There are many applications that require the capture and analysis of radio signals. Government bodies may need to review signals to check compliance with the appropriate regulations, or to assess any problems with interference. For example, in the UK, Ofcom acts as the independent regulator for the communications industry, and in Germany the Bundesnetzagentur ensures compliance with the country's telecommunications act.
Another requirement is for COMINT (communications intelligence) and ELINT (electronic intelligence). This kind of work deals with intercepting and analysing communications, typically for surveillance or information-gathering.
The signals captured can include a wide range of RF frequencies, whether they are from satellites or other sources. Depending on the application, a user may want to record the signals, analyse them in real time, or store them for offline processing. There is also a need to archive the captured signals for later reference.
Typical radio monitoring applications require a flexible access scheme where all intercepted signals are buffered, while operators or automatic classification and analysis tools browse through the available content.
Wider bandwidths needed
While this kind of monitoring and analysis is a long-established application, there is a recent trend towards continuous surveillance of all signals across wider bandwidths. Instead of selectively monitoring individual transmissions, organisations want to run automatic signal collection and analysis, all the time.
The objective of this continuous monitoring is to ensure that no relevant transmissions are missed. This puts additional demands on the equipment used, both in terms of the wider bandwidths targeted, and in the sheer quantity of data generated.
Another driver towards wider bandwidths is cost reduction by minimising the number of RF receivers required. Traditionally, organisations might use many narrowband receivers to monitor a frequency band – possibly as many as several hundred, if needed. If a single device could capture signals across a much wider bandwidth, this would allow fewer receivers to be used, thus saving money.
Finally, wider bandwidths are increasingly required simply due to the wide bandwidth of signals to be monitored. For example, global navigation satellite systems (GNSS), such as GPS and the European Galileo system, typically have signals across a wide bandwidth. GNSS satellites transmit navigation signals in the L band, which covers the 1 to 2 GHz portion of the radio spectrum – for instance, the GPS L1 band uses a centre frequency of 1575.42 MHz. The bandwidth of the signal itself can be measured in tens of MHz, which can cause problems for narrowband receivers – the best way to handle the full bandwidth is to use a wider band receiver.
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