A fast and efficient adaptive channel equalizer for OFDM-based wireless relay system

Summary In this paper, we aim to eliminate the interference signals for a novel wireless communication repeater based on OFDM. The wireless repeater in communication system is important especially for mobile system. Now these days, in order to amplify the signal via repeater, receiver and transmitter of repeater using only one frequency without frequency shift. However, in this case repeater has problem that, amplified signal will feedback to receiver sides and this may cause the internal instability and distortion of repeater system. Therefore, by estimating the feedback signal by adaptive filter, we can eliminate the effects of feedback signal. In this paper we consider LMS, NLMS and RLS algorithms in order to estimate the feedback signal. Furthermore, by these adaptive filters we identify the unknown channel and evaluate the performance of each algorithm by MSE. Here, the LMS does not work and RLS has the best performance comparing to NLMS for identification of the unknown multi path channel. In repeater, the amplified signal not only transmitted to the user but also transmitted to receiver side of repeater by multipath feedback channel. Therefore, in the receiver side of repeater, it will receive reference signal from base station which is ideal input of repeater and the other is feedback signal from repeaters transmitter side which is amplified. Therefore, repeater receives the interference from transmitter side. In this case, repeater system may unstable due to positive feedback. Thus, the interference cancellation system is required in order to cancel the interference signal in receiver side of repeater. In this paper, multipath channel exists in feedback channel and identify the unknown channel by adaptive filter such as LMS, NLMS and RLS. The point of this research is the fast identification of unknown channel due to rapid changing communication channel. Then, we evaluate the performance of each adaptive filter. The Channel equalizer for repeater is shown a- - s follows.