OFDMA based on cognitive radio

• US 20070248173A1
• Filed: 04/25/2006
• Published: 10/25/2007
• Est. Priority Date: 04/25/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Huitema, Christian, Hassan, Amer
• Granted Patent: US 7,933,344 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation
• CPC Class Codes: H04L 5/006 Quality of the received signal, e.g. BER, SNR, water filling
• CPC Class Codes: H04L 5/0064 Rate requirement of the data, e.g. scalable bandwidth, data priority

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. The transmitter is informed by an application that it needs to transmit data a particular rate. The transmitter determines the minimum number of subchannels and maximum energy (or noise) threshold for each subchannel necessary to achieve that data rate and selects a set of subchannels matching those requirements. The subchannels need not be contiguous in the spectrum or belong to the same channel. Once the transmitter has selected the required number of subchannels, it begins transmitting simultaneously on those subchannels across the entire bandwidth used by those subchannels.

Claims

1. A method of wireless communication between two or more devices at a minimum data rate, the method comprising the acts of:

a) determining a minimum number of OFDM subchannels and energy threshold for each subchannel necessary to achieve the minimum data rate; and

b) tuning a transmitter to a set of one or more subchannels; and

c) performing energy detection on one or more subchannels from said set of subchannels; and

d) dropping any subchannels from said set of subchannels whose energy level exceeds a threshold; and

e) adding one or more subchannels to said set of subchannels for each subchannel that has been dropped; and

f) repeating acts (c) through (e) until the minimum number of subchannels whose energy is below the threshold has been selected.

2. The method of claim 1, wherein the arbitrary set of subchannels in act (b) comprises at least the minimum number of subchannels necessary to achieve the minimum data rate.

3. The method of claim 1, wherein the energy detection in act (c) is performed on the entire set of subchannels selected in act (b).

4. The method of claim 1, wherein the receiver determines the set of subchannels to be used by performing acts (a) through (f).

5. The method of claim 1, wherein the transmitter sends a signal to the receiver indicating the set of subchannels it has selected.

6. The method of claim 1, further comprising the act of beginning transmission on the selected subchannels.

7. The method of claim 6, wherein the transmission is accomplished by means of an Inverse Fourier Transform algorithm.

8. The method of claim 1, further comprising the act of transmitting to a receiver on a predetermined frequency the identity of the selected subchannels.

9. A wireless communication system for transmitting data a requested rate, including a plurality of communication devices, the system comprising:

a) a subchannel determining module to determine the number of OFDM subcarriers and energy threshold for each OFDM subcarrier needed to transmit at the data rate; and

b) a signal-to-noise level detection module to detect the signal-to-noise level on each available OFDM subcarrier and to select a set of subcarriers meeting the requirements determined by the subchannel determining module.

10. The system of claim 9, wherein the transmitter tests each available OFDM subcarrier sequentially.

11. The system of claim 9, wherein the transmitter tests all available OFDM subcarriers simultaneously.

12. The system of claim 9, wherein the signal-to-noise level detection module is part of a transmitter.

13. The system of claim 12, wherein the signal-to-noise level detection module relies on feedback from the receiver.

14. The system of claim 12, wherein the transmitter sends a signal to the receiver indicating the list of subcarriers to be used.

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 at a requested data rate, the method comprising:

a) calculating the number of OFDM subchannels and noise threshold for each subchannel necessary to achieve the requested data rate; and

b) selecting those OFDM subchannels for which the noise level is less than said noise threshold.

16. The computer-readable medium of claim 15, wherein the method further comprises transmitting data over the entire bandwidth used by the selected OFDM subchannels using an Inverse Fast Fourier Transform algorithm.

17. The computer-readable medium of claim 15, wherein the method further comprises receiving data over the entire bandwidth used by the selected OFDM subchannels using a Fast Fourier Transform algorithm.

18. The computer-readable medium of claim 15, wherein the method further comprises transmitting to a receiver the identity of the selected subchannels.

19. The computer-readable medium of claim 18, wherein the transmission of the identity of the selected subchannels occurs at a different frequency than that used for transmission of data.

20. The computer-readable medium of claim 15, wherein the wireless communication transmits data modulated by quadrature amplitude modulation.