SDR for wideband & high bandwidth spectrum monitoring & recording

Author : Biftu Omar Hulo, technical writer & Brandon Malatest | Co-founder & COO | Per Vices

01 October 2021

Per Vices_SDR for wideband & high bandwidth spectrum monitoring & recording_RF spectrum stock shot
Per Vices_SDR for wideband & high bandwidth spectrum monitoring & recording_RF spectrum stock shot

Radio frequency (RF) communications has become an integral form of wireless communication, used widely across many industries, including both civil & defence applications. From television broadcasting to military radar systems, industries depend on RF technology to work free of interference & obstructions.

This article was originally featured in the October 2021 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.

As wireless communications technology continues to grow, the capability to identify and remove unwanted interference signals has become increasingly important; consequently, spectrum monitoring and recording has become a very powerful tool in building robust networks. Here, Biftu Omar Hulo, technical writer and Brandon Malatest, co-founder & COO at RF & digital systems innovator, Per Vices explores what spectrum monitoring and recording is – and why software defined radio (SDR) technologies offer a good solution…

Spectrum monitoring equipment employs the use of a radio receiver to capture and record incoming data from within a desired network (for instance, across the network spectrum) and then passes that data to a separate system for storing and analysis, as shown in Figure 1.

The quality and efficiency of spectrum monitoring equipment can be judged based on various parameters, one of which is the equipment’s probability of intercept (POI). In layman’s terms, the POI of a system refers to the minimum amount of time that a signal needs to be present for a spectrum analyzer to be guaranteed to capture it. A high POI is desired, as it indicates a higher probability of intercept, meaning that the equipment could catch signals with shorter durations.

Another parameter by which one can judge the quality of spectrum monitoring equipment is the ability to adjust resolution bandwidth (RBW). The RBW is the bandwidth (in other words, the frequency span) of the final filter used on an input signal. Higher RBWs allow for faster speeds and increases the POI; however, smaller signals can be lost when close to a larger signal. Contrarily, lower RBWs allow for finer identification of signals that are in proximity of each other; however, it comes at the cost of lowering the POI and slowing down the spectrum monitoring equipment.

Finding the balance in the trade-off between POI and RBW is the key to getting the right spectrum monitoring performance for its respective application.

Figure 1. Spectrum monitoring & recording process
Figure 1. Spectrum monitoring & recording process

A final parameter that can be used to evaluate the performance of spectrum monitoring and recording equipment is channel capacity. By today’s telecommunications standards, the wireless spectrum is divided into many channels, each of which operate at a standard centre frequency and bandwidth. The ability of the equipment to tap into these many channels independently and simultaneously is extremely valuable. Having multiple channels allows for more data capture and allows the user to tune multiple channels for different purposes.

Wideband operations & considerations

In the past, RF communications such as two-way radios would traditionally use narrowband wireless protocols. Narrowband is classified as any RF communications whose signal bandwidths are less than the coherent bandwidth –– in which, the frequency fading is flat and uniform across the spectrum. Its frequency spectrum is partitioned into narrow frequency channels, which is ideal for minimising signal interference. The major drawback, however, is that narrowband communication significantly limits how much data can be transferred at one time – and therefore does not meet the growing demand for larger capacity and faster data transmission rates needed for applications such as video streaming and complex surveillance systems. This gave rise to wideband communication channels.

Wideband is classified as communications that use a wide range of frequencies and whose signal bandwidths exceed that of the coherent bandwidth. This allows for users to transmit significantly more information over longer distances and at faster data transmission rates; however, this comes at the cost of more interference signals, higher signal power usage, and it is prone to selective fading across different frequencies. The need for spectrum monitoring and recording equipment that can selectively remove interference signals from wideband operations is therefore exasperated as the demand for wideband communication continues to rise.

In the past, bandwidths exceeding 100 MHz were considered wideband; however, with rapid advancements in technology, the demand for bandwidths up to 1 GHz is growing. As it currently stands, wideband operations have become widespread for both military purposes (such as advanced surveillance and radar systems) and everyday civilian use (such as FM radio, cellphone communications, Wi-Fi and GPS). Different communications are typically assigned specific frequency ranges, and therefore take place in different places in the spectrum. Figure 2 shows where in the spectrum different communications take place. Signals of interest for civilian and military use reaches up to 18 GHz.

As shown in Figure 2, many of the communications that occur today require

Figure 2. Where different communications take place in the RF spectrum
Figure 2. Where different communications take place in the RF spectrum

wideband and ultra-wideband transmission. As previously iterated, meeting the demands for spectrum monitoring and recording, especially among communication crucial for public safety and national defence, is more important than ever.

Benefits of adjustable & high bandwidths

For modern spectrum monitoring and recording equipment to keep up with today’s wideband operations, it must be capable of operating at high bandwidths. High bandwidth allows for the equipment to capture more of the spectrum at any given time, and is ideal for situations where larger data capture is needed for post-processing.

