Analysis CCDF (TD-SCDMA)

Analysis CCDF trace data displays the complementary, cumulative distribution function (CCDF Complementary Cumulative Distribution Function) for the selected Sub-frame (SF 1) Spreading Factor, or 2) service flow: A unidirectional flow of medium access control (MAC) service data units (SDUs) on a connection that is provided a particular Quailty of Service (QoS).) and Timeslot (TS Technical Specification).

Analysis Timeslot and Analysis Sub-frame parameter entry shortcut: Right click on the desired Timeslot in the Overall Time trace data display, then select Copy Marker to Analysis TS/SF.

Overview

The complementary, cumulative distribution function (CCDF) is a statistical-power calculation and can be performed only on time-domain data. As its name suggests, CCDF is the complement of CDF Cumulative Distribution Function: The cumulative probability that a parameter will be less than a given value X. and is defined as follows:

CDF(K) = Probability(x £ K)

CCDF(K) = Probability(x ³ K)

CCDF provides better resolution than CDF for low probability signals, especially when log format is used for the y-axis.

The VSA plots CCDF using units of percent (%) for the y-axis and power (dB) for the x-axis. Power on the x-axis is relative to the signal average power, so 0 dB is the average power of the signal. Therefore, a marker readout of

Trace A Marker 2 dB 12 %

means there is a 12% probability that the signal power will be 2 dB or more above the average power.

CCDF Calculation:

Calculate the RMS value for all measured samples; this becomes the 0 dB point at the left end of the x-axis.
Normalize all samples to the RMS value in units of dB.
Determine which x-axis bin each sample belongs in between 0 and 20 dB.
Calculate the total number of samples that are greater than or equal to each x-axis bin and plot as a percent of the number of samples measured.

Restarting the Power Measurement

Selecting CCDF, restarting the measurement, or changing most measurement parameters restarts the CCDF measurement. For example, changing the range or center frequency resets the number of samples used in the CCDF measurement to zero and restarts the CCDF measurement.

Tips

Note the following when making CCDF measurements:

For best results, set the VSA's displayed frequency span to include all the energy of your signal. In other words, make sure the displayed frequency span includes the entire bandwidth of the measured signal.
The CCDF measurement does not restart:
- After a calibration
- After a continued paused measurement
Many channel specific changes restart the CCDF measurement on both channels, such as changing the range, or input coupling.
The VSA displays DATA? if the average power drifts 8 to 10 dB from the average power measured in the first time record. For example, the VSA would display DATA? if a transmitter signal was measured that was off when the CCDF measurement started but then turned on later in the measurement.