Radio/Network Choices, Options, and Coexistence
9. What are the differences between WMTS and Wi-Fi?
WMTS and Wi-Fi telemetry monitors send patient data to a central station and allow patients to ambulate throughout the hospital, but that is where the similarities end.
WMTS is a set of frequencies comprising 14 MHz of bandwidth within 608–614 MHz, 1395–1400 MHz, and 1427–1432 MHz, and set aside by the FCC for medical telemetry. In various parts of the country, the 608–614 MHz band experiences adjacent TV channel interference. Within the 1427–1432 MHz band, medical telemetry operates on a secondary basis in half of the band (which half depends on location).21 Different manufacturers’ telemetry devices use different, often proprietary, communication protocols and cannot coexist in the same frequency band. The WMTS only exists in the United States.
Some telemetry equipment operating in the WMTS band has a dedicated transmitter-receiver pair for each patient that operates on a fixed frequency and uses one-directional communication. The design of these systems predates cybersecurity issues and mitigation strategies and requires interference-free spectrum to operate.
Newer telemetry equipment protocols that operate in the WMTS support two-way communication and provide features that allow the system to operate safely and effectively, even in the presence of interference. These include frequency hopping, multiple channels, encryption, and authentication. These protocols may include encryption and authentication to help reduce the probability of a successful cyberattack.
Wi-Fi is a standards-based communication protocol (IEEE 802.11) and operates worldwide in several shared-spectrum frequency bands, primarily the 2.4–2.5 GHz and 5.150–5.875 GHz bands. This is more bandwidth than all broadcast television, AM, FM, cellular, and Personal Communication Services (PCS) bandwidth combined. Wi-Fi has no legal protection from interference; rather, the 802.11 communication standards were designed to coexist and reliably transmit data in the presence of interference. Medical devices following the 802.11 standards use spread-spectrum technologies that are resistant to interference and are able to move to channels within a 555 MHz bandwidth (in the 5 GHz band) to minimize interference. Wi-Fi further includes retransmissions, traffic prioritization, and forward error correction to further minimize the effects of interference. Wi-Fi includes AES encryption and enterprise-class (802.1x) authentication, which protects patient data and the network. Because all Wi-Fi medical devices communicate to the hospital wired network via access points (APs), a single wireless network infrastructure can support them. However, this shared network may be subject to security attacks that can come from any Ethernet or Wi-Fi device in the enterprise, particularly when the network must support older medical devices that lack support for Advanced Encryption Standards (AES) and 802.1x. Please refer to the Security section for a guide to reducing the chances of a successful cyberattack.
10. What are MedRadio, MBAN, and MICS, and how are they related? Are there coexistence problems with Wi-Fi or WMTS?
MedRadio, MICS, and MBAN are FCC services used to communicate with body-worn or implanted medical devices.
MICS (Medical Implant Communications Service) is the oldest of the three and operates in the 402–405 MHz portion of the radio spectrum. These radio frequencies were chosen because RF signals here readily pass through human tissue with minimum attenuation, an important feature when communicating with an implanted device. MICS was originally created to allow communications between implanted devices such as pacemakers and their programmer/controllers.
As implanted and body-worn devices became more sophisticated and required more bandwidth than allowed under MICS, the Medical Device Radiocommunications Service (MedRadio) was created to address the problem. Spectrum for MedRadio was originally created by expanding the MICS band to allow operation in the 401–406 MHz portion of the radio spectrum, encapsulating the older MICS band. This was later expanded to include the 413–419 MHz, 426–432 MHz, 438–444 MHz, and 451–457 MHz bands on a secondary basis. These later, expanded frequencies are shared with other users on a noninterference basis, i.e., with amateur radio and government users who have priority in interference cases. Interference is expected to be minimal as MedRadio devices operate at very low power levels to prevent interference with other devices, while incorporating error-correcting protocols to overcome external interference.
The MBAN (Medical Body Area Network) service was created for body-worn devices to communicate with hub devices and operate in the 2360–2400 MHz band, just below the 2.4 GHz ISM band commonly used for Wi-Fi, Bluetooth, and industrial, scientific, and medical (ISM) technologies. The original concept was to modify Bluetooth hardware to operate in the MBAN frequencies, thereby leveraging the economies of scale of consumer Bluetooth technology to provide a low-cost wireless solution and operating in spectrum reserved for medical devices. As of 2019, MBAN remains largely unused, likely due to MDMs who are more attracted to Bluetooth and the ability to use smartphones as readily available hub devices.
For more detail, please see the FCC MedRadio22 page and FCC 11-176.23
11. Is there an issue with Bluetooth and Wi-Fi coexistence?
These systems both include technologies that work in the presence of other transmitters and generally coexist without issue. For more detail, see Question 75, “How does Bluetooth coexist with 802.11?” in the Bluetooth section.
12. Does it work to have two different manufacturers’ Wi-Fi networks operating in the same space? What are the key considerations?
With careful design and monitoring, two overlapping systems can be installed using the 2.4 GHz band, which has only three non-overlapping channels, but such shared spectrum requires serious constraints on the use of systems installed this way.
Overlapping systems are much easier to support in the 5.8 GHz 802.11a band, where there are 24 non-overlapping channels.
An HDO might have two wireless infrastructures while changing to a new wireless vendor. Other hospitals might prefer to keep clinical data completely separate from other IT data.
Key considerations when dealing with two or more disparate Wi-Fi networks in the same airspace include:
- Creating a channel plan to minimize co-channel interference.
- Managing AP power settings for optimum coverage.
- Considering whether seamless roaming is a requirement.
- Considering whether channel bonding, which uses multiple 802.11 channels to support a higher bandwidth, will be used when creating the channel plan.