As noted earlier, operating at high bandwidths simultaneously increases the system’s POI, effectively allowing spectrum monitoring equipment to capture high powered signals that are present for very short periods of time (for instance, burst signals). Other benefits of operating at high bandwidths include:

•  Large channel capacity

•  Resistance to jamming (due to functionality across a wide range of frequencies)

•  High performance in multipath channels

A major drawback, however, is that equipment operating at high bandwidths will perform poorly when discriminating between smaller signals that are in proximity of larger signals. In contrast, by narrowing the bandwidth, one can improve the sensitivity and the spurious free dynamic range.

Per Vices_SDR for wideband & high bandwidth spectrum monitoring & recording_military radar stock shot
Per Vices_SDR for wideband & high bandwidth spectrum monitoring & recording_military radar stock shot

Therefore, having adjustable bandwidth capabilities is useful for enabling high bandwidth operations for high data capture, as well as tuning in to select signals for further analysis. The key to achieving both of these functions independently and simultaneously, however, is heavily dependent on the number of channels that the spectrum monitoring and recording equipment can host.

Channel count: does it count?

Spectrum monitoring equipment that can analyse and monitor multiple parts of the spectrum, and can sweep through frequencies using both narrowband and high bandwidth channels, is important, as it allows for both higher data capture and for precise analysis of individual signals. Achieving this in real time using a singular channel is very difficult, and therefore multiple channels are required to get the best of both worlds. The number of channels that spectrum monitoring equipment can house is directly correlated with the desired channel sizes and the total amount of available bandwidth.

Similar to high bandwidth operations, the more channels that are available, the more data can be captured. Having many channels that run independently of one another allows for a user to dedicate some channels to run at a high bandwidth (to capture large sets of data and identify surge signals), while also dedicating other channels to run at adjustable bandwidths to tune into signals of interest for further analysis.

Another advantage of having a large channel count is the ability to tune each channel (in other words, select the centre frequency and operating bandwidth) in order to monitor the different communications taking place across the spectrum. It allows the user to dedicate channels to a variety of different applications, including, but not limited to: radar communications; 5G networks; AM/FM radio; television broadcasting; air-to-air traffic control; and military communications.

The solution: software defined radios (SDRs)

Figure 3. Cyan software defined radio (SDR) from Per Vices
Figure 3. Cyan software defined radio (SDR) from Per Vices

Thus far, we have established that the ideal spectrum monitoring and recording system must have the following characteristics:

•  High bandwidth and POI for data capture in wideband applications;

•  Adjustable bandwidth for versatility between rapid data capture, signal sensitivity and spurious free dynamic range; and

•  High channel count for high data capture, and for running independent channels at adjustable, user-defined bandwidths simultaneously.

To achieve and optimise the above requirements using today’s traditional radios is difficult. As the market moves towards high-speed 5G ultra-wideband operations, acquiring the necessary hardware becomes slow and costly. Additionally, the lack of adaptability of today’s hardware significantly disadvantages traditional radios in the ever-evolving market, and significantly reduces traditional radio lifetime.

The proposed solution is therefore the emerging technology known as software defined radios (SDRs).

SDRs replace traditional hardware components, such as low-noise amplifiers, filters and mixers, with software that can process transmitted radio signals with the use of a computer. This software is easily programmable and allows the user to change the internal software structure and algorithms to achieve the perfect processor for different forms of communication.

Per Vices_SDR for wideband & high bandwidth spectrum monitoring & recording_communications mast stock shot
Per Vices_SDR for wideband & high bandwidth spectrum monitoring & recording_communications mast stock shot

SDR for high POI, available bandwidth & channel count

Due to the removal of hardware components that contribute to bandwidth limitations, modern SDRs can achieve much higher available bandwidth. As previously outlined, with more available bandwidth, the capacity for more channels will increase and the POI of the system will be driven higher, allowing for higher data throughput and optimal response times of the system. Additionally, modern SDRs can reach up to sixteen independent receive channels, which could potentially allow for one narrowband and one wide bandwidth channel for all eight spectrum classifications (such as HF, VHF, UHF, and so on), as shown in Figure 2. This is ideal, as it allows for dedicated channels for high data capture across desired areas of the spectrum, while simultaneously running dedicated channels to analyse individual signals of interest.

SDR for variable bandwidths

Again, because the hardware components in a traditional radio are replaced by programmable software in an SDR, it is no longer limited to the available amplifier, filter and mixer parameters, and it is much easier to adjust the software to achieve the desired centre frequency and bandwidth of a channel for its respective target area along the spectrum. SDRs are also capable of housing agile processing software that allows the receiver to automate its bandwidth adjustment to capture signals of interest when they are present. This allows spectrum monitoring equipment to adapt bandwidth for the trade-off between high data capture and accurate data analysis.

SDR product example

An example of an SDR currently available on the market is Per Vices’ Cyan (shown in Figure 3). Cyan offers 1GHz per channel bandwidth for up to 16 receive radio channels. This results in an overall bandwidth availability of 16GHz. Cyan has a wide frequency operation range up to 18 GHz, which covers most civilian and military applications of interest. It also comes with four 40 Gbps digital backhauls to support the high data throughput going from the SDR to the storage solution.

In summary, SDRs are the solution to modern spectrum monitoring and recording demands. They meet the requirements for high and adjustable bandwidth availability, high POI and data throughput, and high channel count.

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