Access Probe Power Measurement Description

Last updated: November 17, 2008

How is an Access Probe Power Measurement Made?

The test set's access probe power measurement is a channel power measurement (see Channel Power Measurement Description ) triggered by a rise in RF power detected on the test set's RF input. When an input signal appears that is within +/- 9 dB of the expected power for an access probe, the measurement is triggered. To prevent the measurement from triggering on noise, the signal level must be at least -45 dBm/1.23 MHz.

The access probe power measurement captures an access probe and digitizes the waveform. It then uses DSP to determine the average power level (within the 1.23 MHz measurement bandwidth) of the first ~1.667 ms of the probe.

An access probe is sent by the access terminal as a way to determine the correct power level needed to access the test set. Initially, the access probe power level will be minimal and then increase in amplitude until the test set responds to the signal.

When the Current Access Channel MAC Subtype is the Default , the access probe power measurement is operating in the Default Access Channel MAC protocol. The access probe power measurement looks for a bursted signal that is approximately 200 ms in length and occurs randomly. The power of preamble part is same with the power of the data portion.

When the Current Access Channel MAC Subtype is the Enhanced , the access probe power measurement is operating in the Enhanced Access Channel MAC Protocol. The preamble length is currently fixed to 16 slots by the test set and the length of data portion is from 26.67 ms (when Enhanced Access Rate is 38.4 kbps) to 106.88 ms (when Enhanced Access Rate is 9.6 kbps). When the Enhanced Access Rate is other than 9.6 kpbs, the power of data portion is higher than the preamble power.

Considerations when Making Access Probe Power Measurements

IMPORTANT

If the access probe power measurement is on and waiting to measure a probe, all other measurements (except digital average power) will not be able to execute. It is therefore recommended that you turn off the access probe power measurement before attempting any other measurements.

Access probe sequences consist of a series of RF power "steps" which increase in power according to the step size setting until the maximum number of steps is reached, or the data connection processing event completes (for example when the data connection is established). For the parameters that determine the access probe sequence characteristics, see Access Probe Power Measurement Parameters .

To view the full access probe sequence, you must prevent the test set from responding to the access terminal by turning Call Limit Mode on.

NOTE

It is recommended that you always turn Call Limit Mode on when measuring access probe power. The easiest way to induce access probes from the access terminal is to page the access terminal. If you do not have call limit mode set to on, the connection will complete, which clears the access probe power result from the measurement screen. Set call limit mode back to off when you have finished measuring access probe power.

Access Probe Power Measurement Parameters

Trigger Arm - (see Trigger Arm (Single or Continuous) Description ). When the test set is making access probe power measurements in the continuous trigger arm state, it will display the power level of the most recent access probe power measurement. To measure only the first access probe and prevent triggering on subsequent access probes, setTrigger Arm toSingle . You must then press Start Single to arm the measurement.
Timeout Time/State - (see Measurement Timeouts ).
The following parameters determine the access probe sequence characteristics: Open Loop Adjust , Probe Initial Adjust , Probe Power Step , Probe Num Step , Probe Sequence Max , Preamble Length (Frames) ( only used when the test set is configured to Default Access Channel MAC protocol , see Access Channel MAC Subtype ), Enhanced Access Rate , Preamble Length Slots ( only used when the test set is configured toEnhanced Access Channel MAC protocol, see Access Channel MAC Subtype )

NOTE

The Probe Sequence Max is a "Configurable Attribute" that is configured during the Session Negotiate State . Its value can not be changed when a session is open and Call Limit Mode is on.

Access Probe Power Measurement Results

Integrity Indicator - (see Integrity Indicator ).
Access Probe Power (in dBm/1.23 MHz): The average power level of the first ~1.667 ms of the captured access probe.
The Expected Access Terminal Power (see Expected Power ) is also displayed on the measurement screen when either of the following conditions is met:
- Current physical layer subtype is Subtype 0 (see Release A Physical Layer Subtype ), the receiver power control is set to auto and Test Application Protocol is set to RTAP.
- Current physical layer subtype is Subtype 2 (see Release A Physical Layer Subtype ), the receiver power control is set to auto and Enhanced Test Application Protocol is set to RETAP.

An example measurement result (for subtype 0 physical layer) is shown below:

Access Probe Power Input Signal Requirements

Input Signal Requirements

Key C.S0033 Tests Performed using the Access Probe Power Measurement

4.3.1 Range of Open Loop Output Power

Calibrating the Access Probe Power Measurement

The access probe power measurement is automatically calibrated during a channel power calibration. Follow the channel power calibration schedule and the access probe power measurement will be properly calibrated. Refer to Calibrating the Test Set for a description of channel power calibration.