Clear channel selection system for a cordless telephone

• US 6,041,240 A
• Filed: 03/10/1997
• Issued: 03/21/2000
• Est. Priority Date: 01/05/1994
• Status: Expired due to Term

• Current Assignee: Thomson Consumer Electronics Incorporated (Vantiva SA)
• Original Assignee: Thomson Consumer Electronics Incorporated (Vantiva SA)
• Inventors: Kapadia, Maneck Behram, Fossaceca, John Mark, McCarthy, Dennis Ronald
• Primary Examiner(s): Trost, William G.
• Application Number:
  US08/814,622
• Time in Patent Office: 1,107 Days
• Field of Search: 455/462, 455/464, 455/403, 455/450, 455/452, 455/421, 455/67.1, 455/67.3
• US Class Current: 455/464
• CPC Class Codes: H04M 1/72511 Searching for available channels

Abstract

A radio frequency (RF) signal transmitter/receiver system comprises a pair of transmitter/receiver units. A microcomputer-based RF carrier detect system determines when an RF signal is present or absent. The RF carrier detect system is also responsive to noise interference signals at or near its currently-tuned receiving channel. In periods of inactivity, the RF signal receiver monitors its currently-tuned channel and upon detection of noise interference or upon a determination that the currently-tuned channel is occupied, initiates a fast scan operation to identify an unoccupied and relatively interference-free channel, and transmits a command to its paired transmitter/receiver unit causing it to tune to the newly-identified unoccupied channel.

Claims

1. A cordless telephone set exhibiting an off-hook state for enabling communication via an external telephone network, and an on-hook state, said cordless telephone set comprising:

a base unit operating on one of a plurality of cordless telephone channels;

a handset operating on said one of said plurality of cordless telephone channels;

each of said cordless telephone channels including a first radio frequency for communication from said handset to said base unit and a second radio frequency for communication from said base unit to said handset;

said base unit including an input for receiving a signal from said handset at said first radio frequency of a first cordless telephone channel;

said handset including an input for receiving a signal from said base unit at said second radio frequency of said first cordless telephone channel;

said base unit including a microprocessor for controlling said base unit, a portion of said microprocessor functioning as a signal detector circuit responsive, during said on-hook state, to a baseband signal derived from said first radio frequency signal for producing a first output signal indicative of said first channel being occupied, or indicative of a noise signal being present on said first channel;

said handset including a microprocessor for controlling said handset, a portion of said microprocessor functioning as a signal detector circuit responsive, during said on-hook state, to a baseband signal derived from said second radio frequency signal for producing a second output signal indicative of said first channel being occupied, or indicative of a noise signal being present on said first channel;

said signal detector circuit of said base unit and said signal detector circuit of said handset each having a threshold of detection of a first value in said on-hook state and of a second value, higher than said first value, in said off-hook state;

said signal detector of said base unit and said signal detector of said handset operating in said off-hook mode for detecting baseband digital control signals;

said microcomputer in said handset causes a transmission of a channel change command to said base unit and causes said handset to change to the same new channel in response to said second output signal.

3. The cordless telephone set of claim 1, wherein each of said microcomputers monitors frequency content of a demodulated audio baseband signal to determine that the channel is occupied, the channel is noisy, or the channel is suitable for use.

2. A cordless telephone set exhibiting an off-hook state for enabling communication via an external telephone network, and an on-hook inactive state, said cordless telephone set comprising:

a base unit operating on one of a plurality of cordless telephone channels;

a handset operating on said one of a plurality of cordless telephone channels;

each of said cordless telephone channels including a first radio frequency for communication from said handunit to said base unit and a second radio frequency for communication from said base unit to said handunit;

said base unit including an input for receiving a signal from said handset at said first radio frequency of a first cordless telephone channel;

said base unit including a microcomputer for controlling said base unit, a portion of said microcomputer functioning as a signal detector circuit responsive, during said on-hook state, to a baseband signal derived from said first radio frequency signal for producing a first output signal indicative of said first channel being occupied, or indicative of a noise signal being present on said first channel;

