802.11 Power Management

With transmit and receive currents on the order of 80-200 mA, it is important to understand which options exist both within and beyond the 802.11 standards to power down the transceiver and extend the battery life.

Active Mode

  • Transmitting or receiving function is ON
  • Few hours battery life

802.11 PS-Poll Mode

  • Only power-saving mode specified in 802.11
  • Transceiver function is DUTY-CYCLED
  • Function available during 'infrastructure mode' network configuration only
  • Provides virtual 'always on' power saving capability
  • In PS-Poll mode, the station always maintains a connection to the network
  • Station periodically POLLs the airwaves for the presence of DTIM packets sent by the AP in its beacon transmissions
  • ~200 mS response latency
  • Requires PS supported Access Point (AP) to buffer the packets
  • Few days/weeks battery life

This example shows the best case (lowest latency) DTIM period (n=1 – i.e. every beacon from the AP has a DTIM message).

  • Radio automatically wakes just prior to DTIM beacon.
  • DTIM packet is read.
  • Bit position is checked to see if there is buffered data at AP.
  • If there is no data, then the radio reverts back to sleep.

In this example, the duty cycle = 4/96. So, the 85 mA active RX current drops to 3.5 mA.

power-management-DTIM-example.png
Click image to enlarge.

Product-Specific Power Save Modes

Refer to specific product documentation for all supported power modes.

For the ATWINC1500, power modes are described in Section 4.4 of the "ATWINC15x0 Wi-Fi® Network Controller Software Design Guide."

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