Turbo decoding system using nth root metrics for non-Gaussian communication channels

Abstract

An nth root transformation is used for generating near Gaussian metrics from non-Gaussian metrics for input into a conventional turbo decoder that is based on the assumption that the input sequence to the decoder has a Gaussian distribution. The nth root transformation transforms channel non-Gaussian statistics to near Gaussian statistics for use with conventional turbo decoding for improved noncoherent communications over a non-Gaussian channel, such as a fading channel. For a differential coherent PSK waveform, where the channel statistics of a demodulator are non-Gaussian, for example, in the presence of fading, the nth root transformation is used to transform the non-Gaussian statistics to near Gaussian statistics for generating near Gaussian metrics, for improved PSK communications.

1. A turbo decoding communication system for communicating a data signal over a communication channel, the system comprising,
 a turbo encoder for encoding the data signal into an encoded signal, 
 a modulator for generating a modulated signal from the encoded signal, the modulated signal being communicated over the communication channel, 
 a demodulator for demodulating the modulated signal into a demodulated signal providing non-Gaussian metrics, 
 a transformer for transforming the non-Gaussian metrics into near Gaussian metrics, 
 a turbo decoder for decoding the near Gaussian metrics into the data signal, the turbo decoder decoding the near Gaussian metrics into the data signal using a Gaussian characterization for characterizing of the communication channel, and 
 a decoder reference for providing a Gaussian mean and a Gaussian standard deviation to the turbo decoder for decoding the near Gaussian metrics into the data signal, the Gaussian mean and Gaussian standard deviation being the Gaussian characterization. 
 
     
     
       2. The system of  claim 1 , wherein the system further comprises,
 a channel interleaver for interleaving the encoded signal, and 
 a channel deinterleaver for deinterleaving the demodulated signal. 
 
     
     
       3. The system of  claim 1  wherein,
 the demodulator is a noncoherent demodulator. 
 
     
     
       4. The system of  claim 1  wherein,
 the communication channel is a non-Gaussian communication channel. 
 
     
     
       5. The system of  claim 1  wherein,
 the data signal is communicated over the communication channel using phase shift keying signaling. 
 
     
     
       6. The system of  claim 1  wherein,
 the Gaussian characterization is an Eb/No signal-to-noise ratio. 
 
     
     
       7. A turbo decoding communication system for communicating a data signal using phase shift keying (PSK) signaling over a non-Gaussian communication channel, the system comprising,
 a turbo encoder for encoding the data signal into an encoded signal, 
 a PSK modulator for generating a PSK modulated signal from the encoded signal, the PSK modulated signal being communicated over the non-Gaussian communication channel, 
 a PSK demodulator for demodulating the PSK modulated signal into a PSK demodulated signal providing non-Gaussian metrics, 
 an nth root transformer for transforming the non-Gaussian metrics into near Gaussian metrics where n does not equal one nor equal infinity, 
 a turbo decoder for decoding the near Gaussian metrics into the data signal, the turbo decoder decoding the near Gaussian metrics into the data signal using a Gaussian characterization for characterizing of the communication channel, and 
 a decoder reference for providing a Gaussian mean and a Gaussian standard deviation to the turbo decoder for decoding the near Gaussian metrics into the data signal, the Gaussian mean and Gaussian standard being the Gaussian characterization. 
 
     
     
       8. The system of  claim 7 , wherein the system further comprises,
 a channel interleaver for interleaving the encoded signal, and 
 a channel deinterleaver for deinterleaving the demodulated signal. 
 
     
     
       9. The system of  claim 7  wherein the nth root transformer is a square root transformer. 
     
     
       10. The system of  claim 7  wherein the PSK signaling is binary PSK signaling. 
     
     
       11. The system of  claim 7  wherein the PSK is differential coherent PSK signaling. 
     
     
       12. The system of  claim 7  wherein,
 n defines the root of the nth root transformer, and 
 n is a positive integer greater than one. 
 
