FEC in cognitive multi-user OFDMA

• US 7,929,623 B2
• Filed: 03/30/2007
• Issued: 04/19/2011
• Est. Priority Date: 03/30/2007
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Stark, Wayne, Chou, Philip Andrew, Huitema, Christian, Hassan, Amer A., Wu, Yunnan
• Primary Examiner(s): Bayard; Emmanuel
• Application Number:
  US11/731,269
• Publication Number:
  US 20080240267A1
• Time in Patent Office: 1,481 Days
• Field of Search: 375/260, 375/316, 375/130, 375/295, 370/208, 370/210
• 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 in an area comprising a plurality of computing devices able to communicate wirelessly, the method comprising the acts, carried out by a first computing device, of:

a) detecting, while receiving transmissions from a second computing device, transmission errors on a set of OFDM subchannels based on decoding received wireless communications using an error correction code, the received wireless communications being received with a receiver;

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 an identity of the plurality of undesirable subchannels in a transmitted wireless communication such that the identity of the plurality of undesirable subchannels is receivable by at least one third computing device different from the first computing device and the second computing device.

2. The method of claim 1, further comprising the act by the second computing device of receiving the identity of the plurality of undesirable subchannels.

3. The method of claim 2, further comprising, on the second computing device, selecting OFDM subchannels for transmission based at least in part on the received identity of the plurality of undesirable subchannels by selecting subchannels not in the received identity before selecting subchannels in the received identity.

4. The method of claim 1, wherein identifying the plurality of undesirable subchannels comprises identifying subchannels of the set of OFDM subchannels in which more than a predetermined percentage of transmitted bits are detected in error.

5. The method of claim 1, wherein the identifying the plurality of undesirable subchannels further comprises identifying based on a detected signal strengths for each of the set of OFDM subchannels.

6. The method of claim 1, further comprises repeating the detecting, identifying, and broadcasting periodically.

7. The method of claim 6, wherein the repeating comprises repeating according to a predetermined time interval.

8. The method of claim 1, further comprising, on the at least one third computing device, selecting OFDM subchannels for transmission based at least in part on the received identity of the plurality of undesirable subchannels by selecting subchannels not in the received identity before selecting subchannels in the received identity.

9. A wireless receiver for receiving OFDM transmissions in an area comprising a plurality of computing devices able to communicate wirelessly, the receiver comprising:

at least one processor programmed to act as;

an error detection module for determining, while communicating with a transmitter, transmission errors on a set of OFDM subchannels based on decoding received wireless communications using an error correction code;

an identification module for identifying low fidelity subchannels from the set of OFDM subchannels based at least in part on the determined transmission errors; and

a broadcasting module for broadcasting a vector representing the low fidelity subchannels such that the vector is receivable by at least one computing device different from the transmitter and the receiver.

10. The receiver of claim 9, wherein the identification module uses a hard decision model to identify low fidelity subchannels.

11. The receiver of claim 10, wherein the identification module identifies subchannels as low fidelity if the error detection module detects more than a predetermined percentage of errors.

12. The receiver of claim 9, wherein the identification module uses a soft decision model to identify low fidelity subchannels.

13. The receiver of claim 9, wherein the broadcasting module broadcasts a vector representing the low fidelity subchannels at a programmable frequency.

14. A system comprising the wireless receiver of claim 9, the transmitter, and the at least one computing device different from the transmitter and receiver,

wherein the at least one computing device comprises at least one processor programmed to receive the vector from the wireless receiver and to select OFDM subchannels for transmission based at least in part on the vector by selecting subchannels not in the vector before selecting subchannels in the vector.

15. A computer-readable storage 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 in an area comprising a plurality of computing devices able to communicate wirelessly, the method comprising acts carried out by a first computing device of:

a) receiving data sent by a second computing device across an OFDM spectrum;

b) performing error detection on the received data by decoding received wireless communications using an error correction code;

c) identifying OFDM subchannels in which errors were detected, based on the error detection in b); and

d) advertising, to the plurality of computing devices, the OFDM subchannels in which errors were detected.

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

17. A computer-readable storage 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. A computer-readable storage 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. A computer-readable storage medium of claim 15, wherein advertising the OFDM subchannels in which errors were detected comprises advertising the OFDM subchannels in which more than fifty percent of transmissions are errors.

20. A computer-readable storage 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.