Radio Network Optimization, Real-time Recording and Classification of IQ Data

Real-time spectrum analyzers are the key to efficient and reliable measurements in a wide range of applications. Because they capture and analyze the frequency spectrum in real time, they enable the rapid detection and elimination of interference, the precise measurement of signal parameters, and the efficient management of a frequency spectrum. Real-time spectrum analyzers also help with the optimization of modern WLAN systems, for example. In addition, modern spectrum analyzers have powerful tools for recording and analyzing IQ data, which is essential for investigating and monitoring complex high-frequency networks.

Instead of discrete hardware, digital signal processors (DSP) in measuring devices do the work for real-time spectrum analysis. These can be programmed as required and, if necessary, reprogrammed with relatively little effort. The flexibility of these concepts is a major advantage: new radio systems with modified parameters such as modulation, different bandwidths, time response, and different channel coding methods can be implemented simply by adapting the software. When developing its real-time spectrum analyzers, Aaronia AG relies on a modular hardware concept, supported by the RTSA-Suite PRO analysis software, which is also modularly expandable and adaptable to all requirements.

Within the frequency range from 9 kHz to 55 GHz, the new SPECTRAN® V6 devices in the PLUS series can detect and localize even extremely short interfering signals and determine or eliminate their cause. The sweep speed of the ECO, 5G, and XPLORER series is up to 3 THz/s. This enables faster updating of the spectrum and the detection of transient signals, which is particularly important when analyzing frequency-hopping signals or searching for intermittent interference.

Figure 1: Within the frequency range from 9kHz to 55 GHz, the new SPECTRAN® V6 X devices of the PLUS series can detect and localize even extremely short-term interference signals and determine or eliminate their cause

The Crux of Bandwidth

More and more measurements have to be carried out in high-frequency ranges. The millimeter wave or extremely high frequency (EHF) band from 30 GHz to 300 GHz offers an enormous bandwidth and high resolution due to its high frequencies and the associated short wavelengths. The high frequency poses a major challenge for signal evaluation, as the propagation characteristics of EHF signals are susceptible to absorption and scattering. In addition, short-duration signals often have a low signal-to-noise ratio, and background noise can mask the interfering signals. 5G networks and future 6G networks as well as applications in the fields of aviation, meteorology, and the military use parts of the EHF band for high-speed data transmission. Appropriate measuring devices are therefore essential for meaningful analyses.

Figure 2: The SPECTRAN® V6 only needs 5 ms to cover the entire frequency range of 6 GHz. Even short signals such as Bluetooth or DECT are easily reproduced by the POI in just 5 ms and enable a quasi-real-time display of the entire frequency spectrum from TETRA to GSM, LTE, 5G and 5 GHz Wi-Fi

The SPECTRAN® V6 analyzers from Aaronia are up to these tasks with their real-time bandwidth of up to 450 MHz. By combining several SPECTRAN® V6s, the real-time bandwidth can be increased as required. Cascading just four V6s allows seamless real-time measurement from 20MHz - 1GHz, for example, which means an unbeatable time advantage for a large number of measurements. All SPECTRAN® devices from Aaronia in all price classes have sophisticated, extremely fast switching filter banks, which are otherwise only integrated into expensive high-end devices. "Measurement technology and the demands placed on it are changing rapidly," says Thorsten Chmielus, CEO of Aaronia AG. "With our USB real-time spectrum analyzers, we are able to react quickly to new circumstances. With the continuous further development of the SPECTRAN® series, we are constantly setting new benchmarks and future-proofing our products."

The Supreme Discipline of IQ Data

IQ data refers to in-phase (I) and quadrature (Q) data used in digital signal processing and communication. This data represents the real part (I) and the imaginary part (Q) of a complex signal. By using IQ data, complex radio signals can be effectively captured and analyzed and, if necessary, decoded.

However, only real-time measuring devices are able to reliably record short-term and sporadically occurring signals in a broad spectrum. In classic spectrum analysis, the signal is collected over a certain period of time and then analyzed. Block-by-block processing inevitably leads to delays. Real-time spectrum analysis analyzes the signal continuously and without delays as it is received. 

Furthermore, in conjunction with the modular real-time spectrum monitoring software "RTSA-Suite PRO", they are able to record IQ data in real time. The main feature of this solution is that once the IQ data has been saved, it can be analyzed in detail at any time.

Figure 3: The IQ demodulator block can be used to extract individual or multiple frequency ranges from a complex IQ data stream. This enables massive data reduction or narrowband decoding of several signals. Here are two QAM signals that are tapped individually and decoded independently of each other

Record and Analyze IQ Data

The requirement to record IQ data without any gaps and make it available to the user without restriction is usually an almost impossible task for many of the discrete measuring devices on the market. It requires the simultaneous acquisition of two complex signal components. These signals are generally analog and must be digitized at high sampling rates using very fast analog-to-digital converters (ADCs). As the buffered streaming method is generally used here, the signal is merely buffered in the internal working memory. Only this data is available as IQ data. This is sufficient for visualization, but not for decoding and subsequent analysis of the signal.

This is because recording generates large amounts of data that need to be transmitted and stored extremely quickly. This is where SDRs (Software Defined Radios) show their strengths, as the storage and further processing of IQ data is only limited by the performance of the PC system used. This opens up completely new possibilities for pre-and post-processing. For example, the digitized signals can be transferred to your own software solutions or to existing applications such as MATLAB or similar for further processing.

The major problem for measurement setups is therefore the sheer volume of data that is generated. This quickly fills the mass storage devices used with superfluous information, especially as the extremely fast data storage devices required are currently only available with limited capacity. In addition to this limitation, searching for specific events retrospectively is almost impossible.

Aaronia AG has solved this problem and developed a new tool that only records predefined events. For example, everything that is at 2.4 GHz and has to do with Wi-Fi can be written away during operation. Several events can also be defined if required and the associated metadata can also be written away. In this way, the technician can create a database that contains all the required events as IQ data but only requires a fraction of the storage space. This means that nothing stands in the way of 24/7 IQ capture, as comparatively little hard disk capacity is required. This means that the Aaronia solution can be used for more than just recording IQ data. This tool also makes it possible to find specified pulses and their statistical distribution. The previously critical storage media capacity and speed as well as the associated high costs become secondary.

Depending on the requirements, the RTSA-Suite PRO software can be used on Windows 10 / 11 or Linux systems. At least 2 GB of RAM and a quad-core processor with 1.6 GHz clock frequency and AVX2 support are required. This means that it can also run on smaller computers. For more complex visualizations with several different views at the same time, however, a correspondingly powerful PC hardware is recommended.