Cellular communication system, and mobile and base stations used in the same

• US 6,141,555 A
• Filed: 06/03/1998
• Issued: 10/31/2000
• Est. Priority Date: 06/09/1997
• Status: Expired

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Sato, Toshifumi
• Primary Examiner(s): Vo, Nguyen
• Assistant Examiner(s): NGUYEN, DUC M
• Application Number:
  US09/090,013
• Time in Patent Office: 881 Days
• Field of Search: 455/436, 455/437, 455/438, 455/439, 455/442, 370/331, 370/332, 370/333, 370/342, 370/347
• US Class Current: 455/437
• CPC Class Codes: H04W 36/18 for allowing seamless reselection, e.g. soft reselection
• CPC Class Codes: H04W 36/185 using make before break
• CPC Class Codes: H04W 48/12 using downlink control channel

Abstract

When a mobile station becomes a soft handover state, a reception quality monitor 104 measures reception quality of a pilot signal from each base station. Base station specifying means 105 generates a base-station select signal (BSse1) to specify base stations that have transmitted pilot channels of inferior reception quality. The base-station select signal is multiplexed with transmission data (r-txd), and the multiplexed signal is spread at a spreading circuit. The spread signal is transmitted to plural base stations through a transmitter 111 and a duplexer 102. Then the base stations specified by this base-station specify signal stops transmission of downward signals.

Claims

1. A cellular system using a direct spread code division multiple access system, in which a mobile station performs soft handover with plural base stations,

said mobile station comprising:

downward reception quality monitoring means for monitoring reception quality of downward signals from the plural base stations that are in the soft handover state;

base-station specifying means for comparing reception quality of downward signals from respective base stations monitored at said downward reception quality monitoring means, and for generating a base-station specify signal which specifies a base-station having the best reception quality monitoring result to maintain a signal transmission;

multiplexing means for multiplexing the base-station specify signal into an upward signal to be sent to said plural base stations; and

reception means for performing combined reception of receive signals from said plural base stations that are in the soft handover state, and

said base stations each comprising;

demodulation means for demodulating the base-station specify signal multiplexed in the upward signal; and

transmission control means for receiving the base-station specifying signal demodulated by said demodulation means, for keeping a downward signal transmission when its own base station is specified in the base-station specify signal, and for stopping a downward signal transmission when its own base station is not specified in the base-station specify signal.

2. The cellular system according to claim 1, wherein said transmission control means ignores contents of said base-station specify signal and keeps a downward signal transmission when an error in the base-station specify signal is detected.

3. The cellular system according to claim 1, wherein said base station specifying means generates a base-station specify signal which specifies plural base stations each having a smaller difference of downward reception quality monitoring result than a predetermined value to maintain a signal transmission.

4. The cellular system according to claim 1, wherein said base station specifying means generates a base-station specify signal which specifies plural base stations each having smaller reception quality monitoring result than a predetermined value to maintain a signal transmission.

5. In a cellular system using a direct spread code division multiple access system, a mobile station used in the cellular system for performing soft handover with plural base stations, comprising:

downward reception quality monitoring means for monitoring reception quality of downward signals from the plural base stations that are in the soft handover state;

base-station specifying means for comparing reception quality of downward signals from respective base stations monitored at said downward reception quality monitoring means, and for generating a base-station specify signal which specifies a base-station having the best reception quality monitoring result to maintain a signal transmission;

multiplexing means for multiplexing the base-station specify signal into an upward signal to be sent to said plural base stations; and

reception means for performing combined reception of receive signals from said plural base stations that are in the soft handover state.

6. The mobile station according to claim 5, wherein said base station specifying means generates a base-station specify signal which specifies plural base stations each having a smaller difference of reception quality monitoring result than a predetermined value to maintain a signal transmission.

7. The mobile station according to claim 5, wherein said base station specifying means generates a base-station specify signal which specifies plural base stations each having smaller reception quality monitoring result than a predetermined value to maintain a signal transmission.

8. A base station provided in a cellular system in which a plurality of mobile stations according to claim 5 are utilized, said base station comprising:

demodulation means for demodulating the base-station specify signal multiplexed in the upward signal; and

transmission control means for receiving the base-station specify signal demodulated by said demodulation means, for keeping a downward signal transmission when its own base station is specified in the base-station specify signal, and for stopping a downward signal transmission when its own base station is not specified in the base-station specify signal.

