Microwave Engineering Europe - May 2008 - (Page 16)

16 WIRELESS NETWORKING — INDOOR SOLUTIONS common point of interface (POI), which is typically located at the entrance to the building. The DAS is connected to the POI and distributed throughout the building. Many passive solutions are founded on radiating cables, sometimes called leaky feeders, which have apertures all along the length of the cable ‘outer’ to provide contoured RF coverage. These are ideal in curved spaces where traditional antennas (requiring line-of-sight for coverage) are inappropriate. They also work well in constructions with a metal frame, or where the signal needs to be limited to a small radius (a few metres). Radiating cables are well-suited for distributing WiFi in buildings, especially when high data-rate applications have to be used. Radiating cables are also applicable to situations where avoiding interference with other devices is critical, such as in hospitals; or in circumstances with environmental constraints (down mines, for example, or in prestige locations with visual aesthetics to consider). Figure 2: Passive distributed antenna system. Solutions based on passive DAS are very cost effective, yet still provide futureproof functionalities. RFS radiating cables are WiMAX-ready up to 5.8 GHz, and can combine 2G/3G and WiFi simultaneously. Going hybrid Where ampliﬁcation of the signal is necessary — as in larger buildings or tunnels that are more than 500 metres in length — hybrid solutions often need be deployed. Hybrid solutions mix ‘active’ elements — usually signal ampliﬁers such as ﬁbre-fed repeaters — with ‘passive’ cables and antennas to distribute the signal throughout larger interiors. A typical hybrid network structure is illustrated in Figure 3. This involves transmitting the signal via a ﬁbre optic network to repeaters, which are then used to drive a passive DAS. Fibre-fed systems comprise a ‘master unit’, where the RF signal is converted to an optical signal and then transmitted through a ﬁbre optic network around the building or zone in which service is required. In each remote part of the building or tunnel, a ‘remote unit’ receives and ampliﬁes the signal, converting it back to RF and distributing it through a passive network of cables and antennas. The remote unit is ‘active’ since it ampliﬁes the signal, but the ﬁnal part of the solution (the cables and antennas) is ‘passive’. These hybrid solutions are suited to long tunnels as well as zones that are spread out, such as large buildings and campuses, retail complexes and airports. They also suit structures where it is difﬁcult to install cables vertically through the building levels. Fibre-fed systems can also accommodate WiFi on the same infrastructure. WiFi is the next wave The ability of WINS infrastructures to meet the needs of WiFi is essential in view of the increasing number of consumers who expect their dual-mode WiFi/3G handsets to operate effectively. Although basic WiFi access points provide basic coverage, they do not provide homogeneous coverage or network security. WINS systems can be used to provide either dedicated WiFi coverage or an integrated service with both 2G and 3G mobile communications services. This is achieved by using a broadband passive DAS to distribute the WiFi access points throughout an area. Whether the WINS infrastructure is founded on radiating cable to provide contoured coverage (Figure 4) or a network of distributed point-source antennas, the solution offers savings of up to 20 per cent on deployment costs — with better and more homogeneous coverage. In addition, aesthetics and interference can be properly managed. In view of these many applications, indoor and in-tunnel infrastructure often need to support services that operate at speciﬁc frequency ranges. Radiating cables carry a wide span of frequencies, depending on the application. These range from low radio frequency identiﬁcation (RFID) frequencies, 75 MHz for safety services, 800 to 2100 MHz for commercial mobile communications services, and up to 2.4 GHz and higher for WiFi services. In the future, certain unlicensed WiMAX frequencies could operate at frequencies as high as 3.5 GHz and even 5.8 GHz in some parts of the world. WINS systems transmit these signals through buildings, re-amplifying the signal as necessary. They do not act as a substitute for a carrier’s BTS, private branch exchange (PBX) and wireless local area network (LAN) switches and access points. Wireless coverage solutions do not add anything to the signal except strength: they transmit signals with non-proprietary and technology-agnostic infrastructures. Deﬁned by the application At the end of the day, the quality and selection of an indoor coverage solution is dependent upon the user service or application’s speciﬁc needs. High-data services (video) or real-time requirements (voice) require optimum coverage in order to avoid ruptures in communications, or a slowing-down in transmission rates. Materials used in construction must be taken into account, as must the distance between the signal source (BTS) and the building. Even the shape of the structure Figure 3: Hybrid system using ﬁber-optic network and repeaters. Microwave Engineering Europe ● May 2008 ● www.mwee.com http://www.mwee.com

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Microwave Engineering Europe - May 2008 News Contents Comment Cover Feature: How to Succeed as a GaAs Foundry Wireless Networking: Wireless Coverage Where Everybody WINS Wireless Networking: Achieving Good Coexistence in the 2.4 GHz ISM Band GPS and Satellite: GPS developments: Galileo Moves Forward with Successful Giove-B Satellite Launch — Broadcom Targets AGPS in Mobile Phones and Devices Raising the Bar for the Radio: Making 802.11n Work Reducing Power Consumption in Ultrawideband Chips WiMax Catches Second Test Wave Products Calendar

Microwave Engineering Europe - May 2008

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