Multiple Symbol Noncoherent Soft Output Detector

Abstract

Multiple symbol noncoherent soft output detectors in accordance with embodiments of the invention are disclosed. In a number of embodiments, the multiple symbol noncoherent soft output detector uses soft metrics based on the Log Likelihood Ratio (LLR) of each symbol to provide information concerning the reliability of each detected symbol. One embodiment of the invention includes a receiver configured to receive and sample a phase modulated input signal, and a multiple symbol noncoherent soft output detector configured to receive the sampled input signal and to generate a soft metric indicative of the reliability of a detected symbol based upon observations over multiple symbols.

What is claimed is: 
     
         1 . A receiver system, comprising:
 a receiver configured to receive and sample a phase modulated input signal; and   a multiple symbol noncoherent soft output detector configured to receive the sampled input signal and to generate a soft metric indicative of the reliability of a detected symbol based upon observations over multiple symbols.   
     
     
         2 . The receiver system of  claim 1 , wherein the soft metric is based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols. 
     
     
         3 . The receiver system of  claim 2 , wherein the observations include at least one known symbol. 
     
     
         4 . The receiver system of  claim 2 , wherein the observations include observations over a three symbol sequence. 
     
     
         5 . The receiver system of  claim 1 , wherein:
 the phase modulated input signal comprises data that is phase modulated on a carrier; and   the multiple symbol noncoherent soft output detector assumes that carrier phase of the input signal is constant over the time duration of the observations.   
     
     
         6 . The receiver system of  claim 5 , wherein the phase modulated input signal is a binary phase modulated signal. 
     
     
         7 . The receiver system of  claim 5 , wherein the phase modulated input signal is a Multiple-Phase-Shift Keying modulated signal. 
     
     
         8 . The receiver system of  claim 1 , wherein:
 the multiple symbol noncoherent soft output detector comprises a plurality of matched filters having different numbers of samples configured to integrate the samples during each half-symbol period; and   the multiple symbol noncoherent soft output detector is configured to use the outputs of each of the plurality of matched filters to determine the most likely symbol duration.   
     
     
         9 . A combined receiver system, comprising:
 a plurality of receivers configured to receive and sample an input signal, where the input signal comprises data that is phase modulated onto a carrier;   a plurality of multiple symbol noncoherent soft output detectors configured to receive a sampled input signal from one of the plurality of receivers and to generate a soft metric indicative of the reliability of a detected symbol based upon observations over multiple symbols; and   a combiner configured to receive the soft metrics from the plurality of multiple symbol noncoherent soft output detectors and to detect data based upon the soft metrics.   
     
     
         10 . The combined receiver system of  claim 9 , wherein the combiner is configured to detect data by combining the soft metrics. 
     
     
         11 . The combined receiver system of  claim 9 , wherein the combiner is configured to select at least one of the soft metrics from the plurality of multiple symbol noncoherent soft output detectors based upon a threshold level of reliability. 
     
     
         12 . The combined receiver system of  claim 9 , wherein the soft metrics generated by the plurality of multiple symbol noncoherent soft output detectors are based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols. 
     
     
         13 . The combined receiver system of  claim 12 , wherein the observations include at least one known symbol. 
     
     
         14 . The combined receiver system of  claim 12 , wherein the observations include observations over a three symbol sequence. 
     
     
         15 . The combined receiver system of  claim 9 , wherein each of the plurality of multiple symbol noncoherent soft output detectors assumes that carrier phase of the input signal is constant over the time duration of the observations. 
     
     
         16 . The combined receiver system of  claim 15 , wherein the phase modulated input signal is a binary phase modulated signal. 
     
     
         17 . The combined receiver system of  claim 15 , wherein the phase modulated input signal is a Multiple-Phase-Shift Keying modulated signal. 
     
     
         18 . The combined receiver system of  claim 9 , wherein:
 each of the plurality of multiple symbol noncoherent soft output detectors comprises a plurality of matched filters having different numbers of samples configured to integrate the samples during each half-symbol period; and   each of the plurality of multiple symbol noncoherent soft output detectors is configured to use the outputs of each of the plurality of matched filters to determine the most likely symbol duration.   
     
     
         19 . A radio frequency identification (RFID) receiver system configured to detect phase modulated data transmitted by RFID tags, the RFID receiver system comprising:
 an antenna configured to receive a phase modulated signal comprising symbols transmitted by an RFID tag;   a receiver configured to sample the phase modulated signal; and   a multiple symbol noncoherent soft output detector configured to receive the sampled input signal and to generate soft metrics indicative of the reliability of a detected symbol based upon observations over multiple symbols.   
     
     
         20 . The RFID receiver system of  claim 19 , wherein the soft metric is based on the Log Likelihood Ratio of the detected symbol based upon observations over multiple symbols.