WiFi TX Power Configuration

Overview

WiFi configuration typically allows runtime control of parameters such as channel selection.

However, TX power is not always dynamically configurable and may require configuration during driver initialization.

This is done by providing a TX power configuration binary to the driver.

TX Power Configuration Flow

The general workflow:

  1. Generate TX power configuration binary\
  2. Place it in firmware path\
  3. Load driver with configuration\
  4. Verify applied limits

Generating TX Power Configuration

A configuration file is used to generate a binary representation of TX power limits.

Example:

mlanutl wlan0 hostcmd txpwrlimit_custom1.conf generate_raw txpower.bin

The generated file should be placed in:

/lib/firmware/nxp/txpower.bin

Loading Configuration

TX power configuration is applied during driver load.

Using modprobe

modprobe sdxxx txpwrlimit_cfg=nxp/txpower.bin

Using module configuration

options sdxxx     cfg80211_wext=0xf     sta_name=wlan     wfd_name=p2p     max_vir_bss=1     cal_data_cfg=nxp/cal_data.conf     drv_mode=7     fw_name=nxp/sduart8987_combo.bin     txpwrlimit_cfg=nxp/txpower.bin     reg_alpha2=SE     cfg_11d=1

Verification

TX power limits can be checked after driver initialization:

mlanutl wlan0 get_txpwrlimit 0
  • 0 → 2.4 GHz\
  • Other values correspond to different bands

Regulatory Constraints

TX power is not only limited by hardware, but also by regional regulations.

Two common regulatory domains:

  • Europe (ETSI)\
  • United States (FCC)

2.4 GHz Band

Parameter Europe (ETSI) United States (FCC)

Frequency Range 2400 – 2483.5 MHz 2400 – 2483.5 MHz Max TX Power 20 dBm up to 30 dBm Channels 1 – 13 1 – 11

5 GHz Band (Simplified)

Band Europe (ETSI) United States (FCC) Notes

36 – 48 up to 23 dBm up to 30 dBm Indoor EU 52 – 64 up to 23 dBm up to 30 dBm DFS required 100 – 144 up to 30 dBm up to 30 dBm DFS required 149 – 165 limited up to 30 dBm US preferred

Practical Considerations

  • TX power must follow regulatory limits\
  • Configuration should match deployment region\
  • Single global configuration simplifies deployment but reduces performance\
  • Region-specific configuration improves performance but increases complexity

Summary

  • TX power is configured at driver level\
  • Runtime control is limited or not available\
  • Regulatory domain defines allowed limits\
  • Configuration must align with certification requirements