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

2. 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

3. 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)

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

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

6. 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)

7. 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 b
OFDM: Orthogonal Frequency Division Multiplexing: Multiple simultaneous transmissions a = 5.15GHz GHz and 5.725GHz Ghz
802.11g backward compatible with b (DSSS + PSK) as well as higher data rate (OFDM + AM)
October 2008
Measurement of Hearing Aid Compatibility Workshop, C63.19 (2007)

8. 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)

9. 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)

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

11. Subjective Assessment

13. 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

14. The spectral weighting portion:
737.9 Hz x
(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
new-weighted