At any given time, a typical home or hospital uses a number of wireless systems (e.g., IEEE 802.11a/b/g/n, or WiFi; Bluetooth; ZigBee; cordless phones) operating on the same industrial, scientific, and medical (ISM) band. Given the increasing use of wireless, RF wireless medical devices and other wireless systems operating nearby can interfere with each other.
If a collision between their respective transmissions occurs, data packets transmitted by medical devices could be delayed or blocked, potentially interfering with timely transmissions of critical data. Techniques such as retransmission and forward error correction might no longer be sufficient to overcome interference and spectrum congestion. Hence, methods to design and test wirelessly enabled medical devices for risks associated with coexistence of wireless technologies are essential for innovative, safe, and effective RF wireless medical devices.
Although there is some overlap between electromagnetic compatibility (EMC) and wireless coexistence, differences exist. Wireless coexistence is the ability of one wireless system to perform a task in an environment where other systems that may or may not be using the same set of rules can also perform their tasks. EMC is the ability of a device to function properly in its intended electromagnetic environment without introducing excessive electromagnetic energy that could interfere with other devices.
Manufacturers of electrically powered medical devices routinely test their equipment to applicable national and international consensus safety standards. EMC test results are often used to support safety claims to regulatory agencies such as FDA. Less well-known are the issues and concerns associated with wirelessly enabled medical devices, although this is changing thanks to FDA’s guidance document on wireless medical devices.
To date, no consensus standards adequately address the risks associated with wireless coexistence for medical devices and systems. Current methods of evaluating wireless coexistence use ad hoc test methods that vary widely among device manufacturers and test facilities. Moreover, current medical device EMC standards have no requirements or test procedures to assess the performance of systems containing RF receivers in the presence of in-band transmitters.
This article examines the limitations of present medical device EMC standards for coexistence evaluation, identifies factors to be examined when testing for coexistence, and discusses the status of plans to develop a wireless coexistence test method. It looks at:
•Limitations of medical device EMC standards
•Lack of a standard RF wireless coexistence test
•Considerations for wireless medical devices and wireless coexistence (including radio channel characteristics, polarization, co-channel and adjacent-channel interference, and distance)
•Medical wireless transmission parameters
•General considerations for coexistence testing
The article also includes an extensive set of references. To read it in full, click here.
About the authors
Nickolas LaSorte is pursuing a PhD in electrical engineering at the University of Oklahoma.
Hazem H. Refai is an associate professor in the university’s school of electrical and computer engineering and founding director of the WECAD Center.
Seth Seidman is a research electrical engineer at FDA.
Donald Witters is chairman of the CDRH EMC and Wireless Group.
Jeffrey L. Silberberg is senior electronics engineer for CDRH, Office of Science and Engineering Laboratories, Division of Electrical and Software Engineering.