Adaptive modulation for DFE equalized systems
نویسندگان
چکیده
In this paper, an adaptive quadrature amplitude modulation (AQAM) scheme for an equalized system over a selective channel is investigated. To reduce intersymbol interference (ISI), a minimum-mean-squarederror decision feedback equalizer (MMSE-DFE) with an unbiased decision rule is used. In order to select the appropriate modulation mode, the receiver estimates the MSE at the equalizer output. This estimated MSE is then sent back to the transmitter which adjusts the modulation level. The influence of channel variations on the AQAMDFE performances was also investigated. Simulation results illustrate that the MSE is accurately estimated and represents a viable switching metric. It is also shown that switching between different modulation modes does not affect the equalizer coefficients adaptation. Linear region of practical transmitter amplifiers is limited. Thus when switching from one modulation scheme to an other, it is important to control the peak power. Key–Words: Adaptive modulation, MMSE-DFE, unbiased receiver
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