Pilot signal transmission technique and digital communication system using same

Abstract

In a digital communication system such as a mobile radio system, fading distortion is compensated with a raised precision. In a transmitter, pilot signals are regularly inserted in the information signals. The amplitude of the pilot signals are set larger than the maximum possible amplitude of the information signals. The modulation scheme of the pilot signals may be different from that of the information signals. In a receiver, the fading distortion of each of the pilot signals is determined. The fading distortions of the information signals are estimated by interpolation using the determined fading distortion of the pilot signal, and then compensated. The frequency band of each information signal is preferably limited with a roll-off filter with a roll-off coefficient ranging from 0.1 to 0.4.

What is claimed is:  
     
         1 . A method of transmitting digital data by wireless so as to permit a reception in a reduced bit error rate in a digital wireless communications system, the method including the steps of: 
 converting said digital data into a first stream of information signals through a more-than-7-signal-point modulation scheme;    inserting a pilot signal regularly in said first stream of said information signals into a second stream of said information signals and said pilot signal, an amplitude of said pilot signal being larger than that of any of said information signals; and    transmitting said second stream by wireless.    
     
     
         2 . A method as defined in  claim 1 , wherein said step of inserting a pilot signal includes the step of setting said amplitude of said pilot signal not larger than 1.6 times a maximum possible amplitude of said information signals.  
     
     
         3 . A method as defined in  claim 1 , further including the step of the transmitter limiting a frequency band of each information signal with a roll-off filter with a roll-off coefficient ranging from 0.1 to 0.4.  
     
     
         4 . A method as defined in  claim 1 , wherein said more-than-7-signal-point modulation scheme is a 16-amplitude phase shift keying.  
     
     
         5 . A method as defined in  claim 4 , wherein said step of inserting a pilot signal includes the step of generating said pilot signal so as to make an angle of π/8 with adjacent information signals in an in-phase and quadrature-phase signal space.  
     
     
         6 . A method as defined in  claim 1 , wherein said more-than-7-signal-point modulation scheme is a 2 m -signal-point quadrature amplitude modulation, where m is a positive integer not smaller than 3.  
     
     
         7 . A method as defined in  claim 6 , wherein said step of inserting a pilot signal includes the step of generating said pilot signal so as to be disposed on one of an in-phase axis and a quadrature-phase axis in a signal space of said 2 m -signal point quadrature amplitude modulation.  
     
     
         8 . A method as defined in  claim 1 , wherein said more-than-7-signal-point modulation scheme is an 8 phase shift keying.  
     
     
         9 . A method as defined in  claim 8 , wherein said step of inserting a pilot signal includes the step of generating said pilot signal so as to make an angle of π/8 with adjacent information signals in an in-phase and quadrature-phase signal space of said 8 phase shift keying.  
     
     
         10 . A method of transmitting digital data by wireless so as to permit a reception in a reduced bit error rate, the method including the steps of: 
 converting said digital data into a first stream of information signals through a quadrature phase shift keying modulation;    inserting a pilot signal regularly in said first stream of said information signals into a second stream of said information signals and said pilot signal, an amplitude of said pilot signal being larger than that of any of said information signals; and    transmitting said second stream by wireless.    
     
     
         11 . A method as defined in  claim 10 , wherein said pilot signal is so disposed as to make an angle of π/4 with adjacent information signals in an in-phase and quadrature-phase signal space of said quadrature phase shift keying modulation.  
     
     
         12 . A method as defined in  claim 10 , wherein said step of inserting a pilot signal includes the step of setting said amplitude of said pilot signal not larger than 1.6 times a maximum possible amplitude of said information signals.  
     
     
         13 . A method as defined in  claim 10 , further including the step of limiting a frequency band of each information signal with a roll-off filter with a roll-off coefficient ranging from 0.1 to 0.4.  
     
     
         14 . A system capable of transmitting digital data by wireless so as to permit a reception in a reduced bit error rate, the system including: 
 means for converting said digital data into a first stream of information signals through a more-than-7-signal-point modulation scheme;    means for inserting a pilot signal regularly in said first stream of said information signals into a second stream of said information signals and said pilot signal, an amplitude of said pilot signal being larger than that of any of said information signals; and    means for transmitting said second stream by wireless.    
     
     
         15 . A system as defined in  claim 14 , wherein said inserting means includes means setting said amplitude of said pilot signal not larger than 1.6 times a maximum possible amplitude of said information signals.  
     
     
         16 . A system as defined in  claim 14 , further including means for limiting a frequency band of each information signal with a roll-off filter with a roll-off coefficient ranging from 0.1 to 0.4.  
     
     
         17 . A system as defined in  claim 14 , wherein said more-than-7-signal-point modulation scheme is a 16-amplitude phase shift keying.  
     
     
         18 . A system as defined in  claim 17 , wherein said pilot signal is so disposed as to make an angle of π/8 with adjacent information signals in an in-phase and quadrature-phase signal space.  
     
     
         19 . A system as defined in  claim 14 , wherein said more-than-7-signal-point modulation scheme is a 2 m -signal-point quadrature amplitude modulation, where m is a positive integer not smaller than 3.  
     
     
         20 . A system as defined in  claim 19 , wherein said pilot signal is disposed on one of an in-phase axis and a quadrature-phase axis in a signal space of said 2 m -signal point quadrature amplitude modulation.  
     
     
         21 . A system as defined in  claim 14 , wherein said more-than-7-signal-point modulation scheme is an 8 phase shift keying.  
     
     
         22 . A system as defined in  claim 21 , wherein said pilot signal is so disposed as to make an angle of π/8 with adjacent information signals in an in-phase and quadrature-phase signal space of said 8 phase shift keying.  
     
     
         23 . A system capable of transmitting digital data by wireless so as to permit a reception in a reduced bit error rate, the system including: 
 means for converting said digital data into a first stream of information signals through a quadrature phase shift keying modulation;    means for inserting a pilot signal regularly in said first stream of said information signals into a second stream of said information signals and said pilot signal, an amplitude of said pilot signal being larger than that of any of said information signals; and    means for transmitting said second stream by wireless.    
     
     
         24 . A system as defined in  claim 23 , wherein said pilot signal is so disposed as to make an angle of π/4 with adjacent information signals in an in-phase and quadrature-phase signal space of said quadrature phase shift keying modulation.  
     
     
         25 . A system as defined in  claim 23 , wherein said inserting means includes means setting said amplitude of said pilot signal not larger than 1.6 times a maximum possible amplitude of said information signals.  
     
     
         26 . A system as defined in  claim 23 , further including means for limiting a frequency band of each information signal with a roll-off filter with a roll-off coefficient ranging from 0.1 to 0.4.  
     
     
         27 . A mobile telephone that communicates digital data with a reduced bit error rate, the mobile telephone comprising: 
 a transmission system; and    a receiver system, said transmission system including: 
 means for converting said digital data into a first stream of information signals through a more-than-7-signal-point modulation scheme;  
 means for inserting a pilot signal regularly in said first stream of said information signals into a second stream of said information signals and said pilot signal, an amplitude of said pilot signal being larger than that of any of said information signals; and  
 means for transmitting said second stream.  
   
     
     
         28 . A mobile telephone as defined in  claim 27 , wherein said inserting means includes means setting said amplitude of said pilot signal not larger than 1.6 times a maximum possible amplitude of said information signals.  
     
     
         29 . A mobile telephone as defined in  claim 27 , further including means for limiting a frequency band of each information signal with a roll-off filter with a roll-off coefficient ranging from 0.1 to 0.4.