Orthogonal frequency division multiplex transmission method

Abstract

A spread modulator spreads a signal series. A subcarrier modulator modulates a plurality of subcarriers having different frequencies using the output of the spread modulator. The adder combines modulated subcarriers. A guard interval control unit determines the length of a guard interval depending on the maximum transmission delay difference of the communication link between the transmission device and the reception device. A guard interval insert unit inserts a guard interval into a signal series under the control of a guard interval control unit. A gain adjuster multiplies a transmission signal by a gain coefficient corresponding to the inserted guard interval.

What is claimed is:  
     
         1 . A communications system which transmits a signal from a transmission device to a reception device using orthogonal frequency division multiplex, wherein 
 the transmission device comprises: 
 a modulator which modulates a plurality of subcarriers using a signal series;  
 an inserter which inserts a guard interval into output of said modulator; and  
 a transmitter which transmits a modulation signal into which the guard interval is inserted, and  
   the reception device comprises: 
 a demodulator which regenerates the signal series by performing a deleting process to delete the guard interval and a demodulating process on the modulation signal transmitted from the transmission device for each subcarrier, wherein  
   a length of the guard interval is determined based on a communications environment between the transmission device and the reception device.    
     
     
         2 . The system according to  claim 1 , wherein 
 said transmission device further comprises a power controller which controls transmission power to transmit the modulation signal depending on the length of the guard interval.    
     
     
         3 . A communications system which transmits a signal from a transmission device to a plurality of reception devices including a first reception device and a second reception device using orthogonal frequency division multiplex, wherein 
 the transmission device comprises: 
 a modulator which modulates a plurality of subcarriers using a signal series obtained by multiplexing a first signal series to be transmitted to the first reception device and a second signal series to be transmitted to the second reception device;  
 an inserter which inserts a first guard interval into modulated output of the first signal series and inserting a second guard interval into modulated output of the second signal series; and  
 a transmitter which transmits modulation signals into which the first guard interval and the second guard interval are respectively inserted, and  
   the first reception device comprises: 
 a demodulator which regenerates the first signal series by performing a deleting process to delete the first guard interval and a demodulating process, wherein  
   a length of the first guard interval is determined based on the communications environment between the transmission device and the first reception device, and a length of the second guard interval is determined based on the communications environment between the transmission device and the second reception device.    
     
     
         4 . A communications system which transmits a signal from a transmission device to a plurality of reception devices including a first reception device using orthogonal frequency division multiplex, wherein: 
 the transmission device comprises: 
 a modulator which modulates a plurality of subcarriers using a signal series obtained by multiplexing a first signal series to be transmitted to a first reception device and a second signal series to be transmitted to a plurality of reception devices including the first reception device in a communications area of the transmission device;  
 an inserter which inserts a first guard interval into modulated output of the first signal series and inserting a second guard interval into modulated output of the second signal series; and  
 a transmitter which transmits modulation signals into which the first guard interval and the second guard interval are respectively inserted, and  
   the first reception device comprises: 
 a demodulator which regenerates the first signal series and the second signal series by performing a deleting process to delete the first guard interval and the second guard interval and a demodulating process, wherein  
   a length of the first guard interval is determined based on the communications environment between the transmission device and the first reception device.    
     
     
         5 . The system according to  claim 4 , wherein 
 a length of the second guard interval is determined such that the plurality of reception devices in the communications area can regenerate the second signal series.    
     
     
         6 . The system according to  claim 1 , wherein 
 the reception device further comprises a detector which detects a maximum transmission delay difference of a communication link between the transmission device and the reception device,    said inserter inserts the guard interval, the length of the guard interval depending on the maximum transmission delay difference detected by said detector,    said demodulator deletes the guard interval based on the maximum transmission delay difference.    
     
     
         7 . The system according to  claim 1 , wherein 
 the reception device further comprises an estimation unit which estimates a transmission distance between the transmission device and the reception device,    said inserter inserts the guard interval, the length of the guard interval depending on the transmission distance estimated by said estimation unit,    said demodulator deletes the guard interval based on the estimated transmission distance.    
     
     
         8 . The system according to  claim 1 , wherein 
 the transmission device further comprises an estimation unit which estimates a transmission distance between the transmission device and the reception device,    said inserter inserts the guard interval, the length of the guard interval depending on the transmission distance estimated by said estimation unit,    said demodulator deletes the guard interval based on the estimated transmission distance.    
     
     
         9 . The system according to  claim 8 , wherein 
 said estimation unit estimates the transmission distance based on a time from when a signal is transmitted from the transmission device until when a reply corresponding to the signal is returned from the reception device.    
     
