Method for continually monitoring the status of a radio frequency link

• US 5,371,783 A
• Filed: 09/03/1993
• Issued: 12/06/1994
• Est. Priority Date: 05/29/1991
• Status: Expired due to Term

• Current Assignee: Video Technology Engineering Limited
• Original Assignee: Video Technology Engineering Limited
• Inventors: Rose, Chris, Heung, Charley
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Bost, Dwayne D.
• Application Number:
  US08/116,445
• Time in Patent Office: 459 Days
• Field of Search: 379/58, 379/61, 379/63, 455/34.1, 455/54.1, 455/62, 455/63, 455/67.1, 455/67.3, 455/67.4, 370/95
• US Class Current: 455/464
• CPC Class Codes: H04M 1/724 User interfaces specially adapted for cordless or mobile telephones
• CPC Class Codes: H04M 1/72505 Radio link set-up procedures
• CPC Class Codes: H04M 1/72516 with means for out-of-range alerting
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A digital cordless telephone apparatus comprising a microprocessor based battery powered portable handset unit and a microprocessor based stationary base unit which each transmit and receive digital voice data and digital command data to and from one another over multiple RF channel frequencies in the 902-928 MHz band, is disclosed. The user'"'"'s voice is digitized, scrambled and modulated for transmission and upon reception, the modulated digital voice data signal is demodulated, descrambled and decoded. A command data--voice data interface inserts command data packets into the stream of digital voice data prior to transmission and locates and captures command data packets from the incoming stream of received digital data. A silence sequence replaces the captured command data packet such that no audible sound is heard by the user. A link check command signal is also periodically transmitted by the base unit and acknowledged by the handset unit to evaluate the quality of the RF link toward triggering an automatic channel change or signaling an out-of-range condition.

Claims

1. In a digital cordless telephone apparatus of the type having a microprocessor based battery powered portable handset unit and a microprocessor based stationary base unit which each transmit and receive distinct digital voice data signals and digital command data signals to and from one another over one of two or more radio frequency links, a method for continually monitoring the status of said one of two or more radio frequency links, said method comprising the steps of:

transmitting from said base unit over said one of two or more radio frequency links for reception by said handset unit a link check command code as a digital command data signal;

receiving from said base unit from transmission by said base unit said transmitted link check command code;

transmitting from said handset unit over said one of two or more radio frequency links for reception by said base unit a link check acknowledgment code as a digital command data signal as an indication that said handset unit has received said link check command code;

receiving from said handset unit from transmission by said handset unit said transmitted link check acknowledgement code, receipt of which by said base unit serving to indicate to said base unit that said handset unit received said link check command code;

said link check command code and link check acknowledgment command code each being a constant value;

changing from said one of two or more radio frequency links to another one of said two or more radio frequency links when said one of two or more radio frequency links is no longer viable, the receipt by said handset unit of said link check command code and the receipt by said base unit of said link check acknowledgment code thereby serving to establish the existence and viability of said radio frequency link between said handset unit and said base unit.

2. The invention according to claim 1 wherein each of said one of two or more radio frequency links comprises a pair of radio frequencies, one frequency for transmission from said handset unit to said base unit and the second frequency for transmission from said base unit to said handset unit.

3. In a digital cordless telephone apparatus of the type having a microprocessor based battery powered portable handset unit and a microprocessor based stationary base unit which each transmit and receive distinct digital voice data signals and digital command data signals to and from one another over a radio frequency link, a method for continually monitoring the status of said radio frequency link, said method comprising the steps of:

transmitting from said base unit for reception by said handset unit a constant number of link check command codes as digital command data signals within a predetermined period of time;

receiving from said base unit from transmission by said base unit said transmitted link check command code;

transmitting from said handset unit for reception by said base unit a link check acknowledgment code as a digital command data signal as an indication that said handset unit has received said link check command code;

receiving from said handset unit from transmission by said handset unit said transmitted link check acknowledgment code, receipt of which by said base unit serving to indicate to said base unit that said handset unit received said link check command code;

counting the number of said link check command code signals transmitted by said base unit, the number of said link check command code signals received by said handset unit and the number of said link check acknowledgement code signals received by said base unit;

determining from the number of said link check command code signals transmitted to said handset unit and the number of said link check acknowledgement code signals received by said base unit, the number of missing link check command code signals and missing link check acknowledgement code signals;

counting the number of expected link check command code signals which were not received by said handset unit and the number of expected link check acknowledgement code signals which were not received by said base unit;

determining that said radio frequency link is no longer viable by determining whether said number of missing link check command code signals and said number of missing link check acknowledgement code signals exceed a predetermined number such that a viable radio frequency link is deemed to exist if less than said predetermined number of said link check acknowledgement code signals and link said check command code signals are missing.

4. The invention according to claim 3 wherein said method further includes the step of:

establishing a new radio frequency link between said base unit and said handset unit when said radio frequency link is no longer viable.

