DIGITAL CELLPHONE PROGRESS REPORT HIA Annual meeting
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DIGITAL CELLPHONE PROGRESS REPORT HIA Annual meeting Palm Springs, CA Feb 24, 2000 (Revised Aug 29) Mead C. Killion, Ph.D. Etymotic ResearchI. Background A. In 1994 my new European GSM digital cellphone knocked out TV from across a hotel room in Europe B. European cellphone mfgs took the position that hearing aid wearers shouldnt buy cellphones. U.S. hearing aid wearers had no problem with U.S. cellphones at the time, which were analog. C. 1996 Sprint introduced digital GSM phones inWashington D.C. SHHH members reported they couldnt use their hearing aids with (or even near) the new digital phones.
Videotapes still available
D. SHHHs Donna Sorkin and others mounted a highly successful campaign, arguing that the Americans with Disabilities Act mandated that hearing impaired persons should have access to the better digital cellphones. In other words, this was not Europe, where the digital cellphone manufacturers could (and still do) tell the hearing aid wearers and manufacturers to buzz off. E. Sorkin asked me to be a consumers representative at the joint cellphone/hearing-aid-industry meetings.E. U.S. Congressmen became involved, and FCC chairman Hundt called a summit meeting, saying solve it to the several hundred representatives of cellphone companies and hearing-aid companies in attendance.F. Several meetings ensued, with over 100 engineers and lawyers in attendance. We broke up into groups of 30-50 each to discuss how to solve the problem.
G. Barry Kranz, one of the cellphone representatives, made up this slide, which expressed an ideal result: cellphones would get down to 10 V/m and hearing aid immunity would go up to 30 V/m, giving a good margin of safety. It now appears unlikely that cellphones will get down to 10 V/m. The cellphone must radiate a fair amount of RF. (If progress does come, it will probably be motivated by a desire to reduce RF radiation absorbed by the brain.) The fact that cellphones now work with hearing aids is largely a result of hearing-aid design improvements.
H. NEED FOR A STANDARD 1. Harry Teder and I proposed a $500 suitcase laboratory comprised of Radio Shack sound meters and a boom box playing a special buzz CD we made. 2. The majority of the committee members decided that a more sophisticated measurement was required, and that both sides needed to agree upon a Standard defining how we were going to measure a) cellphones and b) hearing aids. 3. After countless meetings and some four years, we have a draft of a standard that is reasonable but not perfect. No engineer I know is willing to spend another year trying to perfect it.
1. Once the hearing aid engineers you have been sending to these standards meetings are convinced that the standard is workable, give it your support.
Either the dipole method (original U.S. preference) or the GTEM method (European preference) will permit hearing aid manufacturers to legitimately claim that a hearing aid passing the limits will work fine with nearly any digital cellphone, and especially a cellphone that also passes the cellphone limits in the standard.
There are other considerations, however.
FDAGiven the past behavior of the FDA, if we approve a standard there is a fear that the FDA -- in a fit of enthusiasm -- may force us to test all hearing aids according to that standard, adding perhaps $10 to the cost of each hearing aid. Since manufacturers here and abroad report only about 1 in 1000 hearing-aid purchasers request digital cellphone compatability, this would mean a cost of $10,000 for each person needing such an aid.RX: Obtain assurance from the FDA that they will limit their enforcement enthusiasm to truth in packaging: If a hearing aid company wants to claim useable with red-dot digital cellphones, then (and only then) they must measure samples per the standard. If a manufacturer does not want to make any such claims, then that manufacturer has no obligation to do RF testing.
FCC Other than sabre rattling at the beginning, the FCC has done little beyond sending observers to the meetings. Prominent FCC engineers are no longer being sent to our meetings. The FCC receives $4 billion from cellphone companies each time they sell another frequency band for cellphone use.The FCC has not provided any funding, to my knowledge, for any outside research. (Most has come from the cellphone companies. Some has come from HIA.) The only progress on the cellphone front has been voluntary work by cellphone manufacturers who want to be able to say their cellphones are useable with hearing aids.While the FCC would be happy if cellphones didnt interfere with hearing aids, it is not a high priority. The only hope I see for help from the FCC is if SHHH or AG Bell apply additional pressure. I have come to view the FCC as neither friend nor foe.
