RF Planning: Clutter Considerations
Designing a network isn't easy. You have to consider terrain, clutter and anything else that may block RF signals and inhibit coverage. Maximizing coverage, increasing capacity and minimizing capital expenditure throughout the life of a network is an RF engineer's purpose in life. However, most engineers use RF-planning tools only during initial build-out.
Now, that is changing. Companies are offering improved solutions for traditional RF-planning needs as well as additional functionality to help you continue engineering enhancements.
MORE THAN DESIGNTypically, carriers use RF-planning tools to design site placement and coverage, run the basic propagation coverage and propagation analysis, and analyze interference to establish phase-1 networks. Then, engineers go out in the field and collect measurements to see if the model is accurate. Software plots that data and reveals the expected performance of your network.
But engineers need more from their RF-planning tools.
At one time, traditional planning applications sat on one PC or one UNIX box, which made it hard to administer the system and do backups for maintenance checks. According to Richard Russell, Aethos Communication Systems president & founder, carriers need radio-planning tools that will integrate with existing databases and infrastructure.
"They want a system that can be distributed across lots of workstations and PCs. Operators also are looking for the ability to re-tailor the radio-propagation modeling the way they want it," he said. "In the past, you had a black-box model, and if it didn't fit your environment, you were stuck with it."
One of the things that becomes much more challenging once you become operational is that you focus more on getting the most out of what you have as opposed to "green field" designing, said Beth Frasco, Aerial Communications radio-planning manager. Because most radio-planning tools are geared toward the network build-out phase and not the life cycle of a network, radio engineers use them a lot less as they become more familiar with the system. Usually, they get more information from what they personally know about the network as opposed to what the planning tools can tell them. Frasco said it would help if planning tools could integrate some of the real field knowledge back into the tool to make it more reflective of the real network as opposed to just what the model predicts, especially for frequency planning and controlling interference.
Today, carriers want to get a closer view of what the customer perceives. Software vendors recognize this need and realize that carriers want to share RF information and data with all departments so that everyone, including engineers, marketing and customer service, benefits from the valuable data.
Steve Fortin, MapInfo technical advisor, said you can integrate today's RF-planning tools to help the customer-service department. As soon as the CSR receives a call, the caller's location is identified on a map, and the coverage areas also are displayed, enabling CSRs to respond.
SkyTel publishes coverage maps on a web application based on MapInfo's technology. Anyone who goes to the paging provider's web site can type in his address to see if he is covered. SkyTel then monitors its web site to see where customers are asking about coverage. This allows the provider to gain market intelligence as to where customers want coverage and where it should build a new cell site.
Using radio-planning software to provide such real data is a growing need among carriers, said Amy Stephan, Teleworx vice president.
"(Before), RF engineers would design the network, but they did not have much interface with the switch operators at the network control center, or with marketing or customer service," Stephan said. "Now, they can share info across a normal network and layer it on top of what they (RF engineers) are doing."
Layering data saves time for engineers and expenses for organizations. Engineers need to be able to design or build out networks based on information from other departments. According to David Klein, MapInfo DeciBel Planner product marketing manager, it's one thing to build a good, optimized network that's running properly, but you have to make sure you are reaching the right population with that network.
"With many radio-planning-tool software programs, you can combine that demographic information with your network information and see where you'll get the greatest return," he said.
New RF-planning tools also can save you money through networking. Historically, Russell said, planning tools didn't allow a team of engineers to work on one area simultaneously. Instead, each engineer checked out a certain square of geography and worked on that square. When the other engineers finished their squares, they were stitched together, but more than one person wasn't able to work data simultaneously. This common problem slows down the process for RF engineers.
When Western Wireless needed its 50 engineers in 11 markets to work at the same time, Aethos devised a database-locking scheme for its Odyssey radio-planning tools. The system allows all engineers to view the information, but when someone is working on the particular side, the software locks up so everyone else can still view the changes but not make adjustments until that engineer is finished.
"The program speeds up the calculation process so several engineers can work at once," Russell said. "We networked the calculations so that when you hit 'calculate,' the program will look for other idle machines on the network, and it will set the calculations for those machines."
