Method and apparatus for transmitting high-level qam optical signals with binary drive signals

Abstract

Methods and apparatus for power-efficiently and reliably transmitting high-level quadrature amplitude modulation (QAM) optical signals using binary drive signals. Even though binary signals are used to drive a QAM modulator directly, without digital-to-analog conversion, the methods and apparatus disclosed allow the transmission of pilot symbol sequences having near optimal properties, such as a constant power profile in the time domain; a mean power that is approximately the same as the mean power of the data symbols; and roughly uniform amplitude in the frequency domain for non-zero frequency components of the pilot symbol sequence. The binary drive signals can be processed so that the modulated optical signals are selectively constrained to a subset of points of the QAM constellation to form a QAM constellation with reduced size and a mean power that is approximately the same as the mean power of the original QAM constellation.

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