     
         10 . The system according to  claim 1 , wherein 
 the reception device further comprises a monitor unit which monitors communications quality of a signal transmitted from the transmission device to the reception device,    the length of the guard interval is determined such that predetermined communications quality can be satisfied.    
     
     
         11 . A method for transmitting a signal from a transmission device to a reception device using orthogonal frequency division multiplex, comprising: 
 modulating a signal series using orthogonal frequency division multiplex;    inserting a guard interval with a length determined based on a communications environment between the transmission device and the reception device; and    transmitting a modulation signal into which the guard interval is inserted.    
     
     
         12 . The method according to  claim 11 , wherein 
 transmission power of the modulation signal into which the guard interval is inserted is controlled depending on the length of the guard interval.    
     
     
         13 . A method for transmitting a signal from a transmission device to a reception device using orthogonal frequency division multiplex, comprising: 
 modulating a first signal series to be transmitted to a first reception device and a second signal series to be transmitted to a second reception device using orthogonal frequency division multiplex;    inserting a first guard interval with a length determined based on a communications environment between the transmission device and the first reception device into the modulated first signal series, and inserting a second guard interval with a length determined based on a communications environment between the transmission device and the second reception device into the modulated second signal series; and    transmitting modulation signals into which the first guard interval and the second guard interval are inserted.    
     
     
         14 . The method according to  claim 11 , wherein 
 the length of the guard interval is determined based on a maximum transmission delay difference or a transmission distance of a communication link between the transmission device and the reception device.    
     
     
         15 . The method according to  claim 11 , wherein 
 communications quality of a signal transmitted from the transmission device to the reception device is monitored; and    the length of the guard interval is determined such that predetermined communications quality can be satisfied.    
     
     
         16 . A base station apparatus which transmits a signal to a mobile station using orthogonal frequency division multiplex in a cellular communications system, comprising: 
 a modulator which modulates a signal series using orthogonal frequency division multiplex;    an inserter which inserts a guard interval with a length determined based on a communications environment between the base station apparatus and the mobile station for transmitting the signal series; and    a transmitter which transmits a modulation signal into which the guard interval is inserted.    
     
     
         17 . The base station apparatus according to  claim 16 , further comprising 
 a power controller which controls transmission power of the modulation signal depending on the length of the guard interval.    
     
     
         18 . A base station apparatus which transmits a signal to a mobile station using orthogonal frequency division multiplex in a cellular communications system, comprising: 
 a modulator which modulates a first signal series to be transmitted to a first reception device and a second signal series to be transmitted to a second reception device using orthogonal frequency division multiplex;    an inserter which inserts a first guard interval with a length determined based on a communications environment between the base station apparatus and the first reception device into the first signal series modulated by said modulator, and inserting a second guard interval with a length determined based on a communications environment between the base station apparatus and the second reception device into the second signal series modulated by said modulator; and    a transmitter which transmits modulation signals into which the first guard interval and the second guard interval are inserted.    
     
     
         19 . A mobile station which receives a signal transmitted from the base station apparatus according to  claim 16  in the cellular communications system, comprising: 
 a demodulator which performs a deleting process to delete a first guard interval corresponding to the first signal series and a demodulating process.  
 
     
     
         20 . A mobile station which receives a signal transmitted from the base station apparatus according to  claim 18  in the cellular communications system, comprising: 
 a demodulator which performs a deleting process to delete the first guard interval and the second guard interval and a demodulating process.  
 
     
     
         21 . A communications system which transmits a signal from a transmission device to a reception device using orthogonal frequency division multiplex, wherein 
 the transmission device comprises: 
 modulation means for modulating a plurality of subcarriers using a signal series;  
 insertion means for inserting a guard interval into output of said modulation means; and  
 transmission means for transmitting a modulation signal into which the guard interval -is inserted, and  
   the reception device comprises: 
 demodulation means for regenerating the signal series by performing a deleting process to delete the guard interval and a demodulating process on the modulation signal transmitted from the transmission device for each subcarrier, wherein  
   a length of the guard interval is determined based on a communications environment between the transmission device and the reception device.    
     
     
         22 . A base station apparatus which transmits a signal to a mobile station using orthogonal frequency division multiplex in a cellular communications system, comprising: 
 modulation means for modulating a signal series using orthogonal frequency division multiplex;    insertion means for inserting a guard interval with a length determined based on a communications environment between the base station apparatus and the mobile station for transmitting the signal series; and    transmission means for transmitting a modulation signal into which the guard interval is inserted.