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In the cellular environment a signal is transmitted from a handset via free space to the nearest base-station. It is then converted to a stronger signal and repeated over and over until it reaches its destination.
This system works fantastically well in vast open areas where RF can travel unabated over hundreds of km’s. But as soon as we introduce RF reflective structures into the mix, we run into a range of problems.
You may have noticed that certain areas of your home have better mobile phone coverage than other areas close by. Or that you need to walk outside to make a phone call.
So how do we fix this issue and provide full In-Building Coverage (IBC)
The best solution in most cases is a Distributed Antenna System.
A Distributed Antenna System (DAS) is a network of antennas, connected to a common source, distributed throughout a building or an area to improve network performance. The spacing between antennas is such that each antenna gives full coverage without overlapping with other antennas, hence reducing the number of antennas needed to cover the whole building. This network of antennas is also power efficient in comparison to a single, larger antenna covering a wide area.
A Distributed Antenna System can be designed for use indoors or outdoors and can be used to provide wireless coverage in hotels, subways, airports, hospitals, businesses, roadway tunnels etc.
A Distributed Antenna System comprises of two basic components.
1. The Signal Source-A Distributed Antenna System doesn’t generate the cellular signal itself. A DAS needs obtain usable signal from somewhere.
2. RF Distribution System-Once received, the signal must be distributed throughout the building.
Distributed Antenna Systems can be broken down in to three different categories, Active DAS, Passive DAS and Hybrid DAS. Each have their own pros and cons and each best suited to a particular use.
Active DAS uses a dedicated transmission path (Backhaul) as the signal source. This backhaul path is usually assigned by the relevant carrier and its throughput capacity is governed only by the limitations of the network provider. An active DAS is the most apt solution when deploying DAS for Enterprise, Commercial and high user -traffic scenarios. An active DAS can add capacity to the existing carrier network and for this reason it is the preferred choice of the Telco’s.
Passive DAS, sometimes referred to as off-air DAS, utilised a Donor antenna to receive and transmit signal to a slave Base-Station (Mobile Phone Tower). Passive signals are the most common source of signal for a Distributed Antenna System. If the donor signal is strong and clear, then an off-air signal is often the easiest and most cost-effective signal source.
Passive DAS systems can also incorporate what is called an Off-Air Repeater System. An OAR system works by receiving the input /output passive signal and amplifies it bidirectionally. These systems are commonly referred to as Signal Boosters and when incorporated into a distributed antenna configuration, can, in some situations, provide a very cost-effective alternative to a Hybrid/Active DAS system. Output signal levels are unable to be adjusted on a passive OAR system. Therefore, the system must be adequately “balanced” to perform correctly. Failure to balance an OAR system can shut down a slaving BTS. RF engineers should always be engaged to design a Passive OAR system.
A Hybrid DAS is a system that connects to the macro environment using a donor antenna, but which then converts the analogue donor signal to an adjustable digital signal. Hybrid systems are safer to the macro environment as signal levels can be adjusted according to the desired output without compromise to the Tx/Rx levels of the carrier network. Hybrid Systems should not be confused with Small Cells and/or OAR systems.
Always verify that your Distributed Antenna System has been designed and implemented by a compliant RF Engineer. and that carrier approval has been granted. Failure to do so will result in ACMA-Issued fines and a faulty system.
An in-depth sublimity assessment of the premises which will include walk-testing for existing coverage readings and signal availability
MCF 2018-Compliant Distributed Antenna System design complete with line system, component layout and coverage prediction
Desktop analysis of existing coverage vs proposed coverage illustrating proposed RF output and target coverage footprints
Straight line diagram with link budget calculations and cable loss values. Used to balance the output of all antennas in a DAS.
A visual representation of the existing and/or predicted RF propagation through the target coverage footprint.
Topographical model of RF propagation. RFNSA, ACMA and Carrier Databases are used to remotely asses location suitability for a DAS
Always use a licenced professional when in comes to In-Building Coverage.
SEQ Connect has licenced and dedicated team to assist with all facets of Distributed Antenna System design and installation.
If the aim is to provide coverage for up to 100 users over one or two floors of office space, than a Passive OAR system is probably right for you. Should you need to cover more area than this or provide coverage to a greater number of users, then an Active DAS is recommended.
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