Estimating frequency-offsets and multi-antenna channels in MIMO OFDM systems

DC CAFC

US 8,588,317 B2
Filed: 11/21/2011
Issued: 11/19/2013
Est. Priority Date: 05/21/2003
Status: Active Grant

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1. A method comprising:

forming, with a wireless communication device, blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols;

applying, with the wireless communication device, a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, wherein the hopping code causes a position of the null subcarrier to change from block to block, wherein the position change caused by the hopping code is based, at least, on a block length and a cyclic prefix length, wherein the cyclic prefix length is based, at least, on an amount of multipath propagation in the wireless communication channel; and

outputting, via N_tantennas of the wireless communication device, a wireless transmission signal in accordance with the blocks of symbols, the wireless transmission signal being configured to be received via N_rantennas, wherein each of N_tand N_ris an integer, and wherein at least one of N_tand N_ris an integer greater than one.

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Abstract

Techniques are described for carrier frequency offset (CFO) and channel estimation of orthogonal frequency division multiplexing (OFDM) transmissions over multiple-input multiple-output (MIMO) frequency-selective fading channels. A wireless transmitter forms blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols. The transmitter applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, and a modulator outputs a wireless signal in accordance with the blocks of symbols. A receiver receives the wireless signal and estimates the CFO, and outputs a stream of estimated symbols based on the estimated CFO.

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20 Claims

1. A method comprising:
- forming, with a wireless communication device, blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols;
  
  applying, with the wireless communication device, a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, wherein the hopping code causes a position of the null subcarrier to change from block to block, wherein the position change caused by the hopping code is based, at least, on a block length and a cyclic prefix length, wherein the cyclic prefix length is based, at least, on an amount of multipath propagation in the wireless communication channel; and
  
  outputting, via N_tantennas of the wireless communication device, a wireless transmission signal in accordance with the blocks of symbols, the wireless transmission signal being configured to be received via N_rantennas, wherein each of N_tand N_ris an integer, and wherein at least one of N_tand N_ris an integer greater than one.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
- - 2. The method of claim 1, further comprising encoding the information-bearing symbols in space and time.
  - 3. The method of claim 1, wherein inserting training symbols comprises inserting a block of training symbols into each of the blocks of information bearing symbols.
  - 4. The method of claim 3, wherein the blocks of information-bearing symbols comprises a first block of information-bearing symbols and a second block of information-bearing symbols, and forming blocks of symbols comprises:
    - forming a first block of symbols from the first block of information-bearing symbols and the block of training symbols;
      
      applying a first permutation matrix to the second block of information-bearing symbols to rearrange an order of the information-bearing symbols within the second block;
      
      applying a second permutation matrix to the block of training symbols to rearrange the order of the training symbols; and
      
      forming a second block of symbols from the second block having rearranged information-bearing symbols and the block of rearranged training symbols.
  - 5. The method of claim 4, wherein the first permutation matrix and the second permutation matrix are mutually orthogonal.
  - 6. The method of claim 4, wherein the first permutation matrix comprises the last N_ccolumns of an identity matrix having N_c+N_bcolumns, where N_crepresents the number of information-bearing symbols within each of the blocks and N_brepresents the number of training symbols within the block of training symbols.
  - 7. The method of claim 4, wherein the second permutation matrix comprises the first N_bcolumns of an identity matrix having N_c+N_bcolumns, where N_crepresents the number of information-bearing symbols within each of the blocks and N_brepresents the number of training symbols of the block of training symbols.
  - 8. The method of claim 4, wherein forming the first block of symbols and forming the second block of symbols comprises forming the first block of symbols and forming the second block of symbols in a format that the blocks of information-bearing symbols and the blocks of training symbols are separable based on the null subcarriers.
  - 9. The method of claim 1, wherein applying a hopping code comprises inserting two or more null subcarriers within each of the blocks of symbols.
  - 10. The method of claim 1, wherein applying a hopping code comprises inserting N−
    - K null subcarriers within each of the blocks of symbols, where N represents a length of each block, and K=N_c+N_b, where N_crepresents the number of information-bearing symbols in each block of symbols and N_brepresents the number of training symbols inserted in the block of information-bearing symbols.
  - 11. The method of claim 1, wherein outputting the wireless transmission signal comprises transmitting an orthogonal frequency divisional multiplexing (OFDM) signal.
  - 12. The method of claim 11, wherein the position of the null subcarrier changes from block to block by N/(L+1) symbols, where N represents the block length and L represents an order of the wireless communication channel through which the OFDM signal is transmitted.
  - 13. The method of claim 1, wherein the null subcarrier is a zero symbol.
  - 14. The method of claim 1, wherein outputting the wireless transmission signal comprises inserting a cyclic prefix within each of the block of symbols and applying an inverse fast fourier transform (IFFT) of the blocks of symbols.

