High-performance half-rate encoding apparatus and method for a TDM system

Abstract

In a transmitter for transmitting communication signals across a radio channel, an improved encoder includes a half-rate encoder receiving a digitized speech signal and generating a compressed bit stream at half-rate, and a signal expander receiving the compressed bit stream and generating an expanded bit stream at full-rate for transmission across a radio channel. An improved receiver, receives the transmitted communication signal which is selected from the group consisting of (a) a conventional full-rate encoded digitized speech signal, and (b) a half-rate encoded digitized speech signal including the expanded bit stream. The improved receiver includes a full-rate equalizer, a half-rate equalizer, and a switch initially routing the received digitized speech signal to the full-rate equalizer, wherein the full-rate equalizer demodulates the received digitized speech signal producing a full-rate demodulated signal and dibits of soft information corresponding to the full-rate demodulated signal. An analyzer analyzes the dibits of soft information and controls the switch to route the received digitized speech signal to one of the full-rate and half-rate equalizers based upon the analysis.

1 . A method of transmitting a digitized signal across a radio channel comprising the steps of: 
 encoding a digitized signal at a first rate;    expanding the encoded digitized signal to a second rate greater than the first rate; and    transmitting the expanded digitized signal at the second rate across a radio channel.    
     
     
         2 . The method of    claim 1   , wherein the encoded digitized signal comprises a binary bit stream, and wherein the step of expanding the encoded digitized signal to a second rate greater than the first rate comprises the step of repeating each bit in the binary bit stream.  
     
     
         3 . The method of    claim 1   , wherein the encoded digitized signal comprises a binary bit stream, and wherein the step of expanding the encoded digitized signal to a second rate greater than the first rate comprises the step of repeating the binary bit stream.  
     
     
         4 . The method of    claim 1   , wherein the encoded digitized signal comprises a binary bit stream having bits classified as one of critical, important and unimportant, and wherein the step of expanding the encoded digitized signal to a second rate greater than the first rate comprises the step of additionally encoding the binary bit stream according to bit classification.  
     
     
         5 . The method of    claim 4   , wherein the step of additionally encoding the binary bit stream according to bit classification comprises the steps of: 
 deriving parity bits from the critical bits;    encoding the parity bits to produce a first output signal;    combining the critical and important bits and adding six tail bits to produce a second output signal;    encoding the second output signal to produce a third output signal;    encoding the unimportant bits to produce a fourth output signal; and    combining the first, third and fourth output signals to produce the expanded digitized signal at the second rate.    
     
     
         6 . The method of    claim 5   , wherein 
 the step of encoding the parity bits to produce a first output signal comprises the step of encoding the parity bits with a ⅙ rate convolutional encoder;    the step of encoding the second output signal to produce a third output signal comprises the step of encoding the second output signal with a ¼ rate convolutional encoder; and    the step of encoding the unimportant bits to produce a fourth output signal comprises the step of encoding the unimportant bits with a ½ rate convolutional encoder.    
     
     
         7 . The method of    claim 1   , wherein the digitized signal comprises a TDM (Time Division Multiplex) signal.  
     
     
         8 . The method of    claim 1   , wherein the second rate is approximately 2× the first rate.  
     
     
         9 . A method of establishing voice communication across a radio channel in a wireless communication system, said method comprising the steps of: 
 transmitting a digitized speech signal at a full-rate across a radio channel, said digitized speech signal selected from the group consisting of (a) a full-rate encoded digitized speech signal comprising a stream of binary bits, and (b) a half-rate encoded digitized speech signal comprising a stream of binary bits expanded for transmission at the full-rate by repeating each bit in the binary bit stream;    receiving the transmitted digitized speech signal at a receiver;    determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal; and    activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal.    
     
     
         10 . The method of    claim 9   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of information in response thereto;    inputting the dibits of information to an XNOR gate, said XNOR gate outputting a logical one if the bits of the dibit are the same and a logical zero if the bits of the dibit are different;    counting the number of occurrences of logical ones at the output of the XNOR gate; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the number of logical ones exceeds a threshold value.    
     
     
         11 . The method of    claim 9   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the step of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, each soft dibit including soft values;    multiplying the soft values of the soft dibit together at a multiplier, said multiplier outputting a positive value if the soft values of the soft dibit are the same and a negative value if the soft values of the soft dibit are different;    summing the output of the multiplier; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the summed output of the multiplier exceeds a threshold value.    
     
     
         12 . The method of    claim 9   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, said soft dibits plottable on a differential constellation having real and imaginary axes, each plotted soft dibit representing a complex value of a differential symbol;    rotating the differential symbols by π/4, said rotated differential symbols having components on the real and imaginary axes;    summing magnitudes of the rotated differential symbol components on the real and imaginary axes;    calculating a ratio of real axis summed magnitudes versus imaginary axis summed magnitudes; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the ratio exceeds a threshold value.    
     
