ESTIMATING FREQUENCY-OFFSETS AND MULTI-ANTENNA CHANNELS IN MIMO OFDM SYSTEMS

• US 20120155512A1
• Filed: 11/21/2011
• Published: 06/21/2012
• Est. Priority Date: 05/21/2003
• Status: Active Grant

• 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
• Granted Patent: US 8,588,317 B2
• Time in Patent Office: Days
• US Class Current: 375/141
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/046 taking physical layer constraints into account
• CPC Class Codes: H04B 7/063 Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection
• CPC Class Codes: H04B 7/066 Combined feedback for a number of channels, e.g. over several subcarriers like in orthogonal frequency division multiplexing [OFDM]
• CPC Class Codes: H04J 11/0063 of multipath interference, e.g. Rake receivers
• CPC Class Codes: H04L 25/0202 Channel estimation
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0228 with direct estimation from sounding signals
• CPC Class Codes: H04L 25/0242 using matrix methods
• CPC Class Codes: H04L 27/2607 Cyclic extensions
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2671 Time domain
• CPC Class Codes: H04L 27/2672 Frequency domain
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04L 27/2692 with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
• CPC Class Codes: H04L 27/2695 with channel estimation, e.g. determination of delay spread, derivative or peak tracking channel estimation H04L25/0202
• CPC Class Codes: H04L 5/0016 Time-frequency-code

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.

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; and

outputting, N_t antennas 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_r antennas, wherein each of N_t and N_r is an integer, and wherein at least one of N_t and N_r is an integer greater than one.

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 the 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_c columns of an identify matrix having N_c+N_b columns, where N_c represents the number of information-bearing symbols within each of the blocks and N_b represents 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_b columns of an identify matrix having N_c+N_b columns, where N_c represents the number of information-bearing symbols in each of the blocks and N_b represents 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 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_c represents the number of information-bearing symbols in each block of symbols and N_b represents the number of training symbols inserted in the block of information-bearing symbols.

11. The method of claim 1, wherein outputting a wireless communication signal comprises outputting 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 a length of each block and L represents an order of a wireless communication channel through which the 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_r antennas of a wireless communication device, a wireless signal transmitted via N_t antennas 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 each of N_t and N_r is an integer, and wherein at least one of N_t and N_r is an integer greater than one;

and

outputting, with the wireless communication device, estimated symbols based on the received wireless signal.

16. The method of claim 15, wherein outputting estimated symbols comprises:

applying a de-hopping code to the received signal to arrange the null subcarriers in different blocks of the received signal so that the subcarriers in the different blocks are located within the same position;

estimating a carrier frequency offset of the received signal based on the position of the null subcarriers;

estimating a communication channel based on the training symbols within the received signal; and

outputting the estimated symbols based on the estimated carrier frequency offset and the estimated communication channel.

17. The method of claim 16, where estimating a carrier frequency offset comprises:

forming the carrier frequency offset of the received 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 a communication channel comprises:

collecting M blocks of the signal, where M≧

2;

separating the block of training symbols from the information-bearing symbols for each of the M collected blocks; and

forming an estimate of the communication channel based on the training symbols collected from M blocks.

19-20. -20. (canceled)

21. 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; and

a modulator configured to output, via N_t antennas, a wireless transmission signal in accordance with the blocks of symbols, the wireless transmission signal being configured to be received via N_r antennas, wherein each of N_t and N_r is an integer, and wherein at least one of N_t and N_r is an integer greater than one.

22. A wireless communication device comprising:

one or more antennas configured to receive, via N_r antennas, a wireless signal transmitted via N_t antennas 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 each of N_t and N_r is an integer, and wherein at least one of N_t and N_r is an integer greater than one; and

a decoder configured to output a stream of estimated symbols based on the received wireless signal.