDM symbol is 40 ls, 20% of which isthe guard interval (GI) containing redundant data and preventinginter-symbol interference. IEEE 802.11ah allows twice shorterguard interval which 109 times increases data rates.IEEE 802.11ah stations can use up to 4 spatial streams. N spatialstreams N times increase the data rates.TGah moves some MAC functionality from MAC headers to PHYheaders, e.g. acknowledgment indication. Being related to the MAClayer rather than to the PHY layer, these changes are described inSection 4.