     
         13 . The method of    claim 9   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, each soft dibit representing a differential symbol;    determining phase differences between successive differential symbols;    summing the determined phase differences; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the summed phase difference exceeds a threshold value.    
     
     
         14 . The method of    claim 9   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal in parallel using both full-rate and half-rate demodulation branches;    performing CRC (Cyclic Redundancy Check) checks on the demodulated full-rate and half-rate signals; and    deactivating one of the full-rate and half-rate demodulation branches in response to the CRC checks.    
     
     
         15 . The method of    claim 9   , wherein the digitized speech signal comprises a TDM (Time Division Multiplex) signal.  
     
     
         16 . The method of    claim 9   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, said soft dibits plottable on a differential constellation having real and imaginary axes, each plotted soft dibit representing a complex value of a differential symbol;    rotating the differential symbols by π/4, said rotated differential symbols having components on the real and imaginary axes;    squaring the complex values of the rotated differential symbols;    summing the squared values; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the real component of the squared/summed value exceeds a threshold value.    
     
     
         17 . A method of receiving a digitized speech signal transmitted at a full-rate across a radio channel in a wireless communication system, the digitized speech signal selected from the group consisting of (a) a full-rate encoded digitized speech signal comprising a stream of binary bits, and (b) a half-rate encoded digitized speech signal comprising a stream of binary bits expanded for transmission at the full-rate by repeating each bit in the binary bit stream, said method comprising the steps of: 
 receiving the digitized speech signal at a receiver;    determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal; and    activating either a full-rate or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal.    
     
     
         18 . The method of    claim 17   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of information in response thereto;    inputting the dibits of information to an XNOR gate, said XNOR gate outputting a logical one if the bits of the dibit are the same and a logical zero if the bits of the dibit are different;    counting the number of occurrences of logical ones at the output of the XNOR gate; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the number of logical ones exceeds a threshold value.    
     
     
         19 . The method of    claim 17   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, each soft dibit including soft values;    multiplying the soft values of the soft dibit together at a multiplier, said multiplier outputting a positive value if the soft values of the soft dibit are the same and a negative value if the soft values of the soft dibit are different;    summing the output of the multiplier; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the summed output of the multiplier exceeds a threshold value.    
     
     
         20 . The method of    claim 17   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, said soft dibits plottable on a differential constellation having real and imaginary axes, each plotted soft dibit representing a complex value of a differential symbol;    rotating the differential symbols by π/4, said rotated differential symbols having components on the real and imaginary axes;    summing magnitudes of the rotated differential symbol components on the real and imaginary axes;    calculating a ratio of real axis summed magnitudes versus imaginary axis summed magnitudes; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the ratio exceeds a threshold value.    
     
     
         21 . The method of    claim 17   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal at the full-rate equalizer, the full-rate equalizer producing dibits of soft information in response thereto, each soft dibit representing a differential symbol;    determining phase differences between successive differential symbols;    summing the determined phase differences; and    activating the half-rate equalizer to demodulate the received digitized speech signal if the summed phase difference exceeds a threshold value.    
     
     
         22 . The method of    claim 17   , wherein the steps of determining whether the received digitized speech signal is the full-rate or half-rate encoded digitized speech signal and activating either a full-rate equalizer or a half-rate equalizer at the receiver in response to said determination to demodulate the received digitized speech signal comprise the steps of: 
 demodulating the received digitized speech signal in parallel using both full-rate and half-rate demodulation branches;    performing CRC (Cyclic Redundancy Check) checks on the demodulated full-rate and half-rate signals; and    deactivating one of the full-rate and half-rate demodulation branches in response to the CRC checks.    
     
     
         23 . The method of    claim 17   , wherein the digitized speech signal comprises a TDM (Time Division Multiplex) signal.  
     
     
         24 . The method of    claim 17   , wherein the digitized speech signal comprises a TDM (Time Division Multiplex) signal.  
     
     
         25 . In a transmitter for transmitting communication signals across a radio channel, an improved encoder comprising: 
 a half-rate encoder receiving a digitized speech signal and generating a compressed bit stream at half-rate; and    a signal expander receiving the compressed bit stream and generating an expanded bit stream at full-rate for transmission across a radio channel.    
     
     
         26 . The improved encoder of    claim 25   , wherein the full-rate is approximately 2× the half-rate.  
     
     
         27 . The improved encoder of    claim 25   , wherein the signal expander comprises a repeater repeating each bit in the compressed bit stream to generate the expanded bit stream.  
     
     
         28 . The improved encoder of    claim 25   , wherein the signal expander comprises a repeater repeating the compressed bit stream to generate the expanded bit stream.  
     
     
         29 . The improved encoder of    claim 25   , wherein the compressed bit stream includes bits classified as one of critical, important and unimportant, and wherein the signal expander comprises a plurality of encoders additionally encoding the compressed according to bit classification to generate the expanded bit stream.  
     
     
         30 . An improved receiver for receiving a digitized speech signal transmitted at a full-rate across a radio channel in a wireless communication system, the digitized speech signal selected from the group consisting of (a) a full-rate encoded digitized speech signal comprising a stream of binary bits, and (b) a half-rate encoded digitized speech signal comprising a stream of binary bits expanded for transmission at the full-rate by repeating each bit in the binary bit stream, the improved receiver comprising: 
 a full-rate equalizer;    a half-rate equalizer;    a switch initially routing the received digitized speech signal to the full-rate equalizer, wherein said full-rate equalizer demodulates the received digitized speech signal producing a full-rate demodulated signal and dibits of information corresponding to the full-rate demodulated signal; and    an analyzer analyzing the dibits of information, said analyzer controlling the switch to route the received digitized speech signal to one of the full-rate and half-rate equalizers based upon said analysis.    
     
     
         31 . The improved receiver of    claim 30   , wherein said analyzer comprises: 
 an XNOR gate receiving the dibits of information, said XNOR gate outputting a logical one if the bits of the dibit are the same and a logical zero if the bits of the dibit are different;    a counter receiving the output of the XNOR gate, said counter counting the occurrences of logical ones at the output of the XNOR gate; and    a threshold detector connected to the counter, said threshold detector controlling the switch to route the received digitized speech signal to the half-rate equalizer if the number of logical ones counted by the counter exceeds a threshold value.    
     
     
         32 . The improved receiver of    claim 30   , wherein said dibits of information comprise dibits of soft information, each soft dibit including soft values, and wherein said analyzer comprises: 
 a multiplier multiplying the soft values of the soft dibits together, said multiplier outputting a positive value if the soft values of the soft dibit are of like polarity and negative value if the soft values of the soft dibit are of different polarity;    a summer receiving and summing the output of the multiplier; and    a threshold detector connected to the summer, said threshold detector controlling the switch to route the received digitized speech signal to the half-rate equalizer if the summed value exceeds a positive threshold value.    
     
     
         33 . The improved receiver of    claim 30   , wherein said dibits of information comprise dibits of soft information plottable on a differential constellation having real and imaginary axes, each plotted dibit representing a complex value of a differential symbol, and wherein said analyzer comprises: 
 a rotator rotating the differential symbols by π/4, said rotated differential symbols having components on the real and imaginary axes;    a summer summing magnitudes of the rotated differential symbol components on the real and imaginary axes and calculating a ratio of real axis summed magnitudes versus imaginary axis summed magnitudes; and    a threshold detector connected to the summer, said threshold detector controlling the switch to route the received digitized speech signal to the half-rate equalizer if the calculated ratio exceeds a threshold value.    
     
     
         34 . The improved receiver of    claim 30   , wherein said dibits of information comprise dibits of soft information plottable on a differential constellation having real and imaginary axes, each plotted dibit representing a complex value of a differential symbol, and wherein said analyzer comprises: 
 a rotator rotating the differential symbols by π/4, said rotated differential symbols having components on the real and imaginary axes;    a squarer and summer squaring the complex values of the rotated differential symbols and summing the squared values; and    a threshold detector connected to the squarer and summer, the threshold detector controlling the switch to route the received digitized speech signal to the half-rate equalizer if the real component of the squared/summed value exceeds a threshold value.    
     
     
         35 . The improved receiver of    claim 30   , wherein said dibits of information comprise dibits of soft information having a real number magnitude and a real number phase plottable on a differential constellation, each plotted dibit representing a differential symbol, and wherein said analyzer comprises: 
 a phase differentiator determining phase changes between successive differential symbols;    a summer summing the phase changes determined by the phase differentiator; and    a threshold detector connected to the summer, said threshold detector controlling the switch to route the received digitized speech signal to the half-rate equalizer if the summed phase changes exceed a threshold value.    
     
     
         36 . An improved receiver for receiving a digitized speech signal transmitted at a full-rate across a radio channel in a wireless communication system, the digitized speech signal selected from the group consisting of (a) a full-rate encoded digitized speech signal comprising a stream of binary bits, and (b) a half-rate encoded digitized speech signal comprising a stream of binary bits expanded for transmission at the full-rate, the improved receiver comprising: 
 a full-rate demodulation branch comprising a full-rate equalizer and a first CRC (Cyclic Redundancy Check) decoder;    a half-rate demodulation branch comprising a half-rate equalizer and a second CRC decoder;    a switch receiving the digitized speech signal and initially routing the received digitized speech signal to both the full-rate and half-rate demodulation branches, wherein the received digitized speech signal is received by the full-rate and half-rate equalizers producing full-rate demodulated and half-rate demodulated signals, respectively, said full-rate demodulated signal input to the first CRC decoder performing a CRC check on the full-rate demodulated signal and producing a first CRC check signal, and said half-rate demodulated signal input to the second CRC decoder performing a CRC check on the half-rate demodulated signal and producing a second CRC check signal; and    an analyzer analyzing the first and second CRC check signals, said analyzer controlling the switch to route the received digitized speech signal to one of the first and second demodulation branches based on said analyzation.