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.

1 . A method comprising the steps of:
 modulating digital data, by using a QPSK (quadrature phase shift keying) scheme or 2 m -QAM (quadrature amplitude modulation) scheme (m is an integer equal to or higher than 3) in which both absolute values of in-phase (I) and quadrature-phase (Q) components of an information symbol with a maximum amplitude take the same value in an I-Q plane, to generate an orthogonal base band signal including one or more information symbols, each information symbol consisting of I-Q components;   regularly inserting a pilot symbol into the orthogonal base band signal, the pilot symbol being disposed in the I-Q plane so as to equalize a distance in the I-Q plane between the pilot symbol and every one of two neighboring information symbols with the maximum amplitude, the amplitude of the pilot symbol being larger than the maximum amplitude of the information symbol, the absolute value of the amplitude of the pilot symbol taking a fixed value; and   transmitting the base band signal including the pilot symbol and the information symbols by wireless.   
   
   
       2 . The method according to  claim 1 , wherein a phase difference between the pilot symbol and the information symbol with the maximum amplitude is π/4. 
   
   
       3 . The method according to  claim 1 , wherein the pilot symbol is disposed on either the in-phase axis or the quadrature-phase axis. 
   
   
       4 . The method according to  claim 1 , wherein an amplitude of the pilot symbol is not 1.6 times larger than the maximum amplitude of the information symbol. 
   
   
       5 . A wireless transmitting system, comprising:
 a base band signal generator that modulates digital data, by using a QPSK (quadrature phase shift keying) scheme or 2 m -QAM (quadrature amplitude modulation) scheme (m is an integer equal to or higher than 3) in which both absolute values of in-phase (I) and quadrature-phase (Q) components of an information symbol with a maximum amplitude take the same value in an I-Q plane, to generate an orthogonal base band signal including one or more information symbols, each information symbol consisting of I-Q components;   a pilot signal inserter that regularly inserts a pilot symbol into the orthogonal base band signal, the pilot symbol being disposed in the I-Q plane so as to equalize a distance in the I-Q plane between the pilot symbol and every one of two neighboring information symbols with the maximum amplitude, the amplitude of the pilot symbol being larger than the maximum amplitude of the information symbol, the absolute value of the amplitude of the pilot symbol taking a fixed value; and   a wireless transmitter that transmits the base band signal including the pilot symbol and the information symbols by wireless.   
   
   
       6 . The system according to  claim 5 , wherein a phase difference between the pilot symbol and the information symbol with the maximum amplitude is π/4. 
   
   
       7 . The system according to  claim 5 , wherein the pilot system is disposed on either the in-phase axis or the quadrature-phase axis. 
   
   
       8 . The system according to  claim 5 , wherein an amplitude of the pilot symbol is not 1.6 times larger than the maximum amplitude of the information symbol.