Telemetry system having amplitude modulation of Walsh functions

Abstract

A digital communications system employing modulated Walsh functions to convey data across a communications channel. In one embodiment, the system includes a transmitter having a constellation encoder, and a Walsh constellation modulator. The constellation encoder receives a sequence of data words and converts it into a sequence of constellation signal point labels. The modulator receives the sequence of labels, and responsively generates one or more amplitude-modulated Walsh functions which are summed to produce a modulated signal. The modulated signal passes through a communications channel to a receiver. The receiver includes an analog-to-digital converter (ADC) and a demodulation circuit. The ADC oversamples the received signal. The demodulation circuit manipulates the sign of the samples to effectively multiply the received samples with one or more Walsh functions, and sums the resulting values over one symbol interval to determine the modulated amplitude of the corresponding functions.

1. A transmitter that comprises:
 a constellation encoder configured to receive a sequence of n-bit data words and configured to convert the sequence of data words into a sequence of m-bit constellation signal point labels; and  
 a modulator configured to receive the sequence of signal point labels and configured to responsively generate at least one amplitude-modulated bi-valued function having an amplitude in each symbol interval determined by a corresponding signal point label in the sequence of signal point labels.  
 
   
   
     2. The transmitter of  claim 1 , wherein the modulator is further configured to generate a second amplitude-modulated bi-valued fumction that is orthogonal to said at least one amplitude-modulated bi-valued function, wherein the amplitude-modulated square waves are summed to produce a modulated signal. 
   
   
     3. The transmitter of claim l, wherein the bi-valued function is any Walsh function. 
   
   
     4. The transmitter of claim l, wherein the modulator is a digital circuit. 
   
   
     5. A method of data communication, comprising:
 receiving a sequence of data words;  
 converting the sequence of data words into a sequence of sets of constellation signal point coordinate values, wherein the sequence of sets can be represented as: 
   (x 1k , y 1k , x 2k , y 2k , . . . , x (d/2)k , y (d/2)k ), k=1, 2, . . . ,  
 
  wherein k is the sequence index, and d is the dimensionality of the constellation; and  
 producing a modulated signal M(t) that can be represented as: 
         M   ⁢     (   t   )       =       ∑   k     ⁢       ∑     j   =   1       d   /   2       ⁢     (         x   jk     ⁢     cal   ⁢     (     j   ,     t   -   kT       )         +       y   jk     ⁢     sal   ⁡     (     j   ,     t   -   kT       )           )             
 
  wherein T is a symbol period.  
 
   
   
     6. A receiver that comprises:
 an analog-to-digital converter configured to convert a received signal into a sequence of samples, wherein multiple samples are taken in each symbol period;  
 a circuit configured to manipulate the sign of the sequence of samples in accordance with a Walsh function, and further configured to sum the resulting values over each symbol period.  
 
   
   
     7. The receiver of  claim 6 , further comprising:
 a second circuit configured to manipulate the sign of the sequence of samples in accordance with a second, different Walsh function, and further configured to sum a second set of resulting values over each symbol period; and  
 a decision element configured to convert the resulting values into a sequence of signal constellation points.  
 
   
   
     8. The receiver of  claim 7 , further comprising:
 a constellation decoder configured to convert the sequence of signal constellation points into a sequence of n-bit data words.