Spreading code sequence acquisition system and method that allows fast acquisition in code division multiple access (CDMA) systems

Abstract

Methods for generating code sequences that have rapid acquisition properties and apparatus which implement the methods by processing spreading codes on in-phase and quadrature channels. A first method combines two or more short codes to produce a long code. This method may use many types of code sequences, one or more of which are rapid acquisition sequences of length L that have average acquisition phase searches r=log2L. Two or more separate code sequences are transmitted over the complex channels. If the sequences have different phases, an acquisition may be done by acquisition circuits in parallel over the different code sequences when the relative phase shift between the two or more code channels is known. When the received length L codes or the length L correlation codes used to find the phase of the received codes have a mutual phase delay of L/2, the average number of tests to find the code phase of the received code is L/4. The codes sent on each channel may be the same code, with the code phase in one channel being delayed with respect to the other channel, or they may be different code sequences.

The invention claimed is:  
     
       1. A fast acquisition apparatus for quickly synchronizing a spreading code phase of a spread-spectrum communication system to a transmitted code signal having a transmitted in-phase (I) code signal and a transmitted quadrature (Q) code signal, said transmitted I-code signal including a first spreading code sequence and said transmitted Q-code signal including a second spreading code sequence; the transmitted I-code signal and the transmitted Q-code signal having a predetermined mutual code sequence phase offset value, the fast acquisition apparatus comprising: 
       receiving means for receiving the transmitted code signal and for separating, from the received code signal, the transmitted I-code signal and the transmitted Q-code signal;  
       correlating means for correlating code sequences with the transmitted code signal and comprising an I-code signal correlator and a Q-code signal correlator;  
       a local code sequence generator responsive to a code control signal value to generate a local portion of the I-code sequence having an I-code phase value and a local portion of the Q-code sequence having a Q-code phase value; and  
       controller means for determining, obtaining and maintaining code sequence lock said controller means coupled to the I-code signal correlator, the Q-code signal correlator, and the local code sequence generator, said I-code signal correlator correlating said local portion of the I-code sequence with said transmitted I-code signal and generating an I-high value provided to said controller means when the I-code phase value of the local portion of the I-code sequence and a code phase value of the transmitted I-code signal have matching code phase values and said Q-code signal correlator correlating said local portion of the Q-code sequence with said transmitted Q-code signal and generating a Q-high value provided to said controller means when the Q-code phase value of the local portion of the Q-code sequence and a code phase value of the transmitted Q-code signal have matching code phase values;  
       wherein said controller means using said predetermined mutual code sequence phase offset value, generates the code control signal value to lock the I-code phase value of the local portion of the I-code sequence responsive to the I-high value and to set the Q-code phase value of the local portion of the Q-code sequence, and generates the code control signal value to lock the Q-code phase value of the local portion of the Q-code sequence responsive to the Q-high value and to set the I-code phase value of the local portion of the I-code sequence; and said controller means is responsive to the absence of the I-high value and the Q-high value to generate the code control signal value which adjusts the I-code phase value and the Q-code phase value.  
     
     
       2. The fast acquisition apparatus of  claim 1 , wherein the first spreading code sequence is equivalent to the second spreading code sequence, and the transmitted I-code signal and the transmitted Q code signal have the predetermined mutual code sequence phase relationship such that the respective code phases are not identical. 
     
     
       3. The fast acquisition apparatus of  claim 1 , wherein the first spreading code sequence and the second spreading code sequence are each chosen from a plurality of fast acquisition sequences of length L code periods; each of said fast acquisition sequences including a short code portion having length of N code periods and a long code portion having length of M code periods and having a mean search value of log 2L phases wherein said short code portion occurs repetitively, where L, M and N are integers, wherein: 
       said local portion of the I-code sequence includes an I-sequence equivalent to the short code portion of the respective fast acquisition sequence, and said local portion of the Q-code sequence includes a Q-sequence equivalent to the short code portion of the respective fast acquisition sequence;  
       said I-code signal correlator further includes means for generating an I-middle value when the I-code phase value of the local portion of the I-code sequence and the code phase of the transmitted I-code signal have code phase values which correspond to the I-sequence being in phase with one occurrence of the respective short code sequence of the first spreading code sequence;  
       said Q-code signal correlator further includes means for generating a Q-middle value when the Q-code phase of the local portion of the Q-code sequence and the code phase of the transmitted Q-code signal have code phase values which correspond to the Q-sequence being in phase with one occurrence of the respective short code sequence of the second spreading code sequence; and  
       said controller is responsive to the I-middle value and to the absence of the I-high value and the Q-high value for generating the code control signal having a value which adjusts the I-code phase value and the Q-code phase value to maintain the respective local short code sequence portion of the local portion of the I-code sequence in phase with each respective occurrence of the short code sequence of the first spreading code sequence; and being responsive to the Q-middle value and the absence of the I-high value and the Q-high value for generating the code control signal value for adjusting the I-code phase value and the Q-code phase value to maintain the respective Q-sequence of the local portion of the Q-code sequence in phase with each respective occurrence of the short code sequence of the second spreading code sequence.  
     
     
       4. The fast acquisition apparatus of  claim 3 , wherein N is an even integer and M is an odd integer. 
     
     
       5. The fast acquisition apparatus of  claim 3 , wherein N is an odd integer and M is an even integer. 
     
     
       6. The fast acquisition apparatus of  claim 3 , wherein L is equal to M multiplied by N. 
     
     
       7. The fast acquisition apparatus of  claim 3 , wherein L is equal to the least common multiple of M and N. 
     
     
       8. The fast acquisition apparatus of  claim 3 , wherein the first spreading code sequence and the second spreading code sequence are shifted in phase by L/2 code sequences relative to each other. 
     
     
       9. A fast code acquisition detector for a code division multiple access receiver wherein the code sequence of the signal to be received has I- code and Q - code signal components which have a known phase relationship comprising:    
         an I - code despreader for despreading an I - code signal component with a despreading sequence at a selected phase value and outputting the result;    
         a Q - code despreader for despreading a Q - code signal component with a despreading sequence at a selected phase value and outputting the result; and    
         a controller for controlling the selected phase values of said I - code and Q - code despreaders in response to a phase acquisition correlation of each of the outputs of said I - code and  Q -code despreaders such that:    
         said I - code despreader is provided an initial I - code phase value and said Q - code despreader is provided with an initial Q - code phase value which is off - set a predetermined amount from said I - code initial phase value;    
         if the correlation of the output of neither said I - code or Q - code despreaders indicates signal phase acquisition, said controller selectively increments the selected phase value of said I - code and Q - code despreaders; and    
         if the correlation of the output of one of said I - code and Q - code despreaders indicates phase acquisition, said controller selectively increments the selected phase value of the other despreader based on the known phase relationship so that both despreaders output a phase correct despread signal.   
     
     
       10. A fast code acquisition detector according to  claim 9  further comprising: 
         a first demodulator having a received signal input and a filtered I - code signal output coupled to said I - code despreader; and    
         a second demodulator having a received signal input and a filtered Q - code signal output coupled to said Q - code despreader.   
     
     
       11. A fast code acquisition detector according to  claim 9  wherein: 
         said I - code despreader includes a phase adjustable spreading sequence generator which generates an I - despreading sequence at said selected phase value as controlled by said controller; and    
         said Q - code despreader includes a phase adjustable spreading sequence generator which generates a Q - despreading sequence at said selected phase value as controlled by said controller.   
     
     
       12. A fast code acquisition detector according to  claim 9  wherein: 
         each of the I - code and Q - code signal components has a code sequence period of length L consisting of a plurality of subsequences having a period of length N, where L and N are integers such that L>N; and    
         said controller controls the selected phase values of said I - code and Q - code despreaders in response to a correlation of each of the outputs of said I - code and Q - code despreaders such that said controller increments the selected phase value of said I - code and Q - code despreaders by N is the correlation of either said I - code or Q - code despreaders indicates phase acquisition of the signal N - period subsequences and the correlation of the output of neither said I - code or Q - code despreaders indicates signal phase acquisition.   
     
     
       13. A fast code acquisition detector according to  claim 12  further comprising: 
         a first correlator associated with said controller having an I - code despreader energy output detector which utilizes a first threshold for detection of despread N - period subsequences or a higher second threshold; and    
         a second correlator associated with said controller having a Q - code despreader energy output detector which utilizes a first threshold for detection of despread N - period subsequences or a higher second threshold; and    
         said correlators using said second higher threshold after either correlator detects acquisition of despread N - period subsequences.   
     
     
       14. A fast code acquisition detector according to  claim 9  wherein each of the I- code and Q - code signal components has a code sequence period of length L and wherein the phase relationship between the I - code and Q - code signal components is a phase shift of L/ 2  whereby said controller selects a correct phase value for said despreaders within L/ 4  iterations of phase acquisition correlations.   
     
     
       15. A fast code acquisition detector for a code division multiple access receiver, wherein the code sequence of the signal to be received has a period of length L consisting of a plurality of subsequences having a period of length N, where L and N are integers such that L>N, comprising: 
       
         a despreader for despreading a signal with a despreading sequence at a selected phase value and outputting the result; and  
       
       
         a controller for controlling the selected phase value of said despreader in response to a phase acquisition correlation of the output of said despreader such that:  
       
       
         said despreader is provided an initial phase value;  
       
         if the correlation of the output of said despreader does not indicate signal phase acquisition or phase acquisition of the signal N - period subsequences, said controller increments the selected phase value of said despreader by one; and    
         if the correlation of the output of said despreader indicates phase acquisition of the signal N - period subsequences, but not signal phase acquisition, said controller increments the selected phase value of said despreading by N.   
     
     
       16. A fast code acquisition detector according to  claim 15  further comprising: 
         a correlator associated with said controller having a despreader energy output detector which utilizes a first threshold for detection of despread N - period subsequences or a higher second threshold; and    
         said correlator using said second higher threshold after said correlator detects acquisition of despread N - period subsequences.   
     
     
       17. A fast code acquisition detection method for a code division multiple access receiver wherein the code sequence of the signal to be received has I- code and an Q - code signal components which have a known phase relationship comprising:    
         despreading an I - code signal component with a despreading sequence at a selected phase value to produce a despread I signal;    
         despreading a Q - code signal component with a despreading sequence at a selected phase value to produce a despread Q signal;    
         controlling the selected phase values of said I - code and Q - code despreading in response to a phase acquisition correlation of the despread I and Q signals;    
         said I - code despreading being performed at an initial I - code phase value and said Q - code despreading being performed at an initial Q - code phase value which is off - set a predetermined amount from said I - code initial phase value;    
         if the correlation of neither the despread I or Q signals indicates signal phase acquisition, selectively incrementing the selected phase value of said I - code and Q - code despreading; and    
         if the correlation of one of the despread I or Q signals indicates phase acquisition, selectively incrementing the selected phase value of the other despreading based on the known phase relationship so that both said I - code and Q - code despreading produce phase correct despread signals.   
     
     
       18. A fast code acquisition detection method according to  claim 17  further comprising: 
         demodulating and filtering a received signal input to produce a filtered I - code signal component for said I - code despreading; and    
         demodulating and filtering a received signal input to produce a filtered Q - code signal component for said Q - code despreading.   
     
     
       19. A fast code acquisition detection method according to  claim 17  wherein each of the I- code and Q - code signal components has a code sequence period of length L consisting of a plurality of subsequences having a period of length N, where L and N are integers such that L>N, and wherein the controlling of the selected phase values of said I - code and Q - code despreading in response to a correlation of said I and Q signals is such that the incrementing of the selected phase value of said I - code and Q - code despreading is by N when the correlation of either said I or Q signal indicates phase acquisition of the signal N - period subsequences and the correlation of the output of neither said I or Q signal indicates signal phase acquisition.   
     
     
       20. A fast code acquisition detection method according to  claim 19  further comprising: 
         correlating said I signal based on energy detection at a first threshold for detecting despread N - period subsequences or at a higher second threshold;    
         correlating said Q signal based on energy detection at a first threshold for detecting of despread N - period subsequences or at a higher second threshold; and    
         said correlating being at said second higher threshold after either I signal or Q signal correlating detects acquisition of despread N - period subsequences.   
     
     
       21. A fast code acquisition detection method for a code division multiple access receiver, wherein the code sequence of the signal to be received has a period of length L consisting of a plurality of subsequences having a period of length N, where L and N are integers such that L>N, comprising: 
       
         despreading a signal with a despreading sequence at a selected phase value to produce a despread signal; and  
       
       
         controlling the selected phase value of said despreading in response to a correlation of the despread signal against a predetermined threshold;  
       
       
         initially despreading at an initial phase value; and  
       
         if the correlation of the despread signal does not indicate signal phase acquisition or phase acquisition of the signal N - period subsequences, incrementing the selected phase vale of said despreading by one; and    
         if the correlation of the despread signal indicates phase acquisition of the signal N - period subsequences and the correlation does not indicate signal phase acquisition, incrementing the selected phase value of said despreading by N.   
     
     
       22. A fast code acquisition detection method according to  claim 21  further comprising: 
         correlating said despreading based on energy detection at a first threshold for detection of despread N - period subsequences or at a higher second threshold; and    
         said correlating being at said second higher threshold after the correlating detects acquisition of despread N - period subsequences.