By combining microwave backhaul systems with intelligent routing, a rural wireless GSM and WiMax operator expects to save millions in operating expenses by eliminating the 150 leased T1 lines that it uses to connect its cell sites.
"We have the opportunity to stop our op-ex from growing and actually reduce it, so I think it's a smart business decision, and we're making our network more resilient," said Jake Brown, CTO of Hilbert Communications, a Green Bay, Wis.-based wireless operator that offers roaming network services throughout Wisconsin for about 30 carriers. "We're able to completely get rid of the incremental cost to upgrade to 3G."
Hilbert launched the microwave backhaul project -- playfully dubbed "Operation Badger Sky" as a nod to the University of Wisconsin-Madison mascot, the badger -- when it became evident that an all-T1 network could not support a transition from 2G to 3G and 4G, according to director of network design Kevin Kluge.
Hilbert's 2G network had typically required just one T1 line to each cell site, usually costing between $800 and $1,200 each month, Brown said. The total annual expense was $1.5 million last year.
Just upgrading to 3G would require eight leased T1 lines at each site, he said. Multiplied by about 200 cell sites, the math did not make for a pretty financial picture, so the rural wireless operator started vetting microwave backhaul options.
"With the growth of the network, we saw that there was going to be a need to make a change to the backhaul plan somehow to get the sites combined," Kluge said. "Once we started doing that, we saw there was an absolute need to terminate T1s from our network completely."
Intelligent routing and microwave backhaul create redundancy
As part of the ongoing project, Hilbert, which calls its wireless business Bug Tussel LLC -- a reference to the hometown of The Beverly Hillbillies, Bugtussle, Ark. -- built its microwave hops and backhaul links across Wisconsin using a mix of licensed and unlicensed spectrum from Appleton to the western part of the state near the Minnesota border, Kluge said.
Using microwave backhaul systems almost exclusively from Exalt Communications for the past two years, the operator is extending its fiber optic DWDM backbone that runs across the upper Midwest, he said. Radios on its edge tuned to unlicensed spectrum hop onto backhaul links with radios using licensed spectrum.
The systems carry the equivalent of four T1 lines of GSM voice traffic and from 10 to 50 Mbps of Ethernet as far as 20 miles, according to Exalt. The systems will support IP-based traffic for Hilbert as the operator works on its WiMax network, Brown said.
So far, Hilbert expects to shut down 60 leased T1 lines with its microwave backhaul plan.
"We put routers at each [backhaul link] so we can do intelligent routing [to the core]," Brown said. "We typically try to have two points on our fiber network so we can get back into fiber."
"Since there are multiple paths to get back into our aggregator, if we lose a microwave hop, it'll automatically route another direction," he added. "We're getting rid of our T1s, we're increasing our IP capacity and we're also helping our network be more resilient for outages. Not only do we reduce our cap-ex … but we also enable our towers [to eventually migrate to] WiMax."
Making the most out of unlicensed spectrum with microwave backhaul
Unlicensed spectrum is a narrow band between 5.2 GHz and 5.4 GHz, and those blocks have power limitations, Kluge said. The spectrum around 5.8 GHz offers better power output, but Hilbert isn't the only one aware of this, he added. This becomes a problem because the rural wireless operator collocates on 90% of its towers.
"Anybody can use that frequency, so you kind of have to play nice," Brown said.
Other microwave backhaul systems Hilbert has tried didn't have strong fine-tuning capabilities to avoid interference on unlicensed spectrum, both Kluge and Brown said. Exalt has given them more flexibility, they said, making the move to microwave backhaul more successful.
"Technicians go out there and put the microwave up, and they have to pick the channel. But if there's a lot of noise out there, you really have to squeeze in," Brown said. "What we've found with other microwave vendors is they give you a canned or preset frequency, but what we find with Exalt is they give you every tool or widget you can use to tune in."
Exalt's unlicensed spectrum radios offer 1 MHz resolution and use time-division duplexing (TDD), which give an asymmetrical transmission "so you can have more traffic going one way or the other," said Exalt president and CEO Amir Zoufonoun.
The system also allows operators to change the polarization from vertical to horizontal, which in turn allows radios to coexist "on the same link, on the same tower, on the same building and on the same frequency or a very close frequency," Zoufonoun said.
"When you're setting up a wireless network, one issue is spectrum management," he said. "This gives the operator tremendous flexibility in setting up networks."
Let us know what you think about the story; email: Jessica Scarpati, News Writer