What perhaps is really needed to enable the medical and wireless connectivity model?
While much has been written about this topic, the following will be based upon the author’s hands on field and design experience for the past twenty years in the areas of VHF/UHF/WMTS, WLAN (voice over IP), RTLS, Cellular/PCS/Public Safety. A lot of this reference material also centers upon all the recent meetings the medical “wireless” community has had with IEEE and the FDA. The "writer in a typical fashion as described is taking spectrum measurements" in the field.
These topics will be subdivided into specific areas for review.
WLAN (Wireless LANS)
(802.11a/b/g/n). While wireless LANS are widely deployed for data and voice, they are also in a rapid fashion being deployed for the use model of medical devices. All the recent meetings in the past three months have pointed out to the concerns of not only the "air to air" interface, but also to ensure the correct SLA (Service Level Agreement). This should also extend out to both data, voice, and the specific medical device and/or application intended. Early on based upon the author’s experience many of the data wireless networks were not originally engineered and/or designed to handle voice capacity. Witness why some of the push back by IT folks to not have “wireless medical embedded devices”, on their IT network. However with experience at Draeger Medical www.draeger.comand the concept design of OneNet, a shared VLAN based infrastructure architected over five years ago; this simply is not the case going forward. Wireless medical device networks can be deployed in a safe and reliable fashion if design, deployment, and management methdologies are adhered to.
As the healthcare wireless ecosystem now encompasses data, voice, and medical devices, there needs to be a way to ensure that the RF spectrum is properly managed. While different WLAN companies take different approaches, at the end of the day it is about taking the guesswork out of RF management by using automatic, infrastructure based controls to maximize client performance. When discussing RF management, real world Wi-Fi implementations suffer from "three primary shortcomings." Wi-Fi is a shared medium and has a fixed amount of channel bandwidth, and clients must compete for bandwidth simultaneously while avoiding collisions. Multiple client technologies that require interoperability with older clients often incorporate protective mechanisms that often lower overall operating speeds. Client based decision making, i.e. which access point that they should roam to, and what speed that they should send and receive data is often the predictive use model. The use of automated radio management may also significantly for the first time create the true “medical grade wireless network”. The solution to these stated shortcomings is infrastructure based control, through which the healthcare data/voice and medical application and network are purposely adjusted to optimize performance, mitigate interference, and better utilize available resources. The goal of this automated resource management and infrastructure based control design is to optimize spectrum usage, maximize coverage, minimize co-channel interference, ensure compatibility and interoperability, and maximize performance and fair access. This could additionally allow mixed 802.11a, b, g and n client types to interoperate at the highest performance levels, provide RF airtime to be allocated fairly, and ensure that co-channel interference is mitigated or avoided. This shoud ensure low-latency roaming, provide consistently high performance, and maximum client compatibility in a multi-channel environment.
While wireless LANS have been widely deployed based upon differing criteria, it is important to understand how to scale and ensure that all applications actually enterprise scale and work correctly in a harmonious fashion.
“ Definition of a Life Critical Network"
Verification and validation are the final steps in a mission or life critical network design process that begins with requirements generation. It is this process that differentiates a true life critical network from an enterprise class network that is marketed as a medical network. A life critical network is an enterprise class network that has been verified to show that is operates as it was designed and validated for it’s intended uses, including the transmission of life-critical data.”
Dr. Steven D. Baker and David H. Hoglund – IEEE Engineering in Medicine and Biology Magazine March- April 2008.
The medical device company s should take the responsibility of testing and validating with the active participation of the WLAN infrastructure companies. This should include a SLA (Service Level Agreement) testing with
www.veriwave.com
. With WLAN in the enterprise the expectation of the end customer is for the same level of quality that the wired LAN industry has delivered. Because wireless networks provide for a wide variety of clients with many levels of performance requirements, wireless network equipment must be qualified with regards to all traffic behaviors, power management techniques, and security methods, and in the presence of all types of clients simultaneously.
Having a test plan that provides enterprise coverage will ensure compliance and performance of WLAN systems for medical devices. Essential WLAN testing requirements can be categorized into four major areas – functional verification, performance measurement and network capacity assessment, system testing, and stress testing.
The medical device test plan in concert with the WLAN infrastructure vendor should be focused on the aforementioned categories. The test plan should use a testing platform that tests the components of the WLAN, such as APs, Controllers, and LAN switches. i.e. (SUT – Subject under Testing). These tests should be conducted during hardware and software qualification, software/firmware release testing, vendor selection, or as a part of pre-deployment testing.
This real world deployment test should accurately replicate the complex interaction of clients, servers, and traffic profiles in wireless LANS. By creating usage profiles and traffic mixtures in various network environments, these tests measure and report key application layer metrics that could affect the end-user Quality of Experience with the medical device. These tests include some of the following categories.
iLoad, oLoad, and aLoad per Traffic Type, Pass/Fail percentage of Clients that met SLA, iLoad, oLoad, and aLoad per Client Type, MoS Score for VoIP flows, FTP Goodput, HTTP Goodput, TCP Goodput, Forwarding Rate for UDP Flows, Latency and Jitter for UDP flows, Percentage Packet Loss for UDP Flows,
The output of this validation and verification is a design and deployment guide that describes how to configure the WLAN devices to meet the metrics as described in the aforementioned. In concert with this design and deployment guide should be a release management process that allow for the re-validation of the combined medical device WLAN enterprise solution that that takes into account updates and software/hardware releases from the WLAN and medical device companies.
