MIMO OFDM system

• US 7,068,628 B2
• Filed: 02/23/2001
• Issued: 06/27/2006
• Est. Priority Date: 05/22/2000
• Status: Expired due to Term

• Current Assignee: AT&T Intellectual Property II LP (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Winters, Jack Harriman, Li, Ye, Sollenberger, Nelson Ray
• Primary Examiner(s): Pezzlo, John
• Assistant Examiner(s): Mills, Donald L
• Application Number:
  US09/791,523
• Publication Number:
  US 20010053143A1
• Time in Patent Office: 1,950 Days
• Field of Search: 370/210, 370/310, 370/312, 370/334, 370/436, 370/497, 370/343, 370/345, 370/332, 370/329, 375/136, 375/144, 375/147, 375/148, 375/150, 375/152
• US Class Current: 370/334
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

A MIMO OFDM system includes a plurality of space-time encoders for encoding respective data blocks with independent space-time codes. The transformed data block signals are transmitted by a plurality of transmit antennas and received by a plurality of receive antennas. The received data is pre-whitened prior to maximum likelihood detection. In one embodiment, successive interference cancellation can be used to improve system performance. Channel parameter estimation can be enhanced by weighting the channel impulse response estimates based upon a deviation from average.

Claims

1. A method for MIMO-OFDM communication, comprising:

1. on a single transmitting computing device;

(a) encoding a first data block into a first plurality of encoded signals;

(b) encoding a second data block into a second plurality of encoded signals;

(c) transmitting each of the first and second pluralities of encoded signals on respective transmit antennas; and

2. on a single receiving computing device;

(a) simultaneously receiving the transmitted signals on a plurality of receive antennas;

(b) pre-whitening the received signals for each of the first and second data block signals;

(c) performing maximum likelihood detection on each of the pre-whitened received signals;

(d) after decoding the first data block and the second data block of the received signals, performing successive interference cancellation on the received signals by modifying the received signal by re-encoding one of the first or second data block and removing the one of the first or second data block from the received signals; and

(e) and re-decoding the modified received signals.

2. The method according to claim 1, further comprising using CRC codes to perform the successive interference cancellation.

3. The method according to claim 1, further comprising using MMSE levels to perform the successive interference cancellation.

4. The method according to claim 1, further comprising performing channel estimation by weighting channel delay response estimates.

5. The method according to claim 4, wherein performing channel estimation further comprises weighting the channel response estimates based upon a deviation from an average channel response estimate for each delay.

6. The method according to claim 1, further comprising minimizing an NMSE of a channel by weighting channel response estimates.

18. The method of claim 1, wherein the step of successive interference cancellation further comprises:

treating the second data block as interference when detecting and decoding the first data block; and

treating the first data block as interference when detecting and decoding the second data block.

19. The method of claim 18, further comprising determining whether the first data block and the second data block contain errors or were correct, wherein the removed data block from the received signals is the data block determined to be correct.

20. The method of claim 19, further comprising, before removing the correct data block from the received signals, regenerating the encoded signals for the correct data block at the receiver.

21. The method of claim 1, further comprising determining a signal quality for each of the first data block and the second data block, wherein the removed data block from the received signals is the data block with a higher signal quality relative to the other data block.

22. The method of claim 21, wherein the removed data block with a higher signal quality is removed from the received signal because the signal quality for the removed data block is above a predetermined threshold.

23. The method of claim 21, wherein the signal quality is associated with a minimum mean-square error.

27. The method of claim 1, wherein the first or the second data block that is not removed is determined to have errors.

7. A method for MIMO-OFDM communication, comprising;

1. on a single transmitting computing device;

providing a first data block to a first space-time encoder that generates first and second coded signals;

transmitting the first coded signal from a first transmit antenna;

transmitting the second coded signal from a second transmit antenna;

providing a second data block to a second space-time encoder that generates third and fourth coded signals, wherein each of the first, second, third and fourth coded signals forms a respective OFDM block;

transmitting the third coded signal from a third transmit antenna;

transmitting the fourth coded signal from a fourth transmit antenna; and

2. on a receiving computing device;

simultaneously receiving the first, second, third and fourth coded signals on a plurality of receive antennas;

pre-whitening the received signals for the first data block signal;

performing maximum likelihood decoding on the pre-whitened first data block signal;

pre-whitening the received signals for the second data block signal;

performing maximum likelihood decoding on the pre-whitened second data block signal; and

regenerating the received signal with the first data block removed from the received signal, and re-decoding the second data block signal when the decoded first data block has a higher signal quality than the decoded second data block.

8. The method according to claim 7, wherein the signal quality is based upon MMSE.

9. The method according to claim 7, further comprising regenerating the received signal, removing the first data block signal from the received signal, and re-decoding the second data block signal when the decoded first data block does not have decoding errors and the second data block signal does have a decoding error.

10. The method according to claim 7, further comprising using Viterbi decoding.

11. The method according to claim 7, further comprising encoding the first and second data block signals with independent space-time codes.

12. The method according to claim 7, further comprising MMSE restoration of the first and second data block signals.

13. The method according to claim 7, wherein the plurality of receive antennas comprises at least four receive antennas.

14. The method according to claim 7, further comprising weighting channel response estimates based upon channel delay profile information.

15. The method according to claim 7, further comprising performing a weighted DFT of estimated channel responses.

16. The method according to claim 7, further comprising performing channel estimation by computing a weighting factor corresponding to an inverse of a sum of one plus a ratio of noise power to a power of channel response estimates averaged over the receive antennas.

