Pulsed Waterfall
The Pulsed Waterfall shows the entire spectrum based on the selected signal duration. A perfect duration value will offer a view of the fitting signals only:
Left hand side Input:
- Spectra
With the Pulsed Waterfall block you can identify the duration of any signal live within the frequency spectrum at a glance. It somehow works like an analog tv where you need to tune the sync till you get a stable picture otherwise the picture will scroll up or down the screen. The number of Samples, Persistence, Pulse Duration, Jitter and Time Compression are adjustable.
In addition you can use the "Auto Detect" feature which will try to finde the dominant signal duration within the spectrum with a single mouse click:
The following screenshot shows a WiFi 802.11 signal.
The "Auto Detect" function detected a signal duration of 1024µs. This is the WiFi 802.11 beacon interval.
You often read that beacon frames are sent, by default, every 100 ms, but this is only half of the story: Beacons are sent by the AP at a regular interval defined as the so called "Target Beacon Transmission Time" (TBTT).
The TBTT is a time interval measured in time units (TUs). A TU is often mentioned with a duration of 1 ms but this is a bit wrong.
The reality is seen in the definition of a time unit within the 802.11-2012 standard document, which reads, "A measurement of time equals to 1024 µs." and is exactly what we can measure:
The next screenshots shows two channels with a dominant 80 ms pulse duration package looking like a TTI from multiple GSM base stations.
One cluster package is marked with the help of a cursor showing a 10ms overall cluster length. In LTE the TTI length is fixed to 1 ms so for sure this must be a UMTS/HSPA transmission which offers a TTI of 2 ms, 10 ms (or 20 ms, 40 ms, 80 ms for some channels), and fixed for a given channel.
The Transmission Time Interval (TTI) from a UMTS/HSPA is an interval of time for transmission of one layer 2 data unit (PDU). The TTI comprises the group of blocks of resources for the transmission to which the same coding and modulation is applied:
A typical Mission:
The Pulsed Waterfall block now includes a Gated Period Trigger which allows a gated measurement e.g. to extract interfering signals for a better tracking of the source.
We are generating a pulsed QAM signal together with a interfering CW within the same frequency range for test purpose:
Within the "Waterfall Original Signal" you can see this signal mix.
Lets say we want to focus on the interfering CW signal only so we want to get rid of the QAM signal. With the help of the Time gating and the Trigger we can now remove the pulsed QAM signal by simply setting an area between the QAM pulses at the "Pulsed Waterfall" spectrum.
Now we only get the interfering CW signal. This will allow us a much simpler tracking of the signal:
The Pulsed Waterfall block now offers a higher Period Duration, Gate Duration and Gate Offset resolution down to 100ns (original was 10µs):
Please have a look at our latest video showing the usage of this block: Pulsed Waterfall Demo Video