5. In a digital cordless telephone apparatus of the type having a microprocessor based battery powered portable handset unit and a microprocessor based stationary base unit which each transmit and receive distinct digital voice data signals and digital command data signals to and from one another over respective transmission and reception radio frequency channels selected from among multiple predetermined corresponding transmission and reception radio frequency channels, a method for the automatic selection and changing from one radio frequency channel to another without intervention by the user upon the detection of interference in said radio frequency channel or a total loss of the radio link between said base unit and said handset unit, said method comprising the steps of:

transmitting a link check signal from said base unit to said handset unit;

receiving said link check signal and transmitting a link check acknowledgement signal from said handset unit to said base unit;

detecting that said base unit has not received a predetermined number of said link check acknowledgement signals which serves to indicate the presence of undue interference in said radio frequency channel or the total loss of said radio link;

detecting that said handset has not received a predetermined number of said link check command code signals which serves to indicate the presence of undue interference in said radio frequency channel or the total loss of said radio link;

switching said transmission channel of said base unit from channel to channel pausing on each for a predetermined amount of time to generate at least one link check command signal and transmitting said signal to said handset after detection of said undue interference in said radio frequency channel or the total loss of said radio link;

switching said reception channel of said handset from channel to channel pausing on each for a predetermined amount of time to receive said link check signal generated by said base unit after detection of said undue interference in said radio frequency channel or the total loss of said radio link.

6. In a portable communications system of the type having a portable handset unit and a stationary base unit wherein said portable handset unit transmits signals to and receives signals from said stationary base unit over a radio frequency link, a method for continually monitoring the status of said radio frequency link, said method comprising the steps of:

transmitting from said base unit for reception by said portable handset unit a constant number of link check command codes;

receiving in said portable handset unit from said base unit from transmission by said base unit said link check command code;

transmitting from said portable handset unit for reception by said base unit a link check acknowledgment code as an indication that said portable handset unit has received said link check command code;

receiving from said portable handset unit from transmission by said portable handset unit said link check acknowledgment code, receipt of which by said base unit serving to indicate to said base unit that said portable handset unit received said link check command code;

counting the number of said link check command code signals transmitted by said base unit, the number of said link check signals received by said portable handset unit and the number of said link check acknowledgement signals received by said base unit;

determining from the number of said link check command code signals transmitted to said portable handset unit and the number of said link check acknowledgement signals received by said base unit, the number of missing link check command code signals and missing link check acknowledgement signals;

counting the number of expected link check command code signals which were not received by said portable handset unit and the number of expected link check acknowledgement code signals which were not received by said base unit;

determining that said radio frequency link is no longer viable by determining whether said number of missing link check command code signals and said missing link check acknowledgement code signals exceed a predetermined number such that a viable radio frequency link is deemed to exist if less than said predetermined number of link check acknowledgement code signals and link check command code signals are missing.

7. In a digital cordless telephone apparatus of the type having a microprocessor based battery powered portable handset unit and a microprocessor based stationary base unit which each transmit and receive distinct digital voice data signals and digital command data signals to and from one another over one of two or more radio frequency links, a method for continually monitoring the status of said one of two or more radio frequency links, said method comprising the steps of:

transmitting from said base unit over said one of two or more radio frequency links for reception by said handset unit a link check command code as a digital command data signal;

receiving from said base unit from transmission by said base unit said transmitted link check command code;

transmitting from said handset unit over said one of two or more radio frequency links for reception by said base unit a link check acknowledgment code as a digital command data signal as an indication that said handset unit has received said link check command code;

receiving from said handset unit from transmission by said handset unit said transmitted link check acknowledgement code, receipt of which by said base unit serving to indicate to said base unit that said handset unit received said link check command code;

changing from said one of two or more radio frequency links to another one of said two or more radio frequency links when said one of two or more radio frequency links is no longer viable, the receipt by said handset unit of said link check command code and the receipt by said base unit of said link check acknowledgment code thereby serving to establish the existence and viability of said radio frequency link between said handset unit and said base unit.

8. In a digital cordless telephone apparatus of the type having a microprocessor based battery powered portable handset unit and a microprocessor based stationary base unit which each transmit and receive distinct digital voice data signals and digital command data signals to and from one another over one of two or more radio frequency links, each of said two or more radio frequency links comprising a handset transmission channel and a base unit transmission channel, a method for continually monitoring the status of said one of two or more radio frequency links, said method comprising the steps of:

transmitting from said base unit over said one of two or more radio frequency links for reception by said handset unit a link check command code as a digital command data signal;

receiving from said base unit from transmission by said base unit said transmitted link check command code;

transmitting from said handset unit over said one of two or more radio frequency links for reception by said base unit a link check acknowledgment code as a digital command data signal as an indication that said handset unit has received said link check command code;

receiving from said handset unit from transmission by said handset unit said transmitted link check acknowledgement code, receipt of which by said base unit serving to indicate to said base unit that said handset unit received said link check command code;

said link check command code and link check acknowledgment command code being generated independent of the values of said digital voice data and said digital command data;

changing from said one of two or more radio frequency links to another one of said two or more radio frequency links when said one of two or more radio frequency links is no longer viable, said step of changing comprising the sub-steps of;

switching on said portable handset said base unit transmission channel from channel to channel pausing on each for a predetermined amount of time such that said portable base unit may receive said link check command code,

establishing said another one of said two or more radio frequency links comprising the sub-steps of;

switching on said base unit said base unit transmission channel,

transmitting from said base unit on said base unit transmission channel a plurality of said link check command codes,

listening for said link check command acknowledgment code from said portable handset unit,

returning to the sub-step of switching on said base unit until said link check command acknowledgment code is received,

the receipt by said handset unit of said link check command code and the receipt by said base unit of said link check acknowledgment code thereby serving to establish the existence and viability of said radio frequency link between said handset unit and said base unit.

9. The method according to claim 8 wherein said step of establishing further includes the sub-steps of:

listening on said base unit transmission channel for interference; and

returning to the step of switching on said base unit upon detecting undue interference.