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

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 (BSse 1 ) 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.

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; 
 wherein transmission of the downward signals from base stations not specified by the base station specify signal is stopped.  
 
     
     
       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 to 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. 
     
     
       19. A mobile station in a CDMA system, comprising:
   a monitor monitoring reception quality of downward signals from a plurality of base stations that are in a soft handover state;        a base - station selector comparing reception quality of downward signals from respective base stations monitored at the monitor, 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; and        a transmitter sending the base - station specify signal to the base stations that are in the soft handover state;        wherein transmission of the downward signals from base stations not specified by the base station specify signal is stopped.     
     
     
       20. The mobile station as claimed in  claim 19 , further comprising:
   a rake receiver combining reception signals from the base stations that are in the soft handover state.     
     
     
       21. The mobile station as claimed in  claim 19 , wherein the monitor measures the reception quality using a pilot channel from each base station. 
     
     
       22. The mobile station as claimed in  claim 19 , wherein the transmitter has a multiplexer multiplexing a control channel including the base-station specify signal and upward communication channel data to generate an upward signal. 
     
     
       23. The mobile station as claimed in  claim 22 , wherein the transmitter further comprises a spreader spreading the upward signal. 
     
     
       24. A base station in a CDMA system, communicating with a mobile station, comprising:
   a first transmitter transmitting a downward signal to the mobile station;        a receiver receiving a base - station specify signal sent from a mobile station, wherein the mobile station compares reception quality of downward signals from respective base stations that are in a soft handover state and generates the base - station specify signal which specifies one of the base stations that are in a soft handover state, wherein the specified base station has the best reception quality; and        transmission control means keeping transmission of the downward signal when its own base station is specified in the base - station specify signal, and stopping transmission of the downward signal when its own base station is not specified in the base - station specify signal.     
     
     
       25. The base station as claimed in  claim 24 , wherein the transmission control means ignores contents of the base- station specify signal transmitted from the mobile station when there is an error in receiving the base-station specify signal transmitted from the mobile station and keeps transmission of the downward signal to the mobile station even if the base station is not specified in the base - station specify signal.   
     
     
       26. The base station as claimed in  claim 24 , further comprising:
   a second transmitter for transmitting a pilot channel, wherein the mobile station monitors the reception quality of the downward signal from the base station based on the pilot channel.     
     
     
       27. The base station as claimed in  claim 26 , wherein the second transmitter has a first spread circuit for spreading the pilot channel with a first spread code. 
     
     
       28. The base station as claimed in  claim 27 , further comprising:
   a second spread circuit spreading downward communication channel data with a second spread code which is different from the first spread code.     
     
     
       29. A communication system, wherein a mobile station communicates with a plurality of base stations that are in soft handover state, wherein:
   the mobile station comprises:      a monitor monitoring reception quality of downward signals from a plurality of base stations that are in a soft handover state,        a base - station selector comparing reception quality of downward signals from respective base stations monitored at the monitor, 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; and        a transmitter sending the base - station specify signal to the base stations that are in the soft handover state, and        each base station comprises:      a first transmitter transmitting a downward signal to the mobile station,        a receiver receiving a base - station specify signal sent from a mobile station, wherein the mobile station compares reception quality of downward signals from respective base stations that are in a soft handover state and generates the base - station specify signal which specifies one of the base stations that ate in a soft handover state, wherein the specified base station has the best reception quality, and        transmission control means keeping transmission of the downward signal when its own base station is specified in the base - station specify signal, and stopping transmission of the downward signal when its own base station is not specified in the base - station specify signal.         
     
     
       30. The communication system as claimed in  claim 29 , wherein the  transmission control means transmits the downward signals whether or not its own base station is not specified in the base station signal, when there is an error in receiving the base - station specify signal transmitted from the mobile station.   
     
     
       31. A communication method, wherein a mobile station communicates with a plurality of base stations that ate in a soft handover state, comprising:
   monitoring reception quality of downward signals from the base stations that are in a soft handover state;        comparing reception quality of downward signals from respective base stations;        generating a base - station specify signal which specifies a base station having the best reception quality monitoring result to maintain a signal transmission; and        sending the base - station specify signal to the base stations that are in the soft handover state; and        stopping transmission of the downward signals from base stations not specified by the base station specify signal.     
     
     
       32. A communication method, wherein a mobile station communicates with a plurality of base stations that are in a soft handover state, comprising:
   receiving a base - station specify signal sent from the mobile station at the base stations, wherein the mobile station compares reception quality of downward signals from respective base stations that are in the soft handover state and generates the base - station specify signal which specifies one of the base stations that are in a soft handover state, wherein the specified base station by the base - station specify signal has the best reception quality, and        keeping transmission of the downward signal at the specified base station, and stopping transmission of the downward signal at the other base stations which are not specified in the base - station specify signal.     
     
     
       33. A communication method, wherein a mobile station communicates with a plurality of base stations that are in a soft handover state, comprising:
   monitoring reception quality of downward signals from the base stations that are in a soft handover state;        comparing reception quality of downward signals from respective base stations;        generating a base - station specify signal which specifies a base station having the best reception quality monitoring result to maintain a signal transmission;        sending the base - station specify signal to the base stations that are in the soft handover state;        receiving the base - station specify signal sent from the mobile station at the base stations; and        keeping transmission of the downward signal at the specified base station by the base - station specify signal, and stopping transmission of the downward signal at the other base stations which are not specified in the base - stations specify signal.     
     
     
       34. A communication method, wherein in a mobile station communicates with a plurality of base stations that are in a soft handover state, comprising;
   monitoring reception quality of downward signals from the base stations;        specifying one of the base stations, wherein the specified base stations has the best reception quality;        transmitting a base - station specify signal to the base stations that are in the soft handover state, wherein the base - station specify signal specifies the base station having the best reception quality; and        stopping transmission of the downward signals from base stations not specified by the base station specify signal.     
     
     
       35. A communication method, wherein a mobile station communicates with a plurality of base stations that are in a soft handover state, comprising:
   receiving a base - station specify signal specifying one of the base stations that are in the soft handover state, transmitted from the mobile station; and        keeping transmission of a downward signal of the base station specified in the base - station specify signal and stopping transmission of downward signals of the remaining base stations that are in the soft handover state and are not specified in the base - station specify signal.     
     
     
       36. A communication method, wherein a mobile station communicates with a plurality of base stations that are in a soft handover state, comprising:
   transmitting a base - station specify signal from the mobile station to the base stations that are in the soft handover state, wherein the base - station specify signal specifies one of the base stations that are in the soft handover state; and        controlling transmission of downward signals of the base stations that are in the soft handover state based on the base - station specify signal, wherein the transmission of the downward signals of the base stations that are not specified in the base - station specify signal is switched off.     
     
     
       37. The communication method as claimed in  claim 36 , wherein the downward signal of the base station specified in the base- station specify signal is transmitted to the mobile station.