Automatical channel selection system for a cordless telephone

Abstract: In a cordless telephone set, a single RF communications channel selection switch (SW1; SW4), which may be mounted on either of the base unit (120;420) and handset unit (100;400), selects the frequency for the unit to which it is mounted. The other unit of the base unit and handset unit selects alternate frequencies in response to a series of unacknowledged communications, until it receives an acknowledgement on a particular channel. After receiving an acknowledgement, an indication of the current RF communications channel is stored in memory. If no acknowledgement is received after trying all channels, then the original RF communications channel is selected.

Description: Field of the Invention The subject application generally concerns the field of cordless telephones, and specifically concerns cordless telephones having the capability of selecting one of at least two communication channels. Background of the Invention Cordless telephone sets comprise a base unit and a remote handunit which communicate with each other over radio frequency (RF) transmissions. Although these transmissions are of relatively low power, and consequently of limited range, it is nevertheless possible for close neighbors to own cordless telephones which operate on the same frequency, and thus interfere with each other. To alleviate this problem, many cordless telephones include the capability of selecting one of two or more RF channels for communication between the base unit and the remote handunit. Such a cordless telephone set is known from GE cordless telephone model number 2-9675 manufactured by Thomson Consumer Electronics, Inc. Indianapolis, Indiana. In such cordless telephone sets, a channel selection switch on the base unit and a channel selection switch on the remote handunit, select one of two or more crystal oscillator circuits, or program respective digital frequency synthesizers. Clearly, these channel selection switches must be set to select the same channel in order for the unit to operate. The channel selection switches must be user-accessible so that they may be switched when desired, but on the other hand, are usually placed behind covers and hidden from view because these switches are not frequently operated. The inclusion of a channel selection switch on both the base unit and the handunit is a source of problems in setting up the communications channel of the cordless telephone set, because each of the switches must be located by the user, and set to the same channel selection setting. It is also known from Patent JP59200538 or JP1089827 to provide the handy part of a cordless telephone with a resetting type manual switch. When this switch is depressed, a request to switch telephone channels is sent from the handy part of the fixed part of the telephone. A selection of a new channel is then made by the fixed part. An order to change frequency channel is sent from the fixed part to the handy part so that the same frequency channel is used by the two parts of the telephone. Such method of changing frequency channel needs the use of a control channel. this channel will use a part of the available frequency range for other purpose than transmitting the useful information signal. SUMMARY OF THE INVENTION In a cordless telephone set, a single RF communications channel selection switch, which may be mounted on either of the base unit and handset unit, selects the frequency for the unit to which it is mounted. The other unit of the base unit and handset unit selects alternate frequencies in response to a series of unacknowledged communications, until it receives an acknowledgment on a particular channel. After receiving an acknowledgment, an indication of the current RF communications channel is stored in memory. If no acknowledgment is received after trying all channels, then the original RF communications channel is selected. The cordless telephone according to the invention comprises the features exposed in claim 1. BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 shows, in schematic form, a cordless telephone set in accordance with the subject invention. FIGURES 2a and 2b are illustrations of flowcharts of the control program for the base unit controller of FIGURE 1, and are helpful for understanding the invention. FIGURES 3a and 3b are illustrations of flowcharts of the control program for the handunit controller of FIGURE 1, and are helpful for understanding the invention. FIGURE 4 shows another embodiment of the invention. DETAILED DESCRIPTION OF THE EMBODIMENT FIGURE 1 is a simplified illustration of a cordless telephone set comprising a handset unit 100 and a base unit 120. Handset unit 100 receives and transmits RF signals via an antenna 102. Antenna 102 is coupled to a duplex radio transceiver unit 104 which is capable of operation in a receiver mode and in a transmitter mode. In the receiver mode, transceiver unit 104 applied received and demodulated audio signals to an audio processor unit 106 for amplification and ultimate reproduction in speaker 108. Also in the receiver mode, transceiver 104 also provides digital data to the "receive data" (i.e., Rxdata) terminal of controller 112 In the transmitter mode, transceiver 104 receives audio signals, picked-up (i.e., detected) by microphone 110 and amplified by audio processor unit 106, for transmission to base unit 120. Also in transmitter mode, transceiver 104 receives "transmit data" (i.e., Txdata) from controller 112, for transmission to base unit 120. Controller 112 is coupled to a keyboard 114 for receiving keystroke commands from a user. Controller 112 also has two output lines A and B for controlling transceiver 104 to operate on RF communications channel A or on RF communications channel B. Handunit 100 also includes a power supply and charging unit 116 for supplying operating power to the circuitry of the handunit. Base unit 120 receives and transmits RF signals via an antenna 122. Antenna 122 is coupled to a duplex radio transceiver unit 124 which is capable of operation in a receiver mode and in a transmitter mode. In the receiver mode, transceiver unit 124 applies received and demodulated audio signals to an audio processor unit 126 for amplification and coupling to the telephone system via a telephone interface unit 128. Telephone interface unit 128 is connected to the telephone system via two terminals traditionally known as tip (T) and ring (R). Also in the receiver mode, transceiver 124 also provides digital data to the "receive data" (i.e., Rxdata) terminal of controller 132. Controller 132 has a control terminal C by which telephone interface unit 128 can be controlled to establish communication over the telephone system. In the transmitter mode, transceiver 124 receives audio signals, conveyed by the telephone system via telephone interface unit 128 and amplified by audio processor unit 126, for transmission to handunit 100. Also in transmitter mode, transceiver 124 receives "transmit data" (i.e., Txdata) from controller 132, for transmission to handunit 100. Transceiver 124 is coupled to a switch SW1 via two input lines A and B, which control transceiver 124 to operate on RF communications channel A or on RF communications channel B. Base unit 120 also includes an AC power supply unit 136 for supplying operating power to the circuitry of the base unit. Note that handunit 100 does not include a selection switch for selecting RF communication channels. The mounting of selection switch SW1 on base unit 120 only, eliminates the problem of having to locate a possibly-hidden selection switch on the handunit, and having to match the switch settings in order to set up communications between the base unit and handunit. The present invention ensures that the base unit and handunit still operate on the same channel in the following manner. Handunit controller 112, which may be a microcomputer, microprocessor, or a custom integrated circuit, is programmed to receive an acknowledgement from base unit 120 for any "on-hook" or "off-hook" command sent by handunit 100. If no acknowledgement is received, handunit controller 112 will resend the command a predetermined number of times, each time looking for the acknowledgement from the base unit. After the expiration of the predetermined number of transmissions, handunit controller 112 will then cause transceiver 104 to select its next RF communications channel, and repeat its transmission and wait for acknowledgement sequence. Although only two RF communications channels are set forth in the present embodiment, transceiver 104 may have as many as 10 channels in other embodiments. If an acknowledgement is received, handunit controller 112 stores information regarding its currently selected RF communications channel in its memory. If no acknowledgement is received, handunit controller 112 causes transceiver 104 to attempt communication on all channels in turn, and then return to the original channel. FIGURES 2a and 2b are flowcharts of portions of the control program for base unit controller 132, which may be a microcomputer, microprocessor, or a custom integrated circuit. Initialization of registers for execution of the main program is begun at step 200. The main program is entered at step 202.In step 204 a command is received from handunit 100. Steps 206 and 208 prepare for transmission of an acknowledgement to handunit 100 via an interrupt routine shown in FIGURE 2b. Initialization for the interrupt routine is begun at step 220. At step 222, the interrupt routine is entered. A determination is made at step 224 as to whether or not the transmit flag is on. If so, the command to be sent is loaded (step 226) and sent (step 228). If not the routine is exited at step 230, and returns to step 210 of the main program. The main program for handunit controller 112 is shown in FIGURE 3a. Initialization of registers for execution of the main program is begun at step 300. The main program is entered at step 302 wherein a determination is made as to which RF communications channel is the default channel. If channel A is the default channel, the program advances to step 304a, if not then it advances to step 304b. Keyboard 114 is checked at step 306, a key is pressed, the program advances to step 316 for the decoding of an on-hook or of-hook command. The transmit registers are then loaded with the appropriate command (step 318), the counter is loaded with the above-mentioned predetermined number of counts (320), and the transmit interrupt flag is turned on (step 322). The interrupt routine for handunit controller 112 is shown in FIGURE 3B. Initialization of registers for execution of the interrupt program is begun at step 340. The interrupt routine is entered at step 342. At step 344 a check is made to see if any commands need to be sent to base unit 320. If not, the routine is exited at step 370. If so, a check is made to see if all attempts at communication with the base unit have failed (step 346). If yes, then the transmissions are stopped and the original default channel is restored (step 368), and the routine exited at step 370. At step 348, a check is made to see if transmission should be made on the default channel. If yes, the routine advances to step 350 to determine which of A or B is the default channel. If A is the default channel then the routine advances to step 360a, if B is the default channel then the routine advances to step 360b. If at step 348 a determination was made not to transmit on the default channel, then the routine advances to step (355) where a check is made to determine the non-default channel. If A is the non-default channel then the routine advances to step 360a, if B is the non-default channel then the routine advances to step 360b. At step 365 the data is sent to base unit 120, and the routine is exited at step 370. The main program is reentered at step 314, and loops back to step 306. Handunit 100 now expects to receive an acknowledgement to its transmission from base unit 120 and looks for such acknowledgement (step 308). At step 310 a check is made to see what channel the base unit is using. If channel A, then this fact is stored (step 312a), if channel B, then an indication of channel B is stored (step 312b). Thus, a system has been described which allows a base unit and a handunit of a cordless telephone set to operate on the same RF communications channel while requiring only one set-up switch. One skilled in the art will note that the set-up switch could equally be located in the handunit rather than in the base unit, and this modification is fully intended to be within the scope of the invention. Such an arrangement is shown in FIGURE 4 which other than the placement of the selection switch is identical to FIGURE 1, and need not be described in detail again.

Claims: A cordless telephone set, comprising: a handunit (100, 400) including a controller (112; 412); a base unit (120; 420) having a base unit controller (132; 432) and having an output for coupling to a telephone system (T, R); one of said base unit and said handunit being a unit having a user-operable switch (SW1) for selecting one of a plurality of RF communications channels as a default channel for transmitting to the other of said base unit and said handunit; the other of said base unit and said handunit being a unit not having a switch for selecting one of said RF communications channels as a default channel; said controller of said other unit being adapted to cause transmission to said unit having said user-operable switch on a first one of said plurality of said RF communications channels; said controller of said other unit, in the absence of receipt of an acknowledgment signal from said unit having said user-operable switch, being adapted to automatically switch to another of said plurality of said RF communications channels; and said controller of said other unit, upon receipt of said acknowledgment signal from said unit having said user-operable switch, being adapted to determine that the currently selected one of said plurality of RF communications channels is said selected default channel of said unit having said user-operable switch, and stores current channel information as default channel information. The cordless telephone set of Claim 1 wherein: said base unit (120) further includes first antenna means (122) for receiving and transmitting RF signals; first transceiver means (124) coupled to said first antenna means and operating in a first mode for receiving said RF signals from said first antenna means, and a second mode for applying RF signals to said first antenna means, said transceiver means being capable of operating on one of at least two radio frequency (RF) communications channels; telephone system interface means (128) for coupling outgoing audio signals to, and incoming audio signals from, a telephone system; first audio processing means (126) coupled to said telephone system interface means for receiving said incoming audio signals, amplifying said incoming audio signals and applying said amplified incoming audio signals to said transceiver means in said second mode of operation, said audio processing means also amplifying said outgoing audio signals and coupling said amplified outgoing audio signals to said telephone system interface means in said first mode of operation; and first control means (132) coupled to said first transceiver means and to said telephone interface means for controlling connection of said telephone interface means to said telephone system; and said handunit (100) further includes second antenna means (102) for receiving and transmitting RF signals; second transceiver means (104) coupled to said antenna means and operating in a first mode for receiving said RF signals from said antenna means, and a second mode for applying RF signals to said antenna means, said transceiver means being capable of operating on one of at least two radio frequency (RF) communications channels; microphone means (110) for receiving sound and converting it to outgoing audio signals; speaker means (108) for converting incoming audio signals to sound; second audio processing means (106) coupled to said second transceiver means for receiving said incoming audio signals, amplifying said incoming audio signals and applying said amplified incoming audio signals to said speaker means in said first mode of operation, said audio processing means also being coupled to microphone means for amplifying said outgoing audio signals and coupling said amplified outgoing audio signals to said second transceiver means in said second mode of operation; and characterized in that said means for selecting (SW1) said one RF communications channel of said first transceiver is in said base unit and; said handunit control means (112) is coupled to said transceiver means for controlling a selection of said one RF communications channel of said second transceiver means, in response to a signal received from said base unit. The cordless telephone set of claim 2 characterized in that said means for selecting (SW1) said one RF communications channel is a user-operable switch. The cordless telephone set of claim 1, wherein: said handunit (100) further includes second antenna means (402) for receiving and transmitting RF signals; second transceiver means (404) coupled to said antenna means and operating in a first mode for receiving said RF signals from said antenna means, and a second mode for applying RF signals to said antenna means, said transceiver means being capable of operating on one of at least two radio frequency (RF) communications channels; microphone means (410) for receiving sound and converting it to outgoing audio signals; speaker means (408) for converting incoming audio signals to sound; second audio processing means (406) coupled to said second transceiver means for receiving said incoming audio signals, amplifying said incoming audio signals and applying said amplified incoming audio signals to said speaker means in said first mode of operation, said audio processing means also being coupled to microphone means for amplifying said outgoing audio signals and coupling said amplified outgoing audio signals to said second transceiver means in said second mode of operation; and control means (412) coupled to said transceiver means for receiving and sending digital data; a base unit (420) including first antenna means (422) for receiving and transmitting RF signals; first transceiver means (424) coupled to said first antenna means and operating in a first mode for receiving said RF signals from said first antenna means, and a second mode for applying RF signals to said first antenna means, said transceiver means being capable of operating on one of at least two radio frequency (RF) communications channels; telephone system interface means (428) for coupling outgoing audio signals to, and incoming audio signals from, a telephone system; first audio processing means (426) coupled to said telephone system interface means for receiving said incoming audio signals, amplifying said incoming audio signals and applying said amplified incoming audio signals to said transceiver means in said second mode of operation, said audio processing means also amplifying said outgoing audio signals and coupling said amplified outgoing audio signals to said telephone system interface means in said first mode of operation; and first control means (432) coupled to said first transceiver means and to said telephone interface means for controlling connection of said telephone interface means to said telephone system, characterized in that said means for selecting (SW4) said one RF communications channel of said first transceiver is in said handunit and said first control means controlling a selection of said one RF communications channel of said second transceiver means, in response to a signal received from said handunit. The cordless telephone set of claim 4 characterized in that said means for selecting said one RF communications channel is a user-operable switch. The cordless telephone set of claim 1 characterized in that said signal received from the other of said handunit and said base unit is an acknowledgement signal.

Inventors: MCCARTHY DENNIS RONALD, MCCARTHY, DENNIS RONALD
Applicants: THOMSON CONSUMER ELECTRONICS, THOMSON CONSUMER ELECTRONICS, INC.
Application year: 1991
Main classification: H04M1
IPC codes: H04Q7, H04M1