Wireless Networks: Proper Planning for Easier Maintenance
January 23, 2009
Appeared in Healthcare Design Magazine
One of the fastest growth areas in technology today is wireless networking. Facility-wide wireless networks touch almost every industry. In the hospital environment, wireless devices can transport signals from computers, refrigeration monitoring devices, control modules, pagers, medical telemetry, supply order entry systems, physician bedside devices, infant protection and patient wandering systems, bedside equipment including pumps for infusion, feeding, and various ventilators—the list goes on and on. Additionally, these systems can potentially be running on a multitude of wireless networks, managed by a variety of different departments, with little to no communications between them in terms of frequency management and channel interference.
Adding to or replacing a wireless network presents many challenges for building owners. In the process of remaining current and efficiently managing any technology, eventually, a refresh is in order. Asbestos abetment, hospital infection control policies, network downtime scheduling, program space requirements, physical accessibility, and cost are all serious factors to consider. Let's look at two primary methods of transporting wireless signals within a facility and explore methods of both new installations and technology refresh on an existing infrastructure.
Method one: Discrete wireless network
In a discrete network, the antennas (access points) are separate and distinct. Generally speaking, the “antenna” is a two-part unit—the body (intelligence), where a CAT twisted pair data-grade cable connects from the main network source; and the antenna, generally a coaxial cable and antenna unit (pad, pole, etc.). Typically, these access points (APs) are mounted either above the acoustic ceiling tile with a dual antenna whip protruding through holes in the tile (not recommended), or mounted on the wall with the coaxial and antenna mounted below the ceiling, flush against the wall. An alternative method is to mount the devices within a sealed box attached to the deck and flush with the ceiling tiles. This provides easy access, as well as mitigation in violating ICRA policies. To make future troubleshooting easier, antennas should be labeled so they can be seen without lifting ceiling tiles, and given a logical label (like AP-3-North), not something that requires a translational table (like AP124DG8R1). In addition, a visible antenna should not be labeled with its IP address, to avoid giving would-be hackers a head start.
When adding to this type of wireless system, or removing APs and replacing them with a newer model (sometimes as simple as replacing the entire box, other times as complex as opening each box and replacing the control card or radio), using an in-ceiling box that takes the place of the ceiling tile instead of mounting above the ceiling space will eliminate the need to open the ceiling in the future. Also, it's a good idea to place two cables to each AP even though one is only required. As the speed of wireless networks increases, the footprint that each AP can manage decreases, so having an additional cable already placed in the area will ultimately save costs. Generally speaking, the cable that runs yesterday's AP is good enough to run today's AP, so pulling new cable may not be required for a simple refresh of the technology—however, if pulling new cable is required, running two rather than one is highly recommended.
One advantage of a discrete system is the ability to allow each department and/or service provider to control its own wireless network. Another advantage is that location-based services can be arranged to be very granular (room level if desired). One drawback is that if each department controls its own wireless network, it makes for an uncoordinated group of people propagating an undetermined number of frequencies within the building. Another drawback is that this type of system is not a broadband solution—multiple independent frequencies cannot be placed on one holistic or independent discrete wireless environment. Imagine carpooling to work with three others and needing four different antennas on top of the car based on the listening requirements of each person. Now, add another carpooler—and another antenna. Lose a rider; abandon the antenna on the roof?
Method two: Distributed antenna system (DAS)
A DAS uses both hard-line and coaxial cable, distributed throughout the facility. From a centrally placed head-end, this system provides for a variety of frequencies via one antenna. Some DAS systems utilize a “leaky coax” cable that propagates the signal to all areas where the cable is run while others use the coax to attach an end-point antenna. To paint the picture, imagine this system as a tree: the trunk is used to carry water up to the branches and out to the leaves at the end. Similarly, the trunk cable (riser) is used to carry the signals (frequencies) up the building core and out to the floors. Although it is more complex than that, suffice it to say that new construction is far simpler to install than in existing facilities. The beauty of this type of system is in the ability to snap another service (cell, 802.11 wireless, radio and paging systems, atomic clock signals, building controls, etc.) onto the antenna at the head-end without the requirement to lift the ceiling tiles. Generally speaking, these systems have the capability to run frequencies from 450 Mhz to 6 Ghz, skipping some frequencies in between. Now imagine that same carpool within this type of solution: each person can have a different service running in the car on the same antenna, be it 802.11 wireless, cell phone, handheld radio, or other wireless service.
These systems come in multiple flavors for both broadband and multichannel solutions. A broadband system allows for high-capacity, two-way transport for a wide variety of frequencies. A multichannel system has a set number of frequencies that can be employed. Multichannel systems also allow for high-capacity, two-way transport and have a lower initial installation cost; however, there is a channel limit based on the physical capabilities of the head-end hardware. The number of channels selected should never exceed the capability and capacity of the system.
It is this capability of having one antenna for most services that makes this an attractive proposition, but like any technology, drawbacks exist. These include difficulty with RFID tracking since the cable may cover as much as 10,000 square feet of floor (possibly requiring a separate wireless network for RFID/RTLS tracking), the initial expense, installation issues in existing construction, and, as with all wireless systems, finding a single source of frequency management and internal point of control.
Another important consideration is the placement of the head-end. This system will require multiple cabinets as additional services are added, so it's important not to place it in an area that will become landlocked. For example, cellular phone service is not a simple slot card in the head-end that allows signaling from all service providers—it could be multiple units per cellular phone provider (at a cost of roughly $30,000 to $100,000 per provider). Likewise, interfacing a two-way radio system will require another cabinet of electronics; add the 802.11 family of wireless and you can see that this type of design will require space planning.
In summary, both methods work well, and each has its inherent challenges. If the goal is to provide 802.11 WiFi services including real-time location services, a discrete network of APs will do the job. If a building has a few small cellular service dead spots, simple spot coverage may be a good a solution. Spot coverage can be achieved by running a single coaxial cable from a rooftop antenna to a small repeater placed in the area of noncoverage. While not a holistic approach, it will resolve dead spots. If you have a small number of frequencies that need to be transported within the facility or campus, a multichannel DAS is suitable. Should you require several channels and want to future-proof your organization, a broadband DAS is the way to go.
With proper labeling, planning, placement of additional cables marked for future use, and a well-documented wireless survey, maintenance managers will be able to satisfy even the most finicky wireless technology and provide coverage for all the needs of your organization while mitigating disruptions commonly encountered from moves, adds, and changes.