     
     
       13. A turbo decoding communication system for communicating a data signal using differential coherent phase shift keying (DPSK) signaling over a non-Gaussian communication channel, the system comprising,
 a turbo encoder for encoding the data signal into an encoded signal, 
 a DPSK modulator for generating a DPSK modulated signal from the encoded signal, the DPSK modulated signal being communicated over the non-Gaussian communication channel, 
 a DPSK demodulator for demodulating the DPSK modulated signal into a DPSK demodulated signal providing non-Gaussian metrics, and a square root transformer for transforming the non-Gaussian metrics into near Gaussian metrics where n does not equal one nor equal infinity, 
 a turbo decoder for decoding the Gaussian metrics into the data signal, the turbo decoder decoding the near Gaussian metrics into the data signal using a Gaussian characterization for characterizing of the communication channel, and 
 a decoder reference for providing a Gaussian mean and a Gaussian standard deviation to the turbo decoder for decoding the near Gaussian metrics into the data signal, the Gaussian mean and Gaussian standard deviation being the Suasion characterization. 
 
     
     
       14. The system of  claim 13 , wherein the system further comprises,
 a channel interleaver for interleaving the encoded signal, and 
 a channel deinterleaver for deinterleaving the demodulated signal. 
 
     
     
       15. The system of  claim 13 , wherein the non-Gaussian communication channel fades the DPSK modulated signal over the non-Gaussian communication channel. 
     
     
       16. A method for turbo decoding communication system for communicating a data signal over a communication channel, the method comprising:
 encoding the data signal into an encoded signal with a turbo encoder;   generating a modulated signal from the encoded signal;   demodulating the modulated signal into a demodulated signal providing non-Gaussian metrics;   transforming the non-Gaussian metrics into near Gaussian metrics;   decoding the near Gaussian metrics into the data signal;   decoding the near Gaussian metrics into the data signal with a turbo decoder using a Gaussian characterization of the communication channel; and   providing a Gaussian mean and a Gaussian standard deviation with a decoder reference to the turbo decoder for decoding the near Gaussian metrics into the data signal,   wherein the Gaussian mean and Gaussian standard deviation being the Gaussian characterization.   
     
     
       17. The method of claim 16, wherein the method further comprises:
 interleaving the encoded signal; and   deinterleaving the demodulated signal.   
     
     
       18. The method of claim 16, wherein the Gaussian characterization is an E b /N o  signal-to-noise ratio. 
     
     
       19. A method for turbo decoding a data signal using phase shift keying (PSK) signaling over a non-Gaussian communication channel, the method comprising:
 encoding the data signal into an encoded signal;   generating a PSK modulated signal from the encoded signal;   demodulating the PSK modulated signal into a PSK demodulated signal providing non-Gaussian metrics;   transforming the non-Gaussian metrics into near Gaussian metrics with an nth root transformer, where n does not equal one nor equal infinity;   decoding the near Gaussian metrics into the data signal using a Gaussian characterization of the communication channel; and   providing a Gaussian mean and a Gaussian standard deviation for decoding the near Gaussian metrics into the data signal,   wherein the Gaussian mean and Gaussian standard being the Gaussian characterization.   
     
     
       20. The method of claim 19, wherein the method further comprises:
 interleaving the encoded signal; and   deinterleaving the demodulated signal.   
     
     
       21. The method of claim 19, wherein the nth root transformer is a square root transformer. 
     
     
       22. The method of claim 19, wherein the PSK signaling is binary PSK signaling. 
     
     
       23. The method of claim 19, wherein the PSK is differential coherent PSK signaling. 
     
     
       24. The method of claim 19, wherein, n defines the root of the nth root transformer, and n is a positive integer greater than one. 
     
     
       25. A method for turbo decoding a data signal using differential coherent phase shift keying (DPSK) signaling over a non-Gaussian communication channel, the method comprising,
 encoding the data signal into an encoded signal;   generating a DPSK modulated signal from the encoded signal;   demodulating the DPSK modulated signal into a DPSK demodulated signal;   providing non-Gaussian metrics from the DPSK demodulated signal and a square root transformer for transforming the non-Gaussian metrics into near Gaussian metrics where n does not equal one nor equal infinity;   decoding the Gaussian metrics into the data signal;   decoding the near Gaussian metrics into the data signal using a Gaussian characterization of the communication channel; and   providing a Gaussian mean and a Gaussian standard deviation with a decoder reference,   wherein the Gaussian mean and Gaussian standard deviation being the Gaussian characterization.   
     
     
       26. The method of claim 25, further comprising:
 interleaving the encoded signal; and   deinterleaving the demodulated signal.   
     
     
       27. The method of claim 25, wherein the non-Gaussian communication channel fades the DPSK modulated signal over the non-Gaussian communication channel.