2.4GHz (2.4000 GHz to 2.4835 GHz)
– 802.11 (FHSS clause 14 or DSS clause 15 radios)
– 802.11b (HR-DSSS clause 18 radios)
– 802.11g (ERP clause 19 radios)
– 802.11n (HT clause 20 radios)
In addition to being used by wireless networking equipment, 2.4GHz ISM band is also used by microwave oven, cordless phones, baby monitors, wireless video camera & other devices.According to 802.11 standard legacy DSSS channels had to have at least 30MHz of spacing between center frequencies to be considered non-overlapping. So CH1, CH6 & CH11 were considered as overlapping as they separated by 25MHz.
Under HR-DSSS (802.11b) which states channels need a minimum of 25MHz of separation between center frequencies to be considered non-overlapping. So in 802.11b CH1, CH6 & CH11 are non-overlapping.
ERP-DSSS & ERP-OFDM (802.11g) also require 25MHz separation. So under 802.11g CH1 , CH6 & CH11 considered to be non-overlapping.
Transmit Spectrum Mask (DSSS & HR-DSSS)
– first side band frequency (-11MHz to -22MHz & +11MHz to +22MHz from center) must be at least 30dB less than the main frequency.
– any additional sideband carrier frequencies (-22MHz & + 22MHz from center frequency) must be at least 50dB less than the main frequency.
5 GHz (Unlicensed National Information Infrastructure – UNII bands)
– 802.11a defined 3 UNII bands 100MHz wide each & 4 CH in each UNII band.
1. UNII-1 (5.150-5.250 GHz)
2. UNII-2 (5.250-5.350 GHz)
3. UNII-3 (5.725-5.825 GHz)
-802.11h (DFS & TPC) adds UNII-2 Extended 255MHz wide (additional 11 CH)
4. UNII-2 Extended (5.470 -5.725 GHz)
– The centers of the outermost channels must be 30MHz from the band’s edge in the UNII-1 & UNII-2 & must be 20MHz in the UNII-3 band.
– There are 4 non-overlapping channel in above 3 UNII bands with 20MHz separation between center frequencies.
– Centre frequency of each channel (eg 36,40,…100, ..161,165) can be calculated as (5000+5x N_CH) in MHz. Eg CH100 center frequency is 5.500 (5000+5×100)
– IEEE does not specifically define a channel width for 5GHz, however the spectral mask of an OFDM channel is approximately 20MHz.
– Clause 17 OFDM, required only 20MHz of separation between the center frequencies to be considered as non-overlapping (hence all 23 CH are non overlapping)