Having just secured new spectrum in the 600 MHz bands, mobile operators will begin deploying services over these bands and it will be up to in-building wireless systems to support them.

The Spectrum Imperative

Driven by video and other high-bandwidth services, wireless subscribers are demanding more and more bandwidth. Wireless operators must add spectrum and densify their networks to deliver more bandwidth in more places. The indoor environment is especially a challenge, since roughly 80 percent of mobile connections originate indoors, and most buildings lack adequate indoor cellular coverage. In fact, 74 percent of U.S. office workers queried in a recent Zinwave survey complained that they either “frequently” or “sometimes” had problems with poor cellular coverage in the workplace.

Mobile operators are adopting new spectrum to address the capacity challenge, but it is up to enterprises and building owners to deploy indoor wireless systems to ensure strong and pervasive coverage for their workers. Distributed antenna systems are a primary means of solving the indoor coverage problem, but DAS products vary in their ability to support new frequencies as mobile operators add them to their spectrum arsenals.

Supporting Spectrum with Traditional DAS

DAS products distribute wireless signals from a signal source (a base station or small cell) to a series of remote amplifiers and antennas placed throughout a building. Every DAS has a headend where the wireless signals are connected, and a series of remote antennas. To support a new frequency such as 600 MHz, any DAS customer would have to add a new 600 MHz signal source to the headend.

But DAS products differ in how their infrastructure supports specific wireless frequencies, and the move to support the coming 600MHz bands can be expensive in a traditional DAS. Traditional DAS systems use frequency-specific narrowband amplifiers. They need one amplifier to support 700 MHz LTE, another for 1900 MHz, another for 2100 MHz AWS, and so on. Virtually all DAS deployments deliver multiple frequencies to a building’s interior, so every traditional DAS has multiple amplifiers, both at the headend (usually located in the telco or IT room) and at each remote site. Amplifiers are deployed in the headend chassis and in other remote chassis located in wiring closets throughout the building. 

To add a new frequency such as 600 MHz to a traditional DAS, the technician must add 600 MHz amplifier cards to both the headend and to each remote chassis it feeds. Each chassis has a limited number of slots (typically four to six), so the number of frequencies that can be supported is limited to the number of available slots.

If there are available slots in the headend and remote chassis for 600 MHz amplifier modules, then the upgrade entails the cost of the new hardware. This can run into several tens of thousands of dollars for a mid-sized building.

But if all the slots in the existing chassis are already taken, then the customer must deploy a whole additional layer of DAS equipment, including another headend, additional remote units and antennas, and the cabling to connect them.  Obviously, the net result of this could be a doubling of the cost of the DAS system.

Credit: Zinwave

Supporting Spectrum with a Wideband DAS

Wideband DAS products address the spectrum challenge differently. In a wideband DAS, the system uses a single wideband amplifier to handle a broad range of frequencies. In one example, the wideband DAS handles frequencies from 150 MHz to 2.7 GHz. Because the DAS supports this whole frequency range, any new frequency within that range is automatically supported without hardware upgrades, either at the headend or the remote.

To upgrade a wideband DAS to support 600 MHz, all that is necessary is to add a 600 MHz signal source at the DAS headend. Once this is done, the DAS has been upgraded. This approach saves the necessity of upgrading headend and remote amplifiers, and avoids the potential need to install a whole additional layer of DAS equipment in scenarios where all the available chassis slots are already in use.

Given the advent of 600 MHz frequencies in cellular networks, it is clear that those who use wideband DAS will be able to upgrade much more quickly and cost-effectively than those who use traditional DAS products. As we march toward 4.5G and 5G, mobile operators will be adding additional frequencies in the 3.5-6 GHz range. Wideband DAS makers are already working on supporting those frequencies as well.


John Spindler joined Zinwave as VP Marketing and Product Management in November 2015 and has over 30 years of product management and marketing experience in the wireless and telecommunications industries. His most recent role as Director of Product Management was with TE/CommScope, and prior to this as VP Marketing at ADC Telecommunications.