Ovsf code system and methods for cdma stations

Abstract

A code indexing system for a CDMA communication station that uses orthogonal variable spreading factor (OVSF) codes having a single number mapped to each code. The new code number itself not only provides the code signature, but it is also used for the OVSF code generation. In addition, the system provides easy and fast generation of the available code list without the help of look-up table. This capability improves the dynamic code assignment.

1 . A communication station configured for use in a communications system where orthogonal variable spreading factor (OVSF) codes are selected from a set of Walsh codes represented as a binary tree having multiple layers such that a zeroth layer has one Walsh code and each successive layer has twice the number of Walsh codes as the layer it succeeds, the communication station comprising: 
 a memory device having an index of consecutive positive integer index values that have a binary form of significant bits where each successive index value represents one of the OVSF codes such that the index values representing any given layer of Walsh codes are less than the index values representing any Walsh code of any layer of Walsh codes successive to the given layer.    
   
   
       2 . The communication station according to  claim 1  further comprising: 
 a processor associated with said memory device configured to select codes from the set of OVSF codes; and    said processor configured to select a second code that is orthogonal to a previously selected first code such that the binary form of the index value of the first code is not the same as the most significant bits of the binary form of the index value of the second code and the binary form of the index value of the second code is not the same as the most significant bits of the binary form of the index value of the first code.    
   
   
       3 . The communication station according to  claim 2  wherein the processor is configured to select a second code by: 
 first indicating as busy the index value of the previously selected first code and the index values of all other codes where the index value of the first code is the same as the most significant bits of the binary form of the index value of the other code or the binary form of the index value of the other code is the same as the most significant bits of the binary form of the index value of the first code, and    then selecting a code having an index value that is not indicated as busy as the second code.    
   
   
       4 . The communication station according to  claim 2  wherein said processor is configured to determine the relative orthogonality of a selected OVSF code represented by a first index value with another OVSF code represented by a second index value by comparing the binary forms of the first and second index values.  
   
   
       5 . The communication station of  claim 4  wherein said processor is configured to determine OVSF codes to be not orthogonal if either the binary form of the index value of one code is the same as the most significant binary digits of the binary form of the index value of another code or the binary form of the index value of the another code is the same as the most significant binary digits of the binary form of the index value of the one code.  
   
   
       6 . The communication station of  claim 2  wherein said processor is configured to generate OVSF codes as the Kronecker Product of codes represented by index values 2 and 3 corresponding to a sequence of significant binary digits of the binary form of its index value where each binary digit 0 corresponds to the code of index value 2 and each binary digit 1 corresponds to the code of index value 3.  
   
   
       7 . The communication station according to  claim 1  wherein said communication station is a User Equipment.  
   
   
       8 . The communication station according to  claim 1  wherein said communication station is a Node B.  
   
   
       9 . The communication station according to  claim 2  wherein said communication station is a User Equipment.  
   
   
       10 . The communication station according to  claim 2  wherein said communication station is a Node B.  
   
   
       11 . A method for a communication station configured for use in a communications system where orthogonal variable spreading factor (OVSF) codes are selected from a set of Walsh codes represented as a binary tree having multiple layers such that a zeroth layer has one Walsh code and each successive layer has twice the number of Walsh codes as the layer it succeeds, the method comprising: 
 a providing an index of consecutive positive integer index values that have a binary form of significant bits where each successive index value represents one of the OVSF codes such that the index values representing any given layer of Walsh codes are less than the index values representing any Walsh code of any layer of Walsh codes successive to the given layer.    
   
   
       12 . The method according to  claim 11  further comprising: 
 selecting codes from the set of OVSF codes such that a second code that is orthogonal to a previously selected first code is selected such that the binary form of the index value of the first code is not the same as the most significant bits of the binary form of the index value of the second code and the binary form of the index value of the second code is not the same as the most significant bits of the binary form of the index value of the first code.    
   
   
       13 . The method according to  claim 12  wherein the selecting a second code is by: 
 first indicating as busy the index value of the previously selected first code and the index values of all other codes where the index value of the first code is the same as the most significant bits of the binary form of the index value of the other code or the binary form of the index value of the other code is the same as the most significant bits of the binary form of the index value of the first code, and    then selecting a code having an index value that is not indicated as busy as the second code.    
   
   
       14 . The method according to  claim 12  wherein the relative orthogonality of a selected OVSF code represented by a first index value with another OVSF code represented by a second index value is determined by comparing the binary forms of the first and second index values.  
   
   
       15 . The method of  claim 14  wherein OVSF codes are determined to be not orthogonal if either the binary form of the index value of one code is the same as the most significant binary digits of the binary form of the index value of another code or the binary form of the index value of the another code is the same as the most significant binary digits of the binary form of the index value of the one code.  
   
   
       16 . The method of  claim 12  wherein OVSF codes are generated as the Kronecker Product of codes represented by index values 2 and 3 corresponding to a sequence of significant binary digits of the binary form of its index value where each binary digit 0 corresponds to the code of index value 2 and each binary digit 1 corresponds to the code of index value 3.  
   
   
       17 . The method of  claim 11  wherein OVSF codes are generated as the Kronecker Product of codes represented by index values 2 and 3 corresponding to a sequence of significant binary digits of the binary form of its index value where each binary digit 0 corresponds to the code of index value 2 and each binary digit 1 corresponds to the code of index value 3.