| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a digital radio signal demodulator circuit which adds an LLR to a received signal which has been modulated by a nonlinear modulation method to make viterbi demodulation by soft decision possible, thereby ensuring high reception reliability, and a radio receiver unit using the demodulator circuit. <P>SOLUTION: A radio receiver unit RX includes an FSK demodulator circuit 13 provided with a frequency discriminator which demodulates a 4-value FSK modulated received signal as a baseband signal; a demapping circuit 19 which assigns an LLR to the baseband signal from the frequency discriminator, the LLR being derived for each transmission symbol based on a probability density distribution of frequency error after a probability density function of frequency error is calculated based on a probability density function of phase error in the frequency discriminator and a probability density distribution of frequency error is calculated based on the probability density function of frequency error; and a viterbi demodulator circuit 22 which demodulates its input signal by a soft decision viterbi algorithm based on a logarithmic likelihood ratio assigned to by the demapping circuit 19. <P>COPYRIGHT: (C)2012,JPO&INPIT |
