Multicode direct sequence spread spectrum

Abstract

In this patent, we present MultiCode Direct Sequence Spread Spectrum (MC-DSSS) which is a modulation scheme that assigns up to N DSSS codes to an individual user where N is the number of chips per DSSS code. When viewed as DSSS, MC-DSSS requires up to N correlators (or equivalently up to N Matched Filters) at the receiver with a complexity of the order of N2 operations. In addition, a non ideal communication channel can cause InterCode Interference (ICI), i.e., interference between the N DSSS codes. In this patent, we introduce new DSSS codes, which we refer to as the "MC" codes. Such codes allow the information in a MC-DSSS signal to be decoded in a sequence of low complexity parallel operations which reduce the ICI. In addition to low complexity decoding and reduced ICI. MC-DSSS using the MC codes has the following advantages: (1) it does not require the stringent synchronization DSSS requires, (2) it does not require the stringent carrier recovery DSSS requires and (3) it is spectrally efficient.

We claim:  
     
       1. A transceiver for transmitting a first stream of data symbols, the transceiver comprising: 
       a converter for converting the first stream of data symbols into plural sets of N data symbols each;  
       first computing means for operating on the plural sets of N data symbols to produce modulated data symbols corresponding to an invertible randomized spreading of the first stream of data symbols; and  
       means to combine the modulated data symbols for transmission.  
     
     
       2. The transceiver of  claim 1  in which the first computing means includes  comprises: 
       a source of N  more than one and up to M direct sequence spread spectrum code symbols  codes, where M is the number of chips per direct sequence spread spectrum code; and  
       a modulator to modulate each ith  data symbol from each set of N  data symbols with the ith  a code symbol  from the N code symbol  up to M direct sequence spread spectrum codes to generate N  modulated data symbols, and thereby spread each ith data symbol  set of data symbols over a separate code symbol .  
     
     
       3. The transceiver of  claim 2  in which the code symbols  direct sequence spread spectrum codes are generated by operation of a non-trivial N point  transform on a sequence of input signals. 
     
     
       4. The transceiver of  claim 1  in which the first computing means includes  comprises: 
       a transformer for operating on each set of N data symbols to generate N  modulated data symbols as output, the N  modulated data symbols corresponding to spreading of each ith  data symbol over a separate code symbol  selected from a set of more than one and up to M codes, where M is the number of chips per code; and  
       means to combine the modulated data symbols for transmission.  
     
     
       5. The transceiver of  claim 4  in which the transformer effectively applies a first transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform to the N data symbols. 
     
     
       6. The transceiver of  claim 5  in which the first transform is a Fourier transform and it is followed by a randomizing transform. 
     
     
       7. The transceiver of  claim 6  in which the first transform is a Fourier transform and it is followed by a randomizing transform and a second transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform. 
     
     
       8. The transceiver of  claim 4  in which the transformer effectively applies a first inverse transform selected from the group comprising  consisting of a randomizer transform, a Fourier transform and a Walsh transform to the N data symbols, followed by a first equalizer and a second inverse transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform. 
     
     
       9. The transceiver of  claim 8  in which the second transform is followed by a second equalizer. 
     
     
       10. The transceiver of  claim 1  further including  comprising: 
       means for receiving a sequence of modulated data symbols, the modulated data symbols having been generated by invertible randomized spreading of a second stream of data symbols; and  
       second computing means for operating on the sequence of modulated data symbols to produce an estimate of the second stream of data symbols.  
     
     
       11. The transceiver of  claim 10  further including  comprising means to apply diversity to the modulated data symbols before transmission, and means to combine received diversity signals. 
     
     
       12. The transceiver of  claim 10  in which the second computing means includes  comprises: 
       a correlator for correlating each ith  modulated data symbol from the received sequence of modulated data symbols with the ith code symbol  a code from the  a set of N code symbols  more than one and up to M codes, where M is the number of chips per code; and  
       a detector for detecting an estimate of the data symbols from output of the correlator.  
     
     
       13. The transceiver of  claim 10  in which the second computing means includes  comprises an inverse transformer for regenerating an estimate of the N  data symbols. 
     
     
       14. The transceiver of  claim 1  further including  comprising a shaper for shaping the combined modulated data symbols for transmission. 
     
     
       15. The transceiver of  claim 1  further including  comprising means to apply diversity to the combined modulated data symbols before transmission. 
     
     
       16. The transceiver of  claim 1  in which the N  data symbols include a pilot frame and a number of data frames, and is preceded by a request frame, wherein the request frame is used to wake up receiving transceivers, synchronize reception of the N  data symbols and convey protocol information. 
     
     
       17. A transceiver for transmitting a first stream of data symbols and receiving a second stream of data symbols, the transceiver comprising: 
       a converter for converting the first stream of data symbols into plural sets of N data symbols each;  
       first computing means for operating on the plural sets of N data symbols to produce sets of N  modulated data symbols corresponding to an invertible randomized spreading of each set of N data symbols over N code symbols  more than one and up to M direct sequence spread spectrum codes;  
       means to combine the modulated data symbols for transmission;  
       means for receiving a sequence of modulated data symbols, the modulated data symbols having been generated by an invertible randomized spreading of a second stream of data symbols over N code symbols  more than one and up to M direct sequence spread spectrum codes;  
       second computing means for operating on the sequence of modulated data symbols to produce an estimate of the second stream of data symbols; and  
       means to combine output from the second computing means.  
     
