Biomedical Engineering Reference
In-Depth Information
idea, but it had nothing to do with Wi-Fi
or mobile phones, since neither had been
invented at the time. A player piano used
perforated music sheets or metallic rolls
to strike the notes and produce the music
automatically.
The way FHSS works is that one
device pseudo-randomly hops from one
carrier frequency to another once syn-
chronized (or synched) with another
device. The devices are synchronized,
much like the relationship between the
player piano and its instruction sheet (i.e.,
sheet music). The piano plays the keys it
is told to play by the instruction sheet,
with only the piano and the instruction
sheet knowing the sequence and tim-
ing of the notes to be played. The first
intended application for the frequency
hopping patent was for naval warfare.
At the time, naval vessels had difficulty
navigating fired torpedoes via radio
waves without radio interference from
the enemy. Lamarr and Antheil proposed
sending the navigation signals over mul-
tiple carrier frequencies, but the signals
would hop from one carrier frequency
to another in a manner that only the
sender and receiver (torpedo) knew and
to which they were both synchronized.
The relationship between the torpedo and
the transmitter was similar to that of the
piano and instruction sheet. This tech-
nology later evolved into FHSS (Brilliant,
Beautiful, & Bold, n.d.).
no intent or capacity to return a signal.
When this one-way transmission occurs,
it is referred to as
streaming
. A com-
mercially available hearing aid acces-
sory/streaming device is illustrated in
Figure 9-5.
Streaming requires the second de-
vice to receive a signal, but it does not
require that device be able to transmit a
signal. We stream when listening to music
from our smartphone or smart device
via Bluetooth-enabled headphones or
speakers. We stream the audio directions
from our GPS systems to our Bluetooth-
enabled audio systems in cars. In both
of these examples, there is no return sig-
nal, only the one-way signal allowing us
to listen to music or driving directions.
With hearing aids the streaming device is
often placed in a pocket or worn around
the neck. The streaming device transmits
to the hearing aids from another device,
such as a mobile phone (Figure 9-6A).
Because of the reduced energy consump-
tion of Bluetooth LE, hearing aids have
the capacity to interact with external
devices without a streaming device (Fig-
ure 9-6B). While potentially intimidating
to many hearing aid wearers, this technol-
ogy is quite user friendly. For example,
when the hearing aids have been “paired”
with another device, they will recognize
one another each time they are in close
enough proximity. When “paired” with
a mobile phone, the hearing aid wearer
can hear the phone ring directly through
their hearing aids. To answer the phone,
the hearing aid wearer simply presses
the designated button on the streaming
device (Burrows, 2010).
Streaming Devices
There are some Bluetooth devices
designed to receive a signal but with
