Method and apparatus for constructing a sub-carrier map

• US 20030039317A1
• Filed: 08/21/2001
• Published: 02/27/2003
• Est. Priority Date: 08/21/2001
• Status: Abandoned Application

• Current Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Original Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Inventors: Taylor, Douglas Hamilton, Lynch, Bradley Robert
• Application Number:
  US09/932,945
• Publication Number:
  US 20030039317A1
• Time in Patent Office: Days
• US Class Current: 375/295
• CPC Class Codes: H04B 2203/5416 by adding signals to the wave form of the power source
• CPC Class Codes: H04B 2203/5441 Wireless systems or telephone
• CPC Class Codes: H04B 2203/545 Audio/video application, e.g. interphone
• CPC Class Codes: H04B 3/542 the information being in digital form
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

A method and apparatus for selecting a modulation type and forward error correction (FEC) configuration and a sub-carrier map to maximize data throughput in a multi-carrier orthogonal frequency division multiplexing (OFDM) system for use in an inherently noisy network, such as power line distribution networks. A sub-carrier map or is constructed by selecting a sub-set of available sub-carriers using estimated sub-carrier SNR values and two predefined criteria, a SNR threshold and a useful sub-carrier ratio. The invention leverages the error correction capacity of FEC to maximize data throughput.

Claims

1. A method for selecting a modulation configuration in a multi-carrier modulation system that supports a plurality of modulation configurations, comprising steps of:

for each modulation configuration m, determining a number of sub-carriers k_m having a signal-to-noise ratio above a predefined threshold _m;

computing a number of useful sub-carriers n_m by dividing k_m by a predefined ratio r_m;

constructing a sub-set of sub-carriers by selecting n_m sub-carriers having the highest signal-to-noise ratio; and

, computing a throughput t_m, by multiplying n_m by a predefined capacity c_m per sub-carrier; and

selecting the modulation configuration having the highest throughput.

2. A method as claimed in claim 1, wherein the step of computing a number of useful sub-carriers further comprises a step of ensuring that the number of useful sub-carriers is an integer value not greater than n.

3. A method as claimed in claim 2 wherein the step of ensuring is performed using the equation:

n_m=min(n, floor(k_m/r_m)).

4. A method as claimed in claim 1, wherein the predefined threshold _m is selected using empirical data derived from simulation results.

5. A method as claimed in claim 1, wherein the predefined ratio r_m is selected using empirical data derived from simulation results.

6. A method as claimed in claim 5 wherein the ratio r_m is selected to leverage the corrective power of forward error correction associated with the modulation configuration.

7. An apparatus for selecting a modulation configuration, in a multi-carrier modulation system that supports a plurality of modulation configurations, comprising:

means for determining a number of sub-carriers k_m having a signal-to-noise ratio above a predefined threshold _m, for each modulation configuration m;

means for computing a number of useful sub-carriers n_m for each modulation configuration m, by dividing k_m by a predefined ratio r_m;

means for constructing a sub-set of sub-carriers by selecting n_m sub-carriers having the highest signal-to-noise ratio for each modulation configuration m;

means for computing a throughput t_m, for each modulation configuration m, by multiplying n_m by a predefined capacity c_m per sub-carrier; and

means for selecting the modulation configuration having the highest throughput.

8. An apparatus as claimed in claim 7, wherein the means for computing a number of useful sub-carriers further comprises means for ensuring that the number of useful sub-carriers is an integer value not greater than n.

9. A method for selecting sub-carriers in a modulation system, comprising steps of:

selecting a first sub-set of sub-carriers k having a signal-to-noise ratio that exceeds a predetermined threshold;

dividing k by a predetermined ratio r to derive a number of sub-carriers to include in a second, larger sub-set of sub-carriers;

selecting the second sub-set of sub-carriers by selecting n sub-carriers having a highest signal-to-noise ratio; and

using the n sub-carriers for data transmission in the modulation system, whereby the predetermined ratio r is selected to leverage the corrective capacity of a forward error correction used in the modulation system to improve data throughput.

10. A method as claimed in claim 9 wherein the modulation system is a multi-carrier modulation system that supports a plurality m of modulation configurations, and the method further comprises steps of:

performing the steps of selecting the first sub-set, dividing and selecting the second sub-set for each of the modulation configurations m;

computing a throughput t_m, for each modulation configuration m, by multiplying n_m by a predefined capacity c_m per sub-carrier of each second sub-set of sub-carriers; and

using the modulation configuration having the highest throughput.

11. A power network interface (PNI) for connecting an electronic device to a power line network, comprising:

a sub-carrier map selector adapted to receive a signal-to-noise ratio (SNR_i) for each of a plurality of sub-carriers i, i=1,2, . . . , n;

to select a first sub-set of sub-carriers k; and

, to divide k by a predetermined ratio r to derive a second, larger sub-set n of sub-carriers for use by the PNI for the transfer of data over the power line network, whereby r is selected to leverage the corrective capacity of forward error correction associated with a modulation configuration used by the PNI to transmit data over the power line network.

12. A power network interface as claimed in claim 11 wherein the sub-carrier map selector is further adapted to derive the second, larger sub-set n of sub-carriers for each of a plurality of modulation configurations m that may be used by the PNI to transfer data over the power line network.

13. A power network interface as claimed in claim 11 wherein the sub-carrier map selector is further adapted to compute a throughput t_m, for each of the modulation configurations m, by multiplying n_m by a predefined capacity c_m per sub-carrier of each second sub-set of sub-carriers n.

14. A power network interface as claimed in claim 13 wherein the sub-carrier map selector is further adapted to select one of the modulation configurations m having a highest throughput t_m for use by the PNI for the transfer of data over the power line network.

15. A power network interface as claimed in claim 11 wherein the power line network is a home power line network.