Carrier injecting waveform-based modulation scheme for reducing satellite transponder power requirements and earth terminal antenna size

Abstract

A QPSK modulation scheme uses a data spreading mechanism to rob a relatively limited portion of available transmitter power, and inject into the QPSK waveform a prescribed amount of carrier signal power, through which detection and non-regenerative extraction of the carrier at the receiver may be achieved without incurring a signal-to-noise degradation penalty. In addition, the injected carrier-based modulation scheme of the invention may employ high performance forward error correction coding, to significantly reduce the signal power required for achieving a very low energy per bit-to-noise density ratio (E b /N 0 )—on the order of one to zero dB.

1. A method of transmitting information comprising the steps of:
 providing a data signal representative of the information and comprising in-phase (I) and quadrature (Q) components and encoded with a forward error correction code, the forward error correction code being capable of extending error rate performance to a value of energy per bit to noise density ratio ( E   b   /N   o )  less than  4  dB ;  
 biasing at least one of the I and Q components with an offset comprising a direct current (DC) offset;  
 generating a quadrature phase shift keyed (QPSK) waveform based upon a carrier signal: and the at least one biased component; and  
 transmitting the QPSK waveform;  
   receiving the transmitted QPSK waveform;    
   processing the received QPSK waveform to extract said carrier signal therefrom;    
   processing the received QPSK waveform using the carrier signal extracted therefrom to derive said data signal; and    
   decoding the encoded data signal to recover said information from said data signal .  
 
     
     
       2. A method according to  claim 1 , further including the steps of:
 receiving the transmitted QPSK waveform; and    processing the received QPSK waveform to extract said carrier signal therefrom.    
     
     
       3. A method according to  claim 2 , further including the step of:
 processing the received QPSK waveform using the carrier signal extracted therefrom to derive said data signal.    
     
     
       4. A method according to  claim 3 , wherein said data signal is encoded with a forward error correction code, and further including the step of decoding the encoded data signal to recover said information from said data signal. 
     
     
       5. A method according to  claim 4 , wherein said forward error correction code is one capable of extending error rate performance to a value of energy per bit to noise density ratio (E b /N 0 ) less than 4 dB. 
     
     
       6. A method according to  claim 1 , wherein generating the QPSK waveform comprises multiplying the carrier signal with the digital signal. 
     
     
       7. A communication system comprising:
 an encoder operative to encode a data signal with a forward error correction code capable of extending error rate performance to a value of energy per bit to noise density ratio ( E   b   /N   o )  less than  4  dB;   
 a quadrature phase shift keyed (QPSK) waveform generator for generating a QPSK waveform based upon a carrier signal and a data signal, the data signal being representative of information to be transmitted and comprising I and Q components, and said QPSK waveform generator biasing at least one of the I and Q components with an offset prior to generating the QPSK waveform, the offset comprising a direct current (DC) offset voltage; and  
 a transmitter for transmitting the QPSK waveform produced by said QPSK waveform generator; and  
   a receiver operative to      receive said QPSK waveform and to extract said carrier signal therefrom,        process said QPSK waveform using said extracted carrier signal to derive said encoded data signal, and        decode the encoded data signal to recover said information from said data signal .    
 
     
     
       8. A communication system according to  claim 7 , further including a receiver which is operative to receive said QPSK waveform and to extract said carrier signal therefrom. 
     
     
       9. A communication system according to  claim 8 , wherein said receiver is operative to process said QPSK waveform using said extracted carrier signal to derive said data signal. 
     
     
       10. A communication system according to  claim 9 , further including an encoder which is operative to encode said data signal with a forward error correction code, and wherein said receiver is operative to decode the encoded data signal to recover said information from said data signal. 
     
     
       11. A communication system according to  claim 10 , wherein said forward error correction code is one capable of extending error rate performance to a value of E b /N 0  less than 4 dB. 
     
     
       12. A method comprising the steps of:
 (a) providing a carrier signal comprising in-phase (I) and quadrature (Q) components;  
 (b) providing a data signal comprising I and Q components and biasing the I and Q components of the data signal with at least one offset comprising a spreading waveform to provide a carrier extraction reference; and  
 (c) combining the I and Q components of the carrier signal with the biased I and Q components of the data signal, respectively, to produce a quadrature phase shift keyed (QPSK) waveform.  
 
     
     
       13. A method according to  claim 12 , further including the steps of:
 (d) transmitting the QPSK waveform produced in step (c);  
 (e) receiving the QPSK waveform transmitted in step (d);  
 (f) conducting non-regenerative recovery of the QPSK waveform received in step (e) to extract said carrier signal therefrom; and  
 (g) processing the QPSK waveform received in step (e) using the carrier signal extracted therefrom in step (f) to recover said data signal.  
 
     
     
       14. A method according to  claim 13 , wherein said data signal contains information encoded with a forward error correction code, and further including the step (g) of decoding the encoded data signal to recover said information. 
     
     
       15. A method according to  claim 14 , wherein said forward error correction code is a code capable of extending error rate performance to a value of energy per bit to noise density ratio (E b /N 0 ) less than 4 dB. 
     
     
       16. A method according to  claim 12 , wherein combining comprises multiplying the I and Q components of the carrier signal with the biased I and Q components of the data signal, respectively. 
     
     
       17. A method comprising the steps of:
 (a) receiving a quadrature phase shift keyed (QPSK) waveform having in-phase (I) and quadrature (Q) components of a carrier modulated with I and Q components of a data signal, the data signal containing information encoded with a forward error correction code capable of extending error rate performance to a value of energy per bit to noise density ratio ( E   b   /N   o )  less than  4  dB, and  at least one of the I and Q components of the data signal being biased by an offset comprising a direct current (DC) offset voltage; and  
 (b) conducting non-regenerative recovery of the QPSK waveform received in step (a) to extract said carrier signal based upon the offset;  
 ( c )  processing the QPSK waveform received in step  ( a )  using the carrier signal extracted therefrom in step (   b )  to recover said data signal; and    
 ( d )  decoding the encoded data signal to recover said information .  
 
     
     
       18. A method according to  claim 17 , further including the step (c) of processing the QPSK waveform received in step (a) using the carrier signal extracted therefrom in step (b) to recover said data signal. 
     
     
       19. A method according to  claim 18 , wherein said data signal contains information encoded with a forward error correction code capable of extending error rate performance to a value of energy per bit to noise density ratio (E b /N 0 ) less than 4 dB, and further including the step (d) of decoding the encoded data signal to recover said information. 
     
     
       20. A method according to  claim 17 , wherein the at least one offset comprises a respective offset for each of the I and Q components of the data signal. 
     
     
       21. A method of transmitting information comprising the steps of:
 providing a data signal representative of the information and comprising in-phase (I) and quadrature (Q) components;  
 biasing at least one of the I and Q components with an offset comprising a spreading waveform to provide a carrier extraction reference;  
 generating a quadrature phase shift keyed (QPSK) waveform based upon a carrier signal and the at least one biased component; and  
 transmitting the QPSK waveform.  
 
     
     
       22. A method according to  claim 21 , further including the steps of:
 receiving the transmitted QPSK waveform; and  
 processing the received QPSK waveform to extract said carrier signal therefrom.  
 
     
     
       23. A method according to  claim 22 , further including the step of: processing the received QPSK waveform using the carrier signal extracted therefrom to derive said data signal. 
     
     
       24. A method according to  claim 23 , wherein said data signal is encoded with a forward error correction code, and further including the step of decoding the encoded data signal to recover said information from said data signal. 
     
     
       25. A method according to  claim 24 , wherein said forward error correction code is one capable of extending error rate performance to a value of energy per bit to noise density ratio (E b /N 0 ) less than 4 dB. 
     
     
       26. A method according to  claim 25 , wherein generating the QPSK waveform comprises multiplying the carrier signal with the digital signal. 
     
     
       27. A communication system comprising:
 a quadrature phase shift keyed (QPSK) waveform generator for generating a QPSK waveform based upon a carrier signal and a data signal, the data signal being representative of information to be transmitted and comprising I and Q components, and said QPSK waveform generator biasing at least one of the I and Q components with an offset prior to generating the QPSK waveform to provide a carrier extraction reference, the offset comprising a spreading waveform; and  
 a transmitter for transmitting the QPSK waveform produced by said QPSK waveform generator.  
 
     
     
       28. A communication system according to  claim 27 , further including a receiver which is operative to receive said QPSK waveform and to extract said carrier signal therefrom. 
     
     
       29. A communication system according to  claim 28 , wherein said receiver is operative to process said QPSK waveform using said extracted carrier signal to derive said data signal. 
     
     
       30. A communication system according to  claim 29 , further including an encoder which is operative to encode said data signal with a forward error correction code, and wherein said receiver is operative to decode the encoded data signal to recover said information from said data signal. 
     
     
       31. A communication system according to  claim 30 , wherein said forward error correction code is one capable of extending error rate performance to a value of E b /N o   energy per bit to noise density ratio ( E   b   /N   o ) less than 4 dB. 
     
     
       32. A method of transmitting information comprising the steps of:
   providing a data signal representative of the information and comprising in - phase  ( I )  and quadrature  ( Q )  components and encoded with a forward error correction code, the forward error correction code being capable of extending error rate performance to a value of energy per bit to noise density ratio  ( E   b   /N   o )  less than  4  dB;        biasing at least one of the I and Q components with an offset comprising a direct current  ( DC )  offset;        generating a waveform based upon a carrier signal and the at least one biased component;        transmitting the waveform;        receiving the transmitted waveform;        processing the received waveform to extract said carrier signal therefrom;        processing the received waveform using the carrier signal extracted therefrom to derive said data signal; and        decoding the encoded data signal to recover said information from said data signal.     
     
     
       33. A method according to  claim 32 , wherein generating the waveform comprises multiplying the carrier signal with the digital signal. 
     
     
       34. A method of transmitting information comprising the steps of:
   providing a data signal representative of the information and comprising in - phase  ( I )  and quadrature  ( Q )  components;        biasing at least one of the I and Q components with an offset comprising a spreading waveform to provide a carrier extraction reference;        generating a waveform based upon a carrier signal and the at least one biased component; and        transmitting the waveform.     
     
     
       35. A method according to  claim 34 , further including the steps of:
   receiving the transmitted waveform; and        processing the received waveform to extract said carrier signal therefrom.     
     
     
       36. A method according to  claim 35 , further including the step of:
   processing the received waveform using the carrier signal extracted therefrom to derive said data signal.     
     
     
       37. A method according to  claim 36 , wherein said data signal is encoded with a forward error correction code, and further including the step of decoding the encoded data signal to recover said information from said data signal. 
     
     
       38. A method according to  claim 37 , wherein said forward error correction code is one capable of extending error rate performance to a value of energy per bit to noise density ratio ( E   b   /N   0 )  less than  4  dB.   
     
     
       39. A method according to  claim 38 , wherein generating the waveform comprises multiplying the carrier signal with the digital signal. 
     
     
       40. A communication system comprising:
   a waveform generator for generating a waveform based upon a carrier signal and a data signal, the data signal being representative of information to be transmitted and comprising I and Q components, and said waveform generator biasing at least one of the I and Q components with an offset prior to generating the waveform to provide a carrier extraction reference, the offset comprising a spreading waveform; and        a transmitter for transmitting the waveform produced by said waveform generator.     
     
     
       41. A communication system according to  claim 40 , further including a receiver which is operative to receive said waveform and to extract said carrier signal therefrom. 
     
     
       42. A communication system according to  claim 41 , wherein said receiver is operative to process said waveform using said extracted carrier signal to derive said data signal. 
     
     
       43. A communication system according to  claim 42 , further including an encoder which is operative to encode said data signal with a forward error correction code, and wherein said receiver is operative to decode the encoded data signal to recover said information from said data signal. 
     
     
       44. A communication system according to  claim 43 , wherein said forward error correction code is one capable of extending error rate performance to a value of energy per bit to noise density ratio ( E   b   /N   o )  less than  4  dB.