The Effect of Feedback Delay on the Performance of Closed-Loop Rotate Modulations on OFDM/OFDMA Systems

Abstract

In this paper, in order to improve the performance of the OFDM/OFDMA system, novel closed-loop rotate modulation is proposed by utilizing feedback channel state information in the complex values. The basic idea of the proposed rotate modulation is the channel equalizer process, which is applied at the transmitter side; therefore, it does not need to insert guard time to anticipate the problem of channel delay spread. With the purpose of distortionless-transmission, in this paper, the rotate modulation equation has been derivated. Based on the simulation results on this proposed system, when the feedback delay has been zero, the resulting system performance has been similar to the one on the Additive White Gaussian Noise channel. In this ideal condition, the received signal has been similar to the transmitted signal although in real condition the process of transmitting the feedback signal will always result in a delay. Simulation results at low-level modulation such as Binary Phase Shift Keying and Quarternary Phase Shift Keying; the system bit error ratio performance has not shown degradation with the feedback delay. However, for higher level modulation such as 16-Quadrature Amplitude Modulation and 64-Quadrature Amplitude Modulation, the feedback delay has caused degradation on the BER curve.