| 摘要 |
A cable transmitter supports a number of low density parity check (LDPC) coding rates, e.g., ¼, ⅓, ⅖, ½, ⅗, ⅔, ¾, ⅘, ⅚, 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. |
| 主权项 |
1. A method comprising:
adapting a symbol constellation as a function of an error correction coding rate to be either a non-uniform symbol constellation or a uniform symbol constellation, including:
comparing the error correction coding 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 error correction coding rate is greater than, or equal, to the threshold value; andotherwise adapting the associated symbol constellation to be uniform if the error correction coding rate is less than the threshold value; and quadrature amplitude modulating a signal for transmission or demodulating a received signal in accordance with the adapted symbol constellation. |
