ADAPTIVE QAM TRANSMISSION SCHEME TO IMPROVE PERFORMANCE ON AN AWGN CHANNEL

• US 20110090948A1
• Filed: 05/22/2009
• Published: 04/21/2011
• Est. Priority Date: 06/13/2008
• Status: Active Grant

• Current Assignee: InterDigital CE Patent Holdings SAS (InterDigital, Inc.)
• Original Assignee: Thomson Licensing (Vantiva SA)
• Inventors: Zhou, Wei, Zou, Li
• Granted Patent: US 9,036,694 B2
• Time in Patent Office: Days
• US Class Current: 375/240.01
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0044 specially adapted for power saving
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 27/3411 reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set
• CPC Class Codes: H04L 27/3416 in which the information is carried by both the individual signal points and the subset to which the individual points belong, e.g. using coset coding, lattice coding, or related schemes
• CPC Class Codes: H04L 27/366 Arrangements for compensating undesirable properties of the transmission path between the modulator and the demodulator

Abstract

A cable transmitter supports a number of low density parity check (LDPC) coding rates, e.g., 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9 and 9/10; and supports a number of quadrature amplitude modulation (QAM) schemes, e.g., 4-QAM, 16-QAM, 64-QAM, 256-QAM, 1024-QAM or higher. For a selected modulation scheme, the cable transmitter selects between using a non-uniform symbol constellation or a uniform symbol constellation as a function of a selected coding rate.

Claims

1. A method comprising:

adapting a symbol constellation as a function of coding rate to be either a non-uniform symbol constellation or a uniform symbol constellation; and

quadrature amplitude modulating or demodulating a signal for transmission in accordance with the adapted symbol constellation.

2. The method of claim 1, wherein the coding rate is any one of 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9 and 9/10;

and the symbol constellation has a size of m-QAM, where m is an integer greater than one.

3. The method of claim 1, wherein the adapting step comprises:

comparing a selected code rate to a threshold value, where the threshold value is associated with a selected QAM modulation scheme, the QAM modulation scheme having an associated symbol constellation;

adapting the associated symbol constellation to be non-uniform if the comparison is greater than, or equal, to the threshold value; and

otherwise adapting the associated symbol constellation to be uniform if the comparison is less than the threshold value.

4. The method of claim 3, wherein the threshold value is 8/9 for at least one of 256-QAM and 1024-QAM.

5. The method according to claim 1, wherein the adapting step comprises:

receiving control information indicating whether to use a uniform symbol constellation or a non-uniform symbol constellation for the symbol constellation.

6. Apparatus comprising:

a forward error correction encoder for providing encoded data having an associated coding rate; and

a quadrature amplitude modulator for adapting a symbol constellation as a function of the associated coding rate to be either a non-uniform symbol constellation or a uniform symbol constellation and for modulating the encoded data in accordance with the adapted symbol constellation for transmission.

7. The apparatus of claim 6, wherein the forward error correction encoder is a low density parity check encoder and wherein the associated coding rate is any one of 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9 and 9/10;

and the symbol constellation has a size of m-QAM, where m is an integer greater than one.

8. The apparatus of claim 6, wherein the quadrature amplitude modulator adapts the symbol constellation to be non-uniform if the associated coding rate is greater than, or equal to, a threshold value, and otherwise adapts the symbol constellation to be uniform if the comparison is less than the threshold value.

9. The apparatus according to claim 6, further comprising a processor for determining if the associated coding rate is greater than, or equal to, the threshold value, and for controlling the adaptation of the symbol constellation by the quadrature amplitude modulator.

14. The apparatus according to claim 8, wherein the threshold value is associated with a selected QAM modulation scheme.

15. The apparatus of claim 14, wherein the threshold value is 8/9 for at least one of 256-QAM and 1024-QAM.

10. Apparatus comprising:

a quadrature amplitude demodulator for adapting a symbol constellation as a function of an associated coding rate to be either a non-uniform symbol constellation or a uniform symbol constellation and for demodulating received data in accordance with the adapted symbol constellation for providing encoded data; and

.

a forward error correction decoder for processing the encoded data encoded at the associated coding rate and for providing decoded data.

11. The apparatus of claim 10, wherein the forward error correction decoder is a low density parity check decoder and wherein the associated coding rate is any one of 1/4, 1/3, 2/5, 1/2, 3/5, 2/3, 3/4, 4/5, 5/6, 8/9 and 9/10;

and the symbol constellation has a size of m-QAM, where m is an integer greater than one.

12. The apparatus of claim 10, wherein the quadrature amplitude demodulator adapts the symbol constellation to be non-uniform if the associated coding rate is greater than, or equal to, a threshold value, and otherwise adapts the symbol constellation to be uniform if the comparison is less than the threshold value.

13. The apparatus according to claim 10, further comprising a processor for determining if the associated coding rate is greater than, or equal to, the threshold value, and for controlling the adaptation of the symbol constellation by the quadrature amplitude demodulator.