Joe Morrissey Motorola ANSI ASC C63® Subcommittee 8 HEI Study Joe Morrissey Motorola October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

RF Source (Mobile Phone) RF Victim (Hearing Aid) RF Signal Carrier Frequency Burst Structure Modulation Dynamic Signal Field Polarization E- and H- components Handset / Antenna Type / Location Radiation Pattern Distance (Near Field) Transmit Power Receiver Wires (Length / E-Field) Loops (Area / H-Field) Shielding by head Receiver Desired Signal Demodulator Square Law Audio Radio Circuitry Other Noise Audio Band Noise oscillators clocks

Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007) Hearing Aid Anatomy Receiver Microphone Battery Turnpot adjust Molded shell Plastic tube On / Off / TC switch Telecoil Integrated Circuit Wiring October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Captured Acoustic Products October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007) E- vs H- Field October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007) Increasing array of wireless technologies that may enter healthcare facility Some data centric, others developed for voice. Differences in capacity, traffic load, local vs. wide area network distribution, interfering characteristics October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007) Wi-Fi Technology Defined Parameters Dynamic Parameters Frame Duration data rate data length Inter-Frame Spacing traffic signal quality 802.11g backwards compatible (b) higher data rate (a) 802.11b (2.45 GHz) DSSS encoding format GFSK modulation 802.11a (5 GHz) OFDM encoding format PSK,QAM modulation 802.11g (2.45 GHz) DSSS / OFDM encoding format PSK / QAM modulation DSSS: Direct Sequence Spread Spectrum: evolved from frequency hopping (predefined sequence of hops) – reduces interference from neighboring transmitters (different channel frequencies at a given time). 11 overlapping, 3 non-overlapping 22Mhz channels for spread spectrum signal. Modulation using frequency shift or phase shift keying – at the symbol rate (several Msym/sec, so well above acoustic range. Used by CDMA, GPS, and 802.11b OFDM: Orthogonal Frequency Division Multiplexing: Multiple simultaneous transmissions. 802.11a = 5.15GHz - 5.35GHz and 5.725GHz - 5.825Ghz 802.11g backward compatible with 802.11b (DSSS + PSK) as well as higher data rate (OFDM + AM) October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

GSM Bursting Structure During a silent period, when no speech is processed, the speech coder generates what can be referred to as a Silence Descriptor (SID). This silence descriptor is transmitted according to some repetition rate in order to generate "comfort noise" in the receiving end. It is typically the case in a voice communication that there is no complete silence, and to "simulate" the noise usually present in the surroundings of the silent speaker, SIDs are transmitted with a certain repetition rate. October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007) 217 Hz or 4.6 msec October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007) October 2008 Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

Subjective Assessment

The weighting function: The weighting function consists of straightforward spectral weighting followed by temporal weighting. Each step is clearly mathematically definable. Implementation may be in hardware or software. Spectral Weighting RMS Level Measurement Peak Detector from square- law detector to DC meter X2 X0.5 4 msec TC 550 msec T.C. Similar to A-weighting Similar to CISPR, ITU-R 468 Quasi-Peak Detection

The spectral weighting portion: 737.9 Hz x 1.2589 (A-weighted) x2 x2 20.6 Hz 12.2 kHz 107.7 Hz from square- law detector (or conditioned baseband mag- netic probe for ABM2) 3 kHz, 2nd order D.F. = 0.707 369 Hz x 1.0864 new-weighted