Mobile operators have always thought of distributed antenna systems (DAS) as a niche product that is used to meet specific application needs in service area gaps in the outdoor network (tunnels, urban shadow areas, etc.). But as operators move to multi-frequency services that require much more bandwidth per user and signal strength is becoming critical, DAS is becoming a standard part of network architecture.

The shift is much like the migration to Digital Loop Carrier (DLC) systems in the wireline networks. For DLC, the tipping point was the rapid growth and need for distance-limited, high-speed data services. This need rendered the model of building C.O.s ineffective because it was simply too expensive and impractical to put COs in every neighborhood. DLC introduced the concept of moving the services closer to the user over a fiber infrastructure, allowing a rapid ramp in new customer adds while meeting the demand for high-speed data service growth.

Tony LeFebvreWith the adoption of the smartphone, wireless networks are facing the same tipping point. Carriers are faced with providing high-speed services which consume more of a limited spectral resource. Compounding this, the data needs are becoming more synchronous, requiring that the signal be delivered closer to the user equipment.

With a demand for much more bandwidth in the network, carriers must deploy more, smaller cells to increase the frequency re-use and reduce the number of users in a given cell. However, using large booming cell sites to do this is not effective given the constraints of data services, spectrum and zoning. While some carriers are looking at purpose-built microcells or picocells to provide the added capacity in the network, these solutions often lock that site into protocols, channel count and/or frequency, leaving little flexibility for network migration or changes in this rapidly changing environment. Advances in SDR allow for forward-looking changes to protocols, but they often are locked to specific suppliers and do not take into account legacy services. Thus, carriers get a solution set for their next-generation offering but are stranded with inefficient methods for their legacy services.

In addition, fulfilling service needs with microcells or picocells alone will require carriers to provide backhaul for tens of thousands of new cells, driving up operating costs, and those cells will have to be actively managed to avoid co-channel interference between cells. Mircocells, picocells and Remote Radio Heads do not offer the flexibility to accommodate a carrier's entire network, which consists of multiple frequencies, multiple protocols to serve and multiple BTS providers.

A much better approach is to use small cells and DAS architectures, which deliver maximum flexibility for existing and future services along with performance advantages over large cells. DAS systems split the network into signal processing and signal generation functionalities, allowing for optimizing the signal processing function in central locations and then feeding the signal over fiber to small cell sites. This split allows for small cell sites that blend into the environment while delivering the service in close proximity to the user, giving the performance needed for high-speed data over wireless. The fiber connection allows flexibility in allowing operators to house all their spectral assets at the cell site. DAS, which can be independent of protocol and channel, allows carriers to deliver and make changes to what services they offer over all their frequency assets. For example, GSM over 850 today can be LTE over 850 tomorrow without changing the remote cell site. This gives the carrier optimal flexibility.

Many DAS systems offer simulcast capabilities to further improve spectrum management and maximize use of network resources. Simulcast allows carriers to shape coverage and maximize capacity utilization. By delivering service within the clutter, DAS systems can deliver around obstructions with simulcast distributing that capacity over multiple antenna points. In addition, DAS systems that are digitally based allow carriers to make changes to this simulcast ratio through the EMS rather than with RF plumbing. Digital systems allow the ratio of capacity to antenna points to be determined remotely.

By maximizing capacity, carriers not only save on the signal generation equipment but also the backhaul, power and HVAC needs, leading to considerable CAPEX and OPEX savings. Digital simulcast along with the protocol flexibility allows network operators to make changes and optimize their wireless networks in the face of certain changes. With DAS, network operators have optimal flexibility in delivering high-speed wireless networks.

High-speed data is necessitating a change in how wireless networks are built. DAS offers a solution to provide small cells in close proximity to the users with optimal cost and flexibility. Much like the DLC in a wireline network, the DAS extends service out into neighborhoods over a fiber link, allowing carriers to centralize spectrum assets while bringing the signal closer to the end user.

Tony Lefebvre is Director, Product Management, Outdoor Wireless Products, at Tyco Electronics (TE).