A Distributed Antenna System (DAS) includes the use of several antennas as opposed to one antenna to provide wireless coverage to the same area but with reduced total power and additional reliability. Often at times a DAS uses RF directional couplers and/or wireless amplifiers to split and amplify the wireless signal from the source out to the distributed antennas. In many cases a DAS will use a combination of low loss coaxial cabling as well as fiber optic cabling supporting radio over fiber (RoF) technology to distribute the wireless signals to the antennas. A Distributed Antenna System can be designed for use indoors or outdoors and can be used to provide wireless coverage to hotels, subways, airports, hospitals, businesses, roadway tunnels etc. The wireless services typically provided by a DAS include PCS, cellular, Wi-Fi, police, fire, and emergency services.
A wireless communication network employs a distributed antenna system to provide radio coverage. The wireless communication network comprises a plurality of access points providing service in respective coverage areas. The access point within each coverage area connects to a plurality of antennas that are widely distributed within the coverage area. Radio resources at antennas within the overlapping region of two or more neighboring coverage areas are shared by the access points in the neighboring coverage areas according to a multiple access scheme. The sharing of radio resources within the overlapping region of two or more coverage areas allows the overlapping region to be enlarged, thereby providing more time to complete a handover.
A distributed antenna system (DAS) or a distributed radio system (DRS) generally refers to a radio-access architecture comprising a large number of antennas distributed widely across a large coverage area and connected to a centralized Access Point (AP). The radiation coverage of each antenna typically has a much smaller footprint than that of a base-centrally-located antenna/base station in a conventional cellular system. The DAS architecture has two main advantages.
First, it is possible to achieve high spatial re-use capacity due to the small coverage area of each antenna.
Second, the centralized access point has complete control of all the radio resources used at each antenna and can therefore coordinate the transmission and reception of signals to minimize interference in an increased system capacity.
A DAS installation consists of a network of separately installed antenna nodes that are connected to a common source through fiber or coaxial cable. Splitting transmitted power among several antenna elements to cover the same area as a single antenna reduces the total power required and increases the reliability of the signal.
Typically, the antennas in a DAS are connected to the AP through optical fibers. The AP may process the received (uplink) signals from multiple devices using appropriate combining techniques, such as maximum ratio combing (MRC) or interference rejection combining (IRC). On the downlink, the AP may transmit to multiple devices using zero forcing or dirty paper-coding to suppress interference if the forward link channel is known. The AP may also use macro diversity techniques to direct radiation to specific mobile devices if the channel is not known.