Cisco Systems, Inc.
Apparatus and method for receiving quadrature amplitude modulated "QAM" symbol

Abstract:

Techniques are presented for receiving Quadrature Amplitude Modulated (QAM) symbols from a transmitter via a transmission path. In one example, a demodulator is configured to down-convert an incoming Radio Frequency (RF) signal to a baseband signal and convert the baseband signal to digital samples, and output the digital samples. A demapper is configured to receive the digital samples output from the demodulator and output data encoded in QAM symbols. The demapper is further configured to: determine from a constellation of QAM symbols a subset of QAM symbols that a digital sample from the demodulator may represent; apply an offset to each QAM symbol in the subset of QAM symbols of the constellation to result in a subset of offset QAM symbols; determine which QAM symbol in the subset of offset QAM symbols the digital sample most likely represents; and output data representing a determined QAM symbol.