The overall industry should define what are the requirements, not how these requirements are met. Different WLAN companies have different technologies to address certain requirements. For example certain WLAN companies can define a SLA (Service Level Agreement), over the air, without the need for an application appliance for bandwidth shaping. Also, some companies do broadcast/multi-cast suppression without the need of VLANs, and have built in firewalls for authorization without the need to dual purpose their existing LAN firewalls.
Finally any WLAN vendor that insists on mandating their proprietary protocols to be enabled on medical devices to ensure functionality with their WLAN is a bad business idea. First it is not standards based, not peer reviewed, and it puts a lot of pressure on the medical device community at large. This would stifle innovation and add costs, just when the healthcare system is under pressure to contain costs. There are WLAN companies out in the marketplace that do not demand proprietary extensions and the author has seen life critical patient monitoring devices work securely and in a reliable fashion on these networks.
Healthcare has one of the most demanding models for wireless mobility and this demands enterprise management of a mix of generations of WLAN infrastructures and often different vendors. There are solutions to date than can provide comprehensive management that can significantly reduce the cost of ownership of the enterprise WLAN, while automating the process of reporting for HIPPA JACHO compliance. Real time monitoring for every user, AP, controller and other wireless devices on the network can reduce wireless problem resolution by 75% by having access to all this information.
WMTS (Wireless Medical Telemetry Services)
The author has trouble-shot early days VHF (prior), WMTS but using a spectrum analyzer and disconnecting leg by leg the CATV diversity antenna design. Sometimes this took a day, sometimes weeks on larger systems. It is felt that medical devices and WMTS community could benefit from commercial grade products that would provide a proactive approach to address the impact of interference on wireless networks. We are in discussions with
www.iscointl.com
to look at the propensity of using their FastScan 2 digital signal processing technology. This discrete Proteus product and/or an embedded solution could provide many advantages to the makers of WMTS type of systems, as well all other wireless sub-systems within the healthcare enterprise. This would include the ability to actually indentify and remove interference and other unwanted signals versus the real signal. It could also recognize the interference and other unwanted signals. For auditing purposes it could provide the specific frequency, amplitude, duration and time of day of information that this interference occurred, as well as a recording of the data, creation of reports, and the generation of real-time alarms.
DAS (Distributed Antenna Systems) We have also tested the performance of various wireless devices in an actual Farady cage to isolate outside EMI and characterize the correct design requirement. While DAS systems are being deployed in a fairly rapid fashion, healthcare does have some unique requirements that will accelerate this adoption. It has been discussed that healthcare is a fairly mobile marketplace and that is why the need for in-building wireless, both PCS, Cellular, and Public Safety. This requirement is also is centered around construction. Most new hospitals are built along the construction guidelines of poured concrete metal pan floor construction. This in essence creates a so called Farady cage on each floor. All the more need for a DAS deployment. Finally, the need for LEED http://www.usgbc.org building requirements and the use of reflective glass has greatly impeded the outdoor macro signal from penetrating into all the areas of the building environment. Even though the author stood last week in the middle of a wheat field in North Texas measuring signal levels with an spectrum analyzer, this does not guarantee absolute -85dBm required or in the case of 4G for AWS with a design goal of -75dBm
While it has been have written a lot about this subject, what it is believed will enhance the performance of these systems tat will be technologies such as from, ISCO international,
http://www.iscointl.com
There is also a revolution moving away from narrow band BDA(s), bi-directional amplifiers. This new digital technology in BDA(s) uses (DSP), Digital Signal Processing technology to provide precise filtering for signals in the cellular and PCS Frequency Bands. What advantages does this provide to the in-building space? First is Frequency Agility. This frequency agility allows the operator to change filter configurations to support virtually any pass-band combination within a specific set of wireless frequencies. This solves the issue of rebanding or augmenting of existing channels requiring forklift upgrades. Second is Ultimate Rejection. SAW based repeaters provide over all -50 dB of overall rejection. These new digital repeaters provide up to 85 dB, reducing or eliminating potential interference and unwanted coverage. Third is Unlimited Number of Passbands. There is no practical limit to the number of passbands that can be configured for the intended frequency with this new generation of digital repeaters. Fourth, they can work with any wireless protocol. This include iDEN, CDMA, W-CDMA, GSM, GPRS, EDGE, TDMA, UMTS, HSDPA, Analog, etc. Fifth is Filter Selectivity. Exceptional adjacent channel rejection can be achieved with these new digital repeaters. Greater than 40dB signal rejection can be realized in as little as 200 kHz from the pass band edge. Finally, adjacent channel interference mitigation. This permits fine tuning of band edges to eliminate or mitigate adjacent band interferers. Integra Systems, Inc. has recently helped to overview an article for the use model in-building public safety coverage
www.lordcotech.com
. They are an outstanding integrator that provided mission critical public safety applications in the Mid Atlantic corridor. Another great site to go to keep up to date on DAS is
www.thedasforum.org
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