Supercells to the Rescue?


Why Active DAS Hybrids Work for SMB/SMEs —

With the increasing use of and reliance upon mobile phones, meeting skyrocketing cellular demands of consumers and businesses continues to challenge network operators. In most populated areas, base stations have been deployed to provide a broad coverage layer, but densely populated and indoor locations can still suffer from insufficient coverage and/or capacity.

DAS (Distributed Antenna Solutions) can be deployed in the enterprise as a reliable and time-tested solution to address coverage issues. However, as DAS typically comes with a significant upfront CapEx, regardless of venue size, historically the implementation has been subsidized by carriers primarily for large scale facilities: airports, stadiums, campuses, etc. DAS systems are complex and require highly trained RF specialists to install, and carriers do not see sufficient ROI for the CapEx investment at venues under 500,000 sq. ft. For these reasons, DAS has not been widely used in small and medium enterprises.

For these smaller enterprise venues, the other option to add capacity and coverage has been indoor small cells. Unfortunately, the promise made to enterprise users is that they can simply order 1-3 small cells from a carrier, unbox and plug them into the Internet, and start calling. In reality, small cells have been severely hampered by user-experience problems, interference issues, and availability.

A New Option
According to the US Energy Information Administration, there are 1.5 million commercial buildings in the US that are 10,000 to 200,000 sq. ft. What is needed for this in-building wireless (IBW) market segment is a solution with the power and capability of DAS, combined with the user simplicity and ease of installation of small cells promised to enterprise subscribers by the major carriers.

While a variety of IBW hybrid solutions have been introduced, the Active DAS Hybrid technology this article addresses is designed specifically to meet this challenge: SME in-building densification on a massive scale, at a cost that will fit most enterprise budgets.

To accomplish this, the ideal active DAS hybrid:
• Has inherently smart architecture, designed to make a qualified installer’s job easier with intelligent self-configuration and self-optimization.
• Self-adjusts and self-adapts to changes in the environment or network, always maximizing performance after installed. This reduces maintenance costs and alleviates the manpower demands of maintaining a traditional active DAS.
• Utilizes Cat5e (or better) Ethernet cable, eliminating the need for costly fiber installation or complex RF engineering and design. Many commercial buildings are already plumbed with this cabling, further reducing installation costs.
• Has a digital architecture to eliminate attenuation between the head end and remote units so there is maximum possible signal strength at the access points for users.
• Takes advantage of RF over Ethernet (RFoE) and Power over Ethernet (PoE) for greater flexibility to meet the unique coverage needs of each unique venue structure.
• Is designed with operator involvement to ensure it is unconditionally network safe with none of the network interference problems associated with other types of systems, like common bi-directional amplifiers, repeaters, or even traditional DAS.
• Is manageable by both the enterprise and the carrier, to facilitate easy updates, configuration, and support.

The combined capabilities of active DAS and digital architecture eliminates problems associated with other indoor cellular coverage technologies, and offers the following advantages:
• Much higher gain without overloading the network with amplified noise (capacity-killing interference).
• Larger coverage footprint per server antenna.
• While site surveys are recommended, highly sophisticated design tools that are used in typical DAS installations, are not required.
• Dynamically tunes to operator network frequencies.
• Makes the network more efficient (a better signal means the same amount of data may be transmitted in less time with less energy, freeing up network resources for other users).
• System management options available for enterprises that want to implement alarms and alerts.
• Programmable and scalable, future proofing the system for expansion without re-engineering.

Benefits for Small and Medium Enterprises
As remote units in an Active DAS Hybrid are powered antennas (thus the “active” in “Active DAS Hybrid”), they have full transmit power available with no coaxial distribution power loss. This provides stronger cellular signal for end users to carry out mission-critical and business operations on their cellular devices.

The head end and remote unit may be separated by up to 200 meters in an Active DAS Hybrid system, without concern or calculation for power loss from coax-based attenuation, allowing for placement where the coverage is needed the most, regardless of building construction obstacles like elevator shafts, metal walls, or enclosed spaces. Using Cat5e (or better) cabling to connect the head end with up to 4 remote units, the entire system is powered via Ethernet (PoE) from a single power supply at the head end. This means the remote units can be mounted anywhere without the need to install additional AC outlets.

