A baseband adaptive equalizer is constructed for quadrature amplitude modulation(QAM) signal. It is composed of two tapped delay lines (TDL) for inphase and quadrature signals, and each of TDL is controlled by two sets of tap weights. The tap weights are adaptively adjusted by the iterative procedure based on the gradient following algorithm for minimum mean square-error.
The system is implemented by digital circuitry. To understand the quantization effect on the convergence of the tap weights, the relation between the convergence and step-size in the iteration is reviewed for the analog version.
The quantization effect is investigated and compared experimentally. It is shown that 8-bit quantization and multiplication is applicable for 2400Hz binary QAM signal.
Baseband QAM signal 에 적용하기 위한 two dimensional equalizer 를 gradient following algorithm 에 따라 설명하였으며, 이를 토대로 하여 baseband equalizer 를 digital circuit 로 구성하고 그 실험에서 8-bit digitize 할때 2-level signal 에 대한 decision 이 가능함을 보였다. 또한 digital로 signal processing 할 경우 발생되는 quantization 효과를 고려하여, equalizer 가 수렴하기 위한 최적의 step-size 를 Digital Residual Error 에 따라 결정하였으며 이를 실험결과와 검토 하였다.
