In the 802.11ah system, OFDM is used (Orthogonal Frequency Division Multiplexing), as in 802.11ac. Since the spaced subcarriers used to transmit data is equal in OFDM, the number of subcarriers in the 11ah signal depends on the bandwidth, shown in table below (single spatial stream).
|
Bandwidth (MHz) |
Number of Subcarriers |
Subcarriers Transmitting Signal |
|---|---|---|
|
1 |
32 |
-12 to -1 and 1 to 12 |
|
2 |
64 |
-26 to -1 and 1 to 26 |
|
4 |
128 |
-58 to -2 and 2 to 58 |
|
8 |
256 |
-122 to -2 and 2 to 122 |
|
16 |
512 |
-250 to-130, -126 to -6, 6 to 126 and 130 to 250 |
802.11ah defines three formats:
Figure 1. 80211ah SIG greater than or equal to 2 MHz short format
Figure 2. 80211ah SIG greater than or equal to 2 MHz long format
Figure 3. 80211ah SIG 1 MHz format