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How to successfully support in-building communications for public safety and commercial wireless services
Over the last 10 years, natural disasters such as Hurricane Katrina and manmade tragedies such as the events surrounding 9/11 have highlighted significant weakness in the reliability of in-building wireless public safety communications. This has lead to the creation of various codes and ordinances at local and national levels in the United States to ensure that all public buildings provide wireless coverage for the first responder and for public safety. The soon-to-be-released NFPA In-building Public Safety Communications Code will specify service reliability, coverage requirements and frequency agnostic functionality. Efforts are under way to develop and implement these codes nationwide.
In addition to the increased focus on wireless public safety capabilities, the adoption of commercial wireless services by the general public has increased at an astounding rate. In 2005, the number of wireless subscribers overtook the number of landlines in the United States; not surprisingly, the majority of 9-1-1 calls today originate from cell phones. This, as well as the more general widespread usage and popularity of wireless services from mobile data to Wi-Fi, has raised the importance of improving the quality of in-building wireless coverage for commercial services and public safety.
Since the introduction of these regulations, the number of dedicated in-building wireless deployments for public safety services has grown significantly. Currently, the two most common methods of improving the reliability of these services when used indoors include: increasing the wireless signal strength through deployment of additional antenna sites throughout the entire area, and supplementing wireless coverage in specific buildings by installing permanent systems. The benefits of implementing such systems are very clear. When installed properly, these technologies can help save the life of police officers or the public they serve, thus making them priceless.
First responders need to be assured that they have access to time-critical, secure information, often coming in from a number of sources and in a variety of formats. Although voice service is still ranked as the number one application in public safety wireless communications, data services with support for broadband applications are increasingly being demanded. This is especially true in urban areas where coverage from the macro network is obstructed by building structures.
So whether it is cellular calls, e-mails, data streams or two-way radio emergency service, responders may need to depend on wireless coverage for a variety of services and purposes at any given time. All services, whether 3G, Wi-Fi or Land Mobile Radio Systems (LMRS), operate on different wireless frequencies, with varying levels of capacity, coverage and range indoors. Because data services require greater bandwidths and can often operate at a higher frequency, in-building penetration of the wireless signals from the outdoor network is reduced, resulting in lower data rates and, in some instances, complete loss of signal.
The phenomenal public demand for mobile data services has spurred building owners and wireless service providers to start focusing on the bigger value proposition, providing simultaneous in-building coverage support for both commercial and public safety wireless services in commercial buildings. Having separate in-building wireless infrastructure for public safety and commercial services is neither cost efficient nor easy to manage. But currently the question of converging the two services within the same in-building infrastructure has caused conflicting opinions in the market. Historically, both have been kept separate to avoid heavy usage from commercial services hampering the capacity and availability of public safety services. Some believe the two cannot be supported effectively unless they are kept separate.
There are a number of key factors that must be taken into account before deciding on the right type of wireless distribution system, such as spectrum environment, building parameters, operational needs of the users and so on. In addition, advancements in technology, availability of new wireless services, and changes in frequency bands mean that in order to protect initial investments in infrastructure and avoid costly upgrades, in-building wireless coverage systems must be flexible and easily upgradeable. Choosing the right system can be tricky.
Increasing Radio Frequency (RF) signal strengths by deploying additional antenna sites throughout an entire jurisdiction to improve wireless coverage, whether indoor or outdoor, may, on the face of it, seem like the most sensible option. However, lack of wireless spectrum, insufficient funding, and inability to acquire and approve enough transmitter sites are common hurdles that prevent the deployment of ubiquitous coverage through this approach. Additionally, in more urban environments, even the best radios and networks will struggle to always penetrate modern building materials, high-rise buildings, subway tunnels and underground basement floors.
In contrast, the primary and perhaps most obvious trade-off with permanent wireless distribution systems is that they must be installed in each building where coverage is needed. Furthermore, traditional multiple RF distribution systems that support both commercial and public safety may distribute signals that interfere with or degrade the public safety performance. There are three main types of in-building wireless distribution systems used today.