17. A method for MIMO-OFDM communication, comprising:

1. on a single transmitting computing device;

encoding a first data block into a first plurality of encoded signals;

encoding a second data block into a second plurality of encoded signals;

transmitting each of the first and second pluralities of encoded signals on respective transmit antennas; and

2. on a receiving computing device;

simultaneously receiving the transmitted signals on a plurality of receive antennas;

decoding the first and second data block signals; and

estimating channel parameters by weighting channel response estimates based upon a deviation from average.

24. An apparatus for decoding data in a MIMO-OFDM communication, the data being transmitted from a single computing device, the apparatus comprising:

a module that receives a first plurality of encoded signals;

a module that receives a second plurality of encoded signals, the first plurality of encoded signals and the second plurality of encoded signaled being received simultaneously;

a module that pre-whitens the received signals for (1) a first data block associated with the first plurality of encoded signals and (2) a second data block associated with the second plurality of encoded signals;

a module that performs maximum likelihood detection on each of the pre-whitened signals;

a module that, after decoding the first data block and the second data block of the received signals, modifies the received signals by re-encoding the first or second data block and removing the re-encoded first or second data block from the received signals and re-decodes the modified received signals.

25. The apparatus of claim 24, wherein the module that modifies and re-decodes the modified received signals further treats the second data block as interference when re-decoding the first data block and treats the first data block as interference when re-decoding the second data block.

26. The apparatus of claim 24, wherein the first or the second data block that is not removed is determined to have errors.

28. A computing device for decoding data in a MIMO-OFDM communication, the data being transmitted from a single transmitting computing device, the computing device comprising:

a module that receives a first plurality of encoded signals from a first transmit antenna on the single transmitting computing device;

a module that receives a second plurality of encoded signals from a second transmit antenna on the single transmitting computing device;

a module that, after decoding the first data block and the second data block of the received signals, re-encodes the first or second data block, removes the re-encoded first or second data block from the received signals and re-decodes the received signals.

29. The computing device of claim 28, further comprising:

a module that pre-whitens the received signals for (1) a first data block associated with the first plurality of encoded signals and (2) a second data block associated with the second plurality of encoded signals.

30. The computing device of claim 29, further comprising a module that performs maximum likelihood detection on each of the pre-whitened signals.

31. The computing device of claim 28, wherein the process of re-encoding the first or second data block, removing the re-encoded first or second data block from the received signals and re-decoding the received signals further comprises performing successive interference cancellation on the received signals.

32. The computing device of claim 28, wherein the first or second data block that is not removed from the received signal is determined not to have errors.

33. A method for decoding data in a MIMO-OFDM communication, the data being transmitted from a single transmitting computing device, the method comprising:

receiving a first plurality of encoded signals from a first transmit antenna on the single transmitting computing device;

receiving a second plurality of encoded signals from a second transmit antenna on the single transmitting computing device, the first plurality of encoded signals and the second plurality of encoded signaled being received simultaneously;

after decoding the first data block and the second data block of the received signals, re-encoding the first or second data block, removing the re-encoded first or second data block from the received signals to generate modified received signals; and

re-decoding the modified received signals.

34. The method of claim 33, wherein modifying and re-decoding the modified received signals further comprises treating the second data block as interference when re-decoding the first data block and treats the first data block as interference when re-decoding the second data block.

35. The method of claim 33, further comprising:

pre-whitening the received signals for (1) a first data block associated with the first plurality of encoded signals and (2) a second data block associated with the second plurality of encoded signals.

36. The method of claim 35, further comprising performing maximum likelihood detection on each of the pre-whitened signals.

37. The method of claim 33, wherein re-encoding the first or second data block, removing the re-encoded first or second data block from the received signals and re-decoding the received signals further comprises performing successive interference cancellation on the received signals.

38. The method of claim 33, further comprising determining that the first or second data block that is not removed from the received signal is determined not to have errors.

44. The computer-readable medium of claim 33, wherein the instructions farther comprise determining that the first or second data block that is not removed from the received signal is determined not to have errors.

39. A computer-readable medium storing instructions for controlling a computing device to decode data in a MIMO-OFDM communication, the data being transmitted from a single transmitting computing device, the instructions comprising:

receiving a first plurality of encoded signals from a first transmit antenna on the single transmitting computing device;

receiving a second plurality of encoded signals from a second transmit antenna on the single transmitting computing device, the first plurality of encoded signals and the second plurality of encoded signaled being received simultaneously;

after decoding the first data block and the second data block of the received signals, re-encoding the first or second data block, removing the re-encoded first or second data block from the received signals to generate modified received signals; and

re-decoding the modified received signals.

40. The computer-readable medium of claim 39, wherein modifying and re-decoding the modified received signals further comprises treating the second data block as interference when re-decoding the first data block and treats the first data block as interference when re-decoding the second data block.

41. The computer-readable medium of claim 39, wherein the instructions further comprise:

pre-whitening the received signals for (1) a first data block associated with the first plurality of encoded signals and (2) a second data block associated with the second plurality of encoded signals.

42. The computer-readable medium of claim 41, wherein the instructions further comprise performing maximum likelihood detection on each of the pre-whitened signals.

43. The computer-readable medium of claim 39, wherein re-encoding the first or second data block, removing the re-encoded first or second data block from the received signals and re-decoding the received signals further comprises performing successive interference cancellation on the received signals.