Access Probe Power Measurement Description

Last updated: October 28, 2004

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 1.25 ms of the probe.

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 recently measured access probe.

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 are transmitted by the mobile station during registrations or mobile station originated calls. 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 call processing event completes, for example when the call connects.

Changing the number of steps and step size will affect the power level displayed if more than one access probe is transmitted by the mobile station. However, the number of access probes transmitted depends on whether or not the test set responds by acknowledging the access request, thereby ending the access attempt. To view the full access probe sequence, you must prevent the test set from responding to the mobile station access probe request by turning the Call Limit Mode on (key F10 in Call Parms, 2 of 3 screen). For the GPIB command syntax, see CALL:CONNected:LIMit[:STATe]<[:SELected]|:TA2000> .

It is recommended that you always turn the Call Limit Mode on when measuring access probe power. The easiest way to induce access probes from the mobile station is to page the mobile station. If you do not have call limit mode set to on, the call 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.

When the mobile station performs any type of registration, an access probe power measurement will likely be triggered. To control the mobile station's registrations, access the Registration Parameters menu (see D. Registration Parameters ). For GPIB syntax information on the registrations, see CALL:REGister .

Access Probe Power Measurement Parameters

The parameters shown in the Access Probe Power Setup menu are different according to the current access channel configured:

When the current access channel is R-ACH (see Control Channel Configuration ), the parameters such as Nominal Power, Nominal Power Extended, Initial Power, Power Step, Number of Steps, Maximum Response Sequence and Preamble Size will be displayed. See Setting Access Parameters for details on these parameters:
When the current access channel is R-EACH, the parameters such as EACH Nominal Power, EACH Initial Power, EACH Power Step, EACH Number of Steps and Maximum Response Sequence will be displayed. See Setting Enhanced Access Parameters for details on these 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 the START SINGLE hardkey to arm the measurement.
Timeout Time/State - (see Timeouts ).

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 1.25 ms of the captured access probe.
Expected Mobile Power - the Expected Mobile Power (see Expected Power ) is also displayed on the measurement screen when the test set is configured as:
- receiver power control is set to auto (see Automatic Receiver Control ), and
- the R-EACH Rate Supported is not set to support multiple rates (that is, All Rates, 20 ms ) when current access channel is using R-EACH (see Control Channel Configuration ).

A typical measurement result is shown below:

Input Signal Requirements

The access probe power measurement meets or exceeds specifications when the following input signal requirements are met:

The frequency of the signal being measured must be within the range of 412 MHz to 483 MHz, 800 MHz to 960 MHz, or 1.7 GHz to 2.0 GHz, and be within 100 kHz of the expected frequency.
The average power level of the signal at the RF IN/OUT connector must be between -61 dBm to +37 dBm. The test set can autorange to a signal that is within +/- 9 dB of the expected input level (see RFANalyzer:AUTO:POWer[:SELected]? ).

Key TIA/EIA-98-E Tests Performed Using the Access Probe Power Measurement

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.