With The Internet of Things Comes The Interference of Thing
My name is Lee Morgan. I’m a business development manager at Tektronix for IoT and Power applications. I’m a visiting blogger on DesignSpark for the next month.
Much is said about the rapidly approaching “Internet of Things” era. But in reality IoT is a part of modern life now, today, and reports suggest that this market will grow from a $167 billion industry today to $662 billion by 2021. This growth rate represents incredible opportunities for both new and traditional industries alike. With this great opportunity comes many technical challenges for engineers like ourselves. This includes
- the integration of wireless modules and interoperability with standards,
- power consumption restrictions,
- mixed-signal design and verification,
- EMI and EMC certifications,
- And finally combating interference from other RF sources.
Fig 1 – RSA306B Portable Real Time Spectrum Analyzer
Combating these challenges requires a new generation of test and measurement products that were previously only available to high-end research, particularly in the RF domain. One of the problems that engineers face from a test point of view is that traditional, Swept-Tuned Analyzers are not built to handle these modern wireless signals. New tools like Real Time Spectrum Analyzers (RSAs), such as the Tektronix RSA306B, are purpose built for this new digital RF era. With a Swept-Tuned Analyzer it is important to understand that what is being displayed on the left-hand side of the screen and what is seen on the right-hand side of the screen are not in fact happening at the same time. So, if I have a signal that is moving around, or is turning on and off over time, how do I capture this correctly and characterize it? An RSA, on the other hand, is continuously capturing all of the spectral information up to its maximum frequency span. It doesn’t sweep! Meaning, it also captures that time component modern digital RF signals. Now engineers have the ability to see how often something occurs, or how long it lasts for. If I have to employ an RF transceiver in my design that switches on and off, or has to share the spectrum, then an RSA will let me see the signal in much greater detail over a Swept-Tuned Analyzer, such as in Fig 2.
Fig 2 – Real Time Spectrum Analyzer Display With DPX and Spectrogram Information
RF Challenges With IoT Products
Over the past decade there has been a dramatic increase in wireless transmitters. Arguably, the 2.4GHz ISM band is the most popular portion of the spectrum for low-cost IoT devices. This band offers license-free frequencies for millions of these devices to operate in. Utilizing this free spectrum is attractive for its obvious cost savings, but you get no protection from all the other transmitters using the same channels. There are basically two rules to operating in the ISM band – you cannot cause interference to anybody else, and you must be able to deal any interference caused to you. So how do we do this? Well, we employ techniques such as clear channel assessment, meaning we listen before we transmit, and frequency hopping to other available channels. Despite following the certified rules, designers often find that they can have trouble establishing or maintaining radio link communication in the field. In debugging these situations an engineer will often try to draw a picture of what “good” looks like using the specifications, then analyze and characterize the RF environment in order to determine the anomalies and understand how their system interacts with other signals in the spectrum.
A second headache for the design team is the intentional radiation testing that comes with EMI and EMC compliance. This testing is exhaustive, complex and compliance can be expensive. Certification labs can charge anywhere from $1000 to $3000 per day. Pre-compliance testing is commonly used to catch problems early and to greatly improve the probability of successfully passing the full EMI compliance testing, thus reducing the time-to-market. Today, these cost effective test solutions can easily be setup, as show in Fig 3a and 3b. With the right equipment and planning, it can be a valuable tool for troubleshooting your design.
Fig 3a and 3b EMI Radiated and Conducted Emissions Test Setups
The RSA306B will not only closely mimics the emission test setup, but it also employs an accelerated FFT engine called DPX which greatly increases the number of FFTs captured and displayed per second on the screen. DPX is coupled with an intuitive colour grading scheme to visualize the rate of occurrence of a signal. This tool allows the designer to see intermittent or elusive spectral events which may correlate with an EMI failure.
Fig 4 – Tektronix DPX in Action With Intensity Colour Grading To Indicate the Rate Of Occurrence
Another critical feature of the Tektronix RSA306B is its ability to capture and replay data both on and offline of the hardware. The RSA306B’s architecture streams I and Q (amplitude and phase) information out through its USB3.0 port to an external PC or storage drive. Users can then replay this field data back in their labs. The amount of time the user can capture is only limited by the size of their storage device. This streaming, coupled with features invented by Tektronix, such as Frequency Mask Trigger, allows the user to define a trigger based not only on power levels but also the frequencies of a signal. This gives field technicians and engineers the capability to locate and capture those pesky, real world interference signals for further analysis.
The bottom line is, as engineers are building new devices that are fueling the Internet of Things, Tektronix is developing solutions, such as the RSA306B, that are helping unravel the Interference of Things. To learn more about the critical challenges in delivering IoT products, I recommend the Tektronix IoT landing page for a wealth of application notes. In my next blog we will take a closer look at EMI compliance and low-cost methods for EMI Pre-compliance Testing.
If you have a comment or questions, I’d love to hear from you in the chat below!
Lee Morgan is an Account Manager with Tektronix UK Ltd, with over 16 years’ worth of experience in the Test & Measurement sector, covering a multitude of roles in the Mobile Telecommunication, Electrical & Power industry, he has an excellent insight into how modern Test & Measurement Equipment can aid the engineers of today in creating the products of tomorrow.