Sorts Of Signal Distribution Technology

There are four primary sorts of signal distribution technology: active, passive, hybrid and digital.

FREMONT, CA: According to the setup of the DAS, it's possible to mix and match the different signal sources in a single venue. For instance, one might use a small cell signal source for one carrier and bring the remainder of the airlines from an off-air donor antenna.

Signal Distribution Technologies

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Whichever signal source a system utilizes, a DAS needs to amplify, distribute and rebroadcast it using the building. There are four primary sorts of signal distribution technology: active, passive, hybrid and digital.

Passive DAS

A passive DAS employs passive RF components like coaxial cable, splitters, taps, and couplers to dispense signals inside a building. The distance the antenna is from the signal source, and any amplifiers, the further attenuation (loss) will be in the power broadcast with that antenna. Therefore, designing a passive DAS correctly requires calculating precise link budgets to ensure the outputted power at each antenna is equal.

Wilson Electronics and SureCall are the vendors most commonly associated with passive DAS systems. Still, passive DAS equipment is also provided by more traditional vendors like Commscope, SOLiD, and ADRF.

ADVANTAGES

• Low cost because no analog-to-digital converters are not necessary

• Simplified maintenance

• No extra equipment is required to support many carriers

DISADVANTAGES

• Long runs of cable are more challenging to achieve due to signal attenuation

• Plenum-rated coaxial cable, if necessary, can be expensive

• Needs precise link budget calculations to ensure optimal performance

Passive DAS deployments are usually more straightforward than other distributed antenna systems, which our customers appreciate. However, performance limitations often mean we recommend active or hybrid DAS systems for medium-sized & larger buildings.

Active DAS

An Active DAS transmutes the radio frequency transmissions from the signal source signal to distribute them via an optical or ethernet cable. A "master unit" combines the signals from several carriers and performs this conversion. Active DAS systems too "digitize" this signal which adds cost but enhances performance. Once changed, an Active DAS transmits the digital signal above fiber optic ("Fiber DAS") or ethernet cables to remote radio units (RRUs) that transform the signal back to an RF signal. These RRUs are sometimes called "nodes" or even "active antennas," depending on the vendor and the system's architecture.

Unlike their Passive DAS counterparts, Active DAS deployments minimize the coaxial cable used to distribute the signal. Sometimes, there is no coaxial; this is called a "fiber to the antenna" or "fiber to the node" system.

Corning, SOLiD, Commscope, Comba Telecom, and ADRF all provide versions of active and fiber DAS systems.

STRENGTHS

• Ethernet(fiber optic) cable can be shared with WiFi or public safety infrastructure (commonly complex in reality)

• Easily expandable

• No limits to the lengths of cable runs

WEAKNESSES

• Considerably more costly than passive or hybrid systems

• Remote units are more expensive and need a dedicated power

Hybrid DAS

A hybrid DAS combines the features of passive and active systems. However, the RRUs differ from the antennas, allowing the system to use fiber optic and coaxial cables to dispense the signal throughout a building. Because this configuration needs fewer RRUs, a hybrid DAS typically costs less than an active DAS.

A regular hybrid DAS configuration includes an RRU on each floor that converts from the digital signal to analog RF. The analog RF signal is connected to multiple antennas on that floor with a coaxial cable.

The same active DAS vendors (Corning, SOLiD, Commscope, Comba Telecom, and ADRF) all offer hybrid DAS options, usually at a lower cost than their "fiber to the antenna/node" solutions.

Cel-Fi also markets its QUATRA product line as a hybrid system due to its cost savings, even though the system is more similar to an Active DAS in some ways.

STRENGTHS

• Cheaper than Active DAS systems

• Limitless to the length of cables in the digital backbone

WEAKNESSES

• More expensive than a passive system

• Requires link budgeting on each floor

• More complicated to install as it needs both fiber and coaxes

Digital DAS

A Digital DAS converts every carrier's signal to zeros and ones before combining them and transmitting them over fiber optic or ethernet cable. Unfortunately, this conversion and combination process is computationally expensive, which makes digital DAS systems considerably more expensive than their analog counterparts.

One of the major benefits of deploying a Digital DAS is that they are much less sensitive to interference and hence more performant. A second gain is that Digital DAS platforms enable the capacity of the signal sources to be directed to distinct areas of a venue. This is particularly important when the power of a building shifts dynamically – think, for example, of a large cafeteria or event space in a school, university, or office space.

Suppose the signal source and Digital DAS platform support the "Common Public Radio Interface" (CPRI) specification. In that case, a signal source's Baseband Unit (BBU) can communicate directly with the DAS master unit and through to the remote teams without any conversion to an analog RF signal.

Corning, Commscope, ADRF, and SOLiD all provide Digital DAS platforms.

STRENGTHS

• Less noise, and hence higher performance

• Capacity steering through software-controlled sectorization

WEAKNESSES

• Much more pricey than non-digital systems

• Minimum real-world benefit in most buildings

Putting it all together

Twelve possible DAS configurations have three different signal sources and four different distribution systems. In practice, still, there are far fewer. Here is an overview of the most general configurations and the applications for which they are best suited.