The Joint Reply Comments of the Association for Maximum Service Television, Inc. (MSTV) and The National Association of Broadcasters (NAB) supported the "clear majority" of comments criticizing the FCC's Notice of Proposed Rulemaking to use the interference temperature approach to allow unlicensed operation in spectrum currently reserved for licensed use only. The MSTV/NAB comments said, "even proponents of unlicensed devices -- those that stand to gain from unlicensed underlay operations that the interference temperature approach seeks to permit -- recognize that the interference temperature approach suffers from significant technical flaws and is not viable." MSTV/NAB also noted that several other commenters agree with them that once unlicensed devices were introduced into licensed spectrum bands, it would be impossible to locate and control these devices should they cause interference.
MSTV/NAB reiterated their argument that because broadcasters do not control the technical characteristics of TV and AM/FM receivers, "broadcasters would be powerless to even attempt to solve interference problems caused by new unlicensed devices." The potential such interference could also hamper the transition of TV and radio (through IBOC digital technology) to digital was also noted.
Some of the comments from proponents of unlicensed devices about the problems with interference temperature measurements were quoted by MSTV/NAB in their replay comments. The Wi-Fi Alliance said, "In cases dominated by interference from a limited number of sources -- e.g., interference from an RFID transmitter into a broadcast receiver, local propagation conditions vary so much that measuring the noise level at any given point does not provide reliable information about the observed noise level at a nearby point." Proxim Corp., a manufacturer of unlicensed devices, commented, "The problem we have identified here shows a fundamental problem in the use of the interference temperature concept. That is, there is no good way for a sharing device to determine, based on a measurement of its own environment, if it will interfere with another device in its range. And this simulation is a very simplistic one. Adding more complex effects, such as signal fading, would case [sic] even more uncertainty."
The MSTV/NAB reply comments also supported the comments of the Society of Broadcast Engineers opposing the use of the interference temperature approach to allow unlicensed devices in the 12.75 to 12.25 broadcast auxiliary service band.
Get the TV Tech Newsletter
The professional video industry's #1 source for news, trends and product and tech information. Sign up below.