FEC in cognitive multi-user OFDMA

• US 20080240267A1
• Filed: 03/30/2007
• Published: 10/02/2008
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Huitema, Christian, Wu, Yunnan, Stark, Wayne, Hassan, Amer, Chou, Philip
• Granted Patent: US 7,929,623 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 1/0045 Arrangements at the receiver end
• CPC Class Codes: H04L 1/0071 Use of interleaving interleaving per se H03M13/27
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0041 Frequency-non-contiguous
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 5/0058 Allocation criteria
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04W 72/54 based on quality criteria

Abstract

A multiuser scheme allowing for a number of users, sets of user, or carriers to share one or more channels is provided. In the invention, the available channel bandwidth is subdivided into a number of equal-bandwidth subchannels according to standard OFDM practice. A transmitter transmits data on a set of OFDM subchannels that need not be contiguous in the spectrum or belong to the same OFDM channel. A receiver receives and decodes the data and detects errors on subchannels. The receiver then broadcasts the identity of those subchannels on which the error rate exceeds a specific threshold, and the transmitter may select different subchannels for transmission based on this information.

Claims

1. A method of wireless communication, the method comprising the acts of:

a) detecting transmission errors on a set of OFDM subchannels;

b) identifying a plurality of undesirable subchannels from the set of OFDM subchannels based at least in part on the errors detected in act (a); and

c) broadcasting the identity of the plurality of undesirable subchannels.

2. The method of claim 1, further comprising the act by a transmitter of receiving the identity of the plurality of undesirable subchannels.

3. The method of claim 2, further comprising selecting OFDM subchannels for transmission based at least in part on the received identity of the plurality of undesirable subchannels.

4. The method of claim 3, wherein the transmitter excludes the plurality of undesirable subchannels.

5. The method of claim 1, wherein the method is performed by a receiver.

6. The method of claim 1, wherein the plurality of undesirable subchannels comprise subchannels on which more than a predetermined percentage of transmitted bits are detected in error.

7. The method of claim 1, wherein the identifying a plurality of undesirable subchannels is also based on a detected signal strengths.

8. The method of claim 1, wherein the method is repeated periodically.

9. The method of claim 8, wherein the method is repeated according to a predetermined time interval.

10. A wireless receiver for receiving OFDM transmissions, the receiver comprising:

a) an error detection module for determining transmission errors on a set of OFDM subchannels;

b) an identification module for identifying low fidelity subchannels from the set of OFDM subchannels; and

c) a broadcasting module for broadcasting a vector representing the low fidelity subchannels.

11. The receiver of claim 10, wherein the identification module uses a hard decision model to identify low fidelity subchannels.

12. The receiver of claim 11, wherein the identification module identifies subchannels as low fidelity if the error detection module detects more than a predetermined percentage of errors.

13. The receiver of claim 10, wherein the identification module uses a soft decision model to identify low fidelity subchannels.

14. The receiver of claim 10, wherein the broadcasting module broadcasts a vector representing the low fidelity subchannels at a programmable frequency.

15. A computer-readable medium having computer-readable signals stored thereon that define instructions that, as a result of being executed by a computer, instruct the computer to perform a method of wireless communication, the method comprising:

a) receiving data sent across an OFDM spectrum;

b) performing error detection on the received data;

c) identifying OFDM subchannels transmitting errors; and

d) advertising the identity of the OFDM subchannels transmitting errors.

16. The computer-readable medium of claim 15, wherein the method further comprises detecting interference from other transmitters.

17. The computer-readable medium of claim 16, wherein the method further comprises pausing data transmission for a random time interval when interference from other transmitters is detected.

18. The computer-readable medium of claim 16, wherein the method further comprises the following steps when interference is detected from other transmitters:

a) if a sufficient number of non-interfering error-free subchannels are available, transmitting on the non-interfering error-free subchannels; and

b) if a sufficient number of non-interfering error-free subchannels are not available, pausing data transmission for a random time interval before repeating the steps of claim 15.

19. The computer-readable medium of claim 15, wherein the step comprising advertising the identity of the OFDM subchannels transmitting errors is limited to OFDM subchannels on which more than fifty percent of transmissions are errors.

20. The computer-readable medium of claim 15, wherein the step comprising receiving data sent across an OFDM spectrum is performed according to the IEEE 802.11(a), IEEE 802.11(b), or IEEE 802.11(g) standards.