STBC MIMO-OFDM peak-to-average power ratio reduction by cross-antenna rotation and inversion

Abstract

A signal scrambling method is provided for peak-to-average power ratio (PAPR) reduction of STBC MIMO-OFDM signals in a MIMO-OFDM system having Y transmit antenna. In general terms the OFDM sequence of symbols in said signal for each transmit antenna is divided into M sub-blocks of equal size and subclockwise subblockwise rotation and inversions are performed across all transmit antennas to generate [2Y] M permuted sequence sets from the original OFDM sequence. Based on a predetermined criteria, there is then selected from the resulting sets of OFDM sequences the one with the best PAPR properties for transmission. The predetermined criteria preferably comprises identifying maximums for all [2Y] M sequence sets, by calculating the largest PAPR value of Y sequences in each set and selecting a set with the minimum maximum for transmission.

1. A signal scrambling method for peak-to-average power ratio (PAPR) reduction of STBC  multiple- input multiple - output orthogonal frequency divisional multiplexing  (MIMO-OFDM) signals in a MIMO-OFDM system having Y transmit antennas, comprising:
 dividing the OFDM sequence of symbols in said signal for each transmit antenna into M sub-blocks of equal size and performing subclockwise  subblockwise rotation and inversions across all transmit antennas to generate [2Y] M  permuted sequence sets from the original OFDM sequence; and  
 based on a  at least one predetermined criteria  criterion, selecting from the resulting said  sets of OFDM sequences the one with the best PAPR property for transmission.  
 
     
     
       2. A method in accordance with  claim 1  wherein said predetermined criteria comprises identifying maximums for all [2Y] M  sequence sets, by calculating the largest PAPR value of Y sequences in each set and selecting a set with the minimum maximum for transmission. 
     
     
       3. A method in accordance with  claim 1 , in which cross- antenna rotation and inversion  (CARI) is performed on the first subblock for each antenna to obtain a first set of transmit sequences, the PAPR being calculated for all sequences in said first set and the set with the smallest maximum PAPR being retained; and successively performing the same procedure for successive of said sub-blocks across all transmit antennas, whereby the number of permutations considered is reduced, the PAPR is gradually reduced, and wherein the final resulting sequence is selected for transmission. 
     
     
       4. A method in accordance with  claim 1  in which a dimension V×M matrix with random numbers is produced, where V is the total number of permutations; each item in the matrix being an integer random number uniformly distributed over [1, 2Y] representing 2Y predefined different permutation operations carried out on said M sub-blocks, and producing V different said sequence sets; and selecting the sequence with the smallest maximum PAPR for transmission, whereby the side information required for descrambling the signal is significantly reduced. 
     
     
       5. A method in accordance with  claim 1 , in which the number of transmit antennas Y is 2. 
     
     
       6. A method in accordance with  claim 1 , wherein the MIMO- OFDM signals are space - time block - coded  ( STBC )  MIMO - OFDM signals.