White space device proponents that dismiss concerns about interference to over-the-air broadcast TV may have second thoughts after reading a petition from The National Cable and Telecommunications Association (NCTA) regarding unlicensed operation in the TV bands.
NCTA warns that the rules, as they currently exist, will allow TV band devices (TVDBs) to operate at power levels that will cause significant interference to cable TV reception, especially digital services. Other services that depend on the cable TV signal, including cable modem Internet access and telephone service, may also be affected. These conclusions are based on a study by consulting engineering firm Carl T. Jones that showed real world interference was worse than what was originally predicted. Personal/portable TVDBs were found to cause interference to cable TV reception up to 80 feet away.
To get an understanding of how bad the problem is, consider this scenario outlined in the NCTA Petition:
"As for the other measures suggested in the explanatory language, they are either inapplicable to residents of adjacent apartments or wishful thinking. A person experiencing interference is very unlikely to suspect the cause, let alone where it may be coming from. The person causing the interference to a neighbor is unlikely to be aware of it and, furthermore, will have little motive to correct it. Even in the unlikely event that the source of the interference is identified and the neighbors are willing to cooperate in solving it, the device's producer is unlikely to "cooperate in helping consumers to rectify any such interference." After all, the transmitter will likely be manufactured by an offshore company, sold to an equipment supplier, hence through a retailer to the customer. No one in that chain is going to do a house call to attempt to fix the problem. Even if they did, the options suggested are not realistic – the back of a TV set may be more sensitive than the front, but turning the picture towards the wall is not a viable solution. Alternately it is unrealistic to expect the innocent resident experiencing interference to rearrange his furniture so as to move the TV to a different location, or to remove a signal splitter and thus forgo a second outlet or use of a digital video recorder. If the problem is signal pickup in wires buried in the wall between the apartments, should the building owner be obligated to tear out and replace his entire in-building television cabling? Does the owner of the white spaces device have to agree to never use his laptop in the living room? None of these remedies is realistic in practice. Furthermore, after thousands or millions of these devices are sold and in service, there is no retroactive means of fixing widespread interference should it occur."
When it appeared a relatively small percentage of TV viewers out of the 15-25 percent of viewers depending on over-the-air TV might lose their TV reception on Feb. 17, Congress and the FCC moved with extraordinary speed to delay the analog shutdown and to require broadcasters to take additional measures to educate viewers about the coming changes. Imagine the political backlash when cable TV viewers start complaining about their cable Internet connections slowing down and an ever increasing number of cable channels disappearing as TVBDs turn on around them. Many viewers that had problems receiving over-the-air DTV signals will turn to cable TV. Many cable TV companies have offered reduced rates to help these viewers. They won't be happy if a TVBD wipes out their favorite channel on cable TV.
NCTA backs up its concerns with solid engineering in its 144 page petition. NCTA also asks for changes to protect cable TV headends. NCTA is not asking for a ban on TVBDs, but its petition offers solutions including reduced power levels for personal portable devices (50 mW is suggested as a compromise), increased separation for fixed devices or reduced power (400 feet from buildings or a 1 watt power limit), restricting operation of fixed devices in some areas around cable TV headends, and allowing registration of headends in the database regardless of location
Cable TV won't disappear—some cable channels do not fall in TV broadcast spectrum and TVBDs will not be able to operate on every channel in the TV bands, but since there is no "white space" on cable TV, someone's favorite channel or digital service is likely to be affected.
The Community Broadcasters Association (CBA) Petition for Reconsideration is shorter—only 3 pages—and it makes a simple argument. "The protections adopted by the Commission appear to be based on the assumed reception of LPTV stations by only digital receivers, when in fact the vast majority of those stations continue to transmit analog signals, are under no deadline to transition to digital operation, and will continue to be viewed on analog receivers which have different interference-rejection characteristics. More protection is needed for LPTV stations viewed on analog receivers."
CBA continues, "Given the acknowledged fact that the undesired signal must be 9 or 14 dB weaker if a protected first-adjacent channel LPTV station is analog, it is apparent that a uniform maximum power level for unlicensed devices is arbitrary and irrational." CBA asked the FCC to reduce the maximum power by 9 dB for unlicensed portable devices operating on an upper first adjacent channel and by 14 dB for operation on a lower first-adjacent channel. It said the FCC must increase the minimum mileage separation where the protected station is analog, in addition to other adjustments needed to take into account the interference characteristics of analog TV sets.
The Petition for Reconsideration filed by the Society of Broadcast Engineers (SBE) says the 40 mW adjacent channel power limit for personal/portable devices TVBDs is too high and "will not protect consumers and is not justified technically." SBE said variable power levels are not a solution, as weak signals can occur anywhere within a DTV station's protected contour. All viewers should be protected. A much lower power level, such as 2 mW, was suggested. Devices using spectrum-sensing technology should not be allowed "unless and until certain fundamental problems are resolved," SBE states, and the current sensing requirement should be made more rigorous and "should enhance protection for wireless microphones." SBE expressed concerns about the geolocation concept, saying the Commission failed to adequately address a number of geolocation and database issues.
SBE devotes a section of its petition to mobile broadcasting operations, stating, "The Commission correctly pointed out that 'future broadcast uses of the television band will have the right to interference protection from TV band devices.' Although it confirmed that 'future primary use of the band by broadcasters [must] be protected,' the Commission failed to account for new mobile television operations (which are in the process of being introduced and were cited in the comments to this proceeding). The Open Mobile Video Coalition has stated that 'broadcasters have declared their intention to launch mobile DTV across 63 stations in 22 markets, covering 35 percent of U.S. television households' in 2009. SBE explains that the FCC assumed an interference distance of 16 meters for TVBDs. For mobile operations, the interference distance is either 1 or 2 meters. Mobile DTV "will be immediately threatened by WSDs."
Like CBA, SBE points out that the TVDB rules do not protect analog LPTV and TV translator operations. The bias in the rules towards personal/portable devices could actually prohibit wireless Internet service providers (WISPs) and others from providing fixed broadband services in rural areas, SBE argues, because the Section 15.711(f) prohibits a fixed consumer premise device from operating as a client to a fixed WISP base station.
The Petitions for Reconsideration from NCTA, CBA, SBE along with all other filings in the unlicensed TV band devices proceeding are available through the FCC Search for Filed Comments web page. Put 04-186 in box 1, "Proceeding." Because of the large number of filings in this proceeding, you may want to limit the search by putting a search term such as "broadcast' or "wireless" in Box 4, "Filed on Behalf of" to limit search responses to filers with those words in their name.
Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.
Future US's leading brands bring the most important, up-to-date information right to your inbox
Thank you for signing up to TV Tech. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.