15. A method comprising receiving, via N_rantennas of a wireless communication device, a wireless signal transmitted via N_tantennas from a stream of blocks of symbols, wherein each block of symbols includes one or more information-bearing symbols, one or more training symbols, and at least one null subcarrier at a different position within each of the blocks of symbols, wherein a hopping code causes a position of the at least one null subcarrier to change from block to block, wherein the position change caused by the hopping code is based, at least, on a block length and a cyclic prefix length, wherein the cyclic prefix length is based, at least, on an amount of multipath propagation in the wireless communication channel;
- wherein each of N_tand N_ris an integer, and wherein at least one of N_tand N_ris an integer greater than one; and
  
  outputting, with the wireless communication device, estimated symbols based, at least, on the received wireless signal.
- View Dependent Claims (16, 17, 18)
- - 16. The method of claim 15, wherein outputting the estimated symbols comprises:
    - applying a de-hopping code to the received wireless signal to arrange the null subcarriers in different blocks of the received wireless signal so that the subcarriers in the different blocks are located within the same position;
      
      estimating a carrier frequency offset of the received wireless signal based on the position of the null subcarriers;
      
      estimating the wireless communication channel based on the training symbols within the received wireless signal; and
      
      outputting the estimated symbols based on the estimated carrier frequency offset and the estimated wireless communication channel.
  - 17. The method of claim 16, where estimating the carrier frequency offset comprises:
    - forming the estimated carrier frequency offset of the received wireless signal based on the position of the null subcarriers;
      
      applying a fast Fourier transform (FFT) to the de-hopped blocks of symbols; and
      
      removing the null subcarriers based on the carrier frequency offset.
  - 18. The method of claim 16, wherein estimating the wireless communication channel comprises:
    - collecting M blocks of the received wireless signal, where M≧
      
      2;
      
      separating the training symbols from the information-bearing symbols for each of the M collected blocks; and
      
      forming an estimate of the wireless communication channel based on the training symbols collected from the M blocks.

19. A wireless communication device comprising:
- a training symbol insertion module configured to form blocks of symbols by inserting training symbols within two or more blocks of information-bearing symbols, wherein the training symbol insertion module applies a hopping code to each of the blocks of symbols to insert a null subcarrier at a different position within each of the blocks of symbols, wherein the hopping code causes a position of the null subcarrier to change from block to block, wherein the position change caused by the hopping code is based, at least, on a block length and a cyclic prefix length, wherein the cyclic prefix length is based, at least, on an amount of multipath propagation in the wireless communication channel; and
  
  a modulator configured to output, via N_tantennas, a wireless transmission signal in accordance with the blocks of symbols, the wireless transmission signal being configured to be received via N_rantennas, wherein each of N_tand N_ris an integer, and wherein at least one of N_tand N_ris an integer greater than one.

20. A wireless communication device comprising:
- one or more antennas configured to receive, via N_rantennas, a wireless signal transmitted via N_tantennas from a stream of blocks of symbols, wherein each block of symbols includes one or more information-bearing symbols, one or more training symbols, and at least one null subcarrier at a different position within each of the blocks of symbols, wherein a hopping code causes a position of the at least one null subcarrier to change from block to block, wherein the position change caused by the hopping code is based, at least, on a block length and a cyclic prefix length, wherein the cyclic prefix length is based, at least, on an amount of multipath propagation in the wireless communication channel;
  
  wherein each of N_tand N_ris an integer, and wherein at least one of N_tand N_ris an integer greater than one; and
  
  a decoder configured to output a stream of estimated symbols based, at least, on the received wireless signal.

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Current Assignee
Regents of The University of Minnesota (University of Minnesota)
Original Assignee
Regents of The University of Minnesota (University of Minnesota)
Inventors
Giannakis, Georgios B., Ma, Xiaoli
Primary Examiner(s)
Ahn, Sam K
Assistant Examiner(s)
Ali, Shawkat M

Application Number

US13/301,482
Publication Number

US 20120155512A1
Time in Patent Office

729 Days
Field of Search

370/203, 370/213, 370/295, 370/329, 370/442, 370/486, 370/509, 370/210, 375/130, 375/146, 375/147, 375/259, 375/260, 375/267, 375/299, 375/308, 375/316, 375/346, 375/347, 375/132, 375/135, 375/141, 375/295, 380/274, 455/59, 455/69, 455/435.2, 455/456.1, 455/464, 455/515, 455/522
US Class Current

375/260
CPC Class Codes

H04B 7/0413   MIMO systems

H04B 7/046   taking physical layer const...

H04B 7/063   Parameters other than those...

H04B 7/066   Combined feedback for a num...

H04J 11/0063   of multipath interference, ...

H04L 25/0202   Channel estimation

H04L 25/0204   of multiple channels

H04L 25/0228   with direct estimation from...

H04L 25/0242   using matrix methods

H04L 27/2607   Cyclic extensions

H04L 27/2613   Structure of the reference ...

H04L 27/26134   Pilot insertion in the tran...

H04L 27/2626   Arrangements specific to th...

H04L 27/2657   Carrier synchronisation

H04L 27/2671   Time domain

H04L 27/2672   Frequency domain

H04L 27/2675   Pilot or known symbols

H04L 27/2692   with preamble design, i.e. ...

H04L 27/2695   with channel estimation, e....

H04L 5/0016   Time-frequency-code

Estimating frequency-offsets and multi-antenna channels in MIMO OFDM systems

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Estimating frequency-offsets and multi-antenna channels in MIMO OFDM systems

First Claim

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1 Petition

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Accused Products

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Abstract

41 Citations

20 Claims

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