DAS(DISTRIBUTED ANTENNAS SYSTEM)
2022-09-24
Distributed antenna system (DAS) is a mobile communication network composed of multiple antenna nodes separated from each other in a predetermined space or building and connected to a variety of signal sources through a variety of signal transmission media. Distributed antenna system can be deployed indoor (iDAS) or outdoor (oDAS), and customized and upgraded according to the needs.
Passive DAS: Mainly used in small buildings and space.
Only coaxial cable is used to transmit RF signal from base station or repeater to antenna. The electronic components used include: combiner, attenuator, dummy load, circulator, filter and coupler.
Advantages: Intuitive design; high compatibility of electronic components; can withstand harsh environment.
Disadvantages: Time consuming design, complex deployment and difficult upgrade; no network real-time monitoring and early warning system (problems need on-site investigation) and VSWR alarm; coaxial cable may have passive intermodulation (PIM) which may lead to signal to interference; serious signal loss; difficult to balance the link budget of each antenna; high power base station (signal to power) is required.
Active DAS: Mainly used in medium to large project design
(the distance between EU-RU can be up to 250m, and the distance from the main control to the antenna can be up to 5km or more). It is composed of master unit / MU, expansion unit / EU, remote unit / RU and antenna array. The main controller is the brain of the whole DAS, which connects the low-power base station and distributes the signal to EU through optical fiber; EU divides the optical signal of MU into up link (UL) and down link (DL), and converts it into electrical signal, which is sent to the RU of UL and DL respectively through network cable connection; the Ru of DL converts the electrical signal into radio frequency signal, which is sent to the antenna through coaxial cable jumper, and the Ru of UL receives the UL signal of antenna and converts it into electrical signal The signal is sent to the EU.