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The state of the art approach to achieving maximum coverage with minimum interference is a distributed antenna system (DAS). The concept behind DAS is to locate the transceivers for pairwise communication equipment as close to each other as possible and thus lower the transmitted power levels, resulting in reduced interference and increased available bandwidth. Specifically, signals are distributed through a cellular dead zone, usually an office building or private facility, without interfering with the macro network outside of the building or facility. Further, distributive antennas may be designed as multi-band, allowing multiple carries to be used in the same system. DAS may be deployed in passive or active configurations, depending upon the requirements of the system, the size of the site, and budgetary factors. Bascom Hunter, which is equipped to offer both configurations, selects the optimal solution for each situation.

Passive DAS

Passive DAS uses passive RF components to distribute the signals from base stations to antennas. As shown in Figure 1, a passive system incorporates couplers, splitters, and long lengths of coaxial cable in order to connect each of the distributed antennas to the local base station. Connection can be achieved via a landline (physical cable, co-ax, phone line, fiber optics, etc.) or an antenna located on the roof of the building.

Figure 1: Passive DAS using couplers to split and combine the signals.

Active DAS

Active DAS utilizes active components in order to minimize the noise of the system and allow for more efficient bandwidth use. An active system, pictured in Figure 2, employs fiber optic cables to connect the main hub (which is connected to the base station via a landline) to various expansion hubs, usually located on each floor. These expansion hubs are then connected by either coaxial or fiber optic cable to remote access units (RAU) spread through the area of interest. RAUs are usually composed of automatic gain controls (AGC) for both the downlink and uplink in order to provide the proper amount of amplification. When fiber optic cable is used to connect the RAU to the expansion hub, RAUs may also contain opto-electrical converters. The RAUs are generally located as close as possible to their respective antennas in order to amplify the signal after it has experienced only a minimal loss, thereby minimizing the overall noise figure of the system. Since the hubs and RAUs are all active components, control signals maintain uniform activity over each antenna regardless of its proximity to the base station, while allowing for the system to activate and deactivate antennas as needed.

Figure 2: Active DAS utilizing optics for more efficient signal transmission.

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