Public safety is highly dependent on the ability of first responders and other emergency personnel to communicate effectively in emergency situations. The lack of coverage and access deep inside a building can cost first responders valuable time, which can mean the difference between life and death, in some cases. For public areas such as airports, stadiums, hospitals, and hotels, the requirement for a resilient public safety communications infrastructure is vital, because these venues often have a high density of wireless users that may cause interference during an emergency situation.

Dallas Fort Worth International Airport (DFW Airport) is one of the busiest airports in the world. DFW Airport maintains a Critical Communications Infrastructure (CCI) to provide RF communications for all divisions of DFW Airport. The CCI consists of numerous radio system platforms, an in-building distributed antenna system (DAS) and bi-directional amplifier deployments. DFW Airport has made numerous upgrades within the current five active passenger terminals to improve its CCI over the last 20+ years. Cumulatively, these improvements have positively impacted RF propagation within the coverage area but some communication dead spots remain. In addition, similar to some other commercial aviation facilities, the passenger terminals have a “horseshoe” architectural design which results in shadowing around the exterior perimeters of the passenger terminals.

DFW Airport requires a solution that not only provides public safety coverage and access at all times, but also the flexibility and scalability to meet the airport’s existing and future requirements. To address the coverage issues and overcome the physical obstructions caused by the layout of the service area, DFW Airport also required a fully-digital, quad-band solution, capable of transporting all required frequencies over a single fiber. The aggregate transmission delay between the RF input at the headend and RF transmission at all antenna points must not exceed 40 microseconds to minimize latency. In addition, the system should also be scalable to support future expansion or modification of existing terminal buildings, and the addition of new terminal buildings without a complete overhaul of the existing network. Lastly, the system should be future-proof and support additional frequency bands and expansion to LTE SISO without replacement of the cabling infrastructure.

A digital distributed antenna system (DAS) is a natural candidate to satisfy all of DFW Airport’s requirements and future proof its investments. As a global provider of the advanced all-digital DAS, coupled with the expertise of its team, Dali Wireless was chosen in partnership with DFW to design, install, and maintain a digital DAS to provide wireless coverage and access throughout all of DFW Airports’ terminals for public safety.

Comprising the Dali t-Series® PS solution are the headend tHost® PS, and the medium and high power remote units, t37™ PS and t43™ PS. This end-to-end digital DAS ensures there is no signal degradation over the distance of the fiber and provides superior signal performance compared to similar wireless access technologies. This is important because two sets of base station resources are located remotely from the DFW Airport’s headend where the signal is distributed out to all the terminals. Conventional analog systems will require double conversion of signal because the RF-over-fiber signal causes massive signal degradation when traveling over great distances. However, with an all-digital solution, the two base station resources can be aggregated digitally and fed through a single fiber to the headend for distributing the signal to all 12,000,000 square feet within the five terminals (Figure 1).

Figure 1. Digital Aggregation of Signal Sources with No Loss

This capability highlights the flexibility and scalability of a digital DAS platform which is ready to adapt to any future needs of the DFW Airport. For example, with the long reach of Dali’s digital DAS, DFW facilities and office buildings that are within a 20km radius can be served by the same radio source at the headend. Additional remotes and antennas are simply added without interruption to the existing distribution network.

The system is designed to support all the frequency bands in a consolidated all-digital platform with a signal level of -95dBm at greater than 97 percent coverage. The coverage has been extended beyond the exterior perimeters of the passenger terminals to avoid shadowing. To ensure mission critical communication is protected at all times, Dali has designed a fault tolerant deployment architecture with fiber diversity, redundancy and automatic failover capability. The primary host unit is protected by a co-located active hot standby host. With added intelligence, the remote can detect a loss of signal when the primary host fails or when the primary fiber is cut. The remote will then automatically disable the primary optical port and enable the standby optical port. The second fiber connection from the standby host to the remote also provides fiber diversity to avoid single point of fiber failure. This redundant configuration can be incrementally added without any impact to the current deployment.  Such high availability is the first of its kind and by far the most advanced in the industry (Figure 2).

Figure 2. Automatic Failover Host Protection

In addition, the simulcast is designed such that signals from all antennas are normalized to reduce interference to a minimum. With the DalI DAS digital system, delay can be set in the digital domain through the GUI. All of the calibration is done through the GUI so that the antenna can be placed where needed to optimize the signal performance. This also fulfills one of DFW Airport’s requirement: the aggregate transmission delay should not exceed 40 microseconds. It will become important when DFW Airport deploys public safety communication over LTE which has a more stringent delay requirement.

With DFW Airport expecting to upgrade to LTE in the future, they require a system that is flexible enough to accommodate this expansion without replacement of the cabling infrastructure, which is costly and can potentially disrupt existing services. In addition, with the emergence of public safety applications such as live two way video feeds and camera surveillance, DFW Airport needed a system that is robust enough to offer the required bandwidth for media-rich public safety applications as required. With Dali’s all-digital platform that is software configurable, DFW Airport can easily scale to meet LTE requirements, and can easily adapt to existing and new requirements, including FirstNet, P25 Phase I & II, narrowband and broadband public safety.

Installation and testing is expected to be completed by summer of 2016. To ensure a fully functional wireless network capable of handling the stringent requirements of public safety, Dali will perform functional system and coverage acceptance tests. For the coverage acceptance test, each frequency band’s coverage area is divided into uniform test tiles no larger than 25 feet by 25 feet; and each test tile will be tested to meet a mean signal level of at least -95 dBm with a mean signal-to-noise ratio of 18 dB. This tile by tile acceptance test, mandated by the airport, will ensure complete coverage with maximum capacity and the elimination of dead spots

With DFW and Dali Wireless acting as partners and completing the installation of an all-digital DAS throughout the DFW terminals, first responders and other emergency services personnel will receive clear, secure, uninterrupted communications critical during emergency situations.

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