A while back there was quite a discussion on the Biomed Listserv about cell phone usage policy in hospitals. Policies ranged from outright bans to anything goes. Most hospitals had a policy of excluding cell phone use in ICUs or within one meter of a medical device. Cell phones have been found to cause malfunctions in medical devices (ventilators are the classic example). All medical devices are tested by the vendor for susceptibility to interference, and should be able to produce a cell phone intereference statement upon request. You may also request a summary of their electro magnetic interference testing to learn what frequencies were tested (i.e., did they test common cell phone and 802.11 frequencies), and susceptibility (how close a source of RF radiation can come to a device before causing interference problems).

There are numerous hospital and visitor users who benefit from good in-building cell phone coverage including, patients and their families, medical staff, hospital management, and vendors. Good in-building coverage enables low power communications for voice in addition to those fancy Treos and Blackberrys. However, cell phone coverage will never be perfect; there will always be dead spots, and in-building coverage is frequently even more problematic.

Interference problems with cell phones are more about the amount of power of the cell phone radiates than the frequency used by the phone. The greater the distance between a handset and a cell tower, the greater the transmit power that must be used by the cell phone. The signal blocking properties of a building (especially a hospital) require even more power. Cell phones frequently radiate at or close to maximum power when in hospitals and are more likely to cause interference. Risk of interference is reduced significantly if you can get cellular devices to operate at their minimum transmit power.

There are three potential solutions to this problem:

  • Convince the carrier to put up a new cell tower close to your hospital. New cell towers cost around $250,000 and the carrier will expect you to pick up part of the capital cost and commit to a minimum number of subscribers. Oh, and it will take them a year or two to deploy the new tower.
  • Install a microcell in your hospital. This is considerably less expensive (I've heard numbers like $30,000 for one), but some dead spots will persist unless you use an antenna system like Innerwireless. Deployment of this solution is measured in months rather than years.
  • Use an adaptive repeater system like Spotwave.

Spotwave products serve as active (they are powered) repeaters that take the signal from an existing cell site and project it into your building. Each unit is made up of a donor unit and two indoor coverage units that can cover up to 50,000 square feet. Spotwave does a site survey and places their products around your building to ensure coverage. Cost comes to around 15 cents per square foot -- by far the least expensive approach to in-building coverage. Spotwave has units for each individual carrier (although I heard that they've got a multi carrier product in the works), and is approved by all the US carriers. Deployment for a mid sized hospital takes a couple weeks, and best of all you don't have to mess with the carrier!