Identifying and addressing DAS requirements in today’s hospital

By Matthew Schwartz / Special to Healthcare Facilities Today
August 14, 2019

In 2008, the world was transformed when Apple and Google both released their first takes on the smart phone. The iPhone and the G1 immediately put consumers in constant touch with the internet. With access to streaming data, users began to consume music and data at increasing rates.  Fast-forward to today, we live and work alongside an enormous system of devices that rely on cellular connections. Point-of-sale systems deployed by food vendors, inventory tracking devices used in pharmacies, and shipping/receiving verification systems are all dependent on cellular communications. 

Simultaneously, as the requirement for cellular connectivity is increasing, new construction practices are making it more difficult for signal to penetrate into buildings.  Increased insulation found in walls and low-E glass are opaque to cellular signals.  The cellular industry has answered this challenge with Distributed Antenna Systems, or DAS.  DAS allows all users of the building, whether it be communicating infrastructure or a personal or business phone, to connect to their carrier of choice at full signal strength.

Defining owner’s project requirements

Any organization in the market for a DAS should purchase the system needed to fulfill the requirements of the business’s objectives.  A DAS can be designed to support differing carriers, varying occupancy loads, any size of building, and different bandwidth requirements.

A fully featured DAS that supports all carriers on all frequencies is likely beyond the requirements for most organizations.  Arguably, the most important requirement is which carriers are required to safely operate equipment in the facility and allow staff to effectively communicate.  A survey of cellular connected devices in the facility should be performed to catalog the communications vendor for all equipment.  Likewise, an investigation of corporate cellular plans for mobile devices is a must do to understand the usage of the facility and staff.

A DAS, properly designed and implemented, should be minimally constructed to handle peak load.  This is defined as the maximum quantity of end users simultaneously connected to the DAS.  For healthcare facilities, the staff and equipment are just the first part of the occupant load.  The second consideration is the usage of the facility clientele, patients and visitors.  A brief review of waiting rooms anecdotally indicates that cell phone usage is incredibly prevalent.  As an indicator of customer satisfaction, healthcare administrators will often measure the occupancy load of waiting, this metric should be considered in the peak usage measurement.

Voice calls, although absolutely critical for facility operations, represent only a small portion of the traffic on a DAS.  Data traffic dominates the bandwidth requirements of a DAS, which drives an investigation of the usage patterns of equipment, staff, and clientele.  Imaging systems connected to cloud services via cellular connections are a starting point for investigation into bandwidth limits.  Streaming data, whether audio or video, is the other major contributor.  Streaming users are generally classified as patients and visitors consuming media on their cellular devices.

Assessment, discovery and measurement

DAS deployment projects should begin with an assessment of the carrier signal, both in and out of the facility.  Competent recommendations and proposals must be based on measurable and meaningful data.  DAS contractors, and their RF engineering teams, are unable to produce a valid recommendation without first measuring the existing signal at the facility.  A facility manager in charge of purchasing and deploying a DAS should expect a reputable DAS contractor to offer a paid-for service in which the carrier or “macro” signal is measured, analyzed, and reported on.  When the engagement is purchased by the organization, they own the data that is produced.  The baseline survey data allows the organization to engage design/build DAS contractors on an even playing field.

Facility managers should provide recommendations to the DAS surveyor on areas of special importance to the facility.  Waiting rooms and employee break rooms serve as obvious illustrations areas of primary concern.  However, it is important to review the inconspicuous spaces which may lack signal strength but still require cellular connectivity.  Examples of areas to explore include imaging centers, auxiliary buildings, and parking structures.  Imaging centers inside healthcare facilities are commonly shielded from RF signal to prevent staff and patient exposure to dangerous levels of radiation.  Auxiliary buildings can house equipment which is critical to the operation of the facility.  These structures are often connected to the main facility through tunnels, walkways, and skyways; all of which should support DAS coverage to maintain voice services for staff moving between buildings.  Parking structures are notoriously bad for cellular coverage due to the construction methods and materials employed.  It is common for staff traveling to and from the facility to drop calls when entering these structures; enhancing interior coverage allows for continuity of business during transit.