     
       18. The transceiver of  claim 17  in which the first computing means includes  comprises: 
       a source of N  the direct sequence spread spectrum code symbols  codes; and  
       a modulator to modulate each ith  data symbol from each set of N data symbols with the ith code symbol  a code from the N code symbol  up to M direct sequence spread spectrum codes to generate N  modulated data symbols, and thereby spread each ith  data symbol over a separate direct sequence spread spectrum code symbol .  
     
     
       19. The transceiver of  claim 18  in which the code symbols  direct sequence spread spectrum codes are generated by operation of plural non-trivial N point  transforms on a random sequence of input signals. 
     
     
       20. The transceiver of  claim 17  in which the first computing means includes  comprises: 
       a transformer for operating on each set of N data symbols to generate N  modulated data symbols as output, the N  modulated data symbols corresponding to spreading of each ith  data symbol over a separate code symbol .  
     
     
       21. The transceiver of  claim 17  in which the second computing means includes  comprises: 
       a correlator for correlating each ith  modulated data symbol from the received sequence of modulated data symbols with the ith code symbol  a code from the set of N code symbols  up to M direct sequence spread spectrum codes; and  
       a detector for detecting an estimate of the data symbols from the output of the correlator.  
     
     
       22. The transceiver of  claim 17  in which the second computing means includes  comprises an inverse transformer for regenerating an estimate of the N data symbols. 
     
     
       23. A method of exchanging data streams between a plurality of transceivers, the method comprising the steps of: 
       converting a first stream of data symbols into plural sets of N data symbols each;  
       operating on the plural sets of N data symbols to produce modulated data symbols corresponding to a spreading of the first stream of data symbols over N code symbols  more than one and up to M direct sequence spread spectrum codes;  
       combining the modulated data symbols for transmission; and  
       transmitting the modulated data symbols from a first transceiver at a time when no other of the plurality of transceivers is transmitting.  
     
     
       24. The method of  claim 23  in which the spreading is an invertible randomized spreading and operating on the plural sets of N data symbols includes  comprises modulating each ith  data symbol from each set of N data symbols with the ith code symbol  a code from the N code symbols  up to M direct sequence spread spectrum codes to generate N  modulated data symbols, and thereby spread each ith  data symbol over a separate code symbol . 
     
     
       25. The method of  claim 23  in which the spreading is an invertible randomized spreading and operating on the plural sets of N data symbols includes  comprises: 
       transforming, by application of a transform, each set of N data symbols to generate N  modulated data symbols as output.  
     
     
       26. The method of  claim 25  in which transforming each set of N data symbols includes  comprises applying to each set of N data symbols a randomizing transform and a transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform. 
     
     
       27. The method of  claim 25  in which transforming each set of N data symbols includes  comprises applying to each set of N data symbols a Fourier transform, a randomizing transform and a transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform. 
     
     
       28. The method of  claim 25  in which transforming each set of N data symbols includes  comprises applying to each set of N data symbols a first transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform, a randomizing transform and a second transform selected from the group comprising  consisting of a Fourier transform and a Walsh transform. 
     
     
       29. The method of  claim 23  further including  comprising the step of: 
       receiving, at a transceiver distinct from the first transceiver, the sequence of modulated data symbols; and  
       operating on the sequence of modulated data symbols to produce an estimate of the first stream of data symbols.  
     
     
       30. The method of  claim 29  in which operating on the sequence of modulated data symbols includes  comprises the steps of: 
       correlating each ith  modulated data symbol from the received sequence of modulated data symbols with the ith code symbol from the set of N code symbols  a code from the up to M direct sequence spread spectrum codes; and  
       detecting an estimate of the first stream of data symbols from output of the correlator.  
     
     
       31. The method of  claim 23  further including  comprising the step of shaping the modulated data symbols before transmission. 
     
     
       32. The method of  claim 23  further including  comprising the step of applying diversity to the modulated data symbols before transmission. 
     
     
       33. A transceiver for transmitting a first stream of data symbols, the transceiver comprising: 
       
         a converter for converting the first stream of data symbols into plural sets of data symbols each;  
       
       
         first computing means for operating on the plural sets of data symbols to produce modulated data symbols corresponding to an invertible randomized spreading of the first stream of data symbols over more than one and up to M direct sequence spread spectrum codes, where each direct sequence spread spectrum code has M chips; and  
       
       
         means to combine the modulated data symbols for transmission. 
       
     
     
       34. The transceiver of  claim 33  further comprising: 
       
         means for receiving a sequence of modulated data symbols, the modulated data symbols having been generated by invertible randomized spreading of a second stream of data symbols; and  
       
       
         second computing means for operating on the sequence of modulated data symbols to produce an estimate of the second stream of data symbols. 
       
     
     
       35. The transceiver of  claim 34  further comprising means to apply diversity to the modulated data symbols before transmission, and means to combine received diversity signals. 
     
     
       36. The transceiver of  claim 34  in which the second computing means comprises: 
       
         a correlator for correlating each modulated data symbol from the received sequence of modulated data symbols with a code from the set of up to M direct sequence spread spectrum codes; and  
       
       
         a detector for detecting an estimate of the data symbols from output of the correlator. 
       
     
     
       37. The transceiver of  claim 34  in which the second computing means comprises an inverse transformer for regenerating an estimate of the data symbols. 
     
     
       38. The transceiver of  claim 33  further comprising a shaper for shaping the combined modulated data symbols for transmission. 
     
     
       39. The transceiver of  claim 33  further comprising means to apply diversity to the combined modulated data symbols before transmission. 
     
     
       40. The transceiver of  claim 33  in which the data symbols include a pilot frame and a number of data frames, and is preceded by a request frame, wherein the request frame is used to wake up receiving transceivers, synchronize reception of the data symbols and convey protocol information.