Patent ID: 7471903
Filing Date: 2008-12-30
Classification: H04B

Abstract:
1. An optical fiber communications system comprising at least one transmitter site for transmitting optical signals, at least one receiver site for receiving optical signals from the at least one transmitter site, and at least two different optical fiber paths each arranged between the at least one transmitter site and the at least one receiver site, wherein each transmitter site comprises a transmitter having a modulation system enabling modulation using QAM defined by 16 constellation points, the transmitter being adaptable to provide modulation for different signals for respective ones of the paths using different selections of the 16 constellation points including a first selection of 2 of the points, a second selection of 4 of the points, a third selection of 8 of the points and a fourth selection of all 16 of the points, wherein the transmitter is configured to select the different selections for the respective signals in dependence on relative noise characteristics of the respective paths, and wherein each receiver site comprises a receiver having a demodulation system enabling demodulation from the QAM defined by 16 constellation points, and being adaptable to provide demodulation of different signals which have been modulated using the different selections of the 16 constellation points, including demodulation of the signals received from transmitter sites on respective ones of the paths.