Repeaters are used to improve wireless coverage inside buildings by amplifying and hence extending RF signals transmitted from the outdoor base station cell. Because repeaters are fed from the existing macro base station via a donor antenna, this eliminates the need for additional network equipment and, in some instances, can actually be very cost efficient. However, in comparison to competing technologies, repeaters have a comparatively limited bandwidth and can typically only support one or two frequency bands at a time. This means that in order to ensure simultaneous wireless coverage for multiple services, such as cellular, public safety and mobile data, a number of repeaters would need to be installed. In addition, because repeaters are unable to provide the network with extra capacity, they are typically more suited to smaller buildings with fewer tenants where there are lower volumes of data traffic. Ultimately, this makes them financially impractical and unsuitable for supporting emergency service responders in times of crisis.
Picocells, on the other hand, are generally very well suited to providing additional wireless network capacity, particularly in small buildings. A picocell is a relatively straightforward, often low cost, and typically small unit that basically acts as a mini base station to improve wireless coverage indoors. Because these units can provide the network with extra capacity, picocells are more appropriate than repeaters for use in high data traffic environments or situations. However, for multiple wireless service deployments, particularly within larger infrastructures, where a high level of capacity is typically also needed, a higher number of picocells are ultimately required. As each type of wireless service needs its own dedicated cell infrastructure, supporting multiple services using picocells can quickly lead to high investment in equipment.
The last type of approach is known as Distributed Antenna Systems (DAS). These are typically favored in moderate to large infrastructures for their ability to offer improved and unified indoor wireless coverage for multiple services at lower capital expenditure and running costs. A typical DAS comprises a network of antennas which are distributed throughout a building to provide dedicated in-building coverage. There are customarily two types of distributed antenna systems available today: passive and active. Hybrid solutions are also in common use, where active units are distributed throughout a building with each feeding a small passive antenna network.
Both active and passive distributed antenna systems can support multiple service connectivity, meaning they can be used to simultaneously carry multi-operator and multi-service solutions, whether public safety or commercial. Traditional active/hybrid systems achieve multi-service support by deploying service-specific hardware overlays which are then combined onto a common antenna. One of the limitations with these traditional-style solutions is that not all service frequencies are supported in the range of service-specific hardware; this is particularly true for the more specialist services.
Passive distributed antenna systems are made up of a network of coaxial cables, couplers, power splitters and antennas to distribute wireless signals throughout buildings. In contrast, active distributed antenna systems feed cellular signals from a base station or repeater and distribute amplified wireless signals inside buildings over optical and RF cable, which connects to multiple remote antennas placed in various areas of the building.
A Passive DAS is typically cheaper in smaller buildings than its active counterpart and is probably still the most commonly used DAS today. The drawback with these solutions is that the RF signals do not travel very far over the cable. In turn, this means these systems suffer significant signal loss over large distances, with each frequency and service having different loss characteristics. By its very nature, the end components of the system are passive, and as a result there is no inherent fault reporting, which can lead to increased maintenance time and cost. An Active DAS, therefore, has advantages over passive systems in larger infrastructures where passive would encounter length limitations. In addition, because the components are active, if there is a problem with one of the antennas, this can be easily pinpointed, providing more reliable connectivity and manageability.
More recently, a third DAS option has been introduced which has taken a truly wideband, active approach. Active wideband DAS simultaneously supports any number or combination of wireless services, protocols or frequencies on one system without the need for service-specific overlays. In this way, the system is future-proof as it has the ability to add in any service at a later date without additional cost.
Active “true wideband” distributed antenna systems can provide building owners and wireless service providers with a comprehensive in-building coverage solution because they are capable of simultaneously supporting any number or combination of wireless services, protocols or frequencies without the need for service-specific overlays. This means that specialist/unique services are supported. This will guarantee the safety of the building and its employees, as well as emergency service responders entering the building, no matter where they are or what service they are using at the time. The wideband capability also eliminates the need for service-specific equipment, keeping hardware and installation costs low. By being service-agnostic, active wideband distributed antenna systems also provide peace of mind by future-proofing new investments in in-building wireless infrastructure, allowing new services to be added without extra components or costly upgrades.
The need for converged public safety and commercial wireless services is very real. Ultimately, improved in-building coverage for wireless services is the only way to ensure the safety of emergency service responders and the public they protect. Active wideband Distributed Antenna Systems are unique in their capability to deliver on a financial level while also providing reliable widespread coverage to emergency service responders, wherever they may be and whatever service they require.
Jeffery L. Fuller is the President of Zinwave Americas. Reference: National Public Safety Telecommunications Council (NPSTC) Best Practices for In-Building Communications.
Published in Public Safety IT, Jul/Aug 2010
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