During a survey of the facility, an existing legacy DAS may be discovered.  Generally these systems were financed and installed by a carrier, and deployed to support only their cellular.  Carrier-funded systems are becoming increasingly rare, but the existing cabling can often be repurposed to support new DAS deployments.  DAS cabling, designed to carry RF data, was traditionally deployed on coaxial cabling.  Newer DAS infrastructure has maintained compatibility with legacy cabling.  Part of the discovery phase of the project should investigate legacy cabling for reuse.

As mentioned, facility administrators are a good source of information on usage patterns of the building.  Waiting room and patient room statistics can be obtained from these resources.  Requirements for cellular connected equipment can also be discovered through interviews with IT professionals in the facility.  Inventory tracking systems, especially those in pharmacies, are often based on cellular communications.  Point-of-Sales systems used by outside vendors also function as cellular connected devices.

An investigation of existing carrier retransmission agreements and potential space lease options are also necessary when scoping the extent of a DAS project.  Legacy DAS systems inside the building will rely on one or both of these legal agreements.  A retransmission agreement allows the carrier to rebroadcast their “macro” signal through the building on an existing DAS.  Discovery of a lease agreement indicates the carrier is compensating the facility for space inside a network closet for the purpose of housing their equipment.

Planning and design

Armed with data from the survey, a DAS contractor should aim to provide a proposal which encapsulates all Owner Project Requirements as defined during the requirements planning stage.  DAS purchasers should verify that their contractor of choice is providing coverage for the required carriers, in the critical areas of operation.  A well-presented proposal will also include a prediction of the expected signal power inside the building along with some literature outlining the equipment manufacturer used for basis of proposal.

When reviewing proposals, the organization should engage IT to coordinate any efforts in deployment of cabling and antennas.  A DAS implementation is similar in nature to a WiFi deployment, requiring coordination with IT staff to eliminate duplicate efforts.  IT may also maintain a relationship with equipment manufacturers that can provide advantageous pricing on cabling and equipment used in DAS construction.  Strategically leveraging these existing relationships can garner competitive pricing, resulting in a lower total cost of ownership.

Carriers provide equipment and services necessary for a DAS to function.  In all cases, the organization’s DAS must connect to a carrier signal(s).  The most common method of connection to carriers is over-the-air; an FCC sanctioned retransmission agreement with the carrier is required in this case.  Carriers also provide equipment located at the head-end to process their outdoor signal and rebroadcast indoors.  As bandwidth at the tower is consumed by an increasing number of cellular devices, carriers are looking to move cellular users to backhaul circuits.  A carrier-owned fiber circuit and signal source may be provided by the carrier to offload over-the-air saturation.  In either case, the carrier is required to be intimately involved with the project and is asked to provision equipment at their cost.

The most difficult part of standing up a DAS system can be the interaction with the carriers.  Carriers maintain a long queue of regional projects which may number in the thousands, and correlate to a delivery schedule of up to two years.  All new projects entering the queue get pushed to the end of the line.  Carrier account managers handling corporate accounts relating to cellular plans can often be leveraged to decrease the schedule.  The most effective and efficient DAS contractors maintain tight relationships with the carriers, allowing them to quickly navigate the process.

DAS contractors should provide an iBWave certified design prior to commencing construction.  Carriers conduct a review of the design when the requisite funding and schedule availability allow, before making a final decision on when to join the DAS.  The iBWave design documentation provides predictive proof of design performance from the joining carriers. 

