Healthcare is the worst multi-path environment for RF. This is just not me saying this, it is because I had to design antenna systems for VHF telemetry and make stuff actually work!  The problem is all the fluids, metal, and moving objects, but now comes the harder issue.  The majority of wireless LANS were designed for primarily data and voice.  And you have to look at how they are being used for healthcare for the EMR (laptop on wheels, note I am not using the outdated term!), and voice over IP.  However, the laptop is pretty much outside in the hallway, “occasionally” taken into the patient room, and the clinician is using the Vocera,  ASCOM, or Cisco Systems “wireless” voice over IP phone…in the hallway.  As more and more medical devices, pulse oximeters, infusion pumps, patient monitoring are incorporating WiFi, (802.11a/b/g), they will tend to be with the patient. This by virtue of leads, IV tubing that are connected to the patient.  At times they will be walking the hallway, but the majority of times, they will be in bed in the patient room.  Now here comes the challenge.  The AP(s) are the hallway and were site surveyed for data and voice and maybe the medical device application.  Did the site survey taken into account how the signal has to penetrate the firewall (between hallway and patient room), and the glass, steel, and ceramic tile of the bathroom that is often between the hallway and the patient bed where the WiFi enabled medical device is?  Did the site survey take into account these interferers?  

Dealing properly with interference requires something be done to the RF energy coming out of the AP. You need to have complete control over it. The paths that Wi-Fi transmissions take need to be clean. And there needs to be enough paths available to you so if the one you picked is not performing, you can pick another one….REALLY fast. (Hence dealing potential drop-out) And all this needs to happen automatically.  So how does the system know it's picking the right path to the station? Answer: the client can tell you. Clients talk back, telling APs the throughput, packet error rate, RSSI and other things.

So here are some of the issues:

• 2.4GHz only has 3 non overlapping channels so there's only so much changing that can be done.
• Running 40MHz wide channels in the 5GHz band gives you only 11 non-overlapping channels, same problem.
• Changing channels changes everything (over and over)
• RF interference avoidance from the perspective of the APs is just that, the perspective of the AP. Maybe the client sees something different and usually always does. Now what are you going to do?
• Cisco's radio resource management still decides what channel to use with CleanAir.  Many Cisco customers and partners advocate turning RRM off, just Google "RRM problems" Ultimately to fix the RF interference problem it comes down to using a "purpose-built" (Cute meaningless marketing phrase) product – specifically designed with forethought to deal with, and to automatically mitigate, interference – all without network managers having to do anything!  Again, I go back to hospital construction.  Not only are their firewalls and glass and metal between the patient rooms and the hallways, but many ICU/CCU areas also have isolation rooms, or a lead lined room for fluoroscopy (X-Rays).  Did the site survey take this into effect?  Finally what about how the signal get’s through old construction using chicken wire lath, or new construction with poured concrete metal pans between floors.  All this potentially now dictates the use of “smart antennas”.

That's the real beauty of smart antennas and dynamic beamforming.

Smarter approaches to RF optimization in the form of dynamic beamforming solve some of the CORE Wi-Fi challenges facing the industry:

• Virtually eliminating co-channel interference
• Enabling more predicable performance by "steering" signals over the highest performing paths.
• Doubling the effective footprint (coverage area) of an AP (read: fewer APs give better performance).  (NOTE: Adding more AP(s), think of for location tracking (RFLS), only “increases” co-channel interference.  So think of a dense AP environment, with challenging physical construction and a difficult application environment.

The goal of beam forming is to improve the SNR, (signal to noise ratio) provide higher data rates, improve reliable connectivity, and decrease extraneous signals. It should ideally use dynamic antenna array with switching logic.

So how does this dynamic beamforming work?  Smart antennas steer Wi-Fi signals over the best paths to the client, (in this case the medical device), while the client moves the signal path is dynamic and it switchs thus nullifying the sources of interference. The combination of antenna diversity, explicit signal path control and multipath, all to steer signals around all this stuff in the hospital environment.

And what are the benefits?  Forms and steers Wi-Fi clients over the best performing signal path on a per packet basis, while using multipath to it’s advantage.  The client MAC ACKS are used to ensure delivery at the best data rate with the lowest packet loss. This all translates into automatic adaptation to real time change in the healthcare environment and provide increased signal coverage with 2 to 4 times less APs, while finally simplifying RF planned. Lower CAPEX, OPEX, and TCO.  Oh, for those that think WLAN should be on a DAS, (I never was an advocate, even though it sounded like cute marketing KoolAid), how can you take advantage of intelligent beamforming (antenna array), on a DAS whereby diversity was never used for cellular and/PCS.  OK, SISO eventually LTE.

For those that want to delve deeper into this a “black paper” is attached.

Download Wireless_network_perf_bp