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

• US 20130223562A1
• Filed: 03/01/2013
• Published: 08/29/2013
• 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 8,774,309 B2
• Time in Patent Office: Days
• US Class Current: 375/295
• 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

1-20. -20. (canceled)

21. 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.

22. The method of claim 21, 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, and

inserting 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.

23. The method of claim 21, 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.

24. The method of claim 21, 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.

25. The method of claim 24, 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.

26. The method of claim 21, wherein the training symbols within the two or more blocks collectively provide information for estimating a channel.

27. The method of claim 21, wherein inserting the training symbols and the null subcarriers comprises inserting at least one training symbol adjacent to at least one null subcarrier.

28. The method of claim 21, wherein transmitting the transmission signals comprises transmitting transmission signals for a multi-user wireless communications system.

29. The method of claim 21, 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.

30. 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.

31. The method of claim 30, further comprising inserting a cyclic prefix within each of the blocks of output symbols, and applying an inverse fast Fourier transform to the blocks of encoded information-bearing symbols.

32. The method of claim 30, wherein the hopping code is a function of an index of at least one block of the encoded information-bearing symbols.

33. The method of claim 30, wherein the hopping code is a function of a property of the MIMO channel.

34. The method of claim 30, wherein the hopping code is a function of the number of antennas for transmitting the transmission signals.

35. The method of claim 30, wherein inserting the training symbols and the null subcarriers comprises inserting the training symbols before inserting the null subcarriers.

36. The method of claim 30, 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, and

inserting 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.

37. The method of claim 30, 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.

38. The method of claim 30, 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.

39. The method of claim 30, wherein the training symbols within the two or more blocks collectively provide information for estimating the MIMO channel.

40. The method of claim 30, wherein inserting the training symbols and the null subcarriers comprises inserting at least one training symbol adjacent to at least one null subcarrier.

41. The method of claim 30, wherein transmitting the transmission signals comprises transmitting transmission signals for a multi-user wireless communications system.

42. The method of claim 30, wherein inserting the null subcarriers comprises multiplying a block of encoded information-bearing symbols by a null subcarrier insertion matrix.

43. 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.

44. The system of claim 43, 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.

45. The system of claim 43, 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, and

insert 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.

46. The system of claim 43, 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.

47. The system of claim 43, 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.

48. The system of claim 43, wherein the training symbols within the two or more blocks collectively provide information for estimating the MIMO channel.

49. The system of claim 43, wherein the first circuitry is configured to insert at least one training symbol adjacent to at least one null subcarrier.

50. The system of claim 43, wherein the second circuitry comprises one or more modulators.