Concept
Distributed Antenna System (orDAS) is a predetermined space or building with multiple spatially separated antenna nodes connected through multiple signal transmission media A mobile communication network formed by multiple signal sources. The distributed antenna system can be deployed indoors (iDAS) or outdoor (oDAS), and customized and upgraded according to requirements.
Modules
DAS is roughly divided into three modules: signal source, transmission medium, and antenna.
1. Signal source: The signal source of mobile communication can be borrowed through Nearby base station resources, Indoor dedicated base station, Baseband-Unit (BBU )+Remote-Radio-Head(RRH)
2. Transmission media: coaxial cable, optical cable, LAN
3. Antenna: directional antenna, omnidirectional antenna , Horizontal plane antenna, MIMO antenna, gain antenna
Types and solutions
DAS is divided into indoor (iDAS) and outdoor (oDAS)Two solutions. Each solution is subdivided into three types: passive distribution, active distribution, and mixed distribution. Based on project requirements (environment, signal source type, budget, etc.), you can choose the corresponding solution to maximize the coverage and performance of the DAS.
Indoor: Mainly suitable for buildings with no or weak mobile signal coverage. Including that although users are within the coverage of mobile signals, they cannot use the mobile network (using phone calls, text messages, and surfing the Internet) due to the limitations of network capacity.
Outdoor: Mainly suitable for densely populated areas (ancient towns, scenic spots) where signal towers cannot be built, and areas that require centralized network management and real-time monitoring (government agencies, colleges, etc.) And industrial bases, etc.).
Passive DAS(PassiveDAS): Mainly used in small buildings and spaces. Only use coaxial cables to transmit radio frequency signals from the base station or repeater to the antenna. The electronic components used include: splitter, combiner, attenuator, dummy load, circulator, filter, coupler.
Advantages: intuitive design; high compatibility of electronic components; can withstand harsh environments.
Disadvantages: Time-consuming design, complicated deployment, and difficult to upgrade; no real-time network monitoring and early warning system (problems need on-site investigation) and voltage standing wave ratio alarm; coaxial cable has Passive intermodulation (PIM) may occur and cause signal-to-interference; signal loss is severe; it is difficult to balance the link budget of each antenna; high-power base stations (signal sources) are required.
Active distribution(ActiveDAS): Mainly used in the design of medium to large-scale projects (EU-RU distance can reach 250m, main control to antenna can Up to 5km or more). It is composed of a master controller (MasterUnit/MU), an expansion unit (ExpansionUnit/EU), a remote terminal unit (RemoteUnit/RU), and an antenna array. The main controller is the brain of the entire DAS. It connects low-power base stations and uses optical fiber to distribute signals to EU; EU divides the optical signal of MU into uplink (UL) and downlink (DL), and converts them into electrical signals to connect with network cables They are sent to UL and DL RUs respectively; DL RU converts electrical signals into radio frequency signals and sends them to the antenna through a coaxial cable jumper. At the same time, UL RU receives the UL signal from the antenna and converts it into electrical signals and sends it to EU.
Hybrid distribution (HybridDAS): It consists of a main controller (MU) and a hybrid remote terminal unit (HybridRemoteUnit/HRU). The main controller connects the low-power base station to use the optical fiber to distribute the signal to the HRU; the hybrid remote terminal unit integrates the functions of the EU and RU in the active distribution.
Application scenarios
With the popularization of the fifth-generation mobile communication technology (5G), 5G millimeter wave (mmWave) has low penetration in space transmission and is susceptible to interference. Therefore, the deployment requirements of DAS are gradually increasing.
Deploying DAS in office buildings, hospitals, schools, commercial centers, stadiums and other spaces can achieve high-speed, low-latency 5G network coverage and large-scale mobile device access capabilities, thereby providing 5G Internet of Things and remote Medical and other related services.
The increase in the penetration rate of mobile devices will lead to a shortage of electromagnetic spectrum resources, and the frequency available for mobile communications is not enough to support multiple mobile devices per capita accessing the network at the same time in the 5G era. DAS uses frequency reuse technology in a predetermined space to maximize the use of mobile communication frequencies, access more mobile devices, and provide high-quality networks.
Technical limitations
However, the selection of DAS technology and suppliers may be complicated, mainly because the building owner or enterprise needs to resend the Licensed frequency band. Even if the IT department has been running all services in-house before, they should consider cooperating with a supplier who specializes in installing DAS. Because different enterprise IT solutions will use different technologies, and we also need to consider the technology selection and cooperation methods between different operators in order to complete the signal retransmission of the authorized frequency band.