The Federal Communications Commission’s Office of Engineering and Technology (OET) is asking for additional input on evaluations of potential interference from wireless LTE affecting DTV stations conducted recently by OET engineers.
The FCC announced in October 2012 it would be hosting incentive auctions as a means to reallocate broadcast television spectrum for wireless broadband use. These auctions and subsequent spectrum repacking efforts meant that TV stations and wireless networks could end up operating on the same or adjacent channels in nearby markets, requiring thorough investigative efforts to ensure interference was kept to a minimum.
In a public notice released June 20, the OET invited comment on a methodology for predicting inter-service interference, or ISIX.
“For purposes of that methodology,” the agency explained, “OET assumed that wireless services operating in the new 600 MHz band will appear noise-like to DTV receivers and hence, that the interference potential from LTE will be nearly identical to DTV-to-DTV interference. In addition, OET incorporated an off-frequency rejection factor as a function of varying degrees of spectral overlap due to filter roll-off in the misaligned future wireless blocks and existing TV channels in the 600 MHz band. OET also added 0.8 dB to the interfering wireless signal to account for the possibility of co-channel power from multiple wireless blocks affecting one 6 MHz TV channel.”
The request for comments follows concerns raised by several organizations regarding the interference and the way the FCC was measuring it.
“The proposed OET methodology relies on clearly erroneous assumptions and inputs that significantly underestimate inter-service interference,” the National Association of Broadcasters, ABC Television Affiliates Association, FBC Television Affiliates Association, CBS Television Network Affiliates, NBC Television Affiliates, the Association of Public Television Stations, the Corporation for Public Broadcasting and the Public Broadcasting Service said in a joint comment filed March 18. These issues include inaccurate values for wireless base station antenna height and transmitter power, the disregard of the cumulative effects of multiple wireless transmitters, inconsistency with OET-69 service predictions and incorrect application of clutter factors.
Comments on the on the LTE/DTV interference issue will be accepted until July 11, 2014.