Boonton’s Wi-Fi 6 Solutions: Packet Time Gating
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RF power measurements are often taken of an entire Wi-Fi data stream to catch important waveform anomalies, such as power droop, signal dropout, and pulse drift. However, sometimes it is of equal importance to take a more focused approach, zooming and testing specific portions of a Wi-Fi packet. For instance, a signal’s preamble section (see Figure 1) is used as an introduction for the receiver so it can prepare for incoming data and synchronize itself with the transmitter. Depending on the application and testing needs, engineers may need to acquire essential measurements like peak, average, and minimum power of only the preamble section of a packet, or its trailing data portion.
Figure 1: The preamble and data portions of a Wi-Fi packet.
The Boonton RTP Measurement Buffer Mode Application works with the RTP4000 or RTP5000 series of RF power sensors to enable power measurements of entire data streams over very long durations in virtually real time, but also creates a user-friendly environment to target individual areas of interest.
Before acquiring measurements of a desired packet section, precautions must be taken to eliminate false triggers from skewing results. Erroneous triggers are of particular concern when characterizing Wi-Fi 6 signals, since their modulation has noise-like behavior in the time domain. In Figure 2 below, a brief noise spike goes above the gate threshold, which can prematurely prompt the start of measurements outside the desired gate interval, leading to inaccurate results. To prevent interference from random noise spikes, users can define a parameter known as a “start qualifier” within the RTP Measurement Buffer Mode Application. A start qualifier identifies a time interval that a signal must spend above the gate threshold before measurements can begin, meaning quick noise spikes or anomalies will be ignored since they will fail to meet the qualification requirement.
The behavior of Wi-Fi signals can still cause problems after the start qualifier has been successfully satisfied. While inside the desired gate interval, brief modulation dips can travel under the gate threshold, which could cause the measurement window to end too soon. Similar to the start qualifier, an “end qualifier” designates a specific timespan as a prerequisite event in order to stop power measurements.
Figure 2: Gate qualify and delay options can align the buffer gate interval within a packet.
After the start and end qualifiers are set to ensure power measurements will be taken within the desired gate interval, users can now begin to narrow into certain pulse portions. Within the RTP Measurement Buffer Mode Application, a parameter referred to as the “start delay” can essentially push the gate interval ahead in time for a determined duration to exclude the rising edge or preamble of a Wi-Fi signal. By the same token, an “end qualifier” proves useful to end the gate interval early, effectively excluding the falling edge and other trailing regions of a Wi-Fi packet. Although time gating can be performed using gate qualifiers and delays, a similar effect can be achieved within the software by simply setting markers to provide measurement focus.
Boonton’s real-time RF power sensors, including the recently launched RTP5008 that’s built with a focus on Wi-Fi 6 characterization, work in conjunction with Boonton’s complementary software to enable easy and efficient single packet time gating. These sensors are also compatible with the Boonton PMX40 RF power meter for those still wanting a benchtop experience while still reaping the benefits of USB sensor flexibility and performance during Wi-Fi testing.