Making the Most of Microwave

Wireless carriers often cite backhaul difficulties as one of their biggest reliability problems. Some blame backhaul-related problems for 30% to 70% of network headaches.

Although carriers have transport options -- wireline or microwave radio -- microwave has become more widely used among cellular carriers as they grow networks and revenues. In fact, demand for microwave systems in the United States has grown from approximately $450 million in 1991 to an estimated $900 million in 1997, according to the Northern Business Information Group. The U.S. market will continue to grow 15% annually for the next few years, with much of the growth coming from the PCS industry. In the United States alone, PCS will generate about $3 billion in microwave radio business in the next few years.

Although analysts and vendors predict a surge in microwave backhaul, there are still many PCS carriers relying on wireline. According to spokesperson Ashley Pindell, Sprint PCS' first choice is fiber, followed by copper. Microwave is the third choice, depending on cost.

Mort Cohen, Harris manager of marketing development, said the PCS industry has leaned toward wireline because it started building out in urban areas where wireline is plentiful and relatively cheap. PCS hasn't needed much capacity so far. But as capacities increase in urban areas and carriers expand out into suburban and rural areas where there isn't as much wireline available, they will gravitate to microwave.

"Starting this year and next, we're going to see more microwave used for the PCS networks," Cohen said.

When used effectively, microwave offers a relatively fast, flexible and reliable transmission medium.

"There's a perception that microwave is not as reliable as wireline, but the truth is microwave is designed for at least 4-nines (99.99%) reliability," Cohen said. "In most cases, it's 99.995% reliable, which means 320 seconds of outage per year."

By contrast, copper lines offer 99.7% reliability, which translates to about 24 hours of outage per year. Fiber is designed to 99.999%, but vendors can design microwave for 5-nines availability.

According to Graham Barnes, Glenayre vice president of marketing, carriers can design a path that's 99.999% or even 99.9999% available.

"As far as equipment availability goes, we measure the mean time between failure based on units that come back for repair," he said. "It averages about one failure in 10 years for the average piece of equipment, or one of the radios in a certain link would only fail once in 10 years."

Microwave's flexibility allows carriers to own, operate and maintain their own infrastructure, which means you can design microwave to whatever level of reliability you're looking for. Jim Naumann, US Cellular director of network planning and purchasing, said this control is the biggest advantage of using microwave over leased lines.

"If it goes down, then we're in charge of fixing it," he explained. "If it's a cable cut or a circuit is down because of a telco problem, we have no control."

But getting high reliability depends on how you implement microwave backhaul.

"Generally, microwave's pretty reliable, but leased lines are more reliable in the larger metropolitan areas," Naumann said. "When you get out in the rural areas, it's less reliable, and if you have meet-point leased lines, where it goes through two or more companies, that's very unreliable."

Naumann said that microwave makes sense for US Cellular because it serves mostly rural areas.

According to Becky Holland, NEC radio communications systems division marketing and sales manager, microwave radio also becomes a more competitive option as carriers get higher capacity. She said the rule of thumb for microwave cost-effectiveness is multiple T1s.

"At three T1s, four T1s or above, it starts paying for itself," she said. "Microwave is a capital expenditure -- you purchase it, you own it. Leasing facilities is an ongoing expense."

Holland said carriers get what they pay for with microwave, including easy installation, no trenching and no installation costs or delays.

Microwave Choices As you move forward with microwave backhaul, you will face product decisions as well. Cohen said millimeter-wave radios are gaining market acceptance, and the lower-frequency larger radios only are being used where they are absolutely necessary for capacity reasons. A lot of backhaul now can be handled by the high-frequency, millimeter-wave radios that are 18GHz to 38GHz, which range in size from 2 feet in diameter to 15 inches deep to less than one square foot and 4 inches deep, he said.

Many carriers also are finding that spread-spectrum radios are a viable option. Wireless carriers formerly used spread-spectrum radios as an interim measure, putting them in to get a base station up quickly and then replacing them with either licensed microwave or wireline service. But times have changed. Barnes said spread-spectrum radios have worked so well that carriers haven't wanted to take them out.

