USING OF AN ADAPTIVE MATCHED FILTER IN SELF ADAPTIVE EQUALIZATION

This paper deals with a new proposal technique for improving the performance of a communication link. This is carried out by using an adaptive filter cascaded with the matched filter at the receiving end. When this proposal is used to equalizing a communication channel , no need to a training data sequence at the start of the system operation. So, it is important to use it in self adaptive equalization [1]. The matched filter is used to maximize signal to noise ratio at the receiving end. Since the matched filter is designed to match the transmitted signal, which is different from the received signal due to the channel effect the output of the matched filter is different from the designed one. An adaptive filter may be used to avoid these drawbacks caused by the channel since it has the ability to track the channel variation. The paper presents a system based on using adaptive filter together with a matched filter at the receiver. To check the performance of the proposal, a BARKER code is used to modulate four level data. At the receiver, the adaptive filter is cascaded with the matched filter and adapts its weights to get ideal auto-correlation function of the BARKER code. The basic idea in the adaptation process is based on the shape of the auto-correlation function, which has alternative zeroes. So, the adaptive filter adapts its output to zero at these instants and stop adaptation at the next instants, which solves the problem of the distortion in the matched filter output. The main advantage of the adaptation processor of the adaptive filter will modify the tap weights at double the baud interval i.e, slower processor is sufficient to be used. Computer simulation is carried out to test the performance of the proposal. It clarifies the improvement caused when the proposal is used.