Ofdm generation apparatus in a multi-carrier data transmission system

Abstract

The present invention relates to OFDM generation apparatus and methods for generating OFDM transmission signals from OFDM symbols, each comprising a plurality of OFDM subcarriers, for transmission in a multi-carrier data transmission system. An embodiment of the proposed apparatus and method are adapted for using a selected mixing frequency for mixing said complex time-domain samples of said OFDM symbol from a baseband frequency up to a passband frequency by use of a mixing frequency to obtain said OFDM transmission signal, wherein the mixing frequency is selected such that common phase rotations of the OFDM subcarriers of said OFDM symbol with respect to adjacent OFDM symbols of said OFDM transmission signal are avoided or compensated after said mixing. Further embodiments for avoidance or compensation of such common phase rotations are provided.

1 . OFDM generation apparatus for generating OFDM transmission signals from OFDM symbols, each comprising a plurality of OFDM subcarriers, for transmission in a multi-carrier data transmission system, said apparatus comprising
 an inverse DFT means configured to inverse discrete Fourier transform an OFDM symbol into complex time-domain samples, and   a frequency mixing means configured to mix said complex time-domain samples of said OFDM symbol from a baseband frequency up to a passband frequency by use of a mixing frequency to obtain said OFDM transmission signal,   
       wherein the mixing frequency is selected such that common phase rotations of the OFDM subcarriers of said OFDM symbol with respect to adjacent OFDM symbols of said OFDM transmission signal are avoided or compensated after said mixing. 
     
     
         2 . OFDM generation apparatus as claimed in  claim 1 ,
 wherein the mixing frequency f c  is selected as   
       
         
           
             
               
                 f 
                 c 
               
               = 
               
                 
                   k 
                   c 
                 
                 
                   T 
                   U 
                 
               
             
           
         
       
       with the OFDM subcarrier k c  at the mixing frequency f c  fulfilling the condition that 
       
         
           
             
               
                 k 
                 c 
               
               · 
               
                 ( 
                 
                   Δ 
                   
                     T 
                     U 
                   
                 
                 ) 
               
             
           
         
       
       is an integer, wherein T U  is the useful OFDM symbol duration and Δ is the duration of the guard interval. 
     
     
         3 . OFDM generation apparatus as claimed in  claim 1 ,
 wherein the mixing frequency f c  is selected as   
       
         
           
             
               
                 f 
                 c 
               
               = 
               
                 
                   k 
                   c 
                 
                 
                   T 
                   U 
                 
               
             
           
         
       
       with the OFDM subcarrier k c  at the mixing frequency f c  being selected to be close or as close as possible to the central subcarrier among the subcarriers of said OFDM symbol, wherein T U  is the useful OFDM symbol duration. 
     
     
         4 . OFDM generation apparatus as claimed in  claim 1 ,
 wherein the mixing frequency f c  is selected as   
       
         
           
             
               
                 f 
                 c 
               
               = 
               
                 
                   k 
                   c 
                 
                 
                   T 
                   U 
                 
               
             
           
         
       
       with the OFDM subcarrier k c  at the mixing frequency f c  being selected as 
       
         
           
             
               
                 
                   k 
                   c 
                 
                 = 
                 
                   
                     ⌊ 
                     
                       
                         
                           
                             
                               K 
                               max 
                             
                             + 
                             
                               K 
                               min 
                             
                           
                           2 
                         
                         · 
                         
                           Δ 
                           
                             T 
                             U 
                           
                         
                       
                       + 
                       
                         1 
                         2 
                       
                     
                     ⌋ 
                   
                   · 
                   
                     1 
                     
                       ( 
                       
                         Δ 
                         
                           T 
                           U 
                         
                       
                       ) 
                     
                   
                 
               
               , 
             
           
         
         wherein T U  is the useful OFDM symbol duration, Δ is the duration of the guard interval, K min  is the carrier index of first active carrier having the lowest frequency and K max  is the carrier index of last active carrier having the highest frequency.