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

DC CAFC

US 8,774,309 B2
Filed: 03/01/2013
Issued: 07/08/2014
Est. Priority Date: 05/21/2003
Status: Active Grant

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1. A method comprising:

forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over two or more antennas, wherein the forming comprises encoding two or more blocks of information-bearing symbols for transmissions over the two or more antennas, and inserting training symbols and null subcarriers within the two or more blocks of information-bearing symbols at positions determined by a hopping code; and

transmitting, via the two or more antennas, transmission signals in accordance with the two or more blocks of output symbols, wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein transmitting the transmission signals comprises;

transmitting, via a first antenna of the two or more antennas, a first transmission signal in accordance with the first block of output symbols; and

transmitting, via a second antenna of the two or more antennas, a second transmission signal in accordance with the second block of output symbols.

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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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29 Claims

1. A method comprising:
- forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over two or more antennas, wherein the forming comprises encoding two or more blocks of information-bearing symbols for transmissions over the two or more antennas, and inserting training symbols and null subcarriers within the two or more blocks of information-bearing symbols at positions determined by a hopping code; and
  
  transmitting, via the two or more antennas, transmission signals in accordance with the two or more blocks of output symbols, wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein transmitting the transmission signals comprises;
  
  transmitting, via a first antenna of the two or more antennas, a first transmission signal in accordance with the first block of output symbols; and
  
  transmitting, via a second antenna of the two or more antennas, a second transmission signal in accordance with the second block of output symbols.
- View Dependent Claims (2, 3, 4, 5, 6, 7)
- - 2. The method of claim 1, wherein transmitting the transmission signals comprises inserting a cyclic prefix within each of the blocks of output symbols, and wherein the transmission signals provide information for estimating a carrier frequency offset associated with received versions of the transmission signals.
  - 3. The method of claim 2, wherein the transmission signals provide information for estimating a phase noise of the received versions of the transmission signals based on the estimated carrier frequency offset.
  - 4. The method of claim 1, wherein the training symbols within the two or more blocks collectively provide information for estimating a channel.
  - 5. The method of claim 1, wherein inserting the training symbols and the null subcarriers comprises inserting at least one training symbol adjacent to at least one null subcarrier.
  - 6. The method of claim 1, wherein transmitting the transmission signals comprises transmitting transmission signals for a multi-user wireless communications system.
  - 7. The method of claim 1, wherein encoding the two or more blocks of information-bearing symbols comprises encoding the two or more blocks of information-bearing symbols in space and time.

8. A method comprising:
- encoding information-bearing symbols;
  
  forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over a multiple-input multiple-output (MIMO) channel, wherein the forming comprises inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code; and
  
  transmitting, via two or more antennas, transmission signals in accordance with the two or more blocks of output symbols, wherein the method further comprises;
  
  inserting a cyclic prefix within each of the blocks of output symbols, andapplying an inverse fast Fourier transform to the blocks of encoded information-bearing symbols.

9. A method comprising:
- encoding information-bearing symbols;
  
  forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over a multiple-input multiple-output (MIMO) channel, wherein the forming comprises inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code, wherein the hopping code is a function of an index of at least one block of the encoded information-bearing symbols; and
  
  transmitting, via two or more antennas, transmission signals in accordance with the two or more blocks of output symbols.

10. A method comprising:
- encoding information-bearing symbols;
  
  forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over a multiple-input multiple-output (MIMO) channel, wherein the forming comprises inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code, wherein the hopping code is a function of a property of the MIMO channel; and
  
  transmitting, via two or more antennas, transmission signals in accordance with the two or more blocks of output symbols.
- View Dependent Claims (11, 12)
- - 11. The method of claim 10, wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein inserting the training symbols and null subcarriers comprises:
    - inserting a first null subcarrier at a first subcarrier position within the first block of output symbols,inserting a second null subcarrier at a second subcarrier position within the second block of output symbols,inserting a first training symbol at a first training symbol position within the first block of output symbols,inserting a second training symbol at a second training symbol position within the second block of output symbols, wherein the first subcarrier position is different from the second subcarrier position, and wherein the first training symbol position is different from the second training symbol position.
  - 12. The method of claim 11, wherein the two or more blocks of output symbols are consecutive, wherein the transmitting the transmission signals comprises transmitting the transmission signals over a downlink portion of the MIMO channel, and wherein forming the two or more blocks of output symbols comprises inserting at least two training symbols and at least two null subcarriers within each block of encoded information-bearing symbols.

13. A method comprising:
- encoding information-bearing symbols;
  
  forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over a multiple-input multiple-output (MIMO) channel, wherein the forming comprises inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code, wherein the hopping code is a function of the number of antennas for transmitting the transmission signals; and
  
  transmitting, via two or more antennas, transmission signals in accordance with the two or more blocks of output symbols.
- View Dependent Claims (14)
- - 14. The method of claim 13, wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein inserting the training symbols and null subcarriers comprises:
    - inserting a first null subcarrier at a first subcarrier position within the first block of output symbols, andinserting a second null subcarrier at a second subcarrier position within the second block of output symbols, wherein the first subcarrier position is different from the second subcarrier position.

15. A method comprising:
- encoding information-bearing symbols;
  
  forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over a multiple-input multiple-output (MIMO) channel, wherein the forming comprises inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code, wherein inserting the training symbols and the null subcarriers comprises inserting the training symbols before inserting the null subcarriers; and
  
  transmitting, via two or more antennas, transmission signals in accordance with the two or more blocks of output symbols.

