Transmit Power-on and Power-down Ramp - Power versus Time

The transmit power-on ramp measurement verifies that the transmit power reaches 90% of maximum power in a 2usec envelope. The transmit power-down measurement verifies that the transmit power falls off to 10% of maximum power in a 2usec envelope.

The standard specifies "the transmit power-on ramp for 10%-90% of maximum power shall be no greater than 2usec". See Image 1 (View larger image).

"The transmit power-down ramp for 90%-10% shall be no greater than 2usec." See Image 2 (View larger image).

Transmit Power-on and Power-down Ramp - Power versus Time Image

This ensures that the power of the burst turns on/off at the correct rate, neither rising nor falling too quickly or too slowly.


  • IEEE Std 802.11b-1999 16 September 1999 Paragraph Transmit power-on and power-down ramp

Measurement Subtleties

802.11 WLAN signals are bursted. If not controlled, many transmitter parameters can reduce the performance of WLAN systems, or even prevent RF devices from working together. Verifying the transmit power-on and power-down ramps, you can help avoid interoperability problems between WLAN devices and ensure that firmware or other variations in devices do not cause unexpected burst profiles.

For example, if the power burst ramps up too slowly, part of the header might be cut off preventing the receiver from demodulating the packet correctly. Similarly, if the power ramps down too quickly, part of the payload will be truncated.

Test Tools

You can make transmit power-on and power-down measurements with a variety of tools.

The Keysight 89607A WLAN test suite software comes pre-programmed with the IEEE802.11a/b/g transmitter performance specifications for automated measurements using the 89600 series vector signal analyzer. You will find that it is also the easiest way to make this measurement. This software is a subset of the 89601A software, and can be ordered individually, or as part of option B7R with the 89600. To make the measurement, you connect the appropriate measurement hardware, connect the device under test (DUT), and set up the 89604 software.

You can use the 89600 Series vector signal analyzer standalone, in conjunction with the ESA and PSA Series spectrum analyzers, and with several of Keysight's Infiniium family of oscilloscopes. You can also use the ESA or PSA Series spectrum analyzers as down-converting front ends for the 89600 (with specific options). This provides vector signal analysis capabilities up to 50 GHz. You can also use 89600 hardware as standalone. This provides vector signal analysis up to 6 GHz, with one or two channel inputs, for IQ, IF, and RF measurements. The power-on and power-down measurement is typically an RF measurement.

The PSA and ESA spectrum analyzers offer built-in 802.11 spectral emission mask (SEM) measurements.

Keysight's advanced design software (ADS) can also make this measurement in simulation.