Interference Standards an Issue that Won’t Go Away, Knapp Says

Receiver standards have been back in the news in recent months due to the fight over LightSquared and the strong opposition from GPS, concerned about interference (CD Feb 16 p1). Recently enacted spectrum legislation requires the GAO to study receivers and spectrum efficiency. Knapp said information collected by the FCC could prove helpful to GAO as it looks more closely at the issue.

"To take away any suspense in the room, LightSquared is for receiver standards,” said Doug Smith, chief network officer at the would-be competitor, during a Monday afternoon panel. “We've been at this over 10 years. … We'll have the final chapter to come at some point.” Receiver standards offer some of the best hope for making more effective use of the limited spectrum available, Smith said. Currently, “there’s a high risk for anybody who wants to enter the market and try to innovate and make investments because the rules aren’t clear,” he said. “I think clarity around the rules that we will play by is paramount to any new investment. We've learned that lesson the hard way.”

Rules don’t have to be “overly prescriptive” but should establish a few minimum standards, Smith said. “GPS standards certainly do have a different point at which they are impacted and it’s a wide array and receiver standards could help tighten that up,” he said. The rules also should provide more clarity of what constitutes “harmful interference.”

"This has been a topic that’s been discussed for a long time,” Knapp said. “It’s an issue that’s not going to go away. It’s an issue that we really need to better understand and tackle.” Some interference issues -- for example, FM radio interference to aeronautical radios -- have “been around as long as I can remember,” he said. The lines between spectrum blocks are often hazy, especially for receivers, Knapp said. “Just as the transmitters cannot completely prevent emitting some energy outside of their frequency bands, receivers generally cannot completely eliminate reception of energy outside the bands they're attempting to use,” he said. “It can lead to spectrum lying fallow, or lightly used, simply to avoid causing harmful interference to receivers.”

The ability to control interference is a function of the limits of technology, costs and other design variables, Knapp said. “In an ideal world, everything would stay right inside the lines, but in the real world that’s not always possible to achieve and there are tradeoffs that have to be made.” Resolving conflicts has often been a lengthy process, he said. “We'd like to try to develop some new approaches to spectrum management that focus on spectrum efficiency and receiver performance that could enable more assured deployment of new services and reduce the necessity for the involvement of regulators,” Knapp said. This is not the first time the FCC has tried to tackle the issue, with the most recent question the agency asked about receivers in its wireless innovation notice of inquiry, he said. While about 300 responses were filed, most didn’t respond to questions about receivers, he said.

Tackling the problem won’t be easy, Knapp said. “The difficulty is that there are many services that use weak signals and they're spread throughout the spectrum,” he said. “The bottom line as we are looking for spectrum for new broadband services our ability to completely avoid operating next to weak signal services is very often quite limited."

"There are two sides to every story,” Nebbia said. “Spectrum management is not just about transmitters any more than spectrum use is strictly about transmitters. I'm not aware that there are any radio services that take place without a receiver.” The government has long held that receivers were the responsibility of consumers, Nebbia said. “If you want better reception, you buy a system with a better receiver,” he said. “That construct or philosophy works as long as receiver standards are not the determining factor in our spectrum management decisions.” When the government has to leave channels vacant to protect receivers or when allocation decisions are controlled by adjacent band receivers “we have to consider receiver characteristics and their role in our process,” Nebbia said. Even at the NTIA, where there are few questions about the agency’s ability to dictate standards for government receivers, receiver requirements are few, he said. “We have never taken a strong stand in moving that forward."

The examination of receivers is important because both government users and commercial operators face growing demands for spectrum, Nebbia said. “It’s to ensure that we have spectrum for the future that we have to do our best in looking at how we're looking at today,” he said. “While costs associated with improved receiver design can impact manufacturing decisions they can leave to costs for others for lost opportunity.” Nebbia said receiver design and performance “must become part of the equation if we're going to open up as much spectrum as possible."

Fences

"Good fences make good neighbors,” said Larry Krevor, a Sprint Nextel vice president. “Certainly, receiver standards should be looked at at this point,” Krevor said. “The spectrum environment changed dramatically from even 20 or 25 years ago. We have so much more use of the spectrum, so much more attempted use … so much more data throughput.” There are also more competitors, he said. “Communications policy is directed toward competition,” Krevor said. “At the same time, the other half of this is … you come to an existing spectrum allocation done under certain assumptions 30 or 35 years ago and technology and needs and public demands have changed.”

"The concept of good fences and good neighbors is appropriate; the question is where do we put the fence,” said Paul Galyean, director of advanced engineering at NavCom Technology. “I don’t know how I could be responsible for my neighbor’s receiver when I don’t know anything about it,” said LightSquared’s Smith. “It’s not public information. There’s no spec that has been designed to that’s publicly available.”

In another panel, industry officials discussed the lay of the land and the receivers they deploy. “We've got a tremendous challenge here in that we are providing a nationwide service that has to have ubiquitous coverage at an extraordinarily high service availability [rate],” said Terry Smith, chief engineering officer at Sirius XM. “Customers … expecting high-quality streaming audio don’t take kind to interruptions in that service.” Making changes takes years for satellite radio, especially units sold in new cars, Smith said. “If I had a technical solution that I wanted to deploy today, many of our partners wouldn’t start to put it into their vehicles; it may take another three years to deploy it across all of their vehicles,” he said. “Of course they expect that technology to continue to be supported for seven to 10 years going forward. It’s a very long cycle.”

Garmin has to carefully weigh costs versus performance for the components in its receivers, said John Foley, a director at the company. “When we evaluate GPS chipsets we look at a number of characteristics in order to achieve this balance,” Foley said. “We look at the physical size of the chipset and its power requirements, receiver sensitivity, balancing that with interference rejection, and integration with other wireless technologies like Bluetooth, Wi-Fi.” Receivers have to be able to receive signals from multiple Global Navigation Satellite System constellations, while rejecting out of band interference from known sources. “For some devices like this GPS-enabled wristwatch I am wearing, a small form factor is crucial for customer acceptance,” he said. “Power consumption and the size of the components are very important.”

Carriers have relatively few vendors to choose from in buying the components of receivers, said Kathy Barnes, a senior director at T-Mobile. International considerations are important, she said. “We are not in just a U.S.- or North American-centric ecosystem,” Barnes said. “This is a global ecosystem. Mobility is important worldwide.” The workshop continues Tuesday.