Even though RF tools are advancing, some engineers don't find these features beneficial for mature networks. Frasco said Aerial didn't use the census direct data in its radio-planning tools after the initial network-design phase. She said that many interesting features of planning tools, such as being able to spread traffic over the predicted coverage using census and demographic data, are really necessary only during early design stages because then you don't have real data from the network yet. Once you get the knowledge of who your customer base is and information from your marketing department, that feature isn't as necessary.
RF PLANNINGBecause your main concern is providing reliable, quality coverage, geographical planning, including terrain and clutter, is still your most important concern. Like many operators, Aerial has gone to great lengths to get the most up-to-date terrain and clutter information possible.
"We use mathematical models to predict the propagation loss, but we do use real data to characterize the terrain, and we also use satellite imagery," Frasco said.
Aerial does quality assurance on the satellite imagery with aerial photography if it's available.
Real terrain and clutter data also can help you plan for rural and urban environments.
"Some operators will want to go for a more microcellular approach in the urban areas, and therefore they'd be interested in much-higher-resolution data of the buildings," Frasco explained. "For other operators that have a more macrocellular approach, that's not going to be as helpful. They are going to need different methods of propagating the signal loss with the two types of data."
Stephan said that because networks for rural and urban environments are designed differently, the tools will be used differently and must be able to handle those kinds of network features.
"The size of a market nowadays is not an issue; it's the complexity of the market," she said. "Especially in a dense urban area, we rely on using real data as opposed to modeled data."
For instance, Stephan said Teleworx's 2- and 3-dimensional models of Manhattan help it analyze the actual data. Teleworx's Automatic Frequency Planner tool also increases the number of air lengths by square miles, allowing carriers to use fewer sites and provide coverage in dense urban areas.
SOFTWARE NOT A PANACEAAccording to Stephan, the RF tools out there are good, but cost is still an issue. Carriers are trying to reduce their internal spending.
"They want to minimize the engineering work and the price they have to pay for these tools," she said.
But the prices are going down. Now, good data that provides exact building placement and height has become more available and affordable.
RF-planning tools actually have reduced Aerial's capital costs, Frasco said, but its success can be attributed to overall good planning and timing as well.
"We had an initial target for the number of sites in our network and for the number of sites in each of our market," she said. "We took great care to make sure that the data we had in our radio- planning tools was accurate. We also spent some time trying to calibrate the propagation models and doing coverage tests of each site."
Those steps allow Aerial to develop an accurate picture of what the network was going to look like once it was built out. But minimizing capital costs is never as simple as just having a good radio-planning tool.
"It comes down to how well site acquisition and RF can work together to pick the right sites," she said.
Although RF-planning tools can never be all things to all carriers, engineers can now look to them to provide more than just design tips for initial build-out.
RF-planning tools have come along way in the last decade. However, they can't do everything. Underground coverage still poses challenges. Although specific tools may not be available, there are some things you should keep in mind when planning for tunnel, subway and railway coverage. For example, waves do bend (reflect and retract) in tunnels. Using techniques that are reflective and refractive, you can extend the signal, said Lee Masoian, AeroComm president.
However, there is some loss. The signals may get weaker as they travel around the bend because when they hit the wall, some of the energy reflects back and travels forward in a different direction, said Khoa Khuu, AT&T Wireless spectrum-planning engineer.
"The propagation (the way the signals go through any particular medium) is either by reflection (when the signal bounces off something), refraction (it bends with the curvature) or line of sight (direct)," Masoian explained. "It comes down to what the composition of the tunnels is, but because of the concrete walls, the signal will reflect off of those surfaces and will also penetrate a portion and come out again refracted."
The signal will propagate on all three modes, he said, when you use antennas or radiating cable. Masoian, who has wired tunnels in large urban environments, said most carriers have to plan for tunnel coverage without software planning tools.
"The software's at the level yet where you could put the parameters of the tunnel in and then have it come out where anybody would believe it," he said. "It's different outdoors because that's a well-documented thing."
Instead of software planning tools, AeroComm erects transmitters inside the tunnel and performs drive tests to collect the field-strength data. But carriers who struggle to provide coverage in subterranean environments without the aid of planning software may get some help soon.
"In the future, we'll be able to use software (for planning coverage in tunnels)," Masoian said. "The software packages will grow as the applications grow."
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