Study On Noise Reduction And Echo Cancellation Based On Vehicle Hand-free Phone System

With the common understanding that using the phone is dangerous when driving,“phoning without hand, driving is safer”becomes an aim that people make great efforts together and go in for, so vehicle hand-free phone system emerges as the times require. Contradiction of driving and phoning urges people to seek all kinds of means to accomplish vehicle hand-free phone function, however the key problems of vehicle hand-free phone system are noise reduction and echo cancellation,which have been a significative study problem in signal procession field.Noise reduction segment precedes echo cancellation segment using serial adaptive echo cancellation machine structure, so the speech which is inputted to microphone reduces noise before canceling echo, and the stability for canceling echo can be assured effectively. Using the improved spectrum subtraction method as noise reduction method in echo cancellation machine, and using with and without acoustic frame detection to estimate noise, noise can be updated at any moment. Test results indicate that the effect of noise reduction is all right, with little calculation number and accomplishing easily. A double-talk detector is designed and accomplished based on the angle of two vectors. Every sampling value of input signal from near end microphone and estimated echo signal outputted by adaptive filter become two vectors respectively, and the angle of two vectors should be calculated at any moment. With exact estimation and appropriate calculation number, this method avoids wrong estimation which other double-talk detectors often have. In echo cancellation segment, improved NLMS is used to estimate echo signal. The improved NLMS method improves the disadvantage of slow convergence for conventional LMS, reserves the advantage of little calculation number, and utilizs the sparse feature of echo path,which make the filter estimate nonzero impact response function in echo path. Test results testify that the convergence rate is fast and the effect of echo cancellation is all right. in a word, this method improves phoning quality of the system.