Simply put, a Distributed Antenna System – or DAS – uses a clustered installation of antennas to boost cellular network coverage in areas with weak to no signals. These systems are often installed in areas with poor line-of-sight to existing towers, such as deep within very large facilities or inside underground transportation systems. Another common use is for areas with concentrated demand that would otherwise overwhelm existing network coverage, such as in hospitals, airports, and sports arenas.
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A DAS installation consists of a network of separately installed antenna nodes that are connected to a common source through fiber or coaxial cable. Splitting transmitted power among several antenna elements to cover the same area as a single antenna reduces the total power required and increases the reliability of the signal.
Well, for one, the mere presence of additional antennas increases the chance of a good line-of-sight channel. The drop in power consumption has a slightly more complicated, less intuitive answer. Providing cellular signals is a power hungry task, often because of signal losses due to penetration and shadowing. To overcome these feeder losses, a DAS can use either a configuration of passive splitters and feeders, or active-repeater amplifiers. In short, this type of configuration introduces efficiencies into the system that wouldn’t otherwise be there, and thus results in less power being used.
Because DAS antenna node installations are compact, they can be deployed indoors and outdoors. Their size and power requirements also allow their installation in areas where traditional cell towers cannot be placed due to zoning restrictions. DAS systems may be tied to a particular wireless carrier, such as AT&T or Verizon, but the best bang for your buck is a neutral-host provider that can work with multiple carriers.
Of course, DAS installations are expensive. To justify the investment, providers and carriers prefer long contract terms, with ten years quickly becoming the industry standard. In a carrier-owned DAS, a wireless service provider pays for the equipment and installation costs, as well as maintenance and upgrades. In return, the service is typically exclusive to the carrier that installed the DAS. However, a carrier may voluntarily allow its competition to make use of its investment – for a fee, of course. When a third-party neutral-host provider installs a DAS, this entity bears all of the costs, which can be recouped by charging any or all of the service providers to have access to the system.
That said, the cost is probably worth it. Cell phones aren’t just about convenience; they offer safety, but only can do so when the user has a signal. In this way, calls made via WiFi are inadequate. Why? WiFi was never designed to provide location information, which is required when an emergency call is made to 911.
To explain how DAS are different from cellular repeaters / boosters, it is important to understand just what each technology does. Since we explained the ins and outs of DAS in the sections above, let’s look into repeaters / boosters here.
Cell phone signal boosters take an existing cellular signal, amplify it, and then broadcast it. Boosters require an existing signal because they are unable to create their own signals, making them fundamentally different technology than DAS. Since boosters require an existing, stable signal in order to work, they cannot be placed in areas with very poor reception.
Let’s say you have a college campus located in a hilly area just outside a mid-sized city. The part nearest the city (Area A) receives an adequate signal, but the new set of dorms on the opposite side (Area B) has terrible service. Installing boosters in Area B would do no good because the acquired signal wouldn’t be strong enough for a boost. It’s not quite as simple a concept as multiplying by zero, but if that helps to frame it, so be it.
You could, however, install boosters in Area A. This would amplify reception for Area A and it might help Area B as well. However, the same changes in terrain between the two zones would degrade the boosted signal as well.
So, the best way to fix reception in Area B would be to install a DAS because it would generate its own signal.
Within the United States, Corning Mobile Access, CommScope, and TE Connectivity all serve as DAS hardware vendors. Other manufacturers include Axell Wireless, Comba, Ericsson, Kathrein-Werke, NSN, Optiway, PowerWave Technologies, Solid, and Zinwave. In the world of cellular service providers, AT&T has a large and growing, albeit not exclusive DAS practice.
Corning MobileAccess DAS solutions include the single operator MobileAccess 1000 and the multi-operator MobileAccess 2000. Both are designed for indoor use and have a single, broadband infrastructure with service-specific, chassis-based modules that automatically groom wireless signals. The 1000 model hosts up to four wireless services in medium-to-large-scale environments; whereas, the 2000 model’s modularity enables users to introduce new wireless or operator services at any time and is suitable for large-scale, multi-operator facilities.
CommScope offers outdoor wireless solutions, such as the Andrew DAS, which supports all current system architecture and power ranges and is ready to handle more advanced technologies like high-speed packet access (HSPA+) and evolution-data optimized (EV-DO).
Manufactured by TE, the FlexWave Prism is also designed for outdoor use. The package offers mobile operators a way to extend macro network coverage for 2G, 3G, and 4G services. TE’s indoor product is called the FlexWave Spectrum, which can extend wireless services throughout a building, multiple buildings, or a campus.
TE also has a product geared specifically toward enhancing public safety. The appropriately titled TE Public Safety DAS provides distortion-free transmission and distribution of information. It has been used worldwide to improve vital communications in systems for first responders, government, transit, commercial enterprises, education, security personnel, and the military. It supports primary public safety and critical first responder frequencies in the VHF/UHF/700/800/900/TETRA bands on a single system and provides high reliability coverage for public safety communications services. It functions both indoors and out.
Like Corning, SOLiD has two flagship DAS products that differ mostly by scale and capacity. The cost-effective EXPRESS single-carrier DAS provides in-building or outdoor wireless service for a single wireless provider across multiple frequency bands. It typically uses just one fiber to connect a building. The ALLIANCE DAS system seems to be much of the same, albeit designed as a multi-carrier solution, and presumably a less cost-effective one at that.
Whereas the manufacturers listed so far sell complete Distributed Antenna Systems, Oberon Wireless seems to distinguish itself by selling system components. Its WiFi and DAS antennas come in indoor/outdoor varieties, with a variety of frequency bands to choose from. Some models are dual band, coming in either puck or dome styles. This company also sells the mounting brackets required for installation.
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