By Janet Ooi, IoT Industry Solutions Lead, Keysight Technologies
Navigating regulatory requirements for wireless medical devices.
With the rapid increase of the Internet of Things (IoT), the world around us now has billions of devices connected to the internet. IoT consists of devices for the healthcare industry, consumer marketplace, industrial sensors for manufacturing, and automotive electronics. While all of these devices have gone through performance testing before their introduction, the likelihood of interference in crowded wireless environments means there’s no guarantee they will operate as intended. Standards bodies continue to produce test methodologies to evaluate device operation in the presence of other signals. Design and test using conventional methods are no longer sufficient. Design engineers and manufacturers will need a comprehensive approach to address the multifaceted challenges of IoT.
While medical devices have long operated on specific wireless bands, today’s wireless infrastructure means that manufacturers can now embed a mix of wireless capabilities into their new and existing devices operating on industrial, scientific, and medical (ISM) bands. For example, embedding a blood pressure monitor in a smartwatch or implanting a pacemaker in a patient to regulate their heart rate.
And it doesn’t stop there. Wireless capabilities are now cropping up in everything from consumer and automotive electronics to industrial applications. The explosive growth of the IoT has brought billions of personal and infrastructure devices onto the ISM bands.
This is where your challenges begin. Tens of billions of IoT devices now share the same radio channels and can interfere with the operation of other devices present. Failure to communicate is problematic, especially in a healthcare environment where life-critical incidents can impact patients. To build a reliable and secure IoT device, design engineers and device manufacturers will need to address the 5 C’s of IoT: connectivity, continuity, compliance, coexistence, and cybersecurity.
Compliance and coexistence are only two out of five challenges IoT designers and device manufacturers face, but they are equally critical. In combination, your IoT devices are certified for compliance with regulatory frameworks in the global marketplace and guaranteed to work reliably in a crowded wireless environment.
Standards bodies and regulatory agencies are passing new recommendations and regulations to test wireless devices for robust operation in the presence of other signals. The new recommendations and regulations will ensure the coexistence and compliance of your IoT devices. However, ensuring your devices meet these requirements requires appropriate test and measurement solutions.
Recent tests and regulations have advanced and now require new on-air behavior. The intent of the new criteria and regulations will improve inter-device cooperation, reduce data loss due to conflicts, and improve reliability and throughput of devices.
There are two test parameters IoT devices must meet:
- Ability to share the channel using defined channel access mechanisms that allow time for other devices to use the channel during pauses in transmissions.
- Capacity to continue its regular operation in the presence of different on-air protocols, such as Bluetooth, WLAN, and ZigBee Standard.
Since devices for different protocols cannot actively communicate with one another, the wireless coexistence test addresses the interference problem.
Wireless Coexistence Test
The wireless coexistence test is an empirical method that uses direct observation of the behavior of a device in the presence of interference. Coexistence testing uses unintended (interfering) signals to measure the ability of multiple devices to interact. It determines whether these signals have maintained their functional wireless performance during the interaction.
The American National Standard Institute (ANSI) for Evaluation of Wireless Coexistence, ANSI C63.27; 2017 and 2019 defined the methods for coexistence test. The Association for the Advancement of Medical Instrumentation (AAMI) refined the standard in TIR69 (2017) for wireless medical device use. The U.S. Food and Drug Administration (FDA) approved this update to the standard.
Healthcare devices are among the first to experience communication failures because of the many uses of RF energy in a medical setting. The coexistence test places the device under test in a real or simulated wireless operating environment to ensure it can operate within a crowded RF environment. Passing design validation tests is not sufficient anymore. Wireless coexistence test can reveal defects in hardware and software along with the limits of the operating capabilities of a specific wireless device; antenna, transmitter, receiver, or even the device programming. Device manufacturers can adjust the operating instructions based on the results, setting user expectations for device performance in a particular RF environment.
New ETSI Standard Tests
European Telecommunications Standards Institute (ETSI) is a leading standardization organization for Information and Communication Technology (ICT) standards fulfilling European and global market needs. Originally founded to serve the European market, ETSI now works in partnership with various types of industries across the globe.
Recent revisions of ETSI standards — EN 300 328 for devices using the 2.4 GHz ISM band and EN 301 893 for devices using the 5 GHz RLAN bands — focused on improving spectrum sharing and avoiding interference. The new measurements include adaptivity, average utilization, and other techniques to reduce collisions between transmissions and to improve spectrum efficiency regardless of the protocols in use.
The adaptivity test is now in the new version of the standard, with detailed technical requirements on the interference detection threshold and timing to provide clarity. The adaptivity test has three different types of operational behavior:
- While the channel is busy, as defined by the presence of RF energy above a certain level, the device must wait before transmitting.
- When a device uses more than one 20 MHz channel, testing the operating behaviors must include sensing channel activity on one or more channels before initiating transmissions.
- Even when signals are not detectable while sensing the channel, the device must use a defined channel access mechanism that enforces channel sharing by leaving gaps at random intervals during transmissions. This process enables other users to access the channel.
Another test classification is a refined definition of dynamic frequency selection. ETSI EN 301 893 has requirements for new waveforms from various international geographies, and timing requirements for either a channel availability check (CAC) or an off-channel CAC. Performing checks is necessary to ensure radar is not operating on any selected channel, for both the primary and secondary devices.
Coexistence and compliance tests require precise timing measurements over a long interval of operation with a complex mix of RF channels and radar signal types. Testing can be very tedious when performed manually. When performed accurately, compliance and coexistence tests should improve wireless device operation in crowded environments commonly found in medical facilities.
Building a device based on the 5 C’s of IoT ensures that your complex IoT device reaches the pinnacle of its performance limit. No doubt, it will be a challenging process to deploy at every stage of the device life cycle — from simulation to research and development, conformance, manufacturing, and field deployment. Design engineers and device manufacturers following the comprehensive 5 C’s approach can ensure their device is reliable and secure. For more information, please download the eBook on 5C’s of IoT or go to www.keysight.com/find/5CsofIoT.
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About The Author
Janet Ooi is IoT Industry Solutions Lead at Keysight Technologies.