Pair Necessities for Wireless Medical Devices
With a number of techniques for linking wireless medical devices, designers have options for ensuring coexistence between multiple instances of the same device.
From smart thermostats to wearables, connected devices are all around us and the medical industry is no exception. However, these technologies present original equipment manufacturers (OEMs) with a variety of challenges when the wireless product is a medical device.
With the increasing amount of wireless devices in-and-around medical facilities, it is critically important that wireless medical devices be able to coexist in this environment. Electromagnetic (EM) emissions from wireless devices can interfere with proper operation. If interference occurs, data transmitted by medical devices could be delayed or lost, potentially interfering with timely communications of critical patient information or device control commands.
The U.S. Food & Drug Administration (FDA) defines wireless coexistence as the ability of one wireless system to perform a task in a shared environment where other systems in that environment have an ability to perform their tasks and might or might not be using the same set of rules. Although the FDA does not have specific requirements for coexistence testing, the organization has issued guidance for medical device manufacturers to ensure the safety of devices they market titled, “Radio Frequency Wireless Technology in Medical Devices,” issued Aug. 13, 2013.
To effectively manage conflicts among wireless signals and minimize disruptions in the shared wireless environment, it is important to take into account other wireless technologies and devices that might be expected to be in the vicinity of the wireless medical device and test for coexistence.
One of the specific scenarios mentioned in the FDA’s guidance document is when multiple units of the subject wireless medical devices will be used in the same vicinity. Consideration should be given to how the association and security between devices is established and maintained to prevent crosstalk. One way to address this issue is to utilize a linking or pairing procedure, whereby one transmitter (or transceiver) is linked or paired to one or more receivers (or transceivers).
Linking Wireless Devices
Unlike a wired device, a wireless receiver has the potential to communicate with any like transmitter within range. With the possibility of multiple instances of both transmitters and receivers within range of each other, it is important to pair each transmitter-receiver pair to ensure that the data being received is from the proper transmitter. Medical device designers have a variety of pairing methods to choose from, each having its own benefits and tradeoffs. Here are some of the possible pairing methods:
This method utilizes the same wireless communications channel to pair devices. Typically, the two devices are put into pairing mode, and ID information is transferred/exchanged over the wireless channel. Because it would be possible for multiple units within communications range to be put into pairing mode at the same time, additional confirmation steps should be required to prevent an accidental pairing. This confirmation could vary in complexity, depending on the types of operator inputs and display outputs available on the two devices. It could be as simple as a push button and LED to a more complex solution like entering a PIN code that was displayed on the other device. The more complex the operator interface, the more robust the pairing process can be.
Dedicated Wireless Pairing Channel
Another option is to have a separate wireless channel that is solely dedicated to the pairing function. Some common examples would include Near Field Communications (NFC), infrared (IR) communications or radio-frequency identification (RFID). With this method, once in pairing mode, the two devices to be paired must be brought together in close proximity. Once this communications channel has been established, ID information may be transferred/exchanged.
Having a dedicated pairing channel may be a preferred option for devices with no or limited operator interfaces. Because of the close proximity required during the pairing process, the chances of accidental pairings are greatly reduced. The drawback of this close proximity requirement is that it would not be ideal for large or fixed devices.
Using a pairing cable to physically connect the two devices to be paired eliminates the possibility of accidental pairing. Once the two devices to be paired are connected by the cable, ID information can then be transferred/exchanged. As was the case with a dedicated wireless channel like NFC or IR, using a pairing cable may not be ideal for large devices or those that have a fixed/permanent installation.
Similar to how the pairing cable eliminates the possibility of accidental pairings, using a portable memory device also does this, as the portable memory device is deliberately transferred from the receiver to the transmitter and back to the receiver (for example). The ID information for the devices is written to the non-volatile portable memory device and read by the device to be paired. This method has the benefit of eliminating accidental pairings, but can be used with large or fixed devices, as the small memory device is easy to walk across the room. One additional benefit of using portable memory is that it makes it easy to pair multiple devices. For example, it might be beneficial to be able to send data from a medical instrument to be displayed on multiple monitors for medical personnel to see.
Coexistence is Key
Incorporating wireless technology can enable patients to move freely without being tethered to monitoring equipment. It can also give medical professionals easier access to patient data and eliminate wires in the operating room. The technology also comes with its own set of challenges. As the number of wireless medical devices implemented by hospitals continues to grow, it is more important than ever to ensure that these devices are able to coexist with each other. There are several methods available for linking wireless medical devices. By selecting the appropriate method to pair the transmitter and receiver, designers can ensure coexistence between multiple instances of the same device.
For more information about wireless coexistence and linking wireless medical devices, download a complementary white paper at http://datakey.com/pairing.
Paul Plitzuweit is the senior product manager for the Datakey line of rugged portable memory products at ATEK Access Technologies. He holds a bachelor’s degree in Electrical Engineering from the University of Minnesota. Paul can be reached at email@example.com.