July 27, 2015

You’ve probably heard about the 600MHz auction.

It’s been in the news well, a lot. Quick background: several years ago, as most of us had switched to cable TV, telecom companies asked the FCC to open up the 600-700MHz spectrum, which at the time was still reserved for broadcast TV. The plan was to co-opt the 600MHz spectrum for smartphones, tablets and other devices – data! FierceWireless editor Phil Goldstein recently reported (article below) that the tentative start date for the auction is March 29, 2016. So it’s moving forward, but it has not been without contention from a number of different parties from telecom to TV as well as the providers of wireless microphones who currently use the spectrum.

We won’t be getting into the politics. But there’s a big antenna design issue here that nobody seems to be talking about.

Antenna Design for 600MHz Bands

US carriers are using the 700 to 2500 MHz bands today. When the 700 MHz band was opened up for commercial telecom service a few years ago, that spectrum was like a rare and expensive mineral: extremely valuable, extremely rare, and extremely useful. As the frequency gets smaller, the size of the antenna must increase because the wavelength has to get longer. But as the frequency gets smaller (like 700 MHz versus 1900 or 2500 MHz), the waves propagate through space better.

The 700 MHz band is a beautiful intersection between desirable signal propagation and antennas which can just barely fit into smartphones. Everything is copacetic so far. But along comes the iphone6600MHz band.

Manufacturers like Apple, Samsung and HTC are spending copious R&D dollars to make smartphones, tablets and other devices slimmer and lighter but at the same time more powerful, because nobody likes to drop or break in and out in the middle of an important call (or lose service when your kids are streaming a movie to a tablet in the back seat of the car).

So, how are we going to fit lower-frequency antennas into smaller devices, particularly handhelds? It’s not going to be easy. There will certainly be some RF design voodoo involved, because handhelds force RF engineers to make the antenna electrically small. Fitting larger antennas in smaller devices means the antennas will likely take longer to develop and that there will be less margin for error. Either hardware developers are going to have to hire the right talent in-house or find experts to help them navigate these RF design challenges.

Below are some articles that we rounded up on the topic and thought would be of interest. Thanks for reading!

Back to Basics: Spectrum 101
Doug Lung, RF Technology, TVTechnology
“Designing RF systems that can use bandwidths more than 5 percent of the center frequency is difficult. At 600 MHz this equates to 30 MHz; at 5 GHz this equates to 250 MHz—more than eight times the bandwidth and eight times the data rate for a given SNR. This makes higher frequencies more useful. If someone tried to put a 200 kHz-wide FM signal in the medium wave AM band, there would have only been room for five stations! Wider bandwidths and higher speeds demand higher frequencies.”

NAB and White Space Device Makers Agree on Geolocation
Deborah D. McAdams, TV Technology
““NAB and the TV band device manufacturers recommend that all TV band devices incorporate automatic geolocation capability or be under the control of a device that includes that capability,” the parties wrote in a joint letter to Julius Knapp, chief of the Federal Communications Commission’s Office of Engineering and Technology.”

FCC tentatively sets March 29, 216 as start date for 600MHz auction
Phil Goldstein, FierceWireless
“[Google and Qualcomm] are among those submitting comments on the FCC’s proposed rule changes for unlicensed operations in the television bands, repurposed 600 MHz band, 600 MHz guard bands and duplex gap and Channel 37. The FCC last year issued a Notice of Proposed Rulemaking (NPRM) on rules for unlicensed operations in the frequency bands that are now and will continue to be allocated and assigned to broadcast television services.”

Researchers suggest new method to improve Wi-Fi Propagation
Patrick Nelson, Network World
“If you’ve ever wondered why your Wi-Fi signals are spotty and don’t fill buildings adequately, one reason is that the frequencies that are used aren’t particularly suited for that purpose. That’s despite improving router and antenna design. Wi-Fi generally uses microwave frequencies, at 2.4 GHz and 5 GHz. Those signals don’t travel around or penetrate objects very well.”

White space gives new life to old spectrum
Lou Frenzel, electronic design
“There are many potential applications for the white space channels where other wireless technologies come up short. Those with the greatest potential include wireless Internet service, backhaul for other wireless services, telemetry, and M2M. White space is ideal for providing Internet connectivity in rural areas where long distances and challenging physical environments are involved. Even in mountainous and forested areas, ranges of several miles can be achieved based on actual tests. Users with no cable TV or DSL service can get fast interconnections even in the most remote locations. White space is also a good fit for municipal broadband applications.”

Advocates Ask FCC to Protect ENG Band, Wireless Mics
Tom Butts, Radio World
“A group of industry associations representing broadcasters and advocates for users of unlicensed wireless (“white space”) devices, is asking the FCC to reconsider its proposal to prevent the relocation of TV stations to areas of the broadcast spectrum used by such unlicensed devices and wireless microphones (so-called “duplex gaps”).”

The Future of Wireless Mics is Full of Static
Phil Kurz, TVNewsCheck
“Engineers and wireless equipment vendors say the FCC’s plans to reduce and limit frequencies for wireless devices following the spectrum repack next year are going to cause a myriad of problems.”

Eleven FCC Scenarios for The 600MHz Band Plan
Charles W. Rhodes, Digital TV
“The bandwidth over which the antenna of a handheld cellphone is efficient varies between the scenarios in the FCC Plan for the 600 MHz Band. Antenna efficiency directly affects battery life (time between recharges), as well as the sensitivity of the receiver. Scenarios that provide more than eight pairs of 5 MHz blocks will involve these antenna bandwidth problems. Where the efficiency of a simple passive antenna is poor (lots of signal bandwidth), the antenna can be automatically tuned to improve its efficiency. However this automatic antenna tuner feature requires added circuitry and therefore adds to the manufacturing cost. The insertion loss of this reduces the power to the antenna, which translates to increased power drain on the battery when transmitting.”