Wifi cell coverage density rates?

Installing and Using OpenWrt
1

Hello,
I was wondering how cell coverage density rates are calculated.

Setting cell_density to 'normal' on my QCA9560 802.11bgn interface results in these rates in the hostapd configuration:
supported_rates=55 60 90 110 120 180 240 360 480 540
basic_rates=55 110

The wifi phy supports:
HT TX/RX MCS rate indexes supported: 0-23
RX HT20 SGI
RX HT40 SGI

According to MCS tables the highest rate for MCS index 23 HT, 40 MHz short GI is 450 Mbps and 216.7 Mbps for 20 Mhz short GI.

The configured basic_rates match no valid MCS index data rate, and out of the supported_rates 55 and 110 don't match, 60, 90, 120, 180, 240, 360 only match 40 MHz short GI and 480, 540 are out of range.

Is this fine? Does hostapd ignore invalid rates? What happens if 40 MHz is not available since there's not a single valid 20 MHz rate left?

2

Hi xnor,

Per specification, only DSSS (802.11), HR-DSSS (802.11b) and OFDM (802.11a/802.11g) defined data rates can be used as basic or supported rates. MCS rates are not used to transmit management and control frames.

These are not invalid rates therefore in the config.

You correctly see 802.11b data rates used as the basic rates because you have 802.11b enabled on a 2.4 GHz radio and have chosen the normal density:

supported_rates=55 60 90 110 120 180 240 360 480 540
basic_rates=55 110

The MCS rates are used for exchanging data, as expected, for capable clients and are not impacted or influenced by this.

Best,

Nick