Putting it all together

Construction of a DAS system at the facility looks much like a cabling project for other low voltage systems.  The construction portion of the project involves installation of cabling from the head-end location to remote locations, through established low voltage pathways.  Serving antennas, located in the ceiling grid throughout the facility, are the end points to which cellular devices connect.  Serving antennas are generally installed in the ceiling grid, similar to access points for network systems and speakers for paging systems. It should be expected that sections of the facility will be shut down or cordoned off to allow the DAS contractor to access pathways during construction.  Tight communication is required during this process to ensure access to restricted areas is granted in a timely fashion, or schedule slips and additional labor costs may be incurred.

In part, with installation of cabling and antennas, the DAS contractor will test cabling and connections for several performance criteria not seen in other low voltage systems.  Continuous Wave (CW) testing  is required to validate RF propagation with design requirements.  This testing should be a minimum standard to which the DAS contractor performs.  Additional Passive Intermodulation (PIM) testing is generally required by carriers before joining the system.  This requires specialty testing equipment which the DAS contractor should intend to provide if they have submitted a comprehensive system proposal.

The selected DAS contractor will require power and space for support of DAS equipment.  Head end and remote equipment should be installed inside existing network locations, including data centers, MDF’s, IDF’s, and network closets.  Power to support equipment in these locations will likely be excluded from the scope of the DAS contractor.  Facility managers should expect to engage their electrical staff and contractors to provide dedicated power for the DAS.  UPS power and battery backup is not a requirement of a cellular DAS, but is commonly observed as best practice to protect the sensitive nature of active electronics.

At the completion of cabling work, the DAS contractor will light up the system and measure its operation and function.  System optimization is performed around the supported carriers and metrics are then reported back to the carriers to close out their involvement.  Facility Managers should review the survey findings with the DAS contractor during the close-out process.  The organization should fully expect to see an increase in signal strength and signal quality performance in all areas of the facility which are supported by the new DAS. 

A complete Operations and Maintenance manual with survey results will be provided to the facility at project closeout.  Records of carrier agreements should be included in this package.  A reputable DAS contractor should also offer maintenance agreements for surveys of the facility in future years.  As the facility undergoes remodels and construction projects, there will be a need to revalidate the performance of the system.

The proliferation of cellular connected equipment and mobile devices has stressed existing cellular infrastructure to the point of saturation.  Updates in construction methods for high performance buildings has decreased the ability of cellular signal to penetrate into buildings.  The confluence of these events is driving the requirements for DAS inside healthcare facilities.

Selection of a qualified DAS contractor that can properly articulate the Owner’s Project Requirements for the engagement is key to success.  Selection of the contractor should be based on proven ability to interact with carriers and deploy similar systems. 

 Application in healthcare facilities and public safety DAS

Hospitals are now seeing deployment of cellular connectivity in vendor equipment, allowing vendors to directly access and monitor their equipment with zero reliance on IT staff.  Refrigerators, patient beds, imaging equipment and other devices are all “phoning home” to report status.

Aside from the tangible need of a hospital or clinic to provide cellular connection for equipment to the internet, there are other considerations.  Communications between staff is more and more frequently reliant on cellular devices.  Consumers of the health care service expect an experience in the waiting room which is often defined as access to the internet through their mobile device.

Because the users of cellular data in a health care facility are stationary, the usage pattern often involves large downloads of data through streaming services.  Hospitals, which are open 24/7 see a demand for cellular data throughout the entire day.  The usage pattern of health care facilities dictates a strong need for cellular connectivity.

A subset of DAS technology is the Public Safety, FirstNet, Emergency Responder Radio Coverage system.  It must be noted that nearly all new buildings are required to provide a signal source inside the building for emergency responders to communicate with two-way radios.  These systems are similar to DAS systems which support carrier signal, but are optimized to carry only 700MHz and 800MHz bands which are required by code.  Installation of a public safety system does not provide cellular signal for phones, the reverse also holds true.

EMS staff communicate through 2-way radio systems from healthcare facilities to mobile trauma centers and ambulances.  2-way radio systems are independently deployed from DAS.

Matt Schwartz is Director of Technology and Engineering at Parallel Technologies.


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