Method to minimize compatibility error in hierarchical modulation using variable phase

Abstract

The present invention provides a method, receiver and transmitter for use in a SDAR system. The method involves generating a first modulated signal based on first input data. Additional modulation is superimposed on the first modulated signal based on additional input data, being spread across a plurality of symbols in the first modulated signal in a predetermined pattern to generate a modified signal which is then transmitted. The modified signal is decoded by performing a first demodulation of the first modulated signal then additional demodulation is performed to obtain additional input data. The superimposing step uses a plurality of offset sequence values to add the additional modulation to the first modulated signal. The offset sequence may appear as a pseudo-random distribution of offset sequence values, and may include at least one zero offset value. Alternatively, the additional modulated signal may be a fromed as a direct sequence spread spectrum modulation and the offset sequence appearing as a pseudo-noise distribution. A Hadamard matrix sequence may be used as the direct sequence code.

1 . A method for transmitting at least two levels of data in a hierarchical transmission system comprising the steps of: 
 generating a first modulated signal based on first input data;    superimposing at least a second modulation on the first modulated signal based on at least a second input data, the second modulation being spread across a plurality of symbols in the first modulated signal in a predetermined pattern to create a modified signal;    transmitting the modified signal;    decoding the modified signal by performing a first demodulation of the first modulated signal then a second demodulation to obtain the first input data and the second input data.    
   
   
       2 . The method of  claim 1  wherein the superimposing step uses a plurality of offset sequence values as the predetermined pattern to spread the at least second modulation across the first modulated signal.  
   
   
       3 . The method of  claim 2  wherein the plurality of offset sequence values includes a pseudo-random distribution of offset sequence values.  
   
   
       4 . The method of  claim 2  wherein the plurality of offset sequence values includes at least one zero offset value.  
   
   
       5 . The method of  claim 2  wherein the at least a second modulated signal involves direct sequence spread spectrum modulation and the predetermined pattern is a pseudo-noise distribution.  
   
   
       6 . The method of  claim 5  wherein the predetermined pattern includes a Hadamard matrix sequence.  
   
   
       7 . A receiver for receiving at least two levels of data in a hierarchical transmission system comprising: 
 an antenna for receiving RF signals;    a demodulator coupled to said antenna for downconverting received RF signals;    a first detector coupled to said demodulator, said first detector having a first output and capable of providing digital information based on a first level of data on said first output; and    at least a second detector coupled to said demodulator, said at least a second detector having at least a second output and capable of providing digital information based on at least a second level of data on said at least a second output, said at least a second detector being adapted to detect the at least a second level of data as a predetermined pattern spread over the first level of data.    
   
   
       8 . The receiver of  claim 7  wherein said at least a second detector uses a plurality of predetermined offset sequence values as the predetermined pattern to detect the at least a second level of data.  
   
   
       9 . The receiver of  claim 8  wherein the plurality of offset sequence values includes a pseudo-random distribution of offset sequence values.  
   
   
       10 . The receiver of  claim 8  wherein the plurality of offset sequence values includes at least one zero offset value.  
   
   
       11 . The receiver of  claim 8  wherein said at least a second detector is capable of detecting a direct sequence spread spectrum modulation with the predetermined pattern including a pseudo-noise distribution.  
   
   
       12 . The receiver of claim  111  wherein said at least a second detector includes a predetermined pattern comprising a Hadamard matrix sequence.  
   
   
       13 . A transmitter for transmitting at least two levels of data in a hierarchical transmission system comprising: 
 an encoder adapted to receive a first and at least a second input data, said encoder capable of providing digital information based on a first level of data on an output stream, said encoder capable of providing digital information based on at least a second level of data on said output stream, said encoder being adapted to superimpose the at least a second level of data as a predetermined pattern spread over the first level of data;    a modulator coupled to said encoder for upconverting said output stream; and    an antenna coupled to said modulator for transmitting RF signals based on the upconverted output stream.    
   
   
       14 . The transmitter of  claim 13  wherein said encoder uses a plurality of predetermined offset sequence values as the predetermined pattern to superimpose the at least a second level of data over the first level of data.  
   
   
       15 . The transmitter of  claim 14  wherein the plurality of offset sequence values includes a pseudo-random distribution of offset sequence values.  
   
   
       16 . The transmitter of  claim 14  wherein the plurality of offset sequence values includes at least one zero offset value.  
   
   
       17 . The transmitter of  claim 14  wherein said modulator is capable of modulating said output stream as a direct sequence spread spectrum modulation and said predetermined pattern includes a pseudo-noise distribution.  
   
   
       18 . The transmitter of  claim 17  wherein said predetermined pattern comprises a Hadamard matrix sequence.