Adaptive pilot structure to assist channel estimation in spread spectrum systems

Abstract

The present invention relates generally to methods for generating a dynamic pilot symbol structure in spread spectrum communication systems, and in particular to the use of pilot symbols by user equipment in channel estimation. In one form, the method includes, allocating basic pilot symbols at the beginning of each data chunk and spread over the plurality of sub-carrier frequencies; and selectively replacing data symbols in each data chunk with adaptive pilot symbols according to the speed of the user equipment.

1 . A method of generating a pilot symbol in a spread spectrum communication systems, wherein data is transmitted between a base station and user equipment in the spread spectrum communication system in data chunks in which data symbols are transmitted in parallel on a plurality of sub-carrier frequencies and at regular temporal positions during a transmission time interval, the method including the steps of:
 allocating basic pilot symbols at the beginning of each data chunk and spread over the plurality of sub-carrier frequencies; and   selectively replacing data symbols in each data chunk with adaptive pilot symbols according to the speed of the user equipment.   
     
     
         2 . A method according to  claim 1 , wherein the adaptive pilot symbols are evenly distributed in the data chunk in the time domain. 
     
     
         3 . A method according to  claim 1 , wherein the adaptive pilot symbols are evenly distributed in the data chunk in the frequency domain. 
     
     
         4 . A method according to  claim 1 , wherein the step of selectively replacing data symbols with adaptive pilot symbols includes:
 at a central sub-carrier frequency of the data chunk, inserting the adaptive pilot symbols along the time domain separated by a temporal distance 2×N T  where:   
       
         
           
             
               
                 N 
                 T 
               
               = 
               
                 ⌊ 
                 
                   1 
                   
                     2 
                     · 
                     
                       f 
                       D 
                     
                     · 
                     
                       T 
                       sym 
                     
                   
                 
                 ⌋ 
               
             
           
         
       
       where └ ┘ is a round down to the nearest integer
 where f D  is the Doppler frequency measured at the user equipment in H z , and 
 where T sym  is the data symbol duration in seconds. 
 
     
     
         5 . A method according to  claim 4 , wherein the first adaptive pilot symbol is inserted at the central sub-carrier frequency at a temporal distance of N T  from the basic pilot symbols. 
     
     
         6 . A method according to  claim 4 , wherein the step of selectively replacing data symbols with adaptive pilot symbols further includes: 
       
         
           
             
               
                 N 
                 F 
               
               = 
               
                 ⌊ 
                 
                   1 
                   
                     
                       2 
                       · 
                       Δ 
                     
                      
                     
                         
                     
                      
                     
                       f 
                       · 
                       
                         τ 
                         max 
                       
                     
                   
                 
                 ⌋ 
               
             
           
         
       
       where └ ┘ is n round down to the nearest integer
 where Δf is the sub-carrier bandwidth in H z , and 
 where τ max  is the maximum delay spread in seconds. 
 
     
     
         7 . A method according to  claim 6 , wherein the cyclic prefix length is for T sym . 
     
     
         8 . A method according to  claim 6 , wherein adaptive pilot symbols inserted in consecutive sub-carrier frequencies are temporally offset by the temporal distance N F . 
     
     
         9 . A method according to  claim 1 , and further including the step of:
 performing data symbol puncturing or reducing data symbol repetition prior to insertion of the adaptive pilot symbols.   
     
     
         10 . A method according to  claim 1 , and further including the step of:
 generating pilot symbol information identifying the location of the adaptive pilot symbols in the data chunk to enable the user equipment to use the adaptive pilot symbols for channel estimation.   
     
     
         11 . A method according to  claim 10 , wherein the pilot symbol information is encoded to reduce the number of bits transmitted to the user equipment. 
     
     
         12 . A method according to  claim 11 , wherein the pilot symbol information is self-decodable by the user equipment. 
     
     
         13 . A method according to  claim 10 , wherein the pilot symbol information is transmitted prior to transmission of the pilot symbols and data chunks to enable detection of the adaptive pilot symbols by the user equipment. 
     
     
         14 . A method according to  claim 1 , wherein the number N ADAPTIVE, PILOT Sym  of adaptive pilots to be inserted within a data chunk is determined from the expression 
       
         
           
             
               
                 N 
                 
                   
                     ADAPTIVE 
                      
                     _ 
                      
                     PILOT 
                   
                    
                   
                     _ 
                      
                     SYM 
                   
                 
               
               = 
               
                 ⌈ 
                 
                   
                     1 
                     2 
                   
                   × 
                   
                     ⌈ 
                     
                       
                         N 
                         
                           subcarrier 
                            
                           
                               
                           
                            
                           per 
                            
                           
                               
                           
                            
                           chunk 
                         
                       
                       
                         N 
                         F 
                       
                     
                     ⌉ 
                   
                   × 
                   
                     ⌊ 
                     
                       
                         N 
                         
                           symbols 
                            
                           
                               
                           
                            
                           per 
                            
                           
                               
                           
                            
                           TTI 
                            
                           
                               
                           
                            
                           per 
                            
                           
                               
                           
                            
                           subcarrier 
                         
                       
                       
                         N 
                         T 
                       
                     
                     ⌋ 
                   
                 
                 ⌉ 
               
             
           
         
       
     
     
         15 . A method according to  claim 14 , wherein, If N T  is greater than number of symbol, per TTI on a single carrier, then adaptive pilot symbols is not required to be inserted. 
     
     
         16 . A method according to  claim 1 , wherein the data chunks are transmitted from the base station to the user equipment using Orthogonal Frequency Division Multiplexing. 
     
     
         17 . A method according to  claim 1 , wherein the spread spectrum communication system conforms to LTE/Super 3G systems standards developed by the 3 rd  Generation Partnership Project (3GPP). 
     
     
         18 . A base station forming part of a spread spectrum communication system, the base station including one or more processing blocks for carrying out a method according to  claim 1 . 
     
     
         19 . A base station according to  claim 18 , wherein the one or more processing blocks are implemented using digital signal processing techniques.