GB2321164A

GB2321164A - Hand-off method in mobile radio communication system

Info

Publication number: GB2321164A
Application number: GB9726797A
Authority: GB
Inventors: Ki-Sung Jung
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1996-12-19
Filing date: 1997-12-19
Publication date: 1998-07-15
Anticipated expiration: 2017-12-19
Also published as: CN1188382A; KR19980049461A; GB9726797D0; KR100223370B1; GB2321164B; BR9706255A; CN1090428C

Abstract

In a hand-off method of a mobile station between base stations, while the mobile station is communicating with a first base station 301, the strength of a signal Va received from that base station is compared 302 with the strength of a signal Vb received from a second base station, and when the signal Vb from the second base station exceeds the signal Va from the first base station, the mobile station is connected to the second base station 303. If the signal strength Va from the first base station exceeds a first threshold value Vth at step 305, then the signal strength Vb from the second base station is compared 306 with a second threshold value Vth. If the signal Vb from the second base station is lower than the second threshold value, then the mobile station is disconnected at step 307 from the second base station and the mobile station then communicates with the first base station 308. If the signal Vb from the second base station is greater at step 306 than the second threshold Vth, then the mobile station remains connected to the second base station and the mobile station communicates with the first and second base stations 304 to repeat step 305.

Description

HAND-OFF METHOD IN MOBILE RADIO COMMUNICATION SYSTEM BACKGROUND OF THE INVENTION The present invention relates to a hand-off method in a mobile radio communication system.

In a mobile radio communication system, when a mobile station which is communicating with a base station moves to another base station, a so-called "hand-off" is performed to maintain the call by handing off the call to another base station.

Fig. 1 is a block diagram of a mobile radio communication system of the type to which the present invention may be applied. The mobile radio communication system includes a mobile station 100, a first base station 110, a second base station 120 and a base station controller (BSC) 130. The mobile station 100 which is a radio terminal detects a radio frequency (RF) signal from each base station and communicates with the first base station 110 or the second base station 120. The BSC 130 controls the first and second base stations 110 and 120.

Fig. 2 shows the relation between the strength of a signal from the base stations of the mobile radio communication system and distance between the mobile station and the base station. As the mobile station 100 moves, the strengths of the RF signals which are received from the first and second base stations 110 and 120 and detected by the mobile station 100 are illustrated.

Assuming that the mobile station 100 travels between the first and second base stations 110 and 120, each curve of Fig. 2 shows the detected strength of the signal received from each base station. Curve Va designates the detected strength of the signal received from the first base station 110 when the mobile station 100 travels from locations DO to D4. The signal Va received from the first base station 110 is strongest when the mobile station 100 is situated at DO and the weakest at D4. That is, the signal Va gradually decreases in strength as the mobile station 100 travels toward D4 from DO. Curve Vb designates the detected strength of the signal received from the second base station 120 when the mobile station 100 travels from DO to D4. The signal Vb received from the second base station 120 is weakest when the mobile station 100 is situated at DO and strongest at D4. That is, the signal Vb gradually increases in strength as the mobile station 100 travels toward D4 from DO.

Fig. 3 is a flow chart showing a conventional hand-off process in the mobile radio communication system, as will now be described with reference to Figs. 1 to 3. Assume that the mobile station 100 travels between DO and D4 as indicated in Fig. 2. If the mobile station 100 starts from DO, the mobile station 100 is connected to the first base station 110 at step 201. The mobile station 100 communicates with the first base station 110 at step 202.

While the mobile station 100 travels towards D4 from DO, the mobile station 100 detects the strengths of the signals received from the first and second base stations 110 and 120.

At step 203, the mobile station 100 checks whether the strength of the signal Vb received from the second base station 120 is greater than a threshold value Vth at which a call can be connected. If the strength of the signal Vb received from the second base station 120 is less than the threshold value Vth, the precess returns to step 202 to continue to communicate with the first base station 110. If the strength of the signal Vb received from the second base station 120 is greater than the threshold value Vth, the mobile station 100 is connected to the second base station 120 at step 204. The mobile station 100 then concurrently communicates with the first and second base stations 110 and 120 at step 205.

At step 206, the mobile station 100 checks whether the strength of the signal Va received from the first base station 110 is greater than the threshold value Vth. If so, the process returns to step 205 to continue to communicate with the first and second base stations 110 and 120. If the strength of the signal Va received from the first base station 110 is less than the threshold value Vth, the mobile station 100 is disconnected from the first base station 110 at step 207. The mobile station 100 communicates with the second base station 120 at step 208.

As mentioned above, while the mobile station 100 travels between locations DO and D3, it communicates with the first base station 110. Moreover, while the mobile station 100 travels between locations D1 and D4, it communicates with the second base station 120. Therefore, while the mobile station 100 travels between locations D1 and D3, it continues to communicate with both the first and second base stations 110 and 120. Since the mobile station 100 communicates with two base stations between D1 and D3, one mobile station occupies two communication channels.

Further, even if the mobile station 100 stops at a position between D1 and D3, the mobile station 100 occupies two communication channels. Hence, the communication channels are inefficiently used and the usable channel capacity of the mobile radio communication system is reduced.

SUMMARY OF THE INVENTION It is therefore an objective of the present invention to provide a hand-off method for more efficient use of communication channels in a mobile radio communication system.

