1. CCDF definition
CCDF is the abbreviation of Complementary Cumulative Distribution Function. It is defined as the probability that the peak-to-average value exceeds a certain threshold in a multi-carrier transmission system. It also refers to a statistical method characterized by the peak power value of the digital modulation signal.
2. The role of CCDF
CCDF measurement is a valuable analysis method in the wireless communication industry of multi-carrier transmission systems. Its application is as follows:
You can see the effect of modulation
Combine multiple signals through the system
Evaluation system spectrum extension characteristics
Design and test RF components, determine device parameters (peak-to-average ratio)
The most important application of the CCDF curve is to clearly specify the power characteristics of the signal during mixing, amplification and decoding in the system. For example, designers of baseband DSP signals can use the CCDF curve to fully clarify the power characteristics of the signal. This helps to avoid problems and signal test data uncertainty during system synthesis.
3. Meter software CCDF analysis
Figure 1 CCDF view
1. The X axis represents the value higher than the average power of the signal in dB;
2. The Y axis represents the percentage of time that the signal is actually above the power level of the corresponding X axis;
3. CCDF template with limited Gaussian noise;
4. Frame average power;
5. The signal power exceeds the average power 3.3dB in 10% of the time;
6. The signal power exceeds the average power by 6.1dB in 1% of the time;
7. The signal power exceeds the average power by 7.3dB in 0.1% of the time;
The X axis in Figure 1 represents the value in dB, which is higher than the average power of the signal. The Y axis represents the percentage of signal power distribution. For example, when Y=1%, the peak-to-average ratio corresponding to the X axis is 5.9dB. This means that the signal power distribution is just 5.9dB larger than the average power, which is 1%.
CCDF analysis of 802.11b standard:
Figure 2 CCDF of 802.11b signal
OFDM signal overload:
Legend: When the Y-axis t=10%, the peak-to-average ratio deviation begins to increase
Figure 3 OFDM signal overload
As shown in Figure 3 above, the phenomenon that the CCDF curve deviates from the template seriously indicates that the OFDM signal is overloaded. The cause of the overload may be
a. Instrument VSA receiving overload
b. DUT transmission overload
Solution to OFDM signal overload phenomenon:
When the OFDM signal is overloaded due to the instrument VSA receiving, click the AutoRange button, and the Meter software will calculate the appropriate reference level according to the signal transmission power to avoid overload; when the OFDM signal is overloaded due to the DUT transmission, you can reduce the DUT Transmit power or modify DUT power amplifier parameters to avoid overload.