The mean EIRP power level for a slave device with TPC must not exceed 24 dBm at the the lowest TPC power level if the device is also capable of radar detection or 17 dBm otherwise. RLAN band 2 (5470 to 5725 MHz)Ĭhannels from 100 to 140 are part of the second RLAN band and have an EIRP power limit of 30 dBm (1000 mW) for TPC and 27 dBm (500 mW) for non-TPC devices or 20 dBm (100 mW) for devices without any TPC or DFS support. This band requires DFS support and is comparable to FCC U-NII-2. For a device with TPC, the mean EIRP at the lowest power level of the TPC range must not exceed 17 dBm (50 mW). In the second sub-band of the RLAN band 1 with channels 52 to 64, the ETSI has set the EIRP power limit to 23 dBm (200 mW) for devices with TPC and 20 dBm (100 mW) for devices without TPC. Indoor only sub-band II (5250 – 5350 MHz) These channels are considered for indoor only usage and do not require any Dynamic Frquency Selection (DFS) or Transmit Power Control (TPC) features. The first RLAN sub-band includes the channels 36 to 48 and has an EIRP power limit to 23 dBm (200 mW). As 802.11 only uses OFDM modulation in this radio band, there are no modulation specific regulations, only frequency specific. Since the 5 GHz band is divided into two different ETSI Radio Local Area Network (RLAN) bands of 5150 to 5350 MHz and 5470 to 5725 MHz, which can be compared to the FCC Unlicensed National Information Infrastructure (U-NII) bands in the US, each band can have different power limits. For OFDM, the spectral mask looks more like a rectangular, so the power is nearly distributed equally, with an idealistic 7 dBm/MHz (5 mW/MHz) over a 20 MHz channel for example, and the maximum power limit of 20 dBm can be used.
So if you don’t lower the Tx power generally to 18 dBm, you exceed the spectral power limitation at the center of a 802.11b 20 MHz channel. As the spectral mask of the CCK modulation looks more like a sombrero, we see a high spectral power per MHz at the center and a lower one at the edges. The spectral power limitation of 10 dBm/MHz (10 mW/MHz) causes the lower power limit for 802.11b. The limit is set to 20 dBm (100 mW) for OFDM and 18 dBm (63 mW) for CCK.
There exists two EIRP power limits for the 2.4 GHz band, one for 802.11b rates with CCK modulation (1, 2, 5.5 and 11 Mbps) and one for 802.11g/n rates with OFDM modulation. Some of the terms related to regulatory demands or transmission power used in this post are explained in this post. The values given here are taken from the ETSI standards and apply to european countries. Each device you can buy, must not exceed any power limits given by the regulatory domain you want to deploy it in. Different radio bands require different regulatory power limits.
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