Distributed Antenna Systems For Indoor Cellular Network

About 70-80 per cent of mobile traffic comes from indoor buildings. This is especially true in urban environments where the mobile users rely on high data levels. Only supporting macro base station within a few hundred meters of the building can provide sufficient level of RF signal for cell 3 G network indoor voice / data services. Just a few real-estate buildings fall into that category.Check this content

Because each indoor mobile phone can be serviced by more than one macro cells (base stations), soft 3 G network transformation will further boost the network traffic load. The only solution is an indoor distributed antenna array (DAS) to provide mobile data networks, such as HSPA (High Speed Packet Access) or EVDO (Evolution-Data Optimized) indoor high speed connectivity.

DAS is used within a building with sufficient strength to provide 3 G voice and data facilities for efficient transmission of the RF signal.

DAS can be used to distinguish the indoor network from the outdoor macro cells which help remove the soft indoor mobile phone switch.

That will reduce the traffic load and increase the speed of the 3 G network. Indoor DAS can also provide security for HSPA high speed data access between served and non-serving outside network cells. This means less interference of the co-channel into the HSPA’s serving cell and results in higher data rate for HSPA service. In order to conquer the building with an indoor range, it is possible to install directional antennas at the edge and corners of the building and to target towards the middle of the room. The overall indoor area is dominated by the indoor node, which at the same time decreases the leakage to the macro network.

DAS distributes a single superior RF signal inside the building to cover the entire system by splitting the signal from the base station inside to many indoor antennas. DAS can be classed as passive or active. Passive DAS transmits the RF signal through passive components. Such passive components are coax cable, splitter, terminator, attenuator, circulator, coupler, and filter (duplexer, diplexer, or triplexer). Planning DAS involves estimating the maximum loss from the base station to each antenna in the systems and having the connection budget for the specific area protected by each antenna. The passive DAS design would adhere to the restriction on where and how to install the thick coax cable in the house. A comprehensive site assessment of the building was needed to ensure there were cable routes for all antennas.

Effective DAS has the ability to dynamically compensate for the cable errors which interconnect the network modules using internal correction signals and amplifiers. What distance does not matter between the antenna and the base station, all antennas in an active DAS will have the same performance (same noise number and downlink power). Active DAS consists of a master unit (MU) of up to 6 km of optical fiber connected to various expansion units (EUs). Through EU in effect connects to several remote units (RU) via a thin coax or CAT5 cable up to 400 m in length. The MU supervises and monitors the DAS production. The EUs scatter throughout the field, and the RUs are located near the antenna. A participating wideband DAS will support multiple networks : GSM, PCS, UMTS, EVDO, WiMax and WiFi.

Because the coax cable and passive components malfunction and attenuate, passive DAS is only used by a small number of indoor antennas in smaller building covers to reduce its degrading impact on HSPA performance. Active DAS is used for larger buildings because there is no shortage of cable and sections and it can raise to the maximum the HSPA production. Passive DAS troubleshooting is difficult, and any system failure at the base station will not trigger a warning, since the computer does not detect errors.

Active DAS monitors all devices within the network and in the event of a malfunction; it sends an alert to the base station which allows the consumer to locate the issue source. Consequently, successful DAS is the preferred solution for large buildings with plenty of indoor antennae.