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Comparing Wi-Fi Options for Medical Devices

Fri, 03/23/2012 - 11:15am
Chris Bolinger, Director of Engineering and Sue White, Documentation and Certification Manager, Laird Technologies

Comparing Wi-Fi Options for Medical Devices

Connecting medical devices to a hospital network improves workflow on both the clinical path and the financial path. Once medical devices are on the network, clinicians can monitor patients from any point in the hospital, and technicians can manage the devices from a central point of control. Because services are recorded electronically at the point of care, a hospital can bill for those services quickly and accurately.

For portable and mobile devices, the optimal technology for network connectivity is IEEE 802.11, better known as Wi-Fi. To add Wi-Fi connectivity to a device, you add a Wi-Fi radio to the device. There are two typical approaches to integrating a Wi-Fi radio into a device: using a simple radio module and using an intelligent radio module.

This article provides an overview of the two types of modules, explains the pros and cons of each, and provides guidance on which type is better for a given medical device.

Two Wi-Fi Radio Options

Standard Module

A standard radio module is made up of integrated circuits enclosed in a single module (or package). The module is soldered directly onto the medical device’s motherboard or connected to that motherboard via a board-to-board connector. Because of its small size, it presents a smaller footprint and is an effective option for space-constrained environments.

The software that drives a standard module runs on the operating system of the device that houses the module. Most general-purpose computing devices, such as mobile phones and laptops, use a standard Wi-Fi module.

Standard_radio
Figure 1: Standard radio module on motherboard.

Intelligent Module

An intelligent Wi-Fi radio module, sometimes called a subsystem module, combines a standard radio module with a processor and memory that runs a specialized or general-purpose operating system. The primary function of that operating system is to run the software that drives the Wi-Fi module, but the operating system can run other applications if the subsystem module has sufficient resources to support those applications. 

standard_module_highlighted
Firgure 2: Subsystem module (standard module highlighted).

Which Module Is Better for a Medical Device?

Some medical devices use standard Wi-Fi modules; others use intelligent Wi-Fi radio modules. To determine the best module type for a medical device, you should consider the following factors:

  • Medical device computing resources.
  • Costs.
  • How Wi-Fi software maintenance and upgrades will be handled.
  • Device design priorities.

Medical Device Resources

As noted earlier, a Wi-Fi radio module is driven by software. Wi-Fi software components include a device driver, a security application called a supplicant that handles network authentication and encryption key derivation, and utilities for configuring and managing the radio. In addition, applications that leverage Wi-Fi connectivity require software resources such as a TCP/IP stack.

A general-purpose computing device has the resources required to support Wi-Fi. Wi-Fi software and related resources such as TCP/IP run on the device’s operating system, which operates on a robust processor with plenty of memory.

A medical device may lack the resources required for Wi-Fi. A typical medical device is designed for a single purpose, not to run general-purpose applications. As a result, while a medical device’s processor, memory and operating system are perfect for its primary application, they may be insufficient for other applications, including native Wi-Fi support.

An intelligent Wi-Fi radio module may be the best choice for a medical device with limited computing resources. This type of Wi-Fi module runs on its own operating system, and the Wi-Fi software operates on that operating system instead of that of the medical device. Rather than using a medical device’s computing resources for Wi-Fi, an intelligent radio module brings a complete Wi-Fi subsystem to the medical device.

Costs

The purchase price of an intelligent Wi-Fi radio module is typically twice as high as that of a standard radio module. But the cost of integrating a standard radio module into a medical device is much higher than the cost of integrating an intelligent module.

An intelligent radio module is like a small computer dedicated to Wi-Fi connectivity. Integrating this Wi-Fi computer to a medical device is a straightforward process, where the primary task is enabling a basic connection (such as a serial connection) through a board-to-board connector. No special software has to be installed or tested on the medical device.

With a standard radio module, the integration process is more complex. With the lowest-cost option, which is a system-in-package (SiP) module, the module must be soldered directly to the host device’s motherboard. Some standard modules support a board-to-board connector, but these modules are more expensive than SiP modules. In addition to potentially difficult hardware integration, a standard module requires integration of Wi-Fi software on the host device. To ensure that the module provides secure and reliable connectivity, rigorous testing of this software on the device is a must.

A company with strong internal Wi-Fi expertise can achieve successful integration of a standard radio module, but the effort may take several months. Companies that use an outside firm for integration of a standard module may find that the project takes six months or longer, and some projects never reach a successful conclusion.

Integrating an intelligent Wi-Fi radio module is the safer approach and also results in a faster time to market. For a high-volume device, however, the higher purchase price of the intelligent module may make it the more expensive option.

Wi-Fi Module Support

Even when a Wi-Fi module has undergone rigorous testing in a lab, Wi-Fi software issues can arise at customer sites. How the module is supported is an important consideration in module selection.

With a standard radio module, the software supplied by the module provider typically is designed for an operating system other than the one that runs on the medical device on which the module is used. Once the medical device maker alters the software for the device’s operating system, the medical device maker assumes the customer support responsibility for the module’s software and, often, the hardware as well. This is true regardless of how the module is integrated into the device – soldered to the motherboard or attached via a board-to-board connector.

Supporting a Wi-Fi module in devices deployed at customer sites can be difficult for a medical device maker because Wi-Fi support requires specialized expertise. Often, device makers rely on contractors to handle Wi-Fi integration projects (including porting of Wi-Fi software to a medical device’s operating system). When a support issue arises at a customer site, the contractors who understand the module and its software best may be unavailable to assist with troubleshooting and resolving the issue.

With an intelligent radio module, the Wi-Fi software runs on the module, not on the medical device. The module supplier typically provides support for the module hardware and software, even after the module is integrated in a medical device and deployed at a customer site.

Because a medical device may be used for 10 years or longer, ongoing support of Wi-Fi modules in deployed devices can represent a significant area of “hidden” costs. The costs and risks of support must be considered before selecting a Wi-Fi module.

Design Priorities

A few more design elements should be considered when deciding which Wi-Fi module option works best for a medical device:

  • Because a standard radio module is smaller in size, a smaller footprint can be realized by connecting the module directly to the device’s motherboard.
  • A standard module consumes less power than an intelligent radio module.
  • With an intelligent radio module, FCC grants for the module can be leveraged for device-level certifications. In other words, once the intelligent module has been fully tested and certified for FCC compliance, compliance extends to the device in which it is integrated because the module and its software remain unchanged after integration. Even when a standard module has its own certifications, additional host device testing is required after the module is integrated.

Summary: Contrasting the Wi-Fi Radio Options

The following table contrasts the differences between integrating a standard Wi-Fi radio module and an intelligent Wi-Fi radio module:

 

Standard Wi-Fi Radio Module

Intelligent Wi-Fi Module

Resources Required

Runs Wi-Fi software on the host device’s operating system.

Runs Wi-Fi software on its own operating system.

Costs

Has a lower purchase price but higher integration costs, including integration and testing of Wi-Fi software on host device.

Has a higher purchase price but lower integration costs.

Support

The medical device maker assumes responsibility for ongoing support and maintenance of Wi-Fi software.

The module provider provides ongoing support and maintenance of Wi-Fi software.

Other Design Considerations

Has a smaller footprint and consumes less power.

FCC grants can be easily leveraged; the fully tested subsystem remains the same on every host device.

For more information visit www.lairdtech.com.

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