Truncated zadoff-chu sequence for lte uplink reference signals

Abstract

A method to generate truncated Zadoff-Chu sequences is disclosed. A large Zadoff-Chu sequence is generated, based on a maximum transmission bandwidth, then the sequence is truncated based on the actual transmission bandwidth. The Zadoff-Chu sequence is cyclicly extended, as needed, to maintain a quasi-orthogonal characteristic. The result is that there is an increased number of available Zadoff-Chu sequences for distribution in a wireless neighborhood and the rate of interference is reduced.

We claim: 
     
         1 . A method, comprising:
 multiplying a maximum resource block size by a number of subcarriers per resource block to obtain a value, wherein the maximum resource block size is based on a bandwidth of a wireless transmission channel;   obtaining a largest prime number smaller than the value, resulting in a second value;   generating a Zadoff-Chu sequence using a formula, wherein the sequence is based on the second value; and   truncating the Zadoff-Chu sequence, resulting in a truncated Zadoff-Chu sequence, based on a second resource block size, wherein the second resource block size is associated with a second bandwidth.   
     
     
         2 . The method of  claim 1 , further comprising:
 coupling the truncated Zadoff-Chu sequence to a signal for transmission over the wireless transmission channel at the second bandwidth.   
     
     
         3 . The method of  claim 1 , wherein the Zadoff-Chu sequence has a size equal to the largest prime number, the method further comprising:
 cyclicly extending the Zadoff-Chu sequence to a second size, wherein the second size equals the maximum resource block size multiplied by the number of carriers per resource block; wherein the Zadoff-Chu sequence is quasi-orthogonal.   
     
     
         4 . The method of  claim 1 , further comprising:
 measuring a peak-to-average power ratio (PAPR) of the Zadoff-Chu sequence; and   if the PAPR exceeds a predetermined value, discarding the Zadoff-Chu sequence.   
     
     
         5 . The method of  claim 4 , further comprising:
 generating a cyclic shift of the Zadoff-Chu sequence, resulting in a cyclic-shifted Zadoff-Chu sequence; and   truncating the cyclic-shifted Zadoff-Chu sequence, resulting in the truncated Zadoff-Chu sequence;   
       wherein the truncated Zadoff-Chu sequence is coupled to the signal for transmission over the wireless transmission channel. 
     
     
         6 . The method of  claim 5 , further comprising:
 storing the Zadoff-Chu sequence in a lookup table; and   storing the cyclic-shifted Zadoff-Chu sequence in the lookup table.   
     
     
         7 . The method of  claim 1 , wherein the bandwidth is 10 MHz and the maximum resource block size is 48. 
     
     
         8 . The method of  claim 7 , wherein each resource block in the 10 MHz bandwidth has twelve data subcarriers. 
     
     
         9 . The method of  claim 1 , generating the Zadoff-Chu sequence using the formula further comprising using the following formula: 
       
         
           
             
               
                 
                   x 
                    
                   
                     ( 
                     n 
                     ) 
                   
                 
                 = 
                 
                    
                   
                     - 
                     
                       
                         jπ 
                          
                         
                             
                         
                          
                         un 
                          
                         
                           ( 
                           
                             n 
                             + 
                             1 
                           
                           ) 
                         
                       
                       
                         N 
                         ZC 
                       
                     
                   
                 
               
               , 
             
           
         
         for 0≦n≦N ZC −1 and wherein N ZC  is the second value. 
       
     
     
         10 . The method of  claim 1 , further comprising:
 generating additional Zadoff-Chu sequences using the second value; and   cyclicly extending the Zadoff-Chu sequences so that the number of Zadoff-Chu sequences is equal to the value, resulting in a plurality of Zadoff-Chu sequences;   
       wherein the plurality of Zadoff-Chu sequences are quasi-orthogonal. 
     
     
         11 . A user equipment, comprising:
 an antenna to transmit signals to and receive signals from a remote entity in a wireless neighborhood;   a transceiver coupled to the antenna;   a memory to store a software program; and   a processor to execute the software program, wherein the software program performs the following operations:
 receiving, from a base station, an assignment of a Zadoff-Chu sequence from a plurality of Zadoff-Chu sequences; 
 receiving, from the base station, an assignment of one or more resource blocks from a plurality of resource blocks, wherein plurality of resource blocks characterize a bandwidth of a wireless transmission channel; 
 obtaining the assigned Zadoff-Chu sequence; 
 truncating the assigned Zadoff-Chu sequence based on the resource block assignment, resulting in a truncated Zadoff-Chu sequence. 
   
     
     
         12 . The user equipment of  claim 11 , wherein the software program further performs the following operation:
 generating the assigned Zadoff-Chu sequence using the following formula:   
       
         
           
             
               
                 
                   x 
                    
                   
                     ( 
                     n 
                     ) 
                   
                 
                 = 
                 
                    
                   
                     - 
                     
                       
                         jπ 
                          
                         
                             
                         
                          
                         un 
                          
                         
                           ( 
                           
                             n 
                             + 
                             1 
                           
                           ) 
                         
                       
                       
                         N 
                         ZC 
                       
                     
                   
                 
               
               , 
             
           
         
       
       for 0≦n≦N ZC −1 and wherein N ZC  is obtained by multiplying a maximum resource block size by a number of subcarriers per resource block to obtain a value, wherein the maximum resource block size is based on the bandwidth of the wireless transmission channel. 
     
     
         13 . The user equipment of  claim 12 , wherein the software program further performs the following operation:
 cyclicly shifting the first Zadoff-Chu sequence, resulting in the assigned Zadoff-Chu sequence.   
     
     
         14 . The user equipment of  claim 11 , further comprising:
 a lookup table loaded into the memory, wherein the software program retrieves the assigned Zadoff-Chu sequence from the lookup table.   
     
     
         15 . The user equipment of  claim 11 , wherein the software program further performs the following operation:
 transmitting the signal to be transmitted with the truncated Zadoff-Chu sequence.   
     
     
         16 . The user equipment of  claim 14 , wherein the software program further performs the following operation:
 retrieving the assigned Zadoff-Chu sequence from the lookup table, wherein the assigned Zadoff-Chu sequence is a cyclic-shifted version of another Zadoff-Chu sequence.   
     
     
         17 . An article comprising a medium storing instructions to enable a processor-based system to:
 generate a Zadoff-Chu sequence using a formula, wherein the formula accepts as input a predetermined value, wherein the predetermined value is based on a bandwidth of a wireless transmission channel;   receive an indication of which resource blocks to use for transmitting a signal over the wireless transmission channel; and   truncate the Zadoff-Chu sequence based on the indication, resulting in a truncated Zadoff-Chu sequence.   
     
     
         18 . The article of  claim 17 , further storing instructions to enable the processor-based system to:
 couple the truncated Zadoff-Chu sequence to a signal for transmission over the wireless transmission channel at a second bandwidth.   
     
     
         19 . The article of  claim 17 , further storing instructions to enable the processor-based system to:
 multiply a maximum resource block size by a number of subcarriers per resource block to obtain a value, wherein the maximum resource block size is based on a bandwidth of a wireless transmission channel;   obtain a largest prime number smaller than the value, resulting in a second value;   subtract one from the second value, resulting in the predetermined number.   
     
     
         20 . The article of  claim 17 , further storing instructions to enable the processor-based system to:
 measure a peak-to-average power ratio of the Zadoff-Chu sequence; and   discard the Zadoff-Chu sequence if the peak-to-average power ratio exceeds a predetermined value.   
     
     
         21 . The article of  claim 17 , further storing instructions to enable the processor-based system to:
 generate a cyclic shift of the Zadoff-Chu sequence, resulting in a cyclic-shifted Zadoff-Chu sequence;   truncate the cyclic-shifted Zadoff-Chu sequence based on the indication, resulting in a cyclic-shifted truncated Zadoff-Chu sequence; and   couple a signal to be transmitted with the cyclic-shifted truncated Zadoff-Chu sequence.