Active Distributed Antenna Systems inside 3G
A DAS contains the same active components present in a DAS passive, with the addition of active devices such as amplifiers, repeaters or amplifiers bidirectional (BDAS) to amplify and / or radio signals shipping. This enables an active DAS to cover a much larger area of a passive DAS. Active distribution systems, however, are more complicated and have more problems of distortion and inter modulation.
They can also fluctuate if used excessive gain. Balance connection remains critical, although the use of active components variable gain can make it easier to adjust the balance link and output power. An active DAS system can also have a system of fiber optic distribution. Distribution networks in fiber does not only apply to internal systems, but have also been incorporated into repeaters and directly into the cells. They work well as DAS for large coverage areas for indoor and remote deployment. RF signal on a fiber can be transported for tens of kilometers converting the RF of light on the fiber and again to RF radiation for using a local
A long feed results in the long propagation delays that may need to be represented. A large delay could affect the processing functions related to the timing and control of power. The fiber optic system has an interface that converts the RF signal to the light. The light is transported over an optical cable through a number of connectors and optical splitters, finally reaching the remote unit with a photo detector. The light wave is then converted to an RF signal radiated from the nodes and internal antenna.
The system usually has an AGC to compensate for any loss of optical transmission, resulting in virtually no loss of power of the RF signal on the Downlink and Uplink at the two ends. The installation of fiber optic transmission lines and their hardware support is generally more expensive than a coaxial cable or other transmission lines. Usually, the optical distribution systems are purchased in a package that includes distribution centers and antenna nodes from the same vendor to ensure interoperability. Fiber hubs combine multiple Node B signals, bandwidth usage figuring and occult RF and optical signals before and after deployment.
The most important characteristics for the fiber are the noise and dynamic range. The laser diode and photodiode receivers contribute to noise and limited dynamic range. Optical transmission usually operates at wavelengths in the range of 1550 nm and uses fiber single-mode. Single-mode fiber cables have a loss less than one meter and the increased bandwidth, and can carry signals over many kilometers. Multimode fibers are used for shorter runs of about 100 m.