Patent ID: 8144800

Claim:
A headend transmitter for transmitting 1024 QAM constellation points, comprising: a 256 QAM modulator including a 256 QAM mapper, that receives first data and processes it into 256 QAM symbols mapping to vectors in a two dimensional plane; a second modulator configured to implement a modulation scheme of lower complexity than the 256 QAM modulation implemented by the 256 QAM modulator, the second modulator having an input to receive second data and being configured to generate an output comprising second symbols mapped to a two-dimensional plane, each second symbol being definable as a vector; a variable gain amplifier coupled to receive the output of the second modulator and configured to provide a variable gain to said output; and a summer configured to perform a vector sum of the output of the variable gain amplifier with a vector representing one of said 256 QAM symbols, wherein headend transmitter transmits an output of the summer on a logical channel to a receiving device, wherein the logical channel is used to receive digital data from the headend transmitter by receiving devices that are 1024 QAM-enabled and by receiving devices that are at most 256-QAM enabled, wherein 1024 QAM-enabled receiving devices and at most 256-QAM enabled receiving devices employ a same symbol rate, wherein, if the receiving device is at most 256-QAM enabled, the receiving device views the output of the variable gain amplifier as noise corruption of the vector representing said one of said 256 QAM symbols, and wherein, if the receiving device is 1024 QAM enabled, the receiving device views the output of the summer as a 1024 QAM symbol.