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Application Guide

Distributed Antenna Systems (DAS)

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DAS Overview

Outdoor wireless licensed RF signals (600 MHz to 2700 MHz) does not travel well from outdoors through building materials like low-E glass, concrete and steel as they attempt to move indoors. Poor performance can also be caused by increased numbers of users and the data they consume. To improve indoor coverage, ensure that signals reach people and devices inside, and increase capacity, the wireless outdoor signal needs to be conditioned, filtered and combined with other carrier signals through a distributed antenna system (DAS).   Note: retransmitting a signal from an existing macro site will not increase capacity.  That is only accomplished by adding an additional BTS sector.  A repeated signal will however allow users to access existing capacity (if the serving sector has ample remaining capacity).

A distributed antenna system allows cellular signal to propagate in a building. You may be asking yourself how does it work? Is a DAS the right technology for the future? These are common questions that will be discussed. The goal of this application guide is to give you an understanding where Belden products fit into today's and tomorrow's DAS, how we can support our organic growth goals and keep Belden in the vanguard of technology.

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Technology

DAS technology was originally developed as a two-way radio communication system using radiating cable within tunnels, mines and subways. Today, in addition to two-way radio communications, DAS is also used in emergency response systems and in areas needing licensed wireless access (hotels, casinos, arenas, airports, etc.) due to high densities of people and high bandwidth levels. With the emergence of 5G, DAS is also a viable solution to bring those licensed network signals indoors.

A DAS uses fiber, coax cable and antennae to distribute signals inside a building either from a donor antenna or a direct connection to the carrier network via a base transceiver station (BTS). Each floor of a building is equipped with a remote unit (RU) that is fed from the DAS Head End Unit (HEU) with fiber optic cabling. The RU converts the light source back to an RF signal (600 MHz to 2700 MHz) and is connected to several passive antennae through low-loss coaxial cable. The DAS provides two-way wireless communication between the carrier and users. This approach enables owners to extend licensed networks inside their buildings. To better understand this system, each part of a DAS will be discussed.

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Donor Antenna

One way the licensed signal is brought into the building is via a connection with a nearby cellular tower. An off-air (repeater) DAS system uses a donor antenna to bring wireless signals into a building. This approach does not improve capacity – it only improves coverage. (In other words, it doesn’t allow more people to connect). This method is used about 5% of the time.

donor-antenna-diagram

Base Transceiver System

The other way the licensed signal is brought into the building is to directly connect to the carrier’s core network using base transceiver station (BTS) – much like a cell tower’s base station. Each carrier requires a fiber backhaul connection to the BTS, typically through an S1 link (S1 link is responsible for delivering user data between the BTS and carrier network). This method is used most of the time as it improves capacity and coverage.

BAS-system-diagram

Head End Unit

The Head End Unit (HEU) is the modular rack unit(s) that houses the Point of Interface (POI), Master Unit (MU), Repeater(s) and Power. The POI conditions the incoming signal from each licensed carrier either from the BTS or Donor Antenna. Each carrier is combined in the MU into one optical signal for transmission on single mode fiber (SMF). Up to six carriers can be combined onto one SMF. DAS MUs are typically powered locally either by AC or DC power sources. Cabling out of the MU can be SMF, New Gen, hybrid fiber, DETM or any combination of each.

head-end-unit-diagram

Remote Unit

The RU converts the optical signal to radio frequencies (RF) in the licensed bands between 600MHz and 2700MHz (and vice versa). The remote unit is fed from the MU through SMF and typically powered by either by AC or DC or Digital ElectricityTM (DETM) power sources. The output is a 4.3/10 DIN interface connector attached to an air dielectric coaxial cable which connects to the antennae throughout the building.

remote-unit-diagram

Passive Antenna

The antenna is a passive antenna that wirelessly connects all carriers to the user. The output is a 4.3/10 DIN connector which is a connector type that is known to have good electrical performance including low passive intermodulation distortion.

passive-antenna-diagram

Challenges

Remote units must be powered. Local power (120VAC) to the RU requires separation of power and data in pathways and spaces. Often, local codes also require 120VAC circuits to be enclosed in conduit. Belden offers cabling to deliver remote power and data to each RU through hybrid cabling (fiber and copper conductors) or Digital ElectricityTM cabling (fiber with copper conductors or copper conductors only). Hybrid and DETM cabling does not require separation of power and data, and can be installed with low voltage installers.

Upgrading can be a concern. As new technology becomes available, the replacement or modification of equipment may be necessary.

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Future

When fiber connects the DAS headend back to the core network, that licensed network can be extended inside the building however the owner prefers. BTS technology will continue to evolve as 3rd Generation Partnership Project (3GPP) standards evolve (3GPP provides with a stable environment for reports and specifications that define mobile wireless technologies).

Most wireless devices today connect using LTE standards and speeds. As LTE standards evolve to LTE Advanced and LTE Advanced Pro, 1 Gb/s connections will soon be possible, meeting requirements set forth by the 5G initiative for user experience data rates. 3GPP is expected to combine LTE Advanced Pro with 5G NR frequency bands to bring the 5G initiative full circle. A well-designed DAS will support 5G as it becomes more realistic. By putting a DAS in place now, building owners will be ready to deliver 5G performance when the time is right, whether they choose to deploy the 5G NR frequency band or LTE Advanced Pro frequency band – or a combination of the two, depending on what their users and devices need.

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The Partnership between JMA and Belden

The partnership between JMA Wireless and Belden pairs JMA’s next-generation communications hardware with Belden’s reliable connectivity. The result: DAS solutions supported by high-performance infrastructure to keep everyone and everything connected. This union helps smart buildings prepare for the future of wireless and 5G, supporting ultra-high speeds and greater capacity than ever before. We’re transforming wireless networking to support organizations as they plan their converged infrastructure and prepare for 5G performance.

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