Detailed Introduction, Classification, and Installation of Indoor Distributed Antenna Systems

What is an Indoor Distributed Antenna System?

An Indoor Distributed Antenna System is a successful solution aimed at improving the mobile communication environment within buildings for indoor user groups; it typically utilizes 1/2 inch or 7/8 inch heliax RF cables, RF connectors, RF power splitters, directional couplers, and indoor antennas to evenly distribute the signal from the mobile base station to every corner of the indoor area, ensuring ideal signal coverage within indoor regions. 

The construction of an indoor coverage system can comprehensively improve call quality within buildings, increase mobile phone connection rates, and create high-quality indoor mobile communication areas. 

In terms of coverage: the lower floors of large buildings, underground malls, and underground parking lots have their signals blocked by the building structure; while on the higher floors of the building, signals from various base stations are received with equal strength, leading to "high-rise interference". Therefore, the construction of a distributed system is required to strengthen coverage. 

In terms of capacity: as the network evolves towards 4G/5G and the number of users gradually increases, the traffic and data load on outdoor macro base stations are nearing their limits, necessitating the construction of indoor distributed systems to share the load of outdoor macro base stations. 

Types of Indoor Distributed Antenna Systems

Indoor Distributed Antenna Systems can be categorized based on the types of components used as: Passive Distributed Systems, Active Distributed Systems, and Radiating Cable Distributed Systems, among others. 

Passive Indoor Distributed Systems (DAS) are composed of traditional signal sources (RRU), RF combiners, point-of-interface units, passive devices (couplers, splitters, etc.), feeder cable, and antennas. This system can provide limited support for 5G systems. 

With the continuous development of wireless technology, traditional indoor coverage solutions are increasingly inadequate for future data growth demands and are lacking in flexibility and scalability. Active distributed antenna systems have emerged to support the smooth evolution to 5G. 

Active Indoor Distributed Systems are composed of a BBU, RHUB, fiber optic cables, network cables, and pRRU. 

Radiating cable systems are used for narrow, band-shaped areas such as tunnels, corridors, mines, elevator shafts; and closed or semi-closed spaces like dense conference halls, underground malls, and underground parking lots, providing a linear coverage solution. This system is composed of traditional signal sources (RRU), POI combiners, passive devices (couplers, splitters, etc.), and radiating cables, and it supports 5G systems. 

Property management needs to cooperate by granting access to electrical conduits on each floor, informing of ceiling inspection ports and allowable drilling locations on each floor. It is generally recommended that feeder cables be laid in the electrical conduits if available. If no electrical conduits or usable space is available, threaded rods or universal angle iron can be used to fix the cables to the ceiling. Some space within the electrical conduit should be reserved for feeder cable routing. If no usable space is available, holes need to be drilled in the conduit floor to add routing paths.

Installation of Indoor Distributed Antenna Systems

Antenna Installation:

Indoor antenna/PRRU installation: The installation location of the antenna must meet the design requirements of the antenna points. Wall-mounted antennas must be firmly installed on the wall to ensure the antenna is vertically aligned and aesthetically pleasing without damaging the interior. If the ceiling is gypsum board or wood, the antenna can be installed inside the ceiling but must be fixed with an antenna bracket. If the ceiling is an enclosed aluminum buckle, to ensure coverage, the antenna needs to be exposed. 

External antenna installation: Antennas can be fixed or pole-mounted on parapet walls, and the coverage direction of the antenna should be unobstructed by buildings, within the lightning rod protection range. 

Property management needs to inform in advance of areas where installation or fixing is not allowed. For installation in elevator shafts, the property management needs to notify the elevator company to facilitate the construction. Whether antennas are installed inside or outside the ceiling should be evaluated based on on-site conditions. Antennas should preferably be installed within rooms. 

Passive Device Installation:

Install strictly according to the required positions in the design drawings, using cable ties and fixtures to secure devices, avoiding any floating, unsecured placements. Each device should be labeled with a number and the construction unit’s mark. Outdoor connections should be waterproofed. 

Device installation is similar to antenna installation. Property management needs to inform in advance of areas where installation or fixing is not allowed. For installation in elevator shafts, the property management needs to notify the elevator company in advance to facilitate the construction. 

Transmission Setup Installation:

Outdoor transmission laying: The three common methods for laying outdoor fiber cables are underground conduit laying (laying fiber cables in underground conduits), direct burial, and aerial laying (laying cables overhead from pole to pole). The method should be chosen based on project conditions, environmental characteristics, and cable type and quantity, while meeting the requirements for reliable operation, ease of maintenance, and technical-economic rationality. 

Indoor transmission laying: Indoor fiber cables should be laid along weak electric routes provided by the property owner, ensuring safety, stability, neatness, and aesthetics. During transmission support construction, the property must provide available conduit resources and weak electric routes in advance to facilitate the activation of equipment. 

Equipment Installation:

Signal source equipment is the signal source for distributed systems. Installation locations should be free from interference by high voltage, strong magnetic fields, and highly corrosive equipment. The location should allow easy access for debugging, maintenance, and cooling needs. The host equipment should ideally be installed indoors. For outdoor installations, waterproofing, and measures to protect from sun and damage are necessary. For indoor installations, no flammable items should be placed indoors; the indoor temperature and humidity should not exceed the normal operating range of the equipment. 

During the equipment installation, property management should provide suitable installation locations based on the required amount of equipment, typically in civil communication rooms, parking lots, and weak electric conduits and should provide corresponding power outlets for the equipment.