Method of changing the code of a radio communication system

A method of changing the code of a radio communication system having a main unit and at least one remote unit is provided. The method generally includes in an embodiment the step of setting the code transmission frequency of the main unit of the radio communication system at a value within a frequency gap separating a first channel from a second channel of the main unit. The method also includes the step of setting the code transmission frequency of the remote unit at a value within a frequency gap separating a first channel from a second channel of that remote unit. The method further includes the step of selecting a code for encoding communication signals between the main and remote units and transmitting the selected code from one of the main and remote units to the other at the code transmission frequency.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a method of changing the code of a radio
 communication system, and more particularly to such a method which
 achieves the change of the code of a radio communication system through a
 gap between channels.
 2. Description of the Prior Art
 In a wireless telephone, a particular code is set for communication between
 the base and the hand set to prevent others from using the line
 unlawfully. However, because the code of a wireless telephone can easily
 be decoded by conventional techniques, the code must be regularly changed.
 Theexposure of the code of a wireless telephone to the public invites
 good-for-nothing persons to use the line without payment, and the wireless
 telephone owner will receive a high amount of debit note from the
 telephone (exchange) company. In order to protect a wireless telephone
 from being used unlawfully, the set code of the wireless telephone must be
 regularly changed. Even if the set code of the telephone line is decoded
 by an intruder, the intruder can only use the line unlawfully for a short
 period of time if the wireless telephone owner frequently changes the set
 code. Conventionally, there are two methods used for changing the code of
 a wireless telephone. One is achieved by means of charging terminals,
 i.e., the code is changed by means of the battery charger when the hand
 set is put back and attached to the base. It is necessary to attach switch
 means 12;15 to the base and the hand set when using charging terminals 11
 and battery charger 11. When charging, the switch means 12;15 are
 respectively switched to the charging circuit 13 and the battery 16. When
 changing the code, the switch means 12;15 are respectively switched to the
 microcontrollers 5;1. However, because the signal for charge charging and
 the signal for code changing are different, it is complicated to design
 the switch means 12;15, and a software must be provided subject to a
 communication protocol for support. Therefore, this method is not
 economic. The other method is achieved by means the hardware of the base
 and the hand set. This method is less expensive, however it interferes
 with the communication signal in the channel under use when changing the
 code. In a regular 25-channel 46/48 MHz wireless telephone, the changing
 of the set code is achieved through the transmitting frequency of 43.72
 MHz.about.46.97 MHz at the base and the transmitting frequency of 48.76
 MHz.about.49.99 MHz at the hand set. However, because the 25 channels of
 the wireless telephone are of regular communication channels, using one of
 the 25 channels to change the set code may: (1) interfere with the
 communication of the subscriber's telephone, (2) cause a code change
 failure, and/or (3) cause a communication failure between the base and the
 hand set due to different codes.
 SUMMARY OF THE INVENTION
 The present invention has been accomplished to provide a method of changing
 the code of a radio communication system which eliminates the aforesaid
 problems. The method of changing the code of a radio communication system
 having a main unit and a remote unit, includes the steps of: (1) setting
 the communication frequency of the main unit of the radio communication
 system at the gap between a first channel and a second channel of the main
 unit, (2) setting the communication frequency of the ot unit at the gap
 between a first channel and a second channel of the remote unit, and (3)
 changing the set code after setting of the communication frequency of the
 main unit and the communication frequency of the remote unit. The
 communication frequency of the main unit is the transmitting frequency of
 the main unit, and is set at the gap between the first channel and the
 second channel of the main unit through a frequency selector mounted in
 the main unit. According to one embodiment of the present invention, the
 frequency of the first channel of the main unit in 46.87 MHz, the
 frequency of the second channel of the main unit is 46.93 MHz, and the
 transmitting frequency set by the frequency selector of the main unit is
 46.90 MHz. The radio communication system can be a wireless telephone. The
 transmitting frequency of the remote unit is the transmitting frequency of
 the remote unit, and is set at the gap between the first channel and the
 second channel of the remote unit through a frequency selector mounted in
 the remote unit. The frequency of the first channel of the remote unit is
 49.93 MHz, the frequency of the second channel of the remote unit is 49.97
 MHz, and the tramsmitting frequency set by the frequency selector of the
 remote unit is 49.95 MHz. The main unit of the radio communication system
 is controlled to: (a) confirm that the remote unit has been put back to
 the main unit, (b) send a recognition signal to the remote unit upon
 receipt of a code change request signal from the remote unit, (c) receive
 a new code from the remote unit, (d) send a new code to the remote unit,
 and (e) receive a recognition signal from the remote unit after dispatch
 of the new code to the remote unit. The remote unit of the radio
 communication system is put back to the main unit, and then controlled to:
 (a) send a code change request signal to the main unit, (b) send a new
 code to the main unit upon receipt of a recognition signal from the main
 unit, (c) receive the new code from the main unit, and, (d) send a
 recognition signal to the main unit upon receipt of the new code from the
 main unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 The present invention uses the hardware architecture of the radio
 communication system (wireless telephone) to achieve a code change. When
 changing the set code, the channel selector is controlled to set the
 communication frequency between two channels, so that the change of the
 set code does not interfere with the communication of the wireless
 telephone. As illustrates in FIG. 2, the wireless telephone is comprised
 of a transmitter unit and a receiver unit. The transmitter unit is
 comprised of a microcontroller 1, a channel selector 2, a modulator and
 transmitter circuit 3, and a transmitting antenna 4. The receiver unit is
 comprised of a microcontroller 5, a channel selector 6, a receiver and
 demodulator circuit 7, and a receiving antenna 8. This design eliminates
 the use of switch means, therefore the cost of the system is low.
 Referring to FIG. 3, the operation of changing the set code is proceeded
 through the gap between a first channel for example channel 23 and a
 second channel for example channel 24. At first, the communication
 frequency of the base is set in gap between the first channel and the
 second channel, then the communication frequency of the hand set is set at
 the gap between the first channel and the second channel, and then the set
 code is changed after the setting of the communication frequency of the
 base and the hand set has been done.
 The main point of the present invention is to use the gap between two
 channels as the communication frequency when changing the set code. This
 design is economic, and does not interfere with the communication of the
 radio communication system.
 In FIG. 3, the communication frequency of the hand set means the
 transmitting frequency, and the hand set has a receiver for receiving
 signal of the transmitting frequency. As indicated, the frequency selector
 of the hand set is set at the gap between 49.93 MHz of channel 23 and
 49.97 MHz of channel 24, i.e., at 49.95 MHz. The communication frequency
 of the base is set at the gap between 46.87 MHz of channel 23 and 46.93
 MHz of channel 24, i.e., at 46.90 MHz. Of course, the hand set has a
 receiver adjusted to 46.90 MHz to receive the signal.
 Referring to FIG. 4, when changing the code, it proceeds to block 31 where
 it is decided if to change the code or not. If the answer is positive, it
 proceeds to block 32. On the contrary, if the answer is negative, it
 proceeds to block 33. When proceeding to block 32, the communication
 frequency is set between two channels 23;24, i.e., at frequency 49.95 MHz
 and 46.90 MHz respectively. The communication frequency can be set between
 either two adjacent channels, however the gap between two adjacent
 channels must be relatively broader, so as to prevent the occurrence of an
 interference. After block 32, it proceeds to block 34 to start code change
 by means of for example hand shaking communication protocol. At first, the
 base sends a code change recognition signal to the hand set to recognize
 the action of code change, then receives a new code from the hand set, and
 then sends the new code to the hand set for recognition, and then receives
 a recognition signal from the hand set. At the same time, the hand set
 sends a signal to the base, asking for changing the set code, then sending
 a new code to the base after receipt of a recognition signal from the
 base, and then receiving the new code from the base, and then sending a
 recognition signal to the base after receipt of the new code from the
 base. If the code is not to be changed, it proceeds to block 33 where the
 hand set and the base are respectively locked at or scan the set channel,
 which can be either of the aforesaid 25 channels. For example, the hand
 set and the base are set at 48.76 MHz and 43.73 MHz of the respective
 first channel. After block 33, it proceeds to block 35 to run different
 procedures for different functions such as dialing, phone on, phone off,
 alarm, etc.
 It is to be understood that the drawings are designed for purposes of
 illustration only, and are not intended as a definition of the limits and
 scope of the invention disclosed. For example, the present invention can
 be used in a wireless telephone as well as any of a variety of radio
 communication systems. By means of selecting a gap frequency between two
 channels, the execution of the change of the set code does not interfere
 with the communication of the radio communication system.