said handset including a microcomputer for controlling said handset, a portion of said microcomputer functioning as a signal detector circuit responsive, during said on-hook state, to a baseband signal derived from said second radio frequency signal for producing a second output signal indicative of said first channel being occupied, or indicative of a noise signal being present on said first channel;

said signal detector circuit of said base unit and said signal detector circuit of said handset each having a threshold of detection of a first value in said on-hook state and of a second value, higher than said first value, in said off-hook state;

said signal detector of said base unit and said signal detector of said handset operating in said off-hook mode for detecting baseband digital control signals;

said microcomputer in said base unit causing a transmission of a channel change command to said handset and causing said base unit to change to the same new channel in response to said first output signal;

said microcomputer in said handset causing transmission of a channel change command to said base unit and causing said handset to change to the same new channel in response to said second output signal.

4. The cordless telephone set of claim 2, wherein each of said microcomputers monitors frequency content of a demodulated audio baseband signal to determine that the channel is occupied, the channel is noisy, or the channel is suitable for use.

5. A cordless telephone set exhibiting an off-hook state for enabling communication via an external telephone network, and an on-hook state, said cordless telephone set comprising:

a base unit operating on one of a plurality of cordless telephone channels under control of a controller;

a handset operating on said one of said plurality of cordless telephone channels under control of a controller;

each of said cordless telephone channels including a first radio frequency for communication from said handunit to said base unit and a second radio frequency for communication from said base unit to said handunit;

said base unit including a controller for controlling said base unit, a portion of said controller functioning as a signal detector responsive, during said on-hook state, to a baseband signal derived from said first radio frequency signal for producing an output signal indicative of said first channel being occupied or noisy;

said handset including a controller for controlling said handset, a portion of said controller functioning as a signal detector responsive, during said on-hook state, to the frequency content of a baseband signal derived from said second radio frequency signal for producing a second output signal indicative of said first channel being occupied or noisy;

said signal detector of said base unit and said signal detector of said handset each having a threshold of detection of a first value in said on-hook state and of a second value, higher than said first value, in said off-hook state;

said signal detector of said base unit and said signal detector of said handset operating in said off-hook mode for detecting baseband digital control signals;

said base unit controller, in response to said first output signal, causing a transmission of a command to said handset for causing said handset to change to a second channel, and causing said base unit to change to said second channel.

6. The cordless telephone set of claim 5, wherein each of said controllers monitors frequency content of a demodulated audio baseband signal to determine that the channel is occupied, the channel is noisy, or the channel is suitable for use.

7. The cordless telephone set of claim 6, wherein each of said controllers monitors frequency content of a demodulated audio baseband signal to determine that a second channel is occupied, noisy, or suitable for use before causing the transmission of said command to change to said second channel.

8. A cordless telephone set exhibiting an off-hook state for enabling communication via an external telephone network, and an on-hook state, said cordless telephone set comprising:

a base unit and a handunit operating on one of a plurality of cordless telephone channels, each of said cordless telephone channels providing for communication between said handunit and said base unit via a base unit transmission frequency and a handunit transmission frequency;

a monitoring circuit located in said base unit or said handunit for monitoring, during said on-hook state, the frequency content of a baseband signal derived from a respective one of said base unit transmission frequency or said handunit transmission frequency for producing an output signal indicative of said one cordless telephone channel being occupied or noisy;

said monitoring circuit having a threshold of detection of a first value in said on-hook state and of a second value, higher than said first value, in said off-hook state;

said monitoring circuit of said base unit and said monitoring circuit of said handunit operating in said off-hook mode for detecting baseband digital control signals;

said cordless telephone set, in response to said output signal, causing said base unit and said handunit to change to a second cordless telephone channel.

9. The cordless telephone set of claim 8, wherein monitoring circuit monitors frequency content of a demodulated audio baseband signal to determine that a second channel is occupied, contains interference, or does not contain interference before causing the transmission of said command to change to said second channel.