Amplitude Transformation-Based Blind Equalization Part I: Suitable for High-Order PAM Signals

In the digital transmission system, constant modulus algorithm (CMA) is a famous blind equalization to overcome the inter-symbol interference without the aid of training sequences. But for the non-constant modulus signals such as higher-order PAM signals, the CMA just achieve moderate steady-state mean square error (MSE) which may not be sufficient for the system to obtain adequate performance. By studying the amplitude relationship between different constellations of PAM signals, a new amplitude transformation method is proposed. According to such method the non-constant modulus signals can be changed to be constant modulus, and then using it to the CMA the zero steady- state MSE can be obtained. The efficiency of the proposed method is proved by computer simulations.