Summary of Technical Analysis of the Low Power FM Service by Wireless Valley Communications
Posted: Monday November 15, 1999
The Federal Communications Commission has proposed a new class of low power FM radio stations (LPFM). A critical element of this proposal is consideration of whether the proposal is technically feasible. Specifically, a key issue is whether these new low power radio stations will cause unacceptable levels of interference to the current FM broadcast stations. Wireless Valley Communications, Inc. was commissioned to provide objective, critical technical analysis of the technical studies submitted by several commenters in the FCC’s proceedings.
Our mission in this report is three-fold: 1) to critique and referee various submissions for fair and accurate technical representation; 2) to compile accurate technical models and trends from various submissions that can be used to analyze the impact of LPFM on current and future station owners and listeners; and 3) to use the technical data from the public comments and the FCC’s NPRM to determine the viability and limitations on LPFM and its potential impact on existing and emerging FM broadcast services and the listening public. In this report, we point out incorrect assumptions, inappropriate models, and erroneous results which do not properly model the impact which LPFM may have on incumbent FM broadcasters or emerging digital radio services in the FM band. Where possible, we suggest alternative and more objective techniques for postulating the technical arguments, and recompute the results.
Our analysis concludes that LPFM will not cause unacceptable levels of interference to existing FM broadcast stations. The receiver studies submitted in this proceeding imply that the true “real word” FM interference environment for household radios is benign, due to the FCC’s unnecessarily high interference protection ratios. The receiver studies offer very strong support for LPFM as a viable service without the need for 2nd and 3rd adjacent protection ratios, because today’s fixed and portable FM radios operate successfully with much less interference protection than what the FCC provides in its present station licensing process. The small additional interference induced by LPFM is miniscule in comparison to already existing levels of interference in the FM band.
Moreover, in reviewing these studies, we have uncovered a clear bias on the part of certain constituencies to overstate the potential interference problems of LPFM. Many commenters who conducted FM receiver studies skewed their results when contemplating how LPFM would impact the listening public. For example, the National Association of Broadcasters commissioned an extensive receiver study of 28 FM radios but then omitted automobile radios (which make up over 20% of the FM radios sold and over 44% of the radios listened to by the public) from its LPFM impact study. Omitting car radios from an LPFM system impact study greatly biases the results for maximum susceptibility to interference (i.e. worst performance). In other comments, a “worst-case” radio, most susceptible to interference, was fabricated from the worst-case measured data of two different radios, even though no such physical FM receiver was found to exist in any of the public comments. Numerous other examples of data manipulation, such as double and triple counting of interference events, portray LPFM in an unfair and non-objective light. Our intention is to expose these incidents and offer more credible methods for extrapolating results to properly quantify the impact of LPFM.
In addition to a review of the submitted studies, we conduct an extensive spectrum simulation to demonstrate that hundreds of LPFM stations may indeed be deployed in the U.S. with minimal impact to incumbent and future digital FM radio stations. We use the FCC’s FM radio license database, the FCC radio propagation programs, and Part 73 interference and coverage rules for FM radio stations, to show that properly certified LPFM transmitters with radiated power levels between 1 and 100 Watts and no 2nd or 3rd adjacent channel protection requirements can serve tens of millions of neighborhood listeners in the U.S., while having minimal interference impact on a few tens of thousands of listeners at most.
Our analysis shows that between 64 and 680 times as many citizens are able to receive LPFM programming over small distances (i.e. within neighborhoods) as those who may rarely experience some level of interference or degraded service. Even those listeners experiencing some degradation of service will likely be able to augment their reception by simply relocating their radio or adjusting their antenna. We also present maps to demonstrate suitable locations of LPFM stations in several representative cities. All of the models, assumptions and techniques used to carry out the analysis and simulations are documented for corroboration by others, and computer source code based on the original FCC LPFM code is provided in this filing. Finally, we analyze the concerns of IBOC digital radio technology, and study some of the cost/performance tradeoffs that digital radio manufacturers make in product design.
We show that, regardless of the specific radio implementation, IBOC will be able to coexist with LPFM in the same manner it will with standard FM broadcast stations, due to the very small interference footprint of LPFM.