"They're very cost- effective, and carriers are trusting higher and higher capacity to these networks," he said. "When we first started, you just got a single T1 on the radio. Now we're shipping 40 capacity and putting nodes and networks of these unlicensed radios together as the networks expand."

Barnes said spread-spectrum radios are not necessarily better than licensed radios, but there are advantages. You can get them up quickly because you don't need permission from the FCC. They're easy to install, and you get good distance. (With 2.4GHz, you can get 20 to 30 miles of coverage.) Spread-spectrum radios are less expensive and lower capacity -- one to four T1 in traffic -- but in cases where that's all the traffic you'll be covering, it's a viable alternative. According to Barnes, cellular carriers are buying spread-spectrum radios more than any other industry.

"There are more small sites than big sites, and generally when you build out networks, you don't put the high-capacity, expensive radios everywhere," he explained. "A single T1 to four T1 fits with a lot of these sites."

You also may want to use a combination of microwave and leased lines in some, if not all, of your backhaul systems. Through diversity, you can ensure that failures due to weather or cut lines will not put your entire network out of service.

Drew Caplan, vice president of telco engineering, said Nextel Communications uses a combination of digital microwave and wireline for backhaul.

Naumann said US Cellular used to employ 90% or 95% microwave, but in the past few years has added more leased lines. US Cellular employs diversity, with half microwave and half leased lines for backhaul.

"Diversity makes it more reliable so you don't have one medium taking your whole network down," he said.

Although US Cellular is using more wireline for backhaul, Nextel is looking to expand its use of digital microwave.

"We're seeing that the variety of products is greater than it was a couple of years ago on the microwave side, and the prices are coming down," Caplan said. "(Microwave) is something we're increasingly focusing on."

Planning Ahead Whether you use only microwave or both microwave and leased lines for backhaul networks, you must plan for the future.

"We're designing hubs for the cellular carriers because they want to bring many backhauls into one single location," said Glenayre's Barnes. "It's a natural evolution of the network -- as it grows out, you see more junctions. In some cases, you just add more radios. In other cases, you use more of the capacity."

Barnes said often carriers will buy a higher-capacity radio than they need now so they have room for expansion later. You can get a high-capacity radio now for not much more than a low-capacity radio and pay for it by leasing the excess bandwidth. According to Barnes, you should look at higher- frequency radios for two reasons. As you build out networks and use more microwave to interconnect with sites, all of the traffic eventually has to get back to the mobile switch, and the closer you get to the switch, the bigger the pipes that are needed to deliver traffic. Also, some operators are dedicating some of their facilities for leasing chunks to other users to defray infrastructure costs.

"Some customers have ended up with a network that almost pays for itself," Barnes said. "For example, they can put an OC-3 pipe in there, segment that into three DS-3s, use one DS-3 for themselves and lease out the other two to other businesses."

That gives manufacturers opportunities to come up with innovative solutions that give more functionality to carriers, he said.

Cost Justification Of course, reliability is not the only critical factor in your network backhaul decisions; cost issues always arise. Drew Caplan, Nextel Communications vice president of telco engineering, said wireline and microwave are both good technologies for the right application, but carriers must consider profit margins too.

"Microwave is a capital cost, whereas leasing telco facilities from another carrier is an operating cost," he said. "From a financial point of view, you have the classic network engineering paradigm, which is the return on your investment."

After carriers invest in networks and their budgets grow, many convert leased lines to microwave to save in the long run.

"For most operators, the microwave backhaul network is usually the most reliable part of their network," Barnes said. "They start converting their leased lines to microwave because they just pay for it once, and there are no monthly charges. That reduces the operating-expense side of the budgets and can make them more profitable."

Particularly in the PCS markets, there have been some operators that have initially said, 'we're not going to put in any microwave,' and then they found that later on it really did make economic sense to convert some leased lines over to microwave, he added.

"For the longest time, Omnipoint said 'no microwave,' but they can't stick with that corporate edict," Barnes said. "They need to put (microwave) in because leased lines in other markets are not available, and if they expand out of that urban core, it's less available too."

And microwave may become more affordable in the future.

"The cost of leased lines is coming down because of competition, and the larger RBOCs are losing business to microwave," US Cellular's Naumann said. "Microwave costs will have to match it."