Joint receiving mechanism based on blind equalization with variable step size for M-QAM modulation

The problem of inter symbol interference (ISI) in wireless communication systems caused by multipath propagation when using high order modulation like M-QAM is solved. Since the wireless receiver doesn't require a training sequence, a blind equalization channel is implemented in the receiver to increase the throughput of the system. To improve the performances of both the blind equalizer and the system, a joint receiving mechanism including variable step size (VSS) modified constant modulus algorithms (MCMA) and modified decision directed modulus algorithms (MDDMA) is proposed to ameliorate the convergence speed and mean square error (MSE) performance and combat the phase error when using high order QAM modulation. The VSS scheme is based on the selection of step size according to the distance between the output of the equalizer and the desired output in the constellation plane. Analysis and simulations show that the performance of the proposed VSS-MCMA-MDDMA mechanism is better than that of algorithms with a fixed step size. In addition, the MCMA-MDDMA with VSS can perform the phase recovery by itself.