GB2303765A

GB2303765A - Low-power Automatic Location Registering Method in a Digital Cordless Telephone System

Info

Publication number: GB2303765A
Application number: GB9613565A
Authority: GB
Inventors: Kyou-Woong Kim; Pil-Woo Lee
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1995-07-25
Filing date: 1996-06-27
Publication date: 1997-02-26
Anticipated expiration: 2016-06-27
Also published as: CN1144448A; GB2303765B; GB9613737D0; KR970008992A; GB9613565D0

Abstract

A method of automatically registering a mobile station at one of a plurality of base stations positioned in respective unit cell areas is disclosed. The mobile station receives in a standby mode a CIS signal transmitted from the base station. The location area identification (LAI) of the base station, included in the CIS signal, is compared with that stored in the mobile station, to determine whether the identification signal originates from the base station at which the mobile station was last registered. If they are different, the LAI of the base station is stored in the mobile station and the mobile station transmits in an active mode a registration message, to register the mobile station at the said base station.

Description

LOW-POWER AUTOMATIC LOCATION REGISTERING METHOD IN DIGITAL CORDLESS TELEPHONE SYSTEM The present invention relates to a digital cordless telephone system, and more particularly, to a low-power automatic location registering method.

With recent developments of mobile communication technology, digital cordless telephone systems have come to the fore. A second generation cordless telephone (CT-2) allows communication within 200m from the place where a public base station called a "Telepoint" is established.

The CT2 includes a handset and private base station, like the conventional cordless telephone system. Further, the CT2 includes a public base station. The base station of the CT2 is connected to a public switched telephone network (PSTN) by a cable. When an incoming call is received from the PSTN, a ring signal is transmitted to some or all of the cordlessly connected mobile stations.

When the incoming call is received from the PSTN, the base station shown in FIG. 1 transmits a ring signal to the mobile station shown in FIG. 2 and then enters a communication mode.

First, the operation of transmitting the ring signal will be described. If the incoming call is received from the PSTN, a line interface 100 of the base station supplies a ring signal and a line signal supplied from the PSTN line and controls the hook-off and hook-on operations. A controller 130 detects the ring signal from the line interface 100 and controls a time division duplex (TDD) processor 120 so that ring data is generated according to the CT2-CAI (Common Air Interface) standardization. The ring data is transmitted to an antenna 180 through a radio frequency (RF) transceiver 140. As described above, if the ring data is transmitted from the base station, an RF transceiver 210 of the mobile station receives the ring data transmitted via an antenna 200. A TDD processor 220 separates control data from the received ring data.When the separated control data is applied, a controller 240 controls a tone generator 260 to generate a tone. The tone is transmitted as a ring signal through a ringer 270.

Next, the operation of establishing a communication mode will be described.

If a subscriber of one of a plurality of mobile stations presses a communication button on a key pad 250 after confirming the ring signal in response to the transmitted ring signal, the base station and mobile station enter a communication mode. In other words, the controller 240 controls the TDD processor 220 so that the control data is generated under the CT2-CAI standardization. The control data is transmitted to the base station through the RF transceiver 210 and antenna 200.

The data transmitted from the mobile station is received by the RF transceiver 140 through the antenna 180 of the base station. The data from which the control data is separated by the TDD processor 120 is applied to the controller 130.

The controller 130 controls the hook controller of the line interface 100 to be in a hook-off state and applies the line signal from the PSTN line to an ADPCM processor 110.

The PSTN line signal is converted into digital data by the ADPCM processor 110. The converted digital data is processed by the TDD processor 120 together with the control data generated by the controller 130 and then is transmitted to the mobile station through the RF transceiver 140 and antenna 180.

The data transmitted from the base station under the CT2 CAI is received in the RF transceiver 210 through the antenna 200 of the mobile station. The received data is separated into voice data and control data by the TDD processor 220. The control data is transmitted to the controller 240 and the voice data is output to a speaker 280 through the ADPCM processor 230.

The communication between the external subscriber of the PSTN and the subscriber of the mobile station is allowed by the aforementioned operation.

The original cordless telephones were used only for calling from a telepoint. However, using manual location registration, a call from a registered location transmitted from the corresponding base station could be received.

However, as shown in FIG. 3, when a handset (HS) of the digital cordless telephone moves through multiple locations (base stations A, B and C), the incoming call from the corresponding base station of the respective locations is only received in the mobile station if a user's registers and releases the base station of the respective locations to which he moves.

To overcome such cumbersome work, there has been proposed an automatic location registration, which is disclosed in detail in Korean Patent Application No. 95-16177, entitled "Automatic location registering method in a digital cordless telephone". According to this automatic location registering method, the mobile station analyzes a cordless fixed part identification and status (CIS) signal which is a position trace signal periodically transmitted from the base station to check whether the mobile station itself is locally registered on the base station. If it is found that the mobile station is not registered, the location area identification of the base station contained in the CIS signal is stored to register the mobile station at the base station and then a call transmitted from the base station can be received.