An off-air configuration uses capacity from the operator’s existing macro network, extending it indoors where it is needed. This can be the fastest and easiest way to provide indoor coverage, not requiring any fixed backhaul (small cell or femto), contracts, or lengthy permit processes. If the system head end is equipped with internal antennas, these can be utilized to capture the off-air signal, or it can be connected to an external antenna. Using a high-gain external directional donor antenna can also be a good way to improve signal quality. In an off-air system, quality of the donor signal provided to the system is perhaps the most important factor in the resulting performance.

Another advantage of the off-air configuration is that remote units need to be placed only where coverage problems exist in the building. In this configuration, the existing macro signal is being boosted only where it is lacking, and a handset simply sees a better macro signal everywhere.

Creative Configurations
In larger or more densely populated spaces, ideally an Active DAS Hybrid system can be tethered to a carrier’s small cell as the donor signal source to add capacity. Cel-Fi QUATRA is an Active DAS Hybrid that can be tethered to a small cell, creating a Supercell™. This Supercell is a large single cell rather than multiple small cells that provides uniform access to the capacity delivered by the small cell. Supercells are inherently uncomplicated from a planning and deployment point of view, and are far more resilient to the potential of interference. This method facilitates a uniform signal distribution in middleprise venues such as healthcare, hospitality, commercial enterprise, real estate, transportation, and industrial.

While waiting for a small cell to be delivered, an enterprise should be able to install the Active DAS Hybrid off-air for immediate extension of cellular coverage, and then simply connect it to the small cell, when that is installed, to add capacity.

Supercells to the Rescue?
Larger or more densely populated installation sites can often benefit from the network capacity delivered by a dedicated small cell. The Supercell configuration has 3 key advantages over a small cell installed alone. These are:
Key Advantage #1 — Small cell dominance.
Key Advantage #2 — Elimination of problems related to potential multiple small cell interference.
Key Advantage #3 — Reduced small cell overhead and OpEx resource requirements (fewer small cells required for the space).

The signal dominance of the Supercell benefits the operator (and the enterprise) by:
1. The installation delivers enough signal dominance (power) over the outside macro network so in-building calls stay on the in-building small cell where they belong.
2. The local small cell also off-loads local traffic from the macro network, freeing up capacity for other macro network subscribers.
3. If the site suffers from network interference problems, such as pilot pollution in a high-rise building where too many macro cell sites are visible and interfering with one another, the Supercell configuration can overcome the interference signal energy that is present.

As a typical example, a building suffers from a lack of signal at its interior, while the perimeter areas of
the building are being adequately served by competing macro cells.

If a small cell is installed in the center of the building, its signal power falls off as callers get closer to the perimeter. This results in service being handed-off to the outdoor network, which defeats the purpose of adding small cell capacity.

The Supercell distributes local capacity in a more uniform fashion, through the Remote Unit. The result is that more areas are covered, and power density (small cell dominance) is improved at the building perimeter.

In this case, the result is a 14-dB improvement for the perimeter offices, plus better coverage throughout the venue. This helps to ensure that local cell phones will be properly served by the local system, and that the macro network will be properly off-loaded as the operator intends.

Like macro network cells, small cells may interfere with each other where their signals overlap, causing reduced performance. The Supercell configuration resolves this problem by creating a single composite cell and eliminating the handoff regions that exist between multiple small cells.

A BIG Solution
Small cells come with the recommendation to have their own high bandwidth backhaul to connect to the operator’s gateway/core network. Therefore, additional small cells may result in an increase in cumulative backhaul requirements and OpEx that must be considered in the total cost of ownership (TCO). Some enterprises will have plenty of bandwidth overhead and can draw from that with small cells. Others will need to increase bandwidth, which comes at a cost. Each small cell has guidance on the bandwidth consumption, so the enterprise can easily determine if its current bandwidth is sufficient.

The industry has struggled to provide affordable cellular coverage solutions to small- and medium-sized businesses — until now. Existing consumer-grade solutions have been limited in performance, while active DAS has been too complex and costly. Active DAS Hybrid systems are flexible and can be scaled to the unique needs of each venue.


About Author

Joe Schmelzer is Senior Director of Products at Nextivity. He has developed a variety of products and industrial devices for chipset vendors, OEMs, and service providers, including products for Sony, Qualcomm, Google, Verizon Wireless, AT&T, Dell, and HP. He enjoys speaking opportunities and writing. For more information, please email or visit

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