16. A method comprising:
- encoding information-bearing symbols;
  
  forming two or more blocks of output symbols for orthogonal frequency division multiplexing (OFDM) transmissions over a multiple-input multiple-output (MIMO) channel, wherein the forming comprises inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code; and
  
  transmitting, via two or more antennas, transmission signals in accordance with the two or more blocks of output symbols, wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein transmitting the transmission signals comprises;
  
  transmitting, via a first antenna of the two or more antennas, a first transmission signal in accordance with the first block of output symbols; and
  
  transmitting, via a second antenna of the two or more antennas, a second transmission signal in accordance with the second block of output symbols.
- View Dependent Claims (17, 18, 19, 20, 21)
- - 17. The method of claim 16, wherein transmitting the transmission signals comprises inserting a cyclic prefix within each of the blocks of output symbols, and wherein the transmission signals provide information for estimating a carrier frequency offset associated with received versions of the transmission signals.
  - 18. The method of claim 16, wherein the training symbols within the two or more blocks collectively provide information for estimating the MIMO channel.
  - 19. The method of claim 16, wherein inserting the training symbols and the null subcarriers comprises inserting at least one training symbol adjacent to at least one null subcarrier.
  - 20. The method of claim 16, wherein transmitting the transmission signals comprises transmitting transmission signals for a multi-user wireless communications system.
  - 21. The method of claim 16, wherein inserting the null subcarriers comprises multiplying a block of encoded information-bearing symbols by a null subcarrier insertion matrix.

22. A system comprising:
- first circuitry configured to (i) encode information-bearing symbols for transmissions over two or more antennas associated with a multiple-input multiple-output (MIMO) channel to produce encoded information-bearing symbols, and (ii) form two or more blocks of output symbols for transmissions over the MIMO channel by inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code; and
  
  second circuitry configured to transmit, via the two or more antennas, orthogonal frequency division multiplexing (OFDM) based transmission signals in accordance with the two or more blocks of output symbols, wherein the second circuitry comprises one or more modulators,wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein the first circuitry is configured to;
  
  insert a first null subcarrier at a first subcarrier position within the first block of output symbols, andinsert a second null subcarrier at a second subcarrier position within the second block of output symbols, wherein the first subcarrier position is different from the second subcarrier position.
- View Dependent Claims (23, 24)
- - 23. The system of claim 22, further comprising:
    - a wireless communication device configured to receive the transmission signals as received signals, wherein the wireless communication device is configured to (i) estimate a carrier frequency offset based on the received signals and (ii) perform channel estimation of the MIMO channel based on the received signals.
  - 24. The system of claim 22, wherein the first circuitry is configured to:
    - insert a third null subcarrier at a third subcarrier position within the first block of output symbols,insert a fourth null subcarrier at a fourth subcarrier position within the second block of output symbols,insert a first training symbol at a first training symbol position within the first block of output symbols,insert a second training symbol at a second training symbol position within the second block of output symbols,insert a third training symbol at a third training symbol position within the first block of output symbols, andinsert a fourth training symbol at a fourth training symbol position within the second block of output symbols, wherein the third subcarrier position is different from the fourth subcarrier position, wherein the first training symbol position is different from the second training symbol position, and wherein the third training symbol position is different from the fourth training symbol position.

25. A system comprising:
- first circuitry configured to (i) encode information-bearing symbols for transmissions over two or more antennas associated with a multiple-input multiple-output (MIMO) channel to produce encoded information-bearing symbols, and (ii) form two or more blocks of output symbols for transmissions over the MIMO channel by inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code; and
  
  second circuitry configured to transmit, via the two or more antennas, orthogonal frequency division multiplexing (OFDM) based transmission signals in accordance with the two or more blocks of output symbols, wherein the second circuitry comprises one or more modulators,wherein the two or more blocks of output symbols include a first block of output symbols and a second block of output symbols, and wherein the second circuitry is configured to;
  
  transmit, via a first antenna of the two or more antennas, a first transmission signal in accordance with the first block of output symbols; and
  
  transmit, via a second antenna of the two or more antennas, a second transmission signal in accordance with the second block of output symbols.
- View Dependent Claims (26)
- - 26. The system of claim 25, wherein the first circuitry is configured to insert a cyclic prefix within each of the blocks of output symbols, and wherein the transmission signals provide information for estimating a carrier frequency offset associated with received versions of the transmission signals.

27. A system comprising:
- first circuitry configured to (i) encode information-bearing symbols for transmissions over two or more antennas associated with a multiple-input multiple-output (MIMO) channel to produce encoded information-bearing symbols, and (ii) form two or more blocks of output symbols for transmissions over the MIMO channel by inserting training symbols and null subcarriers within two or more blocks of the encoded information-bearing symbols at positions determined by a hopping code, wherein the training symbols within the two or more blocks collectively provide information for estimating the MIMO channel; and
  
  second circuitry configured to transmit, via the two or more antennas, orthogonal frequency division multiplexing (OFDM) based transmission signals in accordance with the two or more blocks of output symbols, wherein the second circuitry comprises one or more modulators.
- View Dependent Claims (28, 29)
- - 28. The system of claim 27, wherein the first circuitry is configured to insert at least one training symbol adjacent to at least one null subcarrier.
  - 29. The system of claim 27, wherein each block of output symbols contains a number of training symbols equal to a number of transmit antennas.

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Litigation Data

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)
WANG, TED M

Application Number

US13/783,039
Publication Number

US 20130223562A1
Time in Patent Office

494 Days
Field of Search

375/295, 375/299, 375/260, 375/267, 455/101, 370/334
US Class Current

375/295
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

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29 Claims

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