ENGINEERS (our heroes) The number of players has dwindled over the years. A few on both sides have hung in there, including Tom Victorian of Starkey Laboratories, Ray Kirchhoefer of Knowles, Horst Arndt of Unitron, Tom Scheller, Harry Teder, and Steve Berger of Siemens cellphone division. Why hang in there?Like the garden rake waiting to whack us on the forehead, the basic RF problem holds unpleasant possibilities if we dont solve it. Bluetooth chips are nearing production, and are predicted to replace every wire except the 110V line cord in your computer setup. Your monitor, printer, network connection, and computer will all be connected via this 2.4 GHz digital transmission. Our (Etymotic/Motorola) early experiments indicate Bluetooth transmissions may not be a problem for hearing aids, but if we dont have a standard way to measure the interference from present and future buzz sources, we will be always coming from behind.
ROOM FOR IMPROVEMENT?
On a personal basis, I am still wrestling with the desire for an even simpler standard. At present we have several levels of goodness for both hearing aids and cellphones, which I liked as an engineer, but as a consumer representative I suspect it is more complicated than necessary. On the other hand, we have put about 100 times more manhours into this question than can be justified by anything except sheer stubbornness. To add more effort to make further improvements is hard to justify.
Only for the future can one justify all this work, but the others and I believe that we will ultimately be pleased that we have generated simple instructions for measurements. These should assure that a hearing aid labeled useable with red-dot digital cellphones will work with any digital cellphone that carries the useable-with-hearing-aids red dot.
APPENDIX: THE SEARCH FOR SOLUTIONSA. Efforts to solve the digital cellphone interference problem led to possible solutions:1. Cellphones with remote antennae or earpieces. Those solutions were rejected by SHHH and others as less convenient and creating a stigma.2. Hearing aids with better immunity. It quickly became clear that:a. Older hearing aid designs could probably not be made immune to digital cellphone interference.b. New designs could be made immune.c. The microphone preamplifier introduced the most buzz of any element. It had to be bypassed before any other circuit solutions could work.
100 V/m3. In some cases, by pure luck, older circuit designs were immune. K-AMP
4. Knowles and others made really immune microphones.
5. Most hearing aid manufacturers offered their best new models with cellphone-compatable immunity, although only a fraction of older designs could be used with digital cellphones. 16% of older designs
B. Experiments to determine how much buzz were underwritten by HIA and conducted by two groups: 1. Harry Levitt and Judy Harkins, and 2. Harry Teder, King Chung, and Mead Killion.Basic conclusion: For 90% of the 43 subjects to rate the sound as acceptable for regular use with 50 Hz (TDMA) buzz, an SNR of 20 dB was needed. An SNR of 25 dB was required for a 217 Hz (GSM) buzz. Levitt and Harkins reported similar results for 217 Hz buzz.Note, however: Nearly half of the subjects accepted a 10 or 15 dB SNR. 20 dB SNR, 90% of Ss25 dB SNR, 90% of SsLevitt et al data
C. Serious experiments heading towards a workable RF source were undertaken by Marco Candiago of Unitron, Mike Sasha at Starkey, a few of us at Etymotic Research, and Harry Teder. We all found that what our RF friends warned us was true: the common farfield measurement in a GTEM cell was often not adequate. The cellphone is only a fraction of an inch away and produces a high-gradient signal. The only way to reliably check the immunity of a hearing aid was with a high-gradient (nearfield) source. We settled on a dipole.1. Marco foundthat some hearing aids that looked good in the GTEM cell didnot function well with realcellphones.
2. Interestingly enough, I believe that the same conclusion can be drawn from data generously supplied this week by our European colleagues at DELTA labs in Denmark. GTEM-->One would expect SNR to go up dB for dB once it gets above 0 dB. We dont see that and the scatter is very large. Perhaps adding another test angle to the GTEM test would have helped?
The GTEM limits DELTA proposed gave reasonable SNR correlation and useable SNRs, as shown in the marked-up graphs shown below (Kristenesn).
Our data and Levitts earlier data suggest 25 dB SNR is required for 90% of subjects such a 217 Hz buzz; DELTAs 4 subjects appeared to accept an 8 dB SNR. Perhaps English is harder to understand i