9. The base station according to claim 8, wherein said transmission control means ignores contents of the base-station specify signal and keeps a downward signal transmission when an error is detected in the base-station specify signal.

10. A cellular system using a direct spread code division multiple access system, in which a mobile station performs soft handover with plural base stations,

said mobile station comprising:

reception quality monitoring means for monitoring reception quality of downward signals from the plural base stations that are in the soft handover state and outputting a sub-signal composed of the monitoring results and signals indicative of base stations corresponding to the respective results;

multiplexing means for multiplexing the sub-signal into an upward signal to be sent to said plural base stations; and

reception means for performing combined reception of receive signals from said plural base stations that are in the soft handover state, and

said base stations each comprising;

demodulation means for demodulating the sub-signal multiplexed in the upward signal;

transmission halt signal generating means for receiving the sub-signal demodulated by said demodulation means, comparing reception quality of downward signals from respective base stations monitored at the mobile station indicated in the sub-signal, and for generating a transmission halt signal which indicates a signal transmission instruction whether transmission should be allowed or halted at its own base station in accordance with the reception quality monitoring result indicated in the sub-signal; and

transmission control means for receiving the transmission halt signal from said transmission halt signal generating means, and for setting a signal transmission state of a downward signal from its own base station, whether a signal transmitting or a signal stopping, in accordance with the instruction indicated in the transmission halt signal.

11. The cellular system according to claim 10, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission stopped when the best reception quality monitoring result is not indicated for its own base station in the sub-signal, and said transmission control means sets the signal transmitting state of its own base station to a signal stopping condition when the transmission halt signal indicates the instruction of signal transmission stopped.

12. The cellular system according to claim 10, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission allowed when an error is detected in the sub-signal, and said transmission control means sets the signal transmitting state of own base station to a signal transmitting condition when the transmission halt signal indicates the instruction of signal transmission allowed.

13. The cellular system according to claim 10, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission allowed when reception quality monitoring results of plural base stations in the sub-signal each having smaller difference than a predetermined value, and said transmission control means sets the signal transmitting state of own base station to a signal transmitting when the transmission halt signal indicates the instruction of signal transmission allowed.

14. The cellular system according to claim 10, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission allowed when reception quality monitoring results of plural base stations in the sub-signal are smaller than a predetermined value, and said transmission control means sets the signal transmitting state of its own base station to a signal transmitting condition when the transmission halt signal indicates the instruction of signal transmission allowed.

15. A base station provided in a cellular system in which a plurality mobile stations, each equipped with means for monitoring reception quality of downward signals from plural base stations with soft handover state and transmitting a sub-signal composed of the monitoring results for each base station, are utilized, said base station comprising:

demodulation means for demodulating the sub-signal;

transmission halt signal generating means for receiving the sub-signal demodulated by said demodulation means, comparing reception quality of downward signals from respective base stations monitored at the mobile station indicated in the sub-signal, and for generating a transmission halt signal which indicates a signal transmission instruction whether allowed or halted at its own base station in accordance with the reception quality monitoring result indicated in the sub-signal; and

transmission control means for receiving the transmission halt signal from said transmission halt signal generating means, and for setting a signal transmission state of a downward signal from its own base station, whether a signal transmitting or a signal stopping, in accordance with the instruction indicated in the transmission halt signal.

16. The base station according to claim 15, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission allowed when an error is detected in the sub-signal, and said transmission control means sets the signal transmitting state of its own base station to a signal transmitting condition when the transmission halt signal indicates the instruction of signal transmission allowed.

17. The base station according to claim 15, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission allowed when reception quality monitoring results of plural base stations in the sub-signal each having a smaller difference each other than a predetermined value, and said transmission control means put the signal transmitting when the transmission halt signal indicates the instruction of signal transmission allowed.

18. The base station according to claim 15, wherein said transmission halt signal generating means generates the transmission halt signal with an instruction of signal transmission allowed when reception quality monitoring results of plural base stations in the sub-signal are smaller than a predetermined value, and said transmission control means sets the signal transmitting sate of its own base station to a signal transmitting condition when the transmission halt signal indicates the instruction of signal transmission allowed.