Accordingly, the present invention provides a hand-off method of a mobile station between base stations comprising: while the mobile station is communicating with a first base station, comparing the strength of a signal received from that base station with the strength of a signal received from a second base station; and when the strength of the signal received from the second base station exceeds a predetermined level relative to the strength of the signal received from the first base station, connecting the mobile station to the second base station.

Preferably, the predetermined level is a given fraction of the strength of the signal received from the first base station. Preferably, the given fraction is unity.

Preferably, the method further comprises: comparing the strength of the signal received from the first base station with a first threshold value; and when the strength of the signal received from the first base station is lower than the first threshold value, disconnecting the mobile station from the first base station.

Alternatively, the method further comprises: comparing the strength of the signal received from the first base station with a first threshold value; when the strength of the signal received from the first base station exceeds the first threshold value, comparing the strength of the signal received from the second base station with a second threshold value; and when the strength of the signal received from the second base station is lower than the second threshold value, disconnecting the mobile station from the first base station.

Preferably, the first and second threshold values are equal.

The present invention also provides a radio communication system comprising: a plurality of base stations; a mobile station which is adapted, while communicating with a first base station, to compare the strength of a signal received from that base station with the strength of a signal received from a second base station; the system being such that if the strength of the signal received from the second base station exceeds a predetermined level relative to the strength of the signal received from the first base station, the mobile station is connected to the second base station.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 is a block diagram of a mobile radio communication system; Fig. 2 is a signal strength diagram; Fig. 3 is a flow chart showing a conventional hand-off process; and Fig. 4 is a flow chart showing a hand-off process according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Fig. 4, the hand-off method of the present invention will now be described. While travelling from location DO to D4, the mobile station 100 continues to detect the strength of the signal Va received from the first base station 110 and the strength of the signal Vb received from the second base station 120. When the mobile station 100 begins at location DO, the mobile station 100 communicates with the first base station 110 at step 301.

At step 302, the mobile station 100 checks whether the strength of the signal Vb received from the second base station 120 is greater than the strength of the signal Va received from the first base station 110. If the strength of the signal Vb received from the second base station 120 is less than the strength of the signal Va received from the first base station 100, the process returns to step 301 to communicate with the first base station 110.

However, if the strength of the signal Vb received from the second base station 120 is greater than the strength of the signal Va received from the first base station 110, the mobile station 100 is connected to the second base station 120 at step 303. The mobile station 100 then concurrently communicates with the first and second base stations 110 and 120 at step 304.

At step 305, the mobile station 100 checks whether the strength of the signal Va received from the first base station 110 is greater than the threshold value Vth at which a call can be connected. If so, the mobile station 100 checks whether the strength of the signal Vb received from the second base station 120 is greater than the threshold value Vth at step 306. If so, the process returns to step 304.

However, if the strength of the signal Vb received from the second base station 120 is less than the threshold value Vth, the mobile station 100 is disconnected from the second base station 120 at step 307. At step 308, the mobile station 100 communicates with the first base station 110.

Meanwhile, if the strength of the signal Va received from the first base station 110 is less than the threshold value Vth, the mobile station 100 is disconnected from the first base station 110 at step 309. The mobile station 100 communicates with the second base station 120 at step 310.

At step 311, the mobile station 100 checks whether the strength of the signal Va received from the first base station 110 is greater than the strength of the signal Vb received from the second base station 120. If so, the mobile station is connected to the first base station 110 at step 312 and the process returns to step 304, and if not, the process returns to step 310 to communicate with the second base station 120.

As noted above, the communication channels of the mobile radio communication system can be more effectively used with the present invention, since the time occupied in concurrent communication with two base stations is reduced.

Claims

1. A hand-off method of a mobile station between base stations comprising: while the mobile station is communicating with a first base station, comparing the strength of a signal received from that base station with the strength of a signal received from a second base station; and when the strength of the signal received from the second base station exceeds a predetermined level relative to the strength of the signal received from the first base station, connecting the mobile station to the second base station.

2. A hand-off method according to claim 1 in which the predetermined level is a given fraction of the strength of the signal received from the first base station.

3. A hand-off method according to claim 2 in which the given fraction is unity.

4. A hand-off method according to any preceding claim further comprising: comparing the strength of the signal received from the first base station with a first threshold value; and when the strength of the signal received from the first base station is lower than the first threshold value, disconnecting the mobile station from the first base station.

5. A hand-off method according to any one of claims 1-3 further comprising: comparing the strength of the signal received from the first base station with a first threshold value; when the strength of the signal received from the first base station exceeds the first threshold value, comparing the strength of the signal received from the second base station with a second threshold value; and when the strength of the signal received from the second base station is lower than the second threshold value, disconnecting the mobile station from the first base station.

6. A hand-off method according to claim 5 in which the first and second threshold values are equal.

7. A hand-off method of a mobile station between base stations, the method being substantially as described with reference to and/or as illustrated in FIG. 4 of the accompanying drawings.

8. A radio communication system comprising: a plurality of base stations; a mobile station which is adapted, while communicating with a first base station, to compare the strength of a signal received from that base station with the strength of a signal received from a second base station; the system being such that if the strength of the signal received from the second base station exceeds a predetermined level relative to the strength of the signal received from the first base station, the mobile station is connected to the second base station.

9. A radio communication system according to claim 8 in which the predetermined level is a given fraction of the strength of the signal received from the first base station.

10. A radio communication system according to claim 9 in which the given fraction is unity.

11. A radio communication system substantially as described with reference to FIG. 4 of the accompanying drawings.