With old technology, each of those services would have required its own cabinet and batteries in every location where Sprint needed them, said Joe Meyer, Sprint's vice president of network service management.
"In many cases, you're not going to have the space ... to add more units," Meyer said as he showed off the old and new gear. "We've only been allowed, probably, to use this space here, as it is. So if we had to keep growing this, there'd be no place to go without renegotiating with the landlord."
Network Vision is a huge undertaking for Sprint, announced in 2010 and estimated to cost more than US$4 billion. Sprint expects the work to be largely done by the end of this year. The upgraded network uses equipment from three different vendors, including Ericsson, Alcatel Lucent and, in this region, Samsung.
In addition to saving space and power, the Network Vision architecture actually extends the range of each cell by about 15 percent, Meyer said. That means Sprint subscribers can spend less time roaming on other carriers' networks.
"They won't realize they're roaming, but we have to pay that carrier for every minute that they're using," Meyer said. "We're reducing our roaming costs by millions of dollars by just expanding our footprint."
Part of the performance gain comes from the rest of the equipment up on the roof. In addition to the base station, each cell site has radios and antennas. In the past, the radios have been inside the base station cabinet and linked to the antennas over coaxial cable. Whenever analog signals have to travel from antenna to a radio, part of the signal is lost, and coming down from a full-size cell tower, that can be a big loss. At Sprint's new cell sites, like the one in San Francisco, the radios are smaller and can be mounted right below the antennas. The links from the radios to the base stations are fiber carrying digital bits, with no loss.
Sprint also now uses fiber for the backhaul out of its new base stations to the wired network, which in this case is provided by AT&T, the local incumbent wireline carrier. The fiber carries Ethernet at between 100Mbps (bits per second), many times faster than the former 1.5Mbps leased lines, and is more economical, Meyer said. Where needed, the Ethernet can be turned up to 1Gbps, Samsung engineers said.
Though Network Vision helps with space and other issues, setting up cell sites is still hard work. Getting permission to build under local zoning laws is a challenge, as well as doing the civil engineering to get the gear set up on roofs and towers. And each market has its own issues.
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