In general, the controller 240 of the mobile station is in a low power standby mode in which the transmitting and receiving operations are not performed since the power supply to components except the controller 240 and pulse generator 300 is shut off. During the standby mode, the controller 240 is periodically woken up by the pulse generator 300. In a predetermined time, the power is supplied to a receiver of the RF transceiver 210 and the TDD processor 220 to allow call reception. If the mobile station is called, the controller 240 controls all components of the mobile station to be in an active mode during which power is supplied to all components of the mobile station. If the mobile station is not called, the mobile station returns to the standby mode.

For example, when the mobile station moves from a position 301 within range of base station A (FIG. 3) to a position in range of base station B, if the position trace signal is transmitted from base station B, the controller 240 enters an active mode to check whether the mobile station is registered on the base station B. In such a case, since the mobile station is not registered on the base station B, a registration request message is transmitted. If a registration permit message is received in response to the registration request message, the location area identification of the base station B is stored and the mobile station is automatically registered on the base station B.

According to the conventional automatic location registration, since the checking of the registration is performed in the active mode, power consumption is high. In other words, even if the position trace signal is transmitted from the registered base station, the mobile station must check the registration in the active mode whenever there is a need to do so. Thus, power may be consumed even though no re-registration occurs.

Therefore, it is an object of the present invention to provide an automatic location registering method with less power consumption.

To accomplish the above object, there is provided a method of automatically registering a mobile station at one of a plurality of base stations positioned in respective unit cell areas comprising: receiving at the mobile station in a standby mode an identification signal transmitted from the base station; determining in the standby mode whether the identification signal originates from the base station at which the mobile station was last registered; and if not, transmitting from the mobile station in an active mode a registration message, to register the mobile station at the said base station.

Preferably, the mobile station returns to the standby mode after transmitting the registration message.

To cater for the possibility of an overlap in unit cell areas, it is preferred that the registration message is transmitted only if an identification signal originating from the base station at which the mobile station was last registered is not received in a predetermined period of time.

The unique identification signal may be a CIS signal. In that case, it is preferred that the location area identification (LAI) of the base station, included in the CIS signal, is compared with that stored in the mobile station, to determine whether the identification signal originates from the base station at which the mobile station was last registered and, if they are different, the LAI of the base station is stored in the mobile station.

The above objects and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment with reference to the attached drawings in which: FIG. 1 is a block diagram of a base station for a digital cordless telephone; FIG. 2 is a block diagram of a mobile station for a digital cordless telephone; FIG. 3 shows a mobile station moving between base stations of the digital cordless cellular telephone network; FIG. 4 is a format diagram of a cordless fixed part identification and status (CIS code word) transmitted from the base station; and FIG. 5 is a process flowchart of an automatic location registering method according to the present invention.

First, a cordless fixed part identification and status (to be referred as a "CIS code word" hereinafter) periodically transmitted from the base station for performing the operation of the present invention will be described. The CIS code word is periodically transmitted from the base station to trace the position of the mobile station, which is described in FIG. 4. Accordingly, the mobile station is automatically registered on the base station.

Referring to FIG. 4, a traffic channel available (TCA) 402 represents the availability of traffic channels. A signalling receiver available (SRA) 404 represents the availability of the base station capable of receiving a signal generated from the mobile station. An incoming call indicator (ICI) 406 represents the presence of an incoming call from the base station. An automatic location registration (ALR) 408 represents permission to transmit the automatic location registration message from the mobile station. A power (PWR) 410 represents the power mode of the signal transmitted from the base station: "1" corresponds to a low-power mode transmission.An in-range indicator (IRI) 412 represents the need to notify a user of the presence of a signal from the base station: "0" indicates that the user is not to be notified of the presence of the signal transmitted from the base station, if any.

A format type (FT) 414 and an address code word (ACW) 416 have a value of 0.1 to indicate the CIS code word. A local cell identification (LCI) 418 represents a cell of the base station transmitting the CIS code word. A CIS identification (CIS~I) 422 is an identifier indicating that the current code is a CIS code word. A method (M) 424 represents a CIS code word transmission method. A link identification code (LID) 426 represents the system identity of a base station operator. A CIS error check 428 is a kind of parity and detects whether an error is contained in the CIS code word. Further, a location area identification (LAI) 420, which is directly related to the operation of the present invention, represents a location area identification of the base station transmitting the CIS code word.

To implement the present invention, the mobile handset is capable of supporting location registration by setting the LRP bit in TERM CAP and the ALR bit in the CIS.

If the base station transmits the CIS code word to trace the position of a mobile station, the mobile station performs the operation of the present invention through the process as shown in FIG. 5. It is assumed that the mobile station is in a standby mode.

As described above, during the standby mode of the mobile station, the controller 240 blocks the power supply to all components other than the controller 240 itself and pulse generator 300. The controller 240 is periodically woken up from the low-power mode by the pulses generated by the pulse generator 300 and supplies the power to the receiver of the RF transceiver 210 and TDD processor 220, which are minimum parts for processing the received message, thereby allowing reception. If the CIS code word is transmitted from the base station, the controller 240 checks whether a sync signal is detected in step 502 and checks whether the CIS code word is detected in step 504.

If it is established that the CIS cord word is detected, the controller 240 checks the LID 426 indicating the base station is capable of offering a communication service to determine the communication service possibility from the base station, in step 506. The fact that the LID 426 is detected indicates that the communication service is offered. In this case, in step 508, the controller 240 compares the LAI stored in an incorporated RAM with the LAI 420 within the CIS code word to check whether they are identical with each other. The LAI stored in the RAM incorporated in the controller 240 is the value of the LAI of the CIS code word previously transmitted from the base station. If the mobile station is positioned at 301 of FIG.

3, the LAI stored in the RAM indicates the area information of the base station A.

Thereafter, if the mobile station is still positioned at 301, the LAI stored in an incorporated RAM and the LAI 420 within the CIS code word are identical with each other.

Then, the timer installed within the controller 240 is reset and operates again from the start. The timer begins to operate in accordance with the CIS code word transmission period of the base station and the automatic location registration occurrence period.

In the meanwhile, if the mobile station moves to a position 303, the transmitted CIS code word corresponds to the area of the base station B. Then, in step 508, the controller 240 determines that the LAI stored in the incorporated RAM and the LAI 420 within the CIS code word are different from each other. If it is determined that the LAIs are not identical, in step 512, the controller 240 checks whether the internal timer has expired. Then, in step 514, the controller 240 converts the mode into an active mode during which power is supplied to all components of the mobile station.

Thereafter, in step 516, the controller 240 stores the location area identification of the base station B (the value of the LAI 420 of the CIS code word) in the RAM as that of the mobile station and then sends an FA3.29 message (relocation registration) to the corresponding base station. Then, the controller 240 returns to the standby mode in step 518. Since the location area identification of the base station B is stored in the mobile station, the mobile station can receive an incoming call transmitted from the base station B even if the mobile station is positioned in the area of the base station B. In other words, the mobile station is automatically registered on the base station B.

Referring to FIG. 3, base stations appear to have their own areas. In practice, however, the base stations are devised so as to overlap with one another. Therefore, if the mobile station is moved to a position 302 which is affected by both the base stations A and B, the transmitted LAI of the CIS code word has different values at different times. In such a case, since the timer is reset whenever the CIS code word is received, the location re-registration is not performed. However, if the CIS code word is received differently throughout a preset time, the mobile station is positioned within the area of a new base station.

Therefore, according to the present invention, if it is determined that the LAI of the CIS code word and that stored in the RAM of the mobile station are different from the previous LAI, location re-registration is automatically performed.

As described above, in the automatic location registering method according to the present invention, power consumption can be reduced by checking the registration of a mobile station at a base station in a standby mode and by registering the mobile station in an active mode, only when the mobile station is not registered on the base station.

Also, The location registration is performed only if it is determined that the LAI of the CIS code word and that stored in the RAM of the mobile station are different for a preset interval, thus allowing stable registration of the new location.

Claims

CLAIMS:

1. A method of automatically registering a mobile station at one of a plurality of base stations positioned in respective unit cell areas comprising: receiving at the mobile station in a standby mode an identification signal transmitted from the base station; determining in the standby mode whether the identification signal originates from the base station at which the mobile station was last registered; and if not, transmitting from the mobile station in an active mode a registration message, to register the mobile station at the said base station.

2. A method according to claim 1 in which the mobile station returns to the standby mode after transmitting the registration message.

3. An method according claim 1 or claim 2 in which the registration message is transmitted only if an identification signal originating from the base station at which the mobile station was last registered is not received in a predetermined period of time.

4. A method according to any preceding claim in which the unique identification signal is a CIS signal.

5. A method according to claim 4 in which the location area identification (LAI) of the base station, included in the CIS signal, is compared with that stored in the mobile station, to determine whether the identification signal originates from the base station at which the mobile station was last registered and, if they are different, the LAI of the base station is stored in the mobile station.

6. A method of automatically registering a mobile station at one of a plurality of base stations positioned in respective unit cell areas substantially as described herein with reference to the accompanying drawings.