Browse Prior Art Database

Radio/Cordless Telephone Privacy-Ascertaining Device Disclosure Number: IPCOM000120019D
Original Publication Date: 1991-Mar-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 128K

Publishing Venue


Related People

Tubiana, M: AUTHOR


Disclosed is a radio/cordless telephone privacy-ascertaining device.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Radio/Cordless Telephone Privacy-Ascertaining Device

      Disclosed is a radio/cordless telephone
privacy-ascertaining device.

      With the development of radio or cordless telephones, privacy
as well as security are in danger. Cordless telephones, for instance,
operate like a two-way radio between the handset and the base.
Transmission between these two devices is implemented through
modulation of a preassigned carrier frequency by the user-generated
audio wave.

      Any third party with a phone that happens to be tuned to the
same frequency could listen in. He could also dial and transmit
through the owner's base and, therefore, get the call charged on the
other's bill.

      The solution proposed here is based on user action on the audio
wave. The system is based on providing both the base and the handset
with a user-tunable noise-generating means. Once tuned, the same
noise is added to the audio signal on the handset, while it is
subtracted back on the base. The final audio wave transmitted over
the telephone line would have thus been corrected as required
assuming the telephone is used properly, i.e., by the authorized
user. On the other hand, should an unauthorized user wish to transmit
using your line, the transmitted audio signal would be meaningless
due to the one-way noise affecting it through the base noise

      The above system obviously supports severals implementations.
One of these is shown in Fig. 1. It requires using a digital coder
for coding the audio signal prior to feeding said signal into the
modulator. Assuming different types of coders be implemented by the
manufacturer, chances for two neighboring telephones matching
together are minimized. Also as shown in Fig. 1, a user tunable
scrambler may be inserted between coding and decoding in both the
handset and the base transmit/receive devices. For instance, the
audio signal provided in the handset will be first sampled at 8 Khz,
the PCM samples encoded with 8 bits per sample. The PCM encoded
samples are scrambled as defined by the user. The scrambled samples
are decoded prior to being fed into the handset modulator. In the
base device, the received signal is first demodulated to provide an
audio wave which is sampled at 8 Khz and again PCM encoded. The PCM
encoded samples are descrambled as defined by the user and then
decoded to recover the original voice signal.  A conventional digital
scrambler is represented in Fig. 1A.  It is made of a shift register
provided with tap(s) connected into a feedback loop arrangement.
Scrambler t...