Introduction
WSA-408 is an advanced lab-quality Wireless Signal Analyzer (WSA) series product that was designed for wide variety of outdoor field application scenarios through the simple OTA (Over The Air) antenna interface. This report presents a few actual use case examples demonstrating the WSA product’s powerful software features and superior performances in terms of speed, sensitivity, dynamic range and ease of use etc.
Figure 1, WSA-408
Case 1, FDD-LTE uplink interference finding inside a mall
On October 18, 2024, a WSA-408 was brought to an IKEA mall in Changsha, China, to investigate an indoor 4G-FD-LTE uplink interference problem that had been troubling the China Unicom operators for quite a few months. The Huawei field support engineers had brought a “popular” swept spectrum analyzer to the site, and tried to locate the problem for about a month, but could not find either the problem or the cause. When the WSA-408 was brought to the site, the problem and cause were identified within 10 minutes, literally, by using the unique synchronous co-domain analysis feature (Time-domain-power (scope) plus Frequency-domain spectrum analysis) as shown below. The interference source comes from a security alarm system that was also configured to use the same frequency band as the FD-LTE uplink operated by China Unicom for indoor coverage. Such short-pulse (<100 us long) interference signal can never be found via the conventional swept spectrum analyzer. It can only be found by a true broad-band (100 MHz instantaneous analysis bandwidth) real-time FFT analyzer with flexible feature that permits synchronous co-domain analysis of the suspicious signal to pinpoint the exact cause and problem.
Figure 2, finding an FD-LTE uplink interference by using WSA-408’s synchronous co-domain
analysis feature. The top displays the signal power (within 20 MHz, in this case) vs time for a
span of 10 ms. The bottom displays the spectrum corresponding to a short-segment of signal
highlighted by users through a simple touch and marked by the yellow color.
Case 2, uplink interference due to cell site “mis-alignment”
On December 9, 2024, a WSA-408 was brought to Changsha, China, again to help trouble-shoot yet another FD-LTE uplink interference operated by China Unicom across a few densely populated high-rise building communities. The uplink frequency band in question is centered at 909 MHz, and the corresponding downlink band is at 954 MHz. The “culprit” turns out to be the downlink LTE signal centered at the adjacent frequency band of 939 MHz operated by China Mobile. The following two pictures (Figure 3) show the WSA-408’s LTE analysis results for the two LTE downlink signals (one at 954 MHz by China Unicom and one at 939 MHz operated by China Mobile). China Unicom was reporting uplink interference at 909 MHz band corresponding to cell-ID=105 as shown in Figure 3 (left).
Figure 3, WSA-408’s 4G-LTE analysis results display for China Unicom downlink signal at 954
MHz (left) and for China Mobile downlink signal at 939 MHz (right).
As shown in Figure 3, the 954 MHz downlink’s uplink band at 909 MHz was reporting interference. The “culprit” turns out to be the downlink signal at 939 MHz, not by intention, but by the fact that these two cell sector’s antennas were directly aiming at each other. Both cell sites are each sitting on top of a 40-story tall building, with each other’s antennas aligned exactly towards each other (with a separation distance less than 500 m) in a perfect line of sight with very little tilting angle (almost horizontal). As a result, the minute out of band emission by the 939 MHz downlink caused measurable uplink interference at 909 MHz. This was confirmed by temporarily disconnecting the 939 MHz cell site, and the 909 MHz uplink interference disappeared.
Figure 4, the “culprit” 939 MHz cell site is located on top of this building in picture (left). Near
this cell site, at the 909 MHz uplink band of another adjacent cell site, WSA-408 was measuring
“visible” interference signals shown on right.
Case 3, Finding GPS interference that affects LAE (Low Altitude Economy) operation safety
The Low Altitude Economy is in full swing in China, and “Phoenix Wings” (丰翼) is one of the leading companies providing delivery service using drones or UAVs (Unmanned Aerial Vehicles). These company’s common problem is GNSS signal interference caused by the rampant abuse of hand-held anti-drone signal jamming devices. It’s very difficult for the law enforcement officers to catch such “illegal” actions in real-time on the ground with the conventional slow and bulky instruments. For this reason, Phoenix Wings company put a WSA- 208 module along with power supply and antenna etc. in its UAV’s carrying basket and performed a few experimental flights. And indeed, captured definitive spectral evidence of GNSS band interference as shown in Figure 5.
Figure 5, Left: putting the WSA-208 module along with accessories in a UAV’s carrying basket;
Middle: actual test data showing evidence of GNSS interference due to illegal use of anti-drone
jamming device. This data is captured by WSA’s unique “multi-channel auto spectral recording”
feature; Right: the WSA-208 has been officially mounted on a drone with multiple directional
antennas to serve as a WSA-508 product for quick interference signal detection (or signal
intrusion detection) and direction finding, or Signal Coverage test in air.
Case 4, ensuring adequate 5G signal coverage over the new Shenzhen-Zhongshan Bridge
In the fall of 2024, Shenzhen opened a landmark bridge of more than 15 km long to the public. The construction of such long bridge across the major Pearl River delta region had taken about a decade, even at China speed, so its opening ceremony was a big political fanfare. To ensure smooth opening, folks at the Chinese Radio Monitoring Agency (Chinese equivalent of FCC) Shenzhen branch was tasked to perform 5G signal coverage tests across the bridge right before the opening ceremony. For this task, the Radio Monitoring Agency used WSA-408’s “Multi channel Scanner” feature to simultaneously monitor the 5G signals from China Mobile, China Telecom and China Unicom respectively while driving in a car (so-called drive testing). The following are actual pictures of the real actions and a snap.
Figure 6, perform multi-channel 5G-NR drive testing using a WSA-408 over a new bridge in
Shenzhen, China, right before the opening ceremony.
Case 5: Continuous IQ data recording for ADS-B interference near Shenzhen Airport
The ADS-B (Automatic Dependent Surveillance Broadcast) operated on 1090 MHz is a signal broadcast by each airplane indicating its speed and elevation etc. Correct reception of such signal by each airplane is a vital part of the TCAS (Traffic Collision Avoidance System). Since April 2025, major airline companies have launched complaints to the Chinese Radio Monitoring Agency about frequent ADS-B channel interference over the Shenzhen metropolitan area. The consequence such interference is high false alarm rate: airplanes received alarming signals indicating presence of other planes nearby while in reality there were no other planes at all. To capture concrete evidence of such interference, the Chinese Radio Monitoring Agency, working with a National Lab in Shenzhen, has installed a WSA-408 instrument inside a radio monitoring station near the Shenzhen Airport. The WSA-408 was set to perform a continuous and circular IQ data recording into an external USB hard drive with 9T space. By design, the last 7 days of IQ will be permanently recorded once the recording is stopped by users. Once the Airport reports interference again, the recorded IQ data will go through post analysis to determine the exact cause of interference. As shown in the following pictures, the WSA-408 is essentially performing a task that is normally carried out by the very expensive R&S ESMD system installed inside the same station, at a fraction of the ESMD’s cost and with much higher efficiency and better useability.
Figure 7, Left: Chinese Radio Monitoring Station near the Shenzhen Aiport; Middle: a WSA-408
installed inside the station and tasked to perform continuous and circular IQ data recording over
the 1090 MHz ADS-B channel; Right: the very “expensive” R&S ESMD radio monitoring system
installed at the same location. In reality, a single WSA-408 can perform similar functions at a
fraction of the cost with much better efficiency.
Case 6: DJI UAV flight control signal detection
The drones (UAVs) are a perfect example of a double-edged sword. If used properly, they are wonderful. If not, they can be a menace. For the latter case, detecting the intrusion of a drone is a national security matter. Among all possible methods, the one using radio signal detection is probably the simplest and the easiest. A typical drone will emit a downlink signal to send the video camera image data along with the flight status to the controller, whereas the radio controller will use the uplink to send signals to control the UAV. The downlink is generally a stable (non-hopping) wider-band (10 or 20 MHz wide LTE-OFDM type of signal), while the uplink is a narrower band (around 1 MHz) frequency hopped signal to avoid interference. A radio receiver (signal analyzer like a WSA-408/308/208) capable of intercepting such signal pair reliably can provide the surest way of detecting a drone. The following pictures show the actual experiment performed with a DJI drone and a WSA-408 and the captured signals.
Figure 8, Left: A WSA-408 sitting beside a DJI drone; Middle: the drone signals displayed in 3-
trace mode; Right: the drone signals displayed in Block DPX mode. The 20 MHz wide downlink
signal and the frequency-hopped uplink signals are very obvious on the Block DPX display
presented by the WSA-408.
Case 7: Challenge the HP/Agilent/Keysight “Supremacy” in the instrument market
Before 2000s, the name of HP/Agilent/Keysight is not only synonymous with Silicon Valley, but also with the high-end Spectrum Analyzer, especially the early FFT analyzers. Through chance countering, the WSA-408 (early prototype) entered a fair competition with the “expensive” Keysight products and the actual test results prove that the WSA-408 has actually outperformed the Keysight products in many respects but at only a fraction of the cost, of course. Let the pictures in Figure 10, 11, 12 speak for themselves.
Figure 10. For the pulsed and frequency-hopped signal input, the “expensive” Keysight MXA
N9020B at the left shows a very smooth but very blurred picture of the signal, indicating no
discrete nature of the hopped frequencies. By contrast, the WSA-408 vividly shows the discrete
nature of the hopped frequencies.
Figure 11, under normal 100 MHz spectral display, the “expensive” N9020B at the left is
showing similar spectrum as the early prototype of WSA-408 at the right, but fairly speaking, the
WSA-408’s spectral display shows much better resolutions in terms of amplitude, frequency and
spectral trace, and even better signal to noise ratio.
Figure 12, for the same over the air Wi-Fi signal, the WSA-408 at the left has 100% interception
rate, but the Agilent FieldFox at the right shows almost no presence of signals at all.
