AT&T Deploys Network of Small Cells in San Francisco

Using C-RAN technology, AT&T plans to install 280 more cells this year in the Bay Area
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SAN FRANCISCO � Earlier in February AT&T unveiled its first operational small-cell wireless antenna in the nation, discreetly installed a lamppost on Battery Street in the Financial District. The company says it plans to install about 1,000 such cells across the Bay Area this year in an effort to meet the �ever-increasing demand� for mobile broadband while simultaneously laying the groundwork for future technology, according to the sfgate.com.

The cells, which house antennas in slim cylinders connected to power amplifiers, will be attached to lamp posts and telephone poles around the city. AT&T plans to install 280 more cells this year in San Francisco alone, enough to boost service for about 1 million customers, according to the same article.�

The new network of cells uses C-RAN (Centralized Radio Access Network) technology. Mike Wolfe, in a Commscope blog entry, talks about C-RAN. We�ll be hearing more about this so let�s take a look at how Mike defines it:

�In a traditional distributed cellular network, the RAN is the part of the network that we think of as a cell site, with equipment at the top and bottom of a cell tower. Its primary component is the base band unit, which is radio equipment that processes billions of bits of information an hour and links the end user to the core network.

�Until recently, the BBU was almost always located on-site near the bottom of the tower in some type of shelter or enclosure. The network operators had to lease the space, run power to every BBU and cool the equipment inside. Add it up and about two-thirds of a wireless network�s total cost of ownership is in operational costs such as site power and cooling.

�C-RAN provides a more elegant and efficient alternative. By leveraging fiber�s huge signal-carrying capacity for fronthaul, operators can centralize�multiple BBUs in one location, either at a cell site or at a centralized BBU pool location. Centralizing multiple BBUs simplifies the amount of equipment needed at each individual cell site and presents a host of other key advantages, such as lower latency.�

An interesting term was used in the quote above: �fronthaul.� Many of us are familiar with the term backhaul�so what does fronthaul mean in this context?� �In its simplest form, backhaul connects the mobile network to the wired network by backhauling traffic from geographically dispersed cell sites to Mobile Switching Telephone Offices (MTSOs),� Brian Lavallee writes in a blog entry from Ciena.�

�Fronthaul is associated with a new and different type of Radio Access Network (RAN) architecture consisting of centralized baseband controllers and standalone radio heads installed at remote cell sites located kilometers to tens of kilometers away. These BBU and RU functional blocks, as well as the equipment that performs these functions, are located further away from each other than in the mobile backhaul model.

�In the fronthaul model, the RU equipment is now referred to as a Remote Radio Head (RRH) but is still located at the cell site. The BBU is now relocated to centralized and protected location where it serves multiple RRHs. The optical links that interconnect the newly centralized BBU and the multiple RRHs is referred to as fronthaul.�

The bottom line is that the C-RAN model reduces a carrier�s operating